structure of bacteria

A typical bacterial cell consist of fallowing structural features

1. Capsule and Slime layers: A loose gelatinous sheath called slime layer is usually deposited around the bacterial cell wall. It is usually composed of polysaccharides. In some bacteria, the slime layer becomes thick due to the presence of some nitrogen compounds and forms a capsule. Capsule is particularly common in the parasitic forms.

2. Cell wall: It is the outer tough covering around the cell, which provides specific shape and protection to the bacterium. It prevents the cell from swelling and bursting due to osmotic changes. It is composed of a polysaccharide called murein. It is a peptidoglycan. The cell wall of gram positive bacteria is much thicker and contains less lipids compared to that of gram negative bacteria.

3. Plasma membrane: It is thin, elastic, selectively permeable membrane found internal to the cell wall.

• Mesosomes: These are invaginations formed by the plasma membrane. They are spherical or elongated structures which bring about a functional compartmentalization of the cell. They play important role in cell division and replication.
• Flagella: These are long, slender, thread like structures which help in locomotion. A bacterial cell may have one to many flagella. The flagella are entirely composed of a protein called flagellin.
• Pili(or Fimbriae): These are extremely minute hair like structures found mostly in gram negative bacteria. They are composed of protein subunit called pili. The pili are known to help the bacterial cell in anchoring.

4. Cytoplasm: It is a semifluid ground substance enclosed by the plasma membrane. It appears granular due to the presence of large number of ribosomes. Ribosomes may occur singly or in clusters called polyribosomes. Membrane bound cell organelles like mitochondria, lysosomes, golgi complex, vacuoles and endoplasmic reticulum are absent.

5. Nucleoid: Since the bacterial cells is prokaryotic, a true nucleus is absent. The nuclear material is represented by DNA which is not associated with histones. It is identified as a nucleoid or bacterial chromosome. It is a circular ring like double stranded DNA. It is attached at a point to the plasma membrane.

6. Plasmids: Apart from the nucleoid, certain bacterial cell contain, single, circular, double stranded, self replicating extra chromosomal DNA called Plasmids. Some plasmids may temporarily become associated with nucleoid DNA and are called episomes.

A typical Bacterial cell