1. Cell is defined as the basic structural and fundamental unit of life.
2. All organisms of nature are composed of cells and cell products. Thus cell is called as structural unit of life.
3. All metabolic reactions take place in cells, essential for life. Thus, cell is called as functional unit of life.
4. Every living cell of an organism keeps its chemical composition steady. Such balanced condition is called as Homeostasis.
5. An organism does not have any non-functional cell. Even the dead cell is considered to be functional cells. Thus, dead cell also play a role in multicellular organisms, because all cells are functional.
6. Prions, viroids and viruses are the pathogenic, non-cellular, smallest organisms.
They cannot perform living activities in free form because they do not have protoplasm. Therefore, in free form, they are like non-living particles.
To perform living activities they require protoplasm or cytoplasm of host cell.
COMPOSTITON OF PRIONS, VIROIDS AND VIRUSES
organisms Composition of organisms
PRIONS prions do not have its own genetic structure (DNA or RNA). It is made up of few molecules of proteins.
VIROIDS viroids are made up of single nacked molecule of RNA.
VIRUSES
(non-cellular living organisms) Each molecule of viruses is made up of protein and single molecule of either of DNA or RNA.
Animal viruses mostly contain DNA.
Plant viruses mostly contain RNA.
Viruses are regarded as the connecting link between living and non-living.
The chemical reaction occurs in presence of enzymes is called as biochemical process. This process may occur inside the cell or outside the cell.
The biochemical process occurs inside the living cells in protoplasm are called as metabolism.
Metabolism term was coined by Schwann. Metabolism is of 2 types:-
ANABOLISM CATABOLISM
The process by which complex substances are produced by simpler ones by the use of energy is called as anabolism. The process by which complex higher molecule substances are broken down into simpler and soluble substances is called as catabolism.
Anabolism is an ENDERGONIC (energy absorbing) and constructive process. Catabolism is an EXERGNOIC (energy releasing) and destructive process.
EX-photosynthesis is an anabolic process. Ex: - Respiration is a catabolic process.
CELL AND ITS DISCOVERY
1. In 1665, Robert Hook discovered cell from the cork cambium of OAK plant (quercus suberus).
2. Actually, Robert Hooke placed thin slices of cork cambium under compound microscope. He observed certain bee-hive like structures which he called them as cell.
3. This description of his discovery was given in his own written book “micrographia”.
4. But cork cambium is a dead cell, having no protoplasm. So, Robert Hooke actually discovered cell wall.
5. By this way, the first discovered cell is dead eukaryotic cell.
6. The first living cell was discovered by German
CELL SIZE
TYPE OF CELL EXAMPLE
Smallest cell Mycoplasma gallisepticum
(PPLO-pleuro pneumonic like organisms).
Largest animal cell Ostrich Egg.
(130× 135)
Human body cell 20-30μm. (Average size)
Nerve cell is largest Human body cell.
Longest unicellular plant/
( eukaryotic unicellular algae) Acetobularia
(Up to 10 cm length).
The smallest organisms which can occur in free form as an organism is mycoplasma gallisepticum (PPLO-pleuro pneumonic like organisms). Because it does not have a cell wall, therefore it is known as joker of plant kingdom.
Neurons in embryo and phloem fibres in plants especially angiosperms may be considered as longest cells.
TYPES OF ORGANISMS ON THE BASIS OF NUMBER OF CELLS
a) Unicellular organisms: - unicellular organisms are those organisms whose body is made up of only one cell.
Ex:-certain bacteria, yeast, paramecium (slipper like organism), amoeba
b) Multicellular organisms: - Multicellular organisms are those organisms whose body is made up of more than one cell.
Ex:-most of plants and animals.
NOTES:-
Unicellular organisms are less efficient.
Multicellularity is possible due to division of labour.
CELL THEORY
1. Botanist Schleiden and Zoologist Schwann proposed the fundamental principal of biology in 1838-1839. This principle is known as cell theory.
POSTULATES OF CELL THEORY
1. Cell is the fundamental unit of life and is the building block of life and organisms. All organisms are made up of cell and its products.
2. All type of organisms, whether it is small or large, plant or animal, consists of same protoplasm containing cell. In this way, all organisms of nature are related to each other.
CELL PRINCIPLE
3. Rudolf virchow stated that “omnis cellula e cellula” i.e. new cells arises from pre-existing cell.
NOTES:-VIRUSES are not considered as organisms because viruses are merely nucleo-protein particles and lack cytoplasm and metabolic machinery. So, they are exception to cell theory. Viruses are considered as connective link between living and non-living.
MICROSCOPY
The study of micro-organims and structures of cells under microscope is called as microscopy.
IMPORTANT MICROSCOPE USED DURING STUDY OF CELL BIOLOGY
OBSERVED STRUCTURES
Compound Microscope Cell wall nucleus, plastids, vacuoles, etc.
However, some other organelles such as mitochondria, golgi complex, nucleus, spindle apparatus and chromosomes can be observed with the help of compound microscope only after employing specific staining techniques.
Phase contrast microscope
(Zernike) In a living cell, certain structures and organelles such as chromosomes, spindle apparatus, etc. can be observed with the help of phase-contrast
Microscope.
Electron microscope For ultra structures as well as for submicroscopic structures.
Ribosome discovery made possible due to electron microscope.
Transmission Electron Microscope (TEM) ( developed by Knoll and Ruska)
Scanning Electron Microscope (SEM) Gerd Binning It is used for the study of fine structures and details of sub-microscopic components such as pollen grains, RBC etc.
It is most effective in observing 3-D images.
TYPES OF CELL
On the basis of presence of nucleus, cells are classified into 2 types:-
Prokaryotic cell
Eukaryotic cell
Prokaryotic cell Eukaryotic cell
Prokaryotic cell does not have a true nucleus, but a nucleoid. Nucleoid lacks nuclear membrane Eukaryotic cell has a nucleus covered with a nuclear membrane.
It has a single circular DNA, not associated with protein histone. It has multiple, linear DNA, associated with protein histone.
Cell wall is made up of peptidoglycan. Cell wall is made up of chitin in fungi
cell wall is made up of cellulose in higher plants
Ribosomes of 70S type. Ribosomes of 80S type.
Membrane-bound organelles (such as MPGERL etc) are absent Membrane-bound organelles are present.
Flagella, if present contain tubules of flagellin. Flagella, when present have 9 + 2 microtubules
PROKARYOTIC CELL
Prokaryotic cells are extremely small, least evolved cell.
In these cells, nuclear membrane and cell organelles (like MPGERL) are absent.
Ex:- Mycoplasma, thermoplasma, rikettsia, spirochete, bacteria and cyanobacteria(BGA)
SRUCTURE OF PROKARYOTIC CELL
STRUCTURE FUNCTION
mucilaginous sheath MS is the glycocalyx non-living slime layer present at the outer surface of cell wall.
Mucilaginous heath is a protective covering and protects the cell against harmful radations, high pH and temperature etc.
cell wall Cell wall is the outermost covering of cell and is responsible for protection and mechanical support to the cell.
The cell walls of prokaryotes are made up of peptidoglycon and phospho-lipids.
protoplast (nucloid +cytoplasm)
PROTOPLAST
STRUCTURE FUNCTION
Nucloid/
(incipient or nacked nucleus) In prokaryotes, there is a single ds-DNA occurs in cell. This ds_DNA occurs in free helical or circular form.
There is no nuclear membrane which surrounds this genetic structure. Therefore, therefore this DNA represents the whole genetic structure and is known as nucloid.
mesosomes/ chondroid At certain places, plasma membrane of cell infolds towards its protoplasm. This infolding is known as mesosomes.
Because of presence of respiratory enzymes, mesosomes perform the function of aerobic respiration and produces ATP. Therefore, this structure has been considered as analogous to mitochondria.
Due to development of mesosomes, surface area of plasma membrane increase. This increases the work efficiency in prokaryotes.
storage granules In storage granules, food is stored mostly in the form of lipids and glycogen.
RNA All 3 kinds of non-genetic RNA occur in prokaryotes.
The synthesis of RNA takes place from DNA molecule by the process of transcription.
Ribosomes/ cytoplasmic nucleo-protein ribosomes are membrane less small structure, mainly involve in protein synthesis.
The size of ribosomes in prokaryotic cell is from 64S-72S, but on an average, 70-S type of ribosomes occurs in cytoplasm.
The 70-S type of ribosomes can be split into 2 sub-units of 50-S +30-S.
flagellum
locomotary organs Each flagellum is made up of single hollow rod like fibre.
Flagellum is made up of flagellin protein.
The action of flagellum is like the propellant of boat.
plasmid/ magic rings
(extra-nuclear heredity determinants) a) Plasmid are the cytoplasmic genetic units, other then DNA.
b) Plasmid contains genes. Function of plasmid depends on their constituent genes.
TYPES OF PLASMID:-
a) CONJUGATIVE PLASMID: - plasmids have their self capacity to transform form donor to recipient.
Ex:-F-plasmid (fertility –plasmid), R-plasmid, Col-plasmid.
b) NON-CONJUGATIVE PLASMID:-plasmids, which do not have the self capacity to transfer from donor to recipient.
Ex:-Ti-plasmid, cryptic -plasmid
EUKARYOTIC CELL
1. Eukaryotic cell is the advanced cell with a true and distinct nucleus having a nuclear membrane.
2. Due to presence of various membranes and membrane bound cell organelles , the structural organization of eukaryotic cell becomes more complex.
3. Ex: - all plants and most of the animals.
TYPES OF EUKARYOTIC CELL
Plant cell Animal cell
Cell wall is present in plant cells. It surrounds plasma membrane of the cell. Cell wall is absent in animal cells.
Plant cells have a large central vacuole with a thin layer of cytoplasm. Generally, animal cells do not possess vacuoles (few small vacuoles may be present in some cells).
Chloroplasts are present in all plant cells. It performs photosynthesis. Chloroplasts are absent in animal cells, except in euglena.
Centrosomes are absent. The centrosome is present.
Plant cells have simpler units of Golgi apparatus called dictyosomes. Animal cells have prominent Golgi complex near nucleus.
CELL WALL
Cell wall is the outermost covering of plant cell.
Cell wall is composed mainly of cellulose. Cellulose is a polysaccharide of β-D-glucose.
Other important component of cell wall are:-
COMPONENT OF CELL WALL FUNCTION
Hemicellulose It develops the connection between matrix and fibres of cellulose.
pectin(fruit jelly) Pectin acts as cement. The maximum % of pectin occurs in collenchyma tissue.
lignin Lignin provides hardness and rigidity to the cell.
the maximum % of lignin occurs in sclerenchyma tissue
suberin (wax of fatty acids) suberin provides hardness and rigidity to the cell.
It also provides impermeability for water.
Cell wall is a complex structure and can be differentiated as:
Primary cell wall: - main and oldest layer of cell wall.
Secondary cell wall:- occur in xylem , cork cell and sclerenchyma.
Tertiary cell wall: - occur in few plant tissues like tracheids of xylem.
FUNCTIONS OF CELL WALL
1. It provides mechanical support and protection to plant cells.
2. It facilitates the cellular transport, as it is permeable to water and solute.
3. It determines the shape of the cell and prevents it from desiccation.
MIDDLE LAMELLA
1. Plant cells remain cemented together by dense intercellular matrix, called as middle lamella. It is formed soon after cell division.
2. Middle lamella is composed of pectin, lignin and proteins and salts of calcium and magnesium.
3. Un-ripened fruits are hard due to intake of middle lamella.
PLASMODESMATA
Living cells are connected to each other by fine cytoplasmic channels called as plasmodesmata which pass through cell walls. These facilitate transport of substances between cells.
PLASMA MEMBRANE / PLASMALEMMA/ CELL MEMBRANE
1. PM is living, tri-laminar, and semi-permeable membrane, which covers and protects the protoplasm and cell organelles from surrounding world.
2. It is present just inside the cell wall in a plant cell but it becomes the outermost covering of the animal cell.
3. PM remain in quasi-fluid state. This enables them to undergo dynamic changes.
The older ones are continuously replaced by the new ones.
They can be extended, folded and moved, so that cell can change their form, size and functions.
MODEL FOR ULTRASTRUCTURE OF BIOLOGICAL MEMBRANE
UNIT MEMBRANE MODEL:- BY ROBERTSON
Robertson found trilaminar compositions in most of the membranes of cell organelles. In 1959, he put forward the concept of unit membrane.
A unit membrane has protein-lipid-protein arrangement.
The protein layers are electron dense and lipid layer is electron lucent.
It is found in plasma membrane, endoplasmic reticulum, Golgi complex, lysosomes and plastids. It is also found in mitochondria and nucleus. unit membrane.
FLUID MOSAIC MODEL
- (by singer and Nichelson)
POSTULATES
1. protein icebergs in the sea of lipids: -
According to Singer and Nicholson, PM is made up of a bilayer of phospholipids.
In this bilayer, 3 kinds of potein molecules are floated in phospholipids fluid.
Protein which are present in PM not only give strength to membrane but also function as enzymes (intra-cellular chemical messenger), transport proteins like channels and pumps, or can function as a receptor protein,
2. concept of fluidity:-
The fluidity concept means that the main components of membranes, lipids and oligosaccharides are held in place by non-covalent interactions.
Fluid mosaic model of cell membrane
PHOSPHOLIPID STRUCTURE
Phospholipids are arranged such that its polar heads are towards the cytosol and extra-cellular fluid, while non-polar tails are inwards.
HYDROPHILIC POLAR HEADS
HYDROPHOBIC POLAR TAILS
PROTEINS
Proteins, which are floated in lipid bi-layer, are of 3 types:-
1. INTRINSIC PROTEINS: - intrinsic proteins are embedded completely inside the lipid bi-layer.
2. EXTRINSIC PROETEINS: - extrinsic protein occurs on inner surface or outer surface of lipid membrane.
3. PERIPHERAL PROTEINS:-proteins which are attached superficially are called as peripheral proteins. Large globular integral proteins project beyond the lipid layer. These are believed to have channels through which water-soluble materials can pass.
Plasma membrane under electron microscope
FUNCTION OF PLASMA MEMBRANE
1. SELECTIVE PERMEABILITY: -
Membranes are selectively permeable i.e. they allow useful substance to pass through them, but do not allow harmful substance to pass through them.
Selective permeability of cell is obtained by diffusion and osmosis.
2. CELL RECOGNIZATION:-
Some oligosaccharides project into extracellular fluid from the outer surface of the membranes, which are bound to lipids and integral proteins. The cells interact with one another according to the influence of the oligosaccharides. They recognize each other on the basis of these glycolipids and glycoproteins.
This capacity of cell membranes to recognize each other plays a very important role in blood grouping, immune response, cancer, rejection of transplanted organs, etc.
FUNCTIONS OF CYTOPLASM
1. It possesses sensitivity to stimulation. That is it shows irritability.
2. It transmits substances from one region of the cell to the other.
3. It brings about movement due to cyclosis. The cytoplasm is the seat of various metabolic activities.
MITOCHONDRIA/ POWER HOUSE OF THE CELL
Mitochondria are tiny energy batteries of cell, which provide energy to the cell.
Mitochondria are generally filamentous or granular in shape. But they may change their form depending upon the physiological conditions of the cells. They may be spherical, oval, cylindrical, sausage-shaped in their form.
During cell division, the daughter cell inherits mitochondria from mother cell.
Factors affecting mitochondria distribution and number are:-
• They are present more in number, in regions where RER is present.
• Their number also depends upon the type and functional state of the cell. More active is the cell; more is the number of mitochondria.
• They are abundantly found in the bases of cilia or cells of germinating seeds, because these cells are involved in energy-dependent activities.
STRUCTURE OF MITOCHONDRIA
Mitochondria have a double membrane envelope.
a. OUTER MEMBRANE:-The outer membrane is smooth and has a transport protein called porin. This porin forms aqueous channels through the lipid bilayer. Thus outer membrane is permeable.
b. INNER MEMBRANE:-
The inner membrane is highly convoluted. The inner membrane have several folds, towards the matrix of mitochondria. These folds are called as cristae.
Inner membrane is impermeable. The cristae increase the surface area of the inner membrane.
The outerside of the inner membrane has cytosol or C face. The innerside of the inner membrane has M face.
Attached to the M face are stalked elementary particles or inner membrane subunits called oxysomes ( F1 particles or F0 - F1 particles). These are meant for ATP synthesis and oxidation.
MITOCHONDRIAL MATRIX:-
The mitochondrial matrix is a dense, homogeneous, proteinaceous material.
It contains lipids, proteins, circular DNA molecules, ribosomes, and certain granules.
It contains enzymes essential for respiration (oxidation of food).
FUNCTIONS OF MITOCHONDRIA
1. CELLULAR RESPIRATION:-
Mitochondria carry out oxidation of carbohydrates and fats and releases energy in the form of ATP (adenosine tri-phosphate).Therefore, mitochondria are known as 'power house of the cell.
ATP is known as energy currency of the cell.
2. They perform important functions such as oxidation, dehydration, oxidative phosphorylation, etc.
3. Mitochondria are called as semi-autonomous organelles and are able to synthesize their own proteins.
PLASTID
Plastids are double-layered organelles found only in plant cells.. They are self-replicating organelles
Types of plastids
Plastids are classified according to their structure, pigment and functions:
1. Leucoplasts
2. Chromoplasts
3. Chloroplasts
Leucoplasts
these are colourless plastids.
They are found in fruits, seeds, tubers and rhizomes. They are also found in those regions of plants, which do not receive any light.
They do not contain thylakoids and ribosomes. They store nutrients.
These are again classified into three types:
• Amyloplast – synthesizes and stores starch.
• Elaioplast – stores lipids.
• Proteinoplast – stores proteins and may contain a few thylakoids.
Chromoplasts
These are coloured plastids.
Chromoplasts contains carotenoids and other type of pigments. They provide colour to flowers, fruits and some roots such as carrots.
Chloroplasts
Chloroplasts are green-coloured plastids (in Greek, chloro means 'green')
Chloroplast contains mainly 2 pigments:- chlorophyll-a and chlorophyll-b,
They are the most common plastids in plants and are very important, because they perform the function of photosynthesis.
Generally, chloroplasts are biconvex, but may be found in varying shapes.
STRUCTURE OF CHLOROPLAST
Chloroplast has been classified into three main parts:
1. Envelope:- Each chloroplast is covered by double membrane called the envelope.
a. OUTER MEMBRANE: - The outer membrane is permeable.
b. INNER MEMBRANE: - the inner membrane is less permeable.
2. GRANA: -
grana are stacks of membrane-bounded, flattened disc-like sacs called as thylakoids.
There may be 40 to 80 grana in the matrix of a single chloroplast.
All the granum is connected to each–other by frests.
Thylakoids have quantasomes, which contain nearly 230 molecues of chlorophyll.
3. STROMA/MATRIX
The stroma is a gel-like fluid, which surrounds the thylakoids (grana)..
It contains 50 per cent of the total chloroplast proteins, which are of soluble types.
It also contains ribosomes and DNA molecules.
Grana are the site of light reaction. During photosynthesis, chlorophyll molecules breaks water molecule.
stroma is the site of dark reaction(CO2-fixation). The synthesis of sugars, starch, fatty acids and some proteins occurs in the stroma.
FUNCTIONS OF CHLOROPLAST
1. Chloroplast traps solar energy and convert this inorganic energy into organic energy.
2. Chromoplasts provide various colours to flowers to attract insects for pollination.
3. Leucoplasts store food in the form of carbohydrates (starch), fats(lipids), and protein.
GOLGI BODY/ GOLGI COMPLEX
GB is tiny assembly area for the storage, processing and packaging of various cellular secretions.
In plants, it is called as dictyosome, because in plants cisternae are formed at cis-face of Golgi and vesicles are bounded off from trans face of Golgi.
STRUCTURE OF GOLGI COMPLEX
Golgi complex consists of 3 basic components:
1. CISTERNAE(Flattened sacs)
1. Cisternae are flattened curved closed compartments lying parallel to each other. It has 2 ends:-
1. PROXIMAL END:- The convex end of golgi body is the proximal end. This end is called as the cis-face. The proximal Golgi body is formed by the fusion of ER-derived vesicles.
2. DISTAL END: - the concave end is the distal end. This end is called as the trans-face. The distal GB ‘gives their all’ to vesicle formation and disappear. Thus, Golgi cisternae are constantly renewed.
2. TUBULES:-Tubules surround the cisternae; in fact, they radiate from it.
3. SECRETORY VESICLES:-Vesicles are of three types:
• Transitional vesicles are present on the cis-face of Golgi. These fused together to form new cisternae.
• The secretory vesicles are discharged from the margins of the cisternae. They pinch off as zymogen granules.
• Coated vesicles are found at the periphery of the organelle.
GENERAL FUNCTION OF GOLGI COMPLEX
1. The main function of the golgi apparatus is secretory.
2. Golgi apparatus acts as a way-station or assembly area for the storage, processing and packaging of various cellular secretions.
3. It package materials synthesized in the cell and dispatches them either to
intracellular targets such as plasma membrane and lysosomes or
Extracellular targets (e.g., zymogens).
IN PLANTS
It is involved in secretions of materials of primary and secondary cell wall.
During cell division, vesicles fuse to form cell plate, which becomes a part of the plasma membrane
IN ANIMALS
• Golgi complex is involved in packaging and exocytosis of zymogen (inactivated state of pancreatic enzymes) of exocrine pancreatic cells.
• GB is involved in packaging and exocytosis of mucus from goblet cells of the intestine.
• GB helps in formation of yolk and vitelline membrane of oocytes.
• It helps in the secretion of
lactoprotein of mammary glands,
secretion of hormones from endocrine cells,
secretion of melanin granules and other pigments and
ENDOPLASMIC RETICULUM (ER)
The endoplasmic reticulum (ER) forms a complex network of interconnecting membranes, bound cavities and vacuoles.
ER is absent in erythrocytes, i.e. in RBCs, eggs and embryonic cells.
Spermatocytes have poorly developed ERs.
The ER may occur in three forms:
• Lamellar form or cisternae. Cisternae are long, flattened, sac-like, unbranched tubules. They remain arranged parallel to each other in bundles. RER usually exists in cisternal form.
• Tubular form or tubules. Tubules are branched structures forming a reticular system along with cisternae and vesicles.
• Vesicular form or vesicles. Vesicles are oval, membrane-bound vacuolar structures. This form is seen in SER.
Forms of ER
The ER membrane is composed of a bimolecular layer of phospholipids, in which various proteins are embedded.
The ER membrane is continuous with the plasma membrane, nuclear membrane and Golgi apparatus.
There are two types of ER found in same or different cells: Depending upon the presence of ribosomes on ER, it is classifed into Smooth Endoplasmic Reticulum (SER) and Rough Endoplasmic Reticulum (RER).
specialized functions
Agranular or SER SER is devoid of ribosomes on its surface.
It occurs in cells involved in metabolism of lipids and glycogen.
It is found in adipose cells, interstitial cells, glycogen storing cells of liver, conduction fibres of heart, spermatocytes, leucocytes, muscle cells and retinal cells. It performs synthesis of lipids,glycogen and lipoproteins.
It helps in detoxification.
It helps in the synthesis of:-
1. triglycerides in the intestine
2. visual pigments in the eye.
Granular or RER RER has ribosomes attached to its membranes.
The RER is abundantly found in pancreatic cells, plasma cells, goblet cells, liver cells, endocrine cells, etc. Its main function is protein synthesis.
FUNCTIONS OF SER AND RER
COMMON FUNCTIONS OF SER AND RER
1. ER provides an ultrastructural skeletal framework to cell and provides mechanical support to the cell.
2. It permits exchange of molecules through its membranes.
3. It performs various synthetic and metabolic activities, since it contains many enzymes.
4. It forms nuclear envelope after nuclear division.
ENDO-MEMBRANE SYSTEM
The lipid molecules for cell membrane are formed and inserted into membrane of SER by SER itself.
The protein molecules of cell membrane are mostly synthesized and inserted into membrane at the level of rough ER.
In the process of glycosylation, short chains of sugars, called as oligosaccharides, are added to molecules of proteins and lipids at the level of Golgi apparatus.
EX;- formation of plasma membrane:- ROUGH ER----------SMOOTH ER--------GOLGI APPRATUS---------SECRETORY VESICLES------------PLASMA MEMBRANE
LYSOSOMES/ GARBAGE DISPOSAL SYSTEM/ CELLUAR HOSEKEEPERS
Lysosomes are membrane bound sac-like digestive bags, which contain hydrolytic enzymes for digestion.
Hydrolytic enzymes are made by RER.
FUNCTIONS
1. Lysosomes contain hydrolytic enzymes. They destroy any foreign material which enter the cell such as bacteria and viruses. In this way, they act as intracellular digestive system.
2. lysosomea lso remove the worn out cellular organelles by digesting them to make way for their new replacements. In this way , they remove the ebris.
3. during breaksown of cell structure, lysosomes may somestime sburst. So, hydrolytic enzymes become free. These hydrolytic enzymes then eat up their own cells. Therefore, lysoomse are also known as suicidal bags of cell.
RIBOSOMES
Small, dense, granular particles of ribonucleoprotein are called ribosomes. They occur in most of the prokaryotic and eukaryotic cells.
They are found in the matrix of mitochondria, chloroplast, and cytoplasm and are also attached to the nuclear and ER membrane.
There are two types of ribosomes, which are classified according to their size and sedimentation coefficient:
1. 70 S:-These ribosomes are smaller than 80 S ribosomes. They occur in prokaryotic cells and in mitochondria and chloroplasts of eukaryotic cells. They are further made up of 30Sand 50S sedimentation units ribosomes.
2. 80 S:-these ribosomes are large in size. They occur in the eukaryotic cells of plants and animals. They are further made up of 60Sand 40S sedimentation units ribosomes.
STRUCTURE OF RIBOSOME
1. Ribosomes are spherical in shape having a diameter of 150 to 250 AO.
2. Each ribosome has two unequal subunits composed of RNA and proteins. The smaller subunit is a cap-like structure. These subunits are porous and hydrated.
FUNCTIONS OF RIBOSOME
1. Ribosome plays an important role in the synthesis of proteins.
CENTORSOMES
Centrosomes are found only in animal cell.
It is bounded by no memebrane.
Centrosome consists of 2 granule-like centrioles.
Centrioles are hollow and cylindrical structures which are made up of microtubules.
FUNCTION
Centrosomes help in cell division in animal cells. During cell division, centrioles migrate to the poles of animal cells and are involved in the formation of the spindle.
IMPORTANT MICROBODIES
GLYOXISOMES
Glyoxisomes are single membrane bound living structure of sytoplasm .
This structure is completely absent in aninlas . this occurs in plants mainly in lipid storing organs such as oil-yileding seeds.
In this structure, enzymes of gly-oxillate cycle occur. It means this operates glyoxiallte cycle by which lipids and fatty acids are converted into carbohydrates.
PER-OXISOMES/URICOSOME
Per-oxisomes are spherical orgellees contaiing powerful oxidative enzymes.
They are bounded by single membrane.
Per-oxisomes perform the function of detoxification i.e. removal of toxic substances from the cell.
FUNCTION
1. Catalase enzyme of peroxisomes catalyses the decomposition of hydrogen peroxide (H2O2) to water and oxygen. Hydrogen peroxide is the by-product of certain cell oxidations and is also very toxic. So, it must be eliminated easily.
VACOULES/ STORAGE SACS
Vacuoles are fluid filled or solid filled and membrane bounded spaces.
The vacuolar membrane is typically a single unit membrane and is often considered with the maintenance of water balance.
In plants cells, vacuoles are large, and permanent.
The vacuole is bounded by a membrane called as tonoplast. The vacuole is filled with a cell sap which is watery solution rich sugars, amino acids, protein, mineral and metabolic wastes.
FUNCTION:-
1. Vacuoles help in maintaining the osmotic pressure in a cell. Thus, it helps in osomo-regulation.
2. Vacuoles store toxic metabolic by-products.
3. They provide turgidity and rigidity to plant cell.
NUCLEUS / CONTROLLING CENTRE OF CELL (GENETIC STRUCUTE OF CELL)
1. Nucleus is is the centrally located, spherical, cellular organelle enclosed in a double membrane. It controls all the vital activities in the cytoplasm and carries DNA within itself.
2. Nucleus is responsible to control cellular activities and determination of structure and function of cell.
3. Nucleus was discovered by Robert brown.
4. According to strasburger, formation of new nucleus takes place from pre-existing nucleus by its own division.
5. Most cells are uninucleate, but some cells are binucleate or multinucleate (for example: Paramoecium, which has two nuclei). Cells, which possess many nuclei, are called coenocytic (for example: Fungus Rhizopus and Alga Vaucheria).
STRUCTURE OF NUCLEUS
When a cell is fixed and stained with suitable dyes, several structures became noticeable in the nucleus on observation under a light microscope:
• Nuclear envelope or karyotheca or nuclear membrane
• Nuclear sap or nucleoplasm or karyoplasm
• Nucleolus.
• Chromosomes.
Nucleus
NUCLEAR MEMBRANE
The nucleoplasm is bounded by the nuclear envelope. The nuclear envelope is porous.The nuclear envelope is formed of two concentric unit membranes.
a. The inner nuclear membrane is called the nuclear lamina.
b. The outer nuclear membrane is continuous with the endoplasmic reticulum (ER).
A fluid-filled, perinuclear space is present between the inner and outer nuclear membranes. This perinuclear space is continuous with the ER lumen.
NUCLEOPLASM/KARYOLYMPH
The protoplasm or semi-solid fluid of nucleus is called as nucleoplasm.
Nucleoplasm has main constitutents of nucleoprotein , phosphates, and lipids.
Nuclear proteins are of 2 types:-
Acid protein:-have high molecular weight like phopho-protein
Basic protein:- have lower molecular weight like hisotnes, protamines.
NUCLEOLUS
Nucleolus is a membrane less, dense non-genetic acidophilic body of nucleus of eukaryotic cell.
Nucleolus is mainly composed of phosphoproteins and RNA (or r-RNA).
Nucleolus is involved in synthesis of r-RNA, ribosomes, nucleoprotein, histone protein.
The size of the nucleolus depends upon the activity of the cell.
CHROMOSOEMS/HEREDITY CARRIER
Chromosomes are thread-like genetic structure and it takes part in inheritance from one generation to another.
The number and type of chromosomes is definite and fixed in a particular species. Like in human body, each cell have 46 chromosomes(having 44autosomes and 2 sex-chromosomes)
True chromosomes consists of DNA, RNA, and histone proteins.
Chromatin fibres
Chromatin fibres are thread-like, coiled substances present in the nucleoplasm. These are observed only when the nucleus is in interphase.
During cell division, these chromatin fibres become thick ribbon-like threads known as chromosomes.
Each chromosome consists of a constriction called the centromere. The position of the centromere decides the morphological type of chromosome.
Types of chromosomes
• Telocentric-Centromere is at the proximal end of the chromosome
• Acrocentric-Centromere is present near one of the ends of the chromosome, thus having at one end a very short arm and at other end a long arm.
• Submetacentric-Centromere is present near the centre of the chromosome, thus forming two unequal arms.
• Metacentric-Centromere is present at the centre of the chromosome, thus forming two equal arms.
FUNCTION OF NUCLEUS
1. It contains the genetic information for metabolism, reproduction, development, behaviour of the organism, etc. It duplicates this information and passes it on to next generations.
2. It controls cellular activities and enzyme activities, through formation of RNA.
3. Nucleolus takes part in the biogenesis of ribosomes.
NUCLEIC ACID
DNA(Deoxy-ribonucleic acid):- DNA is the universal genetic structure of cell, having double helix structure.
DNA consists of adenine and guanine as purine bases and cytosine and thymine as pyramidine bases.
RNA (Ribo-nucleic acid):-RNA also becomes the genetic structure in some viruses like in HIV.
RNA consists of adenine and guanine as purine bases but cytosine and uracil as pyramidine bases.
GENE/HEREDITY CHRACTER
The molecule or the segment of a nucleic acid, which can code at least a genetic character and is capable to carry this character generation to generation, is called as gene.
In all cellular oganelles, genes are always made up of pure DNA molecule and is always a ds-DNA. But in few viruses, gene is made up of ssDNA or RNA.
TRANSPORT OF SUBSTANCES THROUGH PLASMA MEMBRANE
1. DIFFUSION
The movement of substances from higher concentration to lower contraction is called as diffusion.
EX: - movement of gases like O2 and CO2 through PM is always through diffusion.
2. OSMOSIS
The movement of water molecules (solvent) from region of lower to higher concentration through SPM is called as osmosis.
EX: - Protoplasm moves in and out from the cell through the process of osmosis.
HYPOTONIC SOLUTION:- When concentration of cell becomes high in comparison to its surrounding solution, the surrounding solution is called as hypotonic solution in compare to cell solution. When a cell is placed in hypotonic solution, then water moves from solution to cell, thus cell swells up.
HYPERTONIC SOLUTION:- When concentration of cell becomes low in comparison to its surrounding solution, the surrounding solution is called as hypertonic solution in compare to cell solution. When a cell is placed in hypertonic solution, then water moves from cell to surrounding solution, thus cell shrinks down.
2. All organisms of nature are composed of cells and cell products. Thus cell is called as structural unit of life.
3. All metabolic reactions take place in cells, essential for life. Thus, cell is called as functional unit of life.
4. Every living cell of an organism keeps its chemical composition steady. Such balanced condition is called as Homeostasis.
5. An organism does not have any non-functional cell. Even the dead cell is considered to be functional cells. Thus, dead cell also play a role in multicellular organisms, because all cells are functional.
6. Prions, viroids and viruses are the pathogenic, non-cellular, smallest organisms.
They cannot perform living activities in free form because they do not have protoplasm. Therefore, in free form, they are like non-living particles.
To perform living activities they require protoplasm or cytoplasm of host cell.
COMPOSTITON OF PRIONS, VIROIDS AND VIRUSES
organisms Composition of organisms
PRIONS prions do not have its own genetic structure (DNA or RNA). It is made up of few molecules of proteins.
VIROIDS viroids are made up of single nacked molecule of RNA.
VIRUSES
(non-cellular living organisms) Each molecule of viruses is made up of protein and single molecule of either of DNA or RNA.
Animal viruses mostly contain DNA.
Plant viruses mostly contain RNA.
Viruses are regarded as the connecting link between living and non-living.
The chemical reaction occurs in presence of enzymes is called as biochemical process. This process may occur inside the cell or outside the cell.
The biochemical process occurs inside the living cells in protoplasm are called as metabolism.
Metabolism term was coined by Schwann. Metabolism is of 2 types:-
ANABOLISM CATABOLISM
The process by which complex substances are produced by simpler ones by the use of energy is called as anabolism. The process by which complex higher molecule substances are broken down into simpler and soluble substances is called as catabolism.
Anabolism is an ENDERGONIC (energy absorbing) and constructive process. Catabolism is an EXERGNOIC (energy releasing) and destructive process.
EX-photosynthesis is an anabolic process. Ex: - Respiration is a catabolic process.
CELL AND ITS DISCOVERY
1. In 1665, Robert Hook discovered cell from the cork cambium of OAK plant (quercus suberus).
2. Actually, Robert Hooke placed thin slices of cork cambium under compound microscope. He observed certain bee-hive like structures which he called them as cell.
3. This description of his discovery was given in his own written book “micrographia”.
4. But cork cambium is a dead cell, having no protoplasm. So, Robert Hooke actually discovered cell wall.
5. By this way, the first discovered cell is dead eukaryotic cell.
6. The first living cell was discovered by German
CELL SIZE
TYPE OF CELL EXAMPLE
Smallest cell Mycoplasma gallisepticum
(PPLO-pleuro pneumonic like organisms).
Largest animal cell Ostrich Egg.
(130× 135)
Human body cell 20-30μm. (Average size)
Nerve cell is largest Human body cell.
Longest unicellular plant/
( eukaryotic unicellular algae) Acetobularia
(Up to 10 cm length).
The smallest organisms which can occur in free form as an organism is mycoplasma gallisepticum (PPLO-pleuro pneumonic like organisms). Because it does not have a cell wall, therefore it is known as joker of plant kingdom.
Neurons in embryo and phloem fibres in plants especially angiosperms may be considered as longest cells.
TYPES OF ORGANISMS ON THE BASIS OF NUMBER OF CELLS
a) Unicellular organisms: - unicellular organisms are those organisms whose body is made up of only one cell.
Ex:-certain bacteria, yeast, paramecium (slipper like organism), amoeba
b) Multicellular organisms: - Multicellular organisms are those organisms whose body is made up of more than one cell.
Ex:-most of plants and animals.
NOTES:-
Unicellular organisms are less efficient.
Multicellularity is possible due to division of labour.
CELL THEORY
1. Botanist Schleiden and Zoologist Schwann proposed the fundamental principal of biology in 1838-1839. This principle is known as cell theory.
POSTULATES OF CELL THEORY
1. Cell is the fundamental unit of life and is the building block of life and organisms. All organisms are made up of cell and its products.
2. All type of organisms, whether it is small or large, plant or animal, consists of same protoplasm containing cell. In this way, all organisms of nature are related to each other.
CELL PRINCIPLE
3. Rudolf virchow stated that “omnis cellula e cellula” i.e. new cells arises from pre-existing cell.
NOTES:-VIRUSES are not considered as organisms because viruses are merely nucleo-protein particles and lack cytoplasm and metabolic machinery. So, they are exception to cell theory. Viruses are considered as connective link between living and non-living.
MICROSCOPY
The study of micro-organims and structures of cells under microscope is called as microscopy.
IMPORTANT MICROSCOPE USED DURING STUDY OF CELL BIOLOGY
OBSERVED STRUCTURES
Compound Microscope Cell wall nucleus, plastids, vacuoles, etc.
However, some other organelles such as mitochondria, golgi complex, nucleus, spindle apparatus and chromosomes can be observed with the help of compound microscope only after employing specific staining techniques.
Phase contrast microscope
(Zernike) In a living cell, certain structures and organelles such as chromosomes, spindle apparatus, etc. can be observed with the help of phase-contrast
Microscope.
Electron microscope For ultra structures as well as for submicroscopic structures.
Ribosome discovery made possible due to electron microscope.
Transmission Electron Microscope (TEM) ( developed by Knoll and Ruska)
Scanning Electron Microscope (SEM) Gerd Binning It is used for the study of fine structures and details of sub-microscopic components such as pollen grains, RBC etc.
It is most effective in observing 3-D images.
TYPES OF CELL
On the basis of presence of nucleus, cells are classified into 2 types:-
Prokaryotic cell
Eukaryotic cell
Prokaryotic cell Eukaryotic cell
Prokaryotic cell does not have a true nucleus, but a nucleoid. Nucleoid lacks nuclear membrane Eukaryotic cell has a nucleus covered with a nuclear membrane.
It has a single circular DNA, not associated with protein histone. It has multiple, linear DNA, associated with protein histone.
Cell wall is made up of peptidoglycan. Cell wall is made up of chitin in fungi
cell wall is made up of cellulose in higher plants
Ribosomes of 70S type. Ribosomes of 80S type.
Membrane-bound organelles (such as MPGERL etc) are absent Membrane-bound organelles are present.
Flagella, if present contain tubules of flagellin. Flagella, when present have 9 + 2 microtubules
PROKARYOTIC CELL
Prokaryotic cells are extremely small, least evolved cell.
In these cells, nuclear membrane and cell organelles (like MPGERL) are absent.
Ex:- Mycoplasma, thermoplasma, rikettsia, spirochete, bacteria and cyanobacteria(BGA)
SRUCTURE OF PROKARYOTIC CELL
STRUCTURE FUNCTION
mucilaginous sheath MS is the glycocalyx non-living slime layer present at the outer surface of cell wall.
Mucilaginous heath is a protective covering and protects the cell against harmful radations, high pH and temperature etc.
cell wall Cell wall is the outermost covering of cell and is responsible for protection and mechanical support to the cell.
The cell walls of prokaryotes are made up of peptidoglycon and phospho-lipids.
protoplast (nucloid +cytoplasm)
PROTOPLAST
STRUCTURE FUNCTION
Nucloid/
(incipient or nacked nucleus) In prokaryotes, there is a single ds-DNA occurs in cell. This ds_DNA occurs in free helical or circular form.
There is no nuclear membrane which surrounds this genetic structure. Therefore, therefore this DNA represents the whole genetic structure and is known as nucloid.
mesosomes/ chondroid At certain places, plasma membrane of cell infolds towards its protoplasm. This infolding is known as mesosomes.
Because of presence of respiratory enzymes, mesosomes perform the function of aerobic respiration and produces ATP. Therefore, this structure has been considered as analogous to mitochondria.
Due to development of mesosomes, surface area of plasma membrane increase. This increases the work efficiency in prokaryotes.
storage granules In storage granules, food is stored mostly in the form of lipids and glycogen.
RNA All 3 kinds of non-genetic RNA occur in prokaryotes.
The synthesis of RNA takes place from DNA molecule by the process of transcription.
Ribosomes/ cytoplasmic nucleo-protein ribosomes are membrane less small structure, mainly involve in protein synthesis.
The size of ribosomes in prokaryotic cell is from 64S-72S, but on an average, 70-S type of ribosomes occurs in cytoplasm.
The 70-S type of ribosomes can be split into 2 sub-units of 50-S +30-S.
flagellum
locomotary organs Each flagellum is made up of single hollow rod like fibre.
Flagellum is made up of flagellin protein.
The action of flagellum is like the propellant of boat.
plasmid/ magic rings
(extra-nuclear heredity determinants) a) Plasmid are the cytoplasmic genetic units, other then DNA.
b) Plasmid contains genes. Function of plasmid depends on their constituent genes.
TYPES OF PLASMID:-
a) CONJUGATIVE PLASMID: - plasmids have their self capacity to transform form donor to recipient.
Ex:-F-plasmid (fertility –plasmid), R-plasmid, Col-plasmid.
b) NON-CONJUGATIVE PLASMID:-plasmids, which do not have the self capacity to transfer from donor to recipient.
Ex:-Ti-plasmid, cryptic -plasmid
EUKARYOTIC CELL
1. Eukaryotic cell is the advanced cell with a true and distinct nucleus having a nuclear membrane.
2. Due to presence of various membranes and membrane bound cell organelles , the structural organization of eukaryotic cell becomes more complex.
3. Ex: - all plants and most of the animals.
TYPES OF EUKARYOTIC CELL
Plant cell Animal cell
Cell wall is present in plant cells. It surrounds plasma membrane of the cell. Cell wall is absent in animal cells.
Plant cells have a large central vacuole with a thin layer of cytoplasm. Generally, animal cells do not possess vacuoles (few small vacuoles may be present in some cells).
Chloroplasts are present in all plant cells. It performs photosynthesis. Chloroplasts are absent in animal cells, except in euglena.
Centrosomes are absent. The centrosome is present.
Plant cells have simpler units of Golgi apparatus called dictyosomes. Animal cells have prominent Golgi complex near nucleus.
CELL WALL
Cell wall is the outermost covering of plant cell.
Cell wall is composed mainly of cellulose. Cellulose is a polysaccharide of β-D-glucose.
Other important component of cell wall are:-
COMPONENT OF CELL WALL FUNCTION
Hemicellulose It develops the connection between matrix and fibres of cellulose.
pectin(fruit jelly) Pectin acts as cement. The maximum % of pectin occurs in collenchyma tissue.
lignin Lignin provides hardness and rigidity to the cell.
the maximum % of lignin occurs in sclerenchyma tissue
suberin (wax of fatty acids) suberin provides hardness and rigidity to the cell.
It also provides impermeability for water.
Cell wall is a complex structure and can be differentiated as:
Primary cell wall: - main and oldest layer of cell wall.
Secondary cell wall:- occur in xylem , cork cell and sclerenchyma.
Tertiary cell wall: - occur in few plant tissues like tracheids of xylem.
FUNCTIONS OF CELL WALL
1. It provides mechanical support and protection to plant cells.
2. It facilitates the cellular transport, as it is permeable to water and solute.
3. It determines the shape of the cell and prevents it from desiccation.
MIDDLE LAMELLA
1. Plant cells remain cemented together by dense intercellular matrix, called as middle lamella. It is formed soon after cell division.
2. Middle lamella is composed of pectin, lignin and proteins and salts of calcium and magnesium.
3. Un-ripened fruits are hard due to intake of middle lamella.
PLASMODESMATA
Living cells are connected to each other by fine cytoplasmic channels called as plasmodesmata which pass through cell walls. These facilitate transport of substances between cells.
PLASMA MEMBRANE / PLASMALEMMA/ CELL MEMBRANE
1. PM is living, tri-laminar, and semi-permeable membrane, which covers and protects the protoplasm and cell organelles from surrounding world.
2. It is present just inside the cell wall in a plant cell but it becomes the outermost covering of the animal cell.
3. PM remain in quasi-fluid state. This enables them to undergo dynamic changes.
The older ones are continuously replaced by the new ones.
They can be extended, folded and moved, so that cell can change their form, size and functions.
MODEL FOR ULTRASTRUCTURE OF BIOLOGICAL MEMBRANE
UNIT MEMBRANE MODEL:- BY ROBERTSON
Robertson found trilaminar compositions in most of the membranes of cell organelles. In 1959, he put forward the concept of unit membrane.
A unit membrane has protein-lipid-protein arrangement.
The protein layers are electron dense and lipid layer is electron lucent.
It is found in plasma membrane, endoplasmic reticulum, Golgi complex, lysosomes and plastids. It is also found in mitochondria and nucleus. unit membrane.
FLUID MOSAIC MODEL
- (by singer and Nichelson)
POSTULATES
1. protein icebergs in the sea of lipids: -
According to Singer and Nicholson, PM is made up of a bilayer of phospholipids.
In this bilayer, 3 kinds of potein molecules are floated in phospholipids fluid.
Protein which are present in PM not only give strength to membrane but also function as enzymes (intra-cellular chemical messenger), transport proteins like channels and pumps, or can function as a receptor protein,
2. concept of fluidity:-
The fluidity concept means that the main components of membranes, lipids and oligosaccharides are held in place by non-covalent interactions.
Fluid mosaic model of cell membrane
PHOSPHOLIPID STRUCTURE
Phospholipids are arranged such that its polar heads are towards the cytosol and extra-cellular fluid, while non-polar tails are inwards.
HYDROPHILIC POLAR HEADS
HYDROPHOBIC POLAR TAILS
PROTEINS
Proteins, which are floated in lipid bi-layer, are of 3 types:-
1. INTRINSIC PROTEINS: - intrinsic proteins are embedded completely inside the lipid bi-layer.
2. EXTRINSIC PROETEINS: - extrinsic protein occurs on inner surface or outer surface of lipid membrane.
3. PERIPHERAL PROTEINS:-proteins which are attached superficially are called as peripheral proteins. Large globular integral proteins project beyond the lipid layer. These are believed to have channels through which water-soluble materials can pass.
Plasma membrane under electron microscope
FUNCTION OF PLASMA MEMBRANE
1. SELECTIVE PERMEABILITY: -
Membranes are selectively permeable i.e. they allow useful substance to pass through them, but do not allow harmful substance to pass through them.
Selective permeability of cell is obtained by diffusion and osmosis.
2. CELL RECOGNIZATION:-
Some oligosaccharides project into extracellular fluid from the outer surface of the membranes, which are bound to lipids and integral proteins. The cells interact with one another according to the influence of the oligosaccharides. They recognize each other on the basis of these glycolipids and glycoproteins.
This capacity of cell membranes to recognize each other plays a very important role in blood grouping, immune response, cancer, rejection of transplanted organs, etc.
FUNCTIONS OF CYTOPLASM
1. It possesses sensitivity to stimulation. That is it shows irritability.
2. It transmits substances from one region of the cell to the other.
3. It brings about movement due to cyclosis. The cytoplasm is the seat of various metabolic activities.
MITOCHONDRIA/ POWER HOUSE OF THE CELL
Mitochondria are tiny energy batteries of cell, which provide energy to the cell.
Mitochondria are generally filamentous or granular in shape. But they may change their form depending upon the physiological conditions of the cells. They may be spherical, oval, cylindrical, sausage-shaped in their form.
During cell division, the daughter cell inherits mitochondria from mother cell.
Factors affecting mitochondria distribution and number are:-
• They are present more in number, in regions where RER is present.
• Their number also depends upon the type and functional state of the cell. More active is the cell; more is the number of mitochondria.
• They are abundantly found in the bases of cilia or cells of germinating seeds, because these cells are involved in energy-dependent activities.
STRUCTURE OF MITOCHONDRIA
Mitochondria have a double membrane envelope.
a. OUTER MEMBRANE:-The outer membrane is smooth and has a transport protein called porin. This porin forms aqueous channels through the lipid bilayer. Thus outer membrane is permeable.
b. INNER MEMBRANE:-
The inner membrane is highly convoluted. The inner membrane have several folds, towards the matrix of mitochondria. These folds are called as cristae.
Inner membrane is impermeable. The cristae increase the surface area of the inner membrane.
The outerside of the inner membrane has cytosol or C face. The innerside of the inner membrane has M face.
Attached to the M face are stalked elementary particles or inner membrane subunits called oxysomes ( F1 particles or F0 - F1 particles). These are meant for ATP synthesis and oxidation.
MITOCHONDRIAL MATRIX:-
The mitochondrial matrix is a dense, homogeneous, proteinaceous material.
It contains lipids, proteins, circular DNA molecules, ribosomes, and certain granules.
It contains enzymes essential for respiration (oxidation of food).
FUNCTIONS OF MITOCHONDRIA
1. CELLULAR RESPIRATION:-
Mitochondria carry out oxidation of carbohydrates and fats and releases energy in the form of ATP (adenosine tri-phosphate).Therefore, mitochondria are known as 'power house of the cell.
ATP is known as energy currency of the cell.
2. They perform important functions such as oxidation, dehydration, oxidative phosphorylation, etc.
3. Mitochondria are called as semi-autonomous organelles and are able to synthesize their own proteins.
PLASTID
Plastids are double-layered organelles found only in plant cells.. They are self-replicating organelles
Types of plastids
Plastids are classified according to their structure, pigment and functions:
1. Leucoplasts
2. Chromoplasts
3. Chloroplasts
Leucoplasts
these are colourless plastids.
They are found in fruits, seeds, tubers and rhizomes. They are also found in those regions of plants, which do not receive any light.
They do not contain thylakoids and ribosomes. They store nutrients.
These are again classified into three types:
• Amyloplast – synthesizes and stores starch.
• Elaioplast – stores lipids.
• Proteinoplast – stores proteins and may contain a few thylakoids.
Chromoplasts
These are coloured plastids.
Chromoplasts contains carotenoids and other type of pigments. They provide colour to flowers, fruits and some roots such as carrots.
Chloroplasts
Chloroplasts are green-coloured plastids (in Greek, chloro means 'green')
Chloroplast contains mainly 2 pigments:- chlorophyll-a and chlorophyll-b,
They are the most common plastids in plants and are very important, because they perform the function of photosynthesis.
Generally, chloroplasts are biconvex, but may be found in varying shapes.
STRUCTURE OF CHLOROPLAST
Chloroplast has been classified into three main parts:
1. Envelope:- Each chloroplast is covered by double membrane called the envelope.
a. OUTER MEMBRANE: - The outer membrane is permeable.
b. INNER MEMBRANE: - the inner membrane is less permeable.
2. GRANA: -
grana are stacks of membrane-bounded, flattened disc-like sacs called as thylakoids.
There may be 40 to 80 grana in the matrix of a single chloroplast.
All the granum is connected to each–other by frests.
Thylakoids have quantasomes, which contain nearly 230 molecues of chlorophyll.
3. STROMA/MATRIX
The stroma is a gel-like fluid, which surrounds the thylakoids (grana)..
It contains 50 per cent of the total chloroplast proteins, which are of soluble types.
It also contains ribosomes and DNA molecules.
Grana are the site of light reaction. During photosynthesis, chlorophyll molecules breaks water molecule.
stroma is the site of dark reaction(CO2-fixation). The synthesis of sugars, starch, fatty acids and some proteins occurs in the stroma.
FUNCTIONS OF CHLOROPLAST
1. Chloroplast traps solar energy and convert this inorganic energy into organic energy.
2. Chromoplasts provide various colours to flowers to attract insects for pollination.
3. Leucoplasts store food in the form of carbohydrates (starch), fats(lipids), and protein.
GOLGI BODY/ GOLGI COMPLEX
GB is tiny assembly area for the storage, processing and packaging of various cellular secretions.
In plants, it is called as dictyosome, because in plants cisternae are formed at cis-face of Golgi and vesicles are bounded off from trans face of Golgi.
STRUCTURE OF GOLGI COMPLEX
Golgi complex consists of 3 basic components:
1. CISTERNAE(Flattened sacs)
1. Cisternae are flattened curved closed compartments lying parallel to each other. It has 2 ends:-
1. PROXIMAL END:- The convex end of golgi body is the proximal end. This end is called as the cis-face. The proximal Golgi body is formed by the fusion of ER-derived vesicles.
2. DISTAL END: - the concave end is the distal end. This end is called as the trans-face. The distal GB ‘gives their all’ to vesicle formation and disappear. Thus, Golgi cisternae are constantly renewed.
2. TUBULES:-Tubules surround the cisternae; in fact, they radiate from it.
3. SECRETORY VESICLES:-Vesicles are of three types:
• Transitional vesicles are present on the cis-face of Golgi. These fused together to form new cisternae.
• The secretory vesicles are discharged from the margins of the cisternae. They pinch off as zymogen granules.
• Coated vesicles are found at the periphery of the organelle.
GENERAL FUNCTION OF GOLGI COMPLEX
1. The main function of the golgi apparatus is secretory.
2. Golgi apparatus acts as a way-station or assembly area for the storage, processing and packaging of various cellular secretions.
3. It package materials synthesized in the cell and dispatches them either to
intracellular targets such as plasma membrane and lysosomes or
Extracellular targets (e.g., zymogens).
IN PLANTS
It is involved in secretions of materials of primary and secondary cell wall.
During cell division, vesicles fuse to form cell plate, which becomes a part of the plasma membrane
IN ANIMALS
• Golgi complex is involved in packaging and exocytosis of zymogen (inactivated state of pancreatic enzymes) of exocrine pancreatic cells.
• GB is involved in packaging and exocytosis of mucus from goblet cells of the intestine.
• GB helps in formation of yolk and vitelline membrane of oocytes.
• It helps in the secretion of
lactoprotein of mammary glands,
secretion of hormones from endocrine cells,
secretion of melanin granules and other pigments and
ENDOPLASMIC RETICULUM (ER)
The endoplasmic reticulum (ER) forms a complex network of interconnecting membranes, bound cavities and vacuoles.
ER is absent in erythrocytes, i.e. in RBCs, eggs and embryonic cells.
Spermatocytes have poorly developed ERs.
The ER may occur in three forms:
• Lamellar form or cisternae. Cisternae are long, flattened, sac-like, unbranched tubules. They remain arranged parallel to each other in bundles. RER usually exists in cisternal form.
• Tubular form or tubules. Tubules are branched structures forming a reticular system along with cisternae and vesicles.
• Vesicular form or vesicles. Vesicles are oval, membrane-bound vacuolar structures. This form is seen in SER.
Forms of ER
The ER membrane is composed of a bimolecular layer of phospholipids, in which various proteins are embedded.
The ER membrane is continuous with the plasma membrane, nuclear membrane and Golgi apparatus.
There are two types of ER found in same or different cells: Depending upon the presence of ribosomes on ER, it is classifed into Smooth Endoplasmic Reticulum (SER) and Rough Endoplasmic Reticulum (RER).
specialized functions
Agranular or SER SER is devoid of ribosomes on its surface.
It occurs in cells involved in metabolism of lipids and glycogen.
It is found in adipose cells, interstitial cells, glycogen storing cells of liver, conduction fibres of heart, spermatocytes, leucocytes, muscle cells and retinal cells. It performs synthesis of lipids,glycogen and lipoproteins.
It helps in detoxification.
It helps in the synthesis of:-
1. triglycerides in the intestine
2. visual pigments in the eye.
Granular or RER RER has ribosomes attached to its membranes.
The RER is abundantly found in pancreatic cells, plasma cells, goblet cells, liver cells, endocrine cells, etc. Its main function is protein synthesis.
FUNCTIONS OF SER AND RER
COMMON FUNCTIONS OF SER AND RER
1. ER provides an ultrastructural skeletal framework to cell and provides mechanical support to the cell.
2. It permits exchange of molecules through its membranes.
3. It performs various synthetic and metabolic activities, since it contains many enzymes.
4. It forms nuclear envelope after nuclear division.
ENDO-MEMBRANE SYSTEM
The lipid molecules for cell membrane are formed and inserted into membrane of SER by SER itself.
The protein molecules of cell membrane are mostly synthesized and inserted into membrane at the level of rough ER.
In the process of glycosylation, short chains of sugars, called as oligosaccharides, are added to molecules of proteins and lipids at the level of Golgi apparatus.
EX;- formation of plasma membrane:- ROUGH ER----------SMOOTH ER--------GOLGI APPRATUS---------SECRETORY VESICLES------------PLASMA MEMBRANE
LYSOSOMES/ GARBAGE DISPOSAL SYSTEM/ CELLUAR HOSEKEEPERS
Lysosomes are membrane bound sac-like digestive bags, which contain hydrolytic enzymes for digestion.
Hydrolytic enzymes are made by RER.
FUNCTIONS
1. Lysosomes contain hydrolytic enzymes. They destroy any foreign material which enter the cell such as bacteria and viruses. In this way, they act as intracellular digestive system.
2. lysosomea lso remove the worn out cellular organelles by digesting them to make way for their new replacements. In this way , they remove the ebris.
3. during breaksown of cell structure, lysosomes may somestime sburst. So, hydrolytic enzymes become free. These hydrolytic enzymes then eat up their own cells. Therefore, lysoomse are also known as suicidal bags of cell.
RIBOSOMES
Small, dense, granular particles of ribonucleoprotein are called ribosomes. They occur in most of the prokaryotic and eukaryotic cells.
They are found in the matrix of mitochondria, chloroplast, and cytoplasm and are also attached to the nuclear and ER membrane.
There are two types of ribosomes, which are classified according to their size and sedimentation coefficient:
1. 70 S:-These ribosomes are smaller than 80 S ribosomes. They occur in prokaryotic cells and in mitochondria and chloroplasts of eukaryotic cells. They are further made up of 30Sand 50S sedimentation units ribosomes.
2. 80 S:-these ribosomes are large in size. They occur in the eukaryotic cells of plants and animals. They are further made up of 60Sand 40S sedimentation units ribosomes.
STRUCTURE OF RIBOSOME
1. Ribosomes are spherical in shape having a diameter of 150 to 250 AO.
2. Each ribosome has two unequal subunits composed of RNA and proteins. The smaller subunit is a cap-like structure. These subunits are porous and hydrated.
FUNCTIONS OF RIBOSOME
1. Ribosome plays an important role in the synthesis of proteins.
CENTORSOMES
Centrosomes are found only in animal cell.
It is bounded by no memebrane.
Centrosome consists of 2 granule-like centrioles.
Centrioles are hollow and cylindrical structures which are made up of microtubules.
FUNCTION
Centrosomes help in cell division in animal cells. During cell division, centrioles migrate to the poles of animal cells and are involved in the formation of the spindle.
IMPORTANT MICROBODIES
GLYOXISOMES
Glyoxisomes are single membrane bound living structure of sytoplasm .
This structure is completely absent in aninlas . this occurs in plants mainly in lipid storing organs such as oil-yileding seeds.
In this structure, enzymes of gly-oxillate cycle occur. It means this operates glyoxiallte cycle by which lipids and fatty acids are converted into carbohydrates.
PER-OXISOMES/URICOSOME
Per-oxisomes are spherical orgellees contaiing powerful oxidative enzymes.
They are bounded by single membrane.
Per-oxisomes perform the function of detoxification i.e. removal of toxic substances from the cell.
FUNCTION
1. Catalase enzyme of peroxisomes catalyses the decomposition of hydrogen peroxide (H2O2) to water and oxygen. Hydrogen peroxide is the by-product of certain cell oxidations and is also very toxic. So, it must be eliminated easily.
VACOULES/ STORAGE SACS
Vacuoles are fluid filled or solid filled and membrane bounded spaces.
The vacuolar membrane is typically a single unit membrane and is often considered with the maintenance of water balance.
In plants cells, vacuoles are large, and permanent.
The vacuole is bounded by a membrane called as tonoplast. The vacuole is filled with a cell sap which is watery solution rich sugars, amino acids, protein, mineral and metabolic wastes.
FUNCTION:-
1. Vacuoles help in maintaining the osmotic pressure in a cell. Thus, it helps in osomo-regulation.
2. Vacuoles store toxic metabolic by-products.
3. They provide turgidity and rigidity to plant cell.
NUCLEUS / CONTROLLING CENTRE OF CELL (GENETIC STRUCUTE OF CELL)
1. Nucleus is is the centrally located, spherical, cellular organelle enclosed in a double membrane. It controls all the vital activities in the cytoplasm and carries DNA within itself.
2. Nucleus is responsible to control cellular activities and determination of structure and function of cell.
3. Nucleus was discovered by Robert brown.
4. According to strasburger, formation of new nucleus takes place from pre-existing nucleus by its own division.
5. Most cells are uninucleate, but some cells are binucleate or multinucleate (for example: Paramoecium, which has two nuclei). Cells, which possess many nuclei, are called coenocytic (for example: Fungus Rhizopus and Alga Vaucheria).
STRUCTURE OF NUCLEUS
When a cell is fixed and stained with suitable dyes, several structures became noticeable in the nucleus on observation under a light microscope:
• Nuclear envelope or karyotheca or nuclear membrane
• Nuclear sap or nucleoplasm or karyoplasm
• Nucleolus.
• Chromosomes.
Nucleus
NUCLEAR MEMBRANE
The nucleoplasm is bounded by the nuclear envelope. The nuclear envelope is porous.The nuclear envelope is formed of two concentric unit membranes.
a. The inner nuclear membrane is called the nuclear lamina.
b. The outer nuclear membrane is continuous with the endoplasmic reticulum (ER).
A fluid-filled, perinuclear space is present between the inner and outer nuclear membranes. This perinuclear space is continuous with the ER lumen.
NUCLEOPLASM/KARYOLYMPH
The protoplasm or semi-solid fluid of nucleus is called as nucleoplasm.
Nucleoplasm has main constitutents of nucleoprotein , phosphates, and lipids.
Nuclear proteins are of 2 types:-
Acid protein:-have high molecular weight like phopho-protein
Basic protein:- have lower molecular weight like hisotnes, protamines.
NUCLEOLUS
Nucleolus is a membrane less, dense non-genetic acidophilic body of nucleus of eukaryotic cell.
Nucleolus is mainly composed of phosphoproteins and RNA (or r-RNA).
Nucleolus is involved in synthesis of r-RNA, ribosomes, nucleoprotein, histone protein.
The size of the nucleolus depends upon the activity of the cell.
CHROMOSOEMS/HEREDITY CARRIER
Chromosomes are thread-like genetic structure and it takes part in inheritance from one generation to another.
The number and type of chromosomes is definite and fixed in a particular species. Like in human body, each cell have 46 chromosomes(having 44autosomes and 2 sex-chromosomes)
True chromosomes consists of DNA, RNA, and histone proteins.
Chromatin fibres
Chromatin fibres are thread-like, coiled substances present in the nucleoplasm. These are observed only when the nucleus is in interphase.
During cell division, these chromatin fibres become thick ribbon-like threads known as chromosomes.
Each chromosome consists of a constriction called the centromere. The position of the centromere decides the morphological type of chromosome.
Types of chromosomes
• Telocentric-Centromere is at the proximal end of the chromosome
• Acrocentric-Centromere is present near one of the ends of the chromosome, thus having at one end a very short arm and at other end a long arm.
• Submetacentric-Centromere is present near the centre of the chromosome, thus forming two unequal arms.
• Metacentric-Centromere is present at the centre of the chromosome, thus forming two equal arms.
FUNCTION OF NUCLEUS
1. It contains the genetic information for metabolism, reproduction, development, behaviour of the organism, etc. It duplicates this information and passes it on to next generations.
2. It controls cellular activities and enzyme activities, through formation of RNA.
3. Nucleolus takes part in the biogenesis of ribosomes.
NUCLEIC ACID
DNA(Deoxy-ribonucleic acid):- DNA is the universal genetic structure of cell, having double helix structure.
DNA consists of adenine and guanine as purine bases and cytosine and thymine as pyramidine bases.
RNA (Ribo-nucleic acid):-RNA also becomes the genetic structure in some viruses like in HIV.
RNA consists of adenine and guanine as purine bases but cytosine and uracil as pyramidine bases.
GENE/HEREDITY CHRACTER
The molecule or the segment of a nucleic acid, which can code at least a genetic character and is capable to carry this character generation to generation, is called as gene.
In all cellular oganelles, genes are always made up of pure DNA molecule and is always a ds-DNA. But in few viruses, gene is made up of ssDNA or RNA.
TRANSPORT OF SUBSTANCES THROUGH PLASMA MEMBRANE
1. DIFFUSION
The movement of substances from higher concentration to lower contraction is called as diffusion.
EX: - movement of gases like O2 and CO2 through PM is always through diffusion.
2. OSMOSIS
The movement of water molecules (solvent) from region of lower to higher concentration through SPM is called as osmosis.
EX: - Protoplasm moves in and out from the cell through the process of osmosis.
HYPOTONIC SOLUTION:- When concentration of cell becomes high in comparison to its surrounding solution, the surrounding solution is called as hypotonic solution in compare to cell solution. When a cell is placed in hypotonic solution, then water moves from solution to cell, thus cell swells up.
HYPERTONIC SOLUTION:- When concentration of cell becomes low in comparison to its surrounding solution, the surrounding solution is called as hypertonic solution in compare to cell solution. When a cell is placed in hypertonic solution, then water moves from cell to surrounding solution, thus cell shrinks down.
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