Sunday, February 19, 2012

Cell organelles in prokaryotes




Name of the cell organelle
Functions

1.     Cell envelope
Outer glycocalyx
Protects the cells, Helps in adhesion

Middle cell wall
Gives definite shape and prevents cell from bursting or collapsing in a hypotonic solution.

Inner plasma membrane
Retains cytoplasm, selectively permeable barrier, helps in movement of molecules, respiration, photosynthesis, synthesis of lipids and cell wall constituents. Holds receptor molecules that help to detect and respond to chemicals in their surroundings.

2.     Membranous structures
Mesosomes
Involves in cell wall formation, chromosome replication and distribution of chromosomes to daughter cells. Involved in secretory processes.
Increases plasma membrane surface area and enzymatic content.

Chromatophores
Found in photosynthetic bacteria like cyanobacteria and purple bacteria.

3.     Cytoplasm
Inclusion bodies
Organic inclusion (Phosphate granules, cyanophycean granules, glycogen granules, b-hydroxybutyrate granules, sulphur granules, carboxysomes & gas vacuoles)
Gas vacuoles occur in cyanobacteria, purple and green photosynthetic bacteria and a few free floating aquatic forms (e.g. planktonic forms).
They are permeable to atmospheric gases but impermeable to water. Helps aquatic bacteria to float on or near surface water and help in positioning themselves in the water column for trapping sunlight for photosynthesis or for avoiding intense sunlight.
Inorganic inclusion or metachromatic granules (polyphosphate granules or volutin granules and sulphur granules).
Volutin granules: storage reservoir for phosphate.
Sulphur granules: These are stored temporarily by some photosynthetic bacteria. These granules may be formed when bacteria use H2S as electron donor during photosynthesis.
Ribosomes
Site of protein synthesis

4.     Nucleoid (Nuclear body or genophore)
Genetic material (DNA) is present

5.     Flagella (filament + hook + basal body)
Found in the mobile bacteria. For locomotion

6.     Pilus (Bacterial surface appendages)
For mating process. During conjugation one of the pili donor cell attaches to recipient cell and forms a conjugation tube through which partial transfer of DNA takes place.

7.     Fimbriae
Help to attach to solid surfaces such as rocks in streams and host tissues. Also responsible for mutual clinging of cells forming a thin film on the liquid and other thick aggregates.

8.     Spinae
Found in some gram positive bacteria. Help to adjust cells to some environmental conditions such as salinity, pH, temperature etc.






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