structure of bacterial cell | class 11 | Dr Mushtaq

Описание: Structure of Bacteria
A bacterium is composed of the following components:
1.Capsule 2. Cell wall 3. Flagella 4.pilli 5. Cell membrane 6. Cytoplasm 7. Ribosom
8. Genomic organization
capsule
some bacteria posses slimy substance on outer surface of cell wall known as capsule. Capsule is composed of polysacharide and proteins. when capsule is loosely attached to cell wall this is known as glycocalyx.
bacteria are clasified into 2 groups on the basis of capsule:
Capsulate Bacteria: Posses capsule
Non-capsulated bacteria: Do not possess capsule
Function: Capsule provides protection from dehydration. Capsule protects bacteria from mechanical injury.
Cell Wall
Cell wall is a rigid and tough structure.
Cell wall is chemically composed of peptidoglycan (protein and polysaccharides).
Flagella
Flagella are thin, hair or whip-like structure. Flagella arise from cell membrane and come out through cell wall.
Flagella are composed of 3 parts:
Basal bodies: They are made of tubulin proteins.
Short curved hook at the base of flagellum.
Helical filament: Both are composed of flagillin proteins.
Classification of bacteria on the basis of Flagella: On the basis of Flagella, bacteria are clasifiled into 2 groups:
Atrichous Bacteria: They lack flagella.
Trichous Bocteria: They have flagella, further divided into
Monotrichous bactria: Possess single flaygellum at one end,
Amphitrihous bacteria: Possess group of flagella at both ends of the cell
Lophotrichous bactela: Possess group of two or more flagella inserted at one pole of the cell
Peritrichous bacteria: Possess flagella dispersed on entire surface of the cell.
Function: Flagella are involved in locomotion



























4. Pilll
Pili are small, hollow appendages arise from cell mernbrane Pilli surround the whole cell surface.
Pilli are smaller than flagella. Pilli have no role in locomotion. Pilli are composed of pillin proteins.
Functions:
i. Pili are involved in attachment to other bacteria (Conjugation tube).
ii. Pilli are involved in attachment with substrate.
5. Cell Menmbrane
Cell membrane is a thin, delicate and elastic structure, lies beneath the cell wall.
Any damage to cell membrane causes cell death.
Cell membrane of bacteria resembles that of eukaryotic cells i.e. both are chemically composed
lipoproteins But bacterial cell membrane contains different types of proteins and lipids.
The energy production is concerned with cell nembrane so it resembles mitochondria of eukaryotes
Mesosome is pocket like or sac-like structure invaginates from cell mermbrane.
Mesosome contains respiratory and DNA replicative enzymes. It means that mesosome has role in respiration and DNA replication (cell division).

6. Cytoplasm
Cytoplasm is viscous, jelly like substance.cytoplasm contains carbohydrates, proteins, lipids, genomic DNA, plasmid DNA, ribosomes, enzymes and inorganic salts etc.
7. Ribosomes
Ribosomes are tiny granules like substance occur in scattered form in cytoplasm. Ribosomes are nucleoprotein structures i.e. composed of proteins and rRNA. Ribosomes are small size i.e. 70S.
A bacterial cell contains about 10,000 ribosomes.
8. Genomic organization
The genome of bacteria consists of DNA and few proteins. Bacteria possess lesS amount of DNA than eukaryotic cell. Bacteria are haploid organisms i.e. consists of single and circular chromosome (DNA). The region where DNA of bacteria is localized is called nucleoid.
Plasmid:
Plasmid is double circular, extra genomic or extra nuclear DNA. It is self-replicating. Plasmid contains disease causing and antiblotic resistant genes.
Copy number of plasmid: (Number of plasmid per bacterial cell)
The number of plasmid can vary from 1 to many in a single bacterial cell.