BACTERIA STRUCTRUE

 

1.1. Bacterial cell

The bacterial cell is made up of various internal as well as external anatomical structure.

A bacterial cell shows various parts and these parts have specific structure and functions.

Some structures are present in that particular species and hence that structure is characteristic feature of that species.

Various parts are as follows

1.     Cell wall

2.    Cell membrane

3.    Mesosoma’s

4.    Capsule

5.    Flagella

6.    Pila

7.    Nuclear material

8.    Ribosomes

1. Cell wall

·         The cell wall is the outer covering of bacterial cell in absence of capsule.

·         The cell wall is rigid in nature which imparts a proper shape to bacteria.

·         Cell wall encloses all internal parts of the cell.

·         On the basis of typical structure, composition and Gram staining the bacterial cells are classified into

1.Gram-Positive Bacterial Cell

2.Gram-Negative Bacterial Cell

2. Cell Membrane

·         The cell membrane is a thin membrane beyond the cell wall and a membrane covering the cytoplasm.

·         It is called cell membrane or cytoplasmic membrane or plasma membrane.

·         It is a bilayered structure made up of phospholipids and proteins.

·         Cell membrane structure can be observed by electron microscope.

3. Mesosoma’s

1.Mesosoma are chemically invasions of cell membrane made up of phospholipid bilayer and proteins.

2.Mesosoma’s are mostly seen in Gram-positive bacteria as well as rarely observed in gram-negative bacteria due to small size.

3.On the basis of location mesosoma’s basically are of two types – Central mesosoma and peripheral mesosoma.

4. Capsule

1.The outer most slimy, gummy coating surrounding the cell wall is called as a capsule.

2.It increases the virulence of bacterial cell as it acts as a protective covering.

3.Micro-organism having capsule is called as capsulated bacteria.

4.On the basis of thickness, capsules are of two types and they are Macro- capsule and micro-capsule.

5. Flagella

·         Flagella is one of the important locomotory organs. The microorganism containing flagella are called as the flagellated micro-organism.

·         The diameter of flagella ranges from 10 to 12 nm and length ranges from 20 microns to 200 microns.

·         On basis of arrangement, flagella are differentiated as monotrichous, lophotrichous, Amphitrichous and peritrichous.

6. Pili

·         Pili are the small, thin and straight appendages present on the surface of bacteria.

·         The diameter of pili ranges from 3 to 25 nm and length ranges up to 12 micros.

·         Pili serve as a site for attachment of bacteriophage.

7. Nuclear material

·         Bacterial cells are prokaryotic in nature and its nuclear material is not enclosed in a nuclear membrane.

·         Nuclear material of bacteria is called a nucleoid, bacterial chromosome or chromatid body.

·         Nuclear material of bacteria is a long molecule of DNA approximately about 3000 microns. It has one copy of chromosome so-called haploid.

8. Ribosomes

·         Ribosomes are small, tiny units distributed evenly in the cytoplasm.

·         Ribosomes may be free or in chain form linked to mRNA molecules. Such ribosomes are called as polysomes.

·         Bacterial ribosome is 70 ‘S’ type. Size of ribosome ranges from 16 to 18 nm.

·         Ribosomes are composed of 60 % or rRNA and 40 % of protein.