ULTRASTRUCTURE OF BACTERIA

 ULTRASTRUCTURE OF BACTERIA

Ultrastructure of Bacteria

Cell wal

·       Cell wall acts as a backbone of cell and gives shape and rigidity to the cell.

·       Gram positive bacteria composed of Peptidoglycan (Thick – Multilayered) and Teichoic acid.

·       Gram negative bacteria composed of Peptidoglycan (Thin – Single layered), Periplasmic space, Outer membrane, Lipopolysaccharides, Lipid and Lipoprotein.

·       Peptidoglycan is a sugar backbone with peptide side chains that are cross linked. It is made up of NAM (N – acetyl muramic acid) and NAG (N – acetyl glucosamine).

·    One of the most abundant polypeptide called porin is present and it helps in the diffusion of solutes.

·  Bacterial cell wall confers Osmotic protection from toxic substances and Gram staining characteristics.

Plasma Membrane

·       Plasma membrane is also called as Cell membrane or Cytoplasmic membrane.

·       Plasma membrane is made up of Phospholipid bilayer.

·      Mesosomes are areas in the cell membrane of bacterial cells that fold inward.  They play a role in Cellular respiration (the process that breaks down food to release energy) and Binary fission (Cell division).

·       The enzymes involved in the oxidation of metabolites (i.e., the respiratory chain) as well as the photosystems used in photosynthesis are present in the plasma membrane.

·       Main functions of Plasma membrane includes,

ü  Selective permeable barrier

ü  Mechanical boundary of cell

ü  Nutrient and waste transport (entry and exit)

ü  Site of Electron transport chain reaction in Prokaryotes

Cytoplasm

·       The region which is present inside the plasma membrane is called Cytoplasm.

·    The liquid portion of the cytoplasm is called Cytosol. It is mostly water, but it also contains dissolved and suspended substances, including ions, carbohydrates, proteins (mostly enzymes), lipids and wastes.

·       Cytoplasm is thick and semi-transparent in nature.

·      All the cell organelles like Ribosomes, Nucleoid, Plasmid, Inclusion bodies and Gas vacuoles are present in the Cytoplasm.

Ribosomes

·       Ribosomes are made up of RNA and Protein.

·       70 S type of Ribosomes are present in bacteria and other prokaryotes. The 70 S Ribosomes are classified into two sub-units. They are 50 S sub-unit and 30 S sub-unit.

·       Number of Ribosomes in bacterial cell varies from 10000 to 15000.

·       The ribosomes are held together by mRNA and form Polyribosomes or Polysomes.

·       The main function of Ribosomes is Protein synthesis (Translation). The process of synthesis of single stranded mRNA from double stranded DNA is called as Transcription. The process of synthesis of protein from mRNA is called as Translation.

Nucleoid

·    The Cytosol of prokaryotes also contains the cell’s DNA in a region called the Nucleoid.

·    The genetic material DNA is present inside the Nucleoid or Genophore and it act as a localization of genetic material.

·     The DNA is circular, tightly coiled and not bound to the Histone proteins.

Plasmids

·       Plasmids are the extra chromosomal DNA present in the bacterial cell.

·       Plasmids are small, double stranded, circular and self replicative.

·       Size of the Plasmid varies from 1 kb to 500 kb.

·       Plasmids contribute about 0.5 to 5 % of the total bacterial DNA.

·   Plasmid helps in the production of Bacteriocins and Toxins which are not found in bacterial chromosome.

·       Based on its functions, Plasmids are classified into five types. They are

a)     F (Fertility) Plasmids

b)     R (Resistance) Plasmids

c)     Col (Colicin) Plasmids

d)     Ri (Root inducing) Plasmids

e)     Ti (Tumor inducing) Plasmids

·       Plasmid plays a major role in Gene transfer mechanism.

·       Plasmid confers Antibiotic resistance to the bacteria.

Inclusion Bodies

·       Inclusion bodies or Cell inclusions are the storage materials of energy, carbon, phosphorous and other substances.

Gas Vacuoles

·       Gas vacuoles gives buoyancy to the bacterial cell and helps to float in the aquatic environment.

Capsules

·       Capsule is a well defined structure of polysaccharides surrounding the cell.

·       Capsule protects the bacteria from Phagocytosis and adherence to cell surface.

Endospores

·       Bacteria form an endospore during unfavourable conditions.

·       Endospores are made up of Keratin like coat and Dipicolinic acid.

·  Endospores provide resistance to bacteria against Heat, Boiling, Radiations, Antibiotics, Dehydration and Chemical disinfectants.

Flagella

·    All the Motile bacteria have single to numerous thin hair like appendages of variable length emerge from the cell wall called Flagella.

·       Flagella are 20 - 30 μm in diameter and 15 μm in length.

·    Flagella are the protein appendages made up of Flagellin protein and used for locomotion or motility.

Fimbriae

·       Fimbriae are the short appendages present around the cell.

·       Fimbriae are made up of protein Fimbrillin protein.

·       Fimbriae mediate attachment of bacteria (Adhesion) to the cell surface.

Pili

·       Pili are the short appendages present at the end of bacterial cell.

·       Pili are made up of the protein Pilin.

·  Pili mediate the attachment of two bacteria during the Gene transfer (Conjugation) and Attachment.