1. Bacteria come under Kingdom Monera.
  2. Prokaryotes, means they lack a true membrane-bound nucleus.
  3. Unicellular, i.e. these are single cell organism.
  4. They have no membrane-bound organelles like mitochondria, chloroplast,nucleus, golgi appratus, endoplasmic reticulum.All these are absent in bacteria.
  5. Bacterial cell wall is made up of Peptidoglycan or murein.
  6. On the basis of Gram staining technique, two categories of bacteria are present: Gram positive & Gram negative. Gram positive retains purple color of stain due to thick peptidoglycan cell wall, while gram-negative has thin layer of peptidoglycan in its cell wall so it loses purple color on washing with alcohol and takes up pink color of safranin.
  7. Gram positive bacteria has 5 times more thick peptidoglycan layer in its cell wall than gram negative.
  8. Gram positive bacteria has teichoic acid molecules in its cell wall while it is absent in gram negative.
  9. Gram negative bacteria has periplasmic space between plasma membrane and outer membrane while it is absent in gram positive bacteria.
  10. Gram negative has extra layer in its cell wall called as outer membrane made of lipopolysaccharide. It is present outside to thin peptidoglycan layer in cell wall. It is absent in gram positive bacteria. It makes gram negative bacteria resistant to antibiotics like penicillin etc.
  11. Some bacteria have additional layer called as S-layer. Helps in adhesion to surface and protection.
  12. Some bacteria (mostly disease-causing) have gelatinous layer called as Capsule. Responsible for disease-causing ability of bacteria (see Bacterial diseases) as it interferes with recognition capacity of immune system of organism.
  13. Bacteria moves with the help of Flagella made up of flagellin protein. So flagella provides mobility to bacteria. Flagella are anchored in the cell wall. Flagella has three 3 main parts- motor, hook and filament.
  14. Pili are hair-like structures on the surface of bacteria. It is shorter than flagella and helps in adhesion & exchange of genetic information(sex pili).
  15. Fimbriae are shorter than pili and more in no. on surface of bacteria. These are also hair-like appendages. Help in adhesion to substrate.
  16. Endospores : some gram-positive bacteria under harsh conditions and environmental stress, like scarcity of nitrogen and carbon sources, replicate their genome/DNA and develop a thick cell wall around their duplicated genome with a small amount of cytoplasm. These structures are called as endospores. Endospores are dominant and resistant to heat, dessication, uv rays, etc. This thick wall is made up of Ca-dipicolinate, which provides heat resistant to endospores. E.g. Bacillus anthracis and Clostridium.
  17. Nucleiod: bacteria lack true nucleus, so the genetic material, i.e. single double-stranded circular DNA/chromosome lies in an irregularly shaped region of cytoplasm called as Nucleiod which is not enclosed by a membrane
  18. Plasmid: In addition to regular chromosomes, some bacteria possess small rings of independently replicating DNA molecules called as plasmid. Plasmids are self-replicating and exist independently of the chromosome. Sometimes found in integration with chromosome. Types of plasmid are:        F-factor (Fertility plasmid) helps in conjugation. If F-factor is integrated into the bacterial chromosome then it is called as Hfr cell(high frequency of recombination).  R-plasmid(Resistance plasmid)provides resistant against antibiotics , Col plasmid(provides proteins that can kill other bacteria), Degradative plasmid– provides capacity to degrade/ digest certain chemicals, e.g. Pseudomonas putida used to clear oil spills.
  19. Inclusion bodies: These are organic or inorganic granules present in the cytoplasm of bacteria. They help in storage. E.g of inclusion bodies- polyphosphate granules, cyanophycin granules, glycogen granules.
  20. Ribosomes are 70S in bacteria.
  21. Mesosomes are folded invaginations in the plasma membrane of bacteria. These are equivalent in function to mitochondria.
  22. Mycoplasma are the only bacteria which lack cell wall.
  23. Mycoplasma are the smallest known bacteria.
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