General Information on Cell
- The Polysaccharides in bacterial cell wall and cellulose in plant cell wall are carbohydrates.
- The living content of the cell is called protoplasm.
- The protoplasm of a eukaryotic cell is divided into nucleus and cytoplasm.
- The material present in between the plasma membrane and the nuclear membrane is called cytoplasm.
- Cytoplasm is formed by an aqueous ground substance which contains:
- Many cell organelles;
- Insoluble wastes and storage products (called inclusions);
- Cytosol (the soluble part of cytoplasm is called cytosol).
- Cytosol is 90% water and 10 % inorganic and organic molecules.
- Cytosol has true solutions and colloidal solutions. The colloidal solution may be sol or gel. Sol is non-viscous and gel is viscous.
- The peripheral part of the cell is like a gel.
- The free floating cell organelles (e.g. Mitochondria) move in the cytoplasm due to cytoplasmic streaming movements and is called active mass movement of cytoplasm.
- De Duve in 1949 isolated lysosomes. They are found in most eukaryotic cells.
- Lysosomes are rich in acid phosphatases and several other hydrolytic enzymes.
- Lysosomes are involved in:
- Autophogy/Self eating (Autophagosomes)
- Extracellular digestion and
- The autophagosomes working on digestive vacuoles are also known as secondary lysosomes.
- Autophagy helps in converting a tadpole larva into an adult amphibian.
- If an enzyme that breaks glycogen to glucose is absent from Lysosomes, the result is disease GlycogenosistypeII.
- TAY-SACH’S DISEASE is due to the absence of an enzyme that is involved in the catabolism of lipids. Accumulation of lipids in brain cells leads to mental retardation and even death.
- De-Duve and coworkers isolated peroxisomes in 1965 from liver cells and other tissues. These are single membrane organelles (0.5 gm in diameter).
- Peroxisomes have oxidative enzymes such as peroxidase, catalase and glycolic acid oxidase etc.
- Peroxisomes contain H2O2 — producing oxidases and catalase.
- In lipid-rich seeds (e.g. castor, bean and soybeans etc.), glyoxysomes are abundant during germination period. In lipid poor seeds (e.g. pea), they are absent.
- Two important enzymes in glyoxysomes are glycolicacidoxidase and catalase.
- In plant seedlings, Glyoxisomes convert stored fatty acids to carbohydrates and provide energy to grow a new plant. This process occurs through glyoxylate cycle. Enzymes of this cycle are present in the glyoxisomes.
- In seeds rich in lipids (such are castor and beans) glyoxysomes break fatty acids to succinate. Central vacuole is formed by combining the smaller vacuoles during the growth and development of plant.
- Vacuoles are bounded by a single membrane (tonoplast).
- The cytosol contains cytoskeletal fabric formed of microtubules, microfilaments and intermediate filaments. This is Cytoskeleton.
- The main proteins in cytoskeleton are tubulin (in microtubules), actin, myosin, tropomyosin and others which are also found in the muscles.
- Microtubules are long, unbranched and slender structures. They are composed of tubulin protein.
- The microtubules are joined in a specific way to form some cell organelles. For examples cilia, flagella, basal bodies and centrioles etc.
- Microfilaments are much more slenders. They are made up of contractile actin protein’ linked to the inner face of the plasma membrane.
- Microfilaments are involved in internal cell motion also called cyclosis.
- Amoeboid movements are because of microfilaments.
- Intermediate filaments play a role in maintaining the cell shape and are also involved in the linkage of the cell parts.
Difference between microtubules and microfilaments
|I. They are non-contractile.||I. They are contractile.|
|II. A microtubulecontains 13 protofilaments.||II. They do not possess longitudinal subunits.|
|III. They are hollow tubules.||III. They are solid structures.|
|IV. They are formed ofα andβ tubulin proteins.||IV. They are mainly made up of protein actin.|
|V. The diameter is 25 nm.||V. The diameter is 6 nm.|
|VI. They occur in centrioles, basal bodies, cilia, flagella, astral rays, spindle fibres, etc.||VI. They occur below cell membrane and at the interphase of plasmagel-plasmasol.|
Difference between cilia and flagella
|I. The number of cilia per cell is usually very large (300—1400).||I. The number of flagella per cell is usually 1—4.|
|II. They are smaller in size.||II. They are larger (100—200 nm in length).|
|III. Cilia are present all over the surface of the cell.||III. Flagella are present only at end of the cell.|
|IV. They beat in a coordinated rhythm either simultaneously or one after the other.||IV. The flagella beat independently.|
|V. They help in locomotion, aeration, feeding and circulation, etc.||V. They help in locomotion.|
- Plastids are membrane bounded, mostly pigment containing bodies present in the plant cells.
- Chloroplasts are membrane bound structures (containing a green pigment) in photosynthetic plant cells.
- Chloroplasts vary in their shape and size with a diameter of about 4-6 µm.
- The electron microscope shows that a chloroplast has three parts, the envelope, the stroma and the thylakoid.
- Light reactions in thylakoids/Grana and Dark reactions in the Stroma.
- About 50 or more thylakoids form one granum.
- Chlorophyll molecules are arranged on the layers of thylakoids. Therefore the grana look green.
- Chlorophyll molecule resembles the haem group of haemoglobin. The main difference between these two molecules is that chlorophyll has Mg++ while haem has Fe++ as the central atom.
- Chromoplasts help in pollination and dispersal of seeds.
- Leucoplasts are triangular, tubular or of some other shape. They are found in the underground parts of the plant and store the food.
SOME IMPORTANT POINTS TO REMEMBER ABOUT CELL
|Property / Character||Value / No.|
|%age of lipids in cell membrane||20-40%|
|%age of proteins in cell membrane||60-80%|
|Amount of water in cytosole||80%|
|Carbohydrates in cell membrane||Small amount|
|Diameter of chloroplast||4-6 µm|
|Number of chromosomes in chimpanzee cell||48|
|Number of chromosomes in frog cell||26|
|Number of chromosomes in fruitfly (Drosophila) cell||8|
|Number of chromosomes in garden pea cell||14|
|Number of chromosomes in human cell||46|
|Number of chromosomes in onion cell||16|
|Number of chromosomes in potato cell||48|
|Number of nuclear pores in egg (undifferentiated cell)||30,000|
|Number of nuclear pores in eryothrocyte (differentiated cell)||3-4|
|Number of thylakoid in granum||50 or more|
|One micro meter =||0.000,001 or 10-6|
|Resolution of compound microscope||2.0 µm|
|Resolution of human naked eye||1.0 mm|
|Resolution of electron microscope||2-4 A|
|Sedimentation rate of eukaryotic ribosome||80 S (60 S + 40 S)|
|Sedimentation rate of prokaryotic ribosome||70 S (50 S + 30 S)|
|Size of peroxisomes||0.5µm|