Structure of Bacteria/ Bacteria Anatomy
1. Flagella
2. Pilli
3. Capsule
Always present outside bacterial cell wall.
4. Cell wall
5. Cytoplasmic membrane , present inside bacterial cell wall.
1. Flagella/Flagellium
Bacteria flagella are hair-like whip like structure allow cell to move.
Flagella stick out through cell wall.
Parts of flagella
1. Basal body; associated with cytoplasmic membrane and cell wall.
2. Short hook
3. Filament; long, helical structure extends from cell surface.
Types of Flagella
On basis of arrangement of flagella on bacteria cell.
1. Monotrichous: single polar (at end) flagella present.
2. Lophotrichous: multiple flagella present at one polar.
3. Amphitrichous: single or multiple flagella present at both poles.
4. Peritrichous; flagella present all around bacterial cell.
2. Pilli or Fimbriae
Numerous short straight and thin like fibers called pili, strick out from surface of cell wall.
Generally present in Gram negative bacteria.
Thinner and shorter than flagella.
Function of pilli
Pilli allow attachment of bacterial cell to specific surface.
Enhance bacterium's ability to colonize an area and cause disease.
Help in bacterial conjugation. (@exchange genetic material)
Help in agglutination and pellicle (membrane) formation.
3. Capsule
Some bacterial cells are surrounded by viscous substance forming envelope around cell wall.
Development of capsule depend upon presence of blood, sugar high concentration, serum or growth in living host.
Function of Capsule
Protect bacteria from body's immune defense mechanism. (Antibiotic therapy)
Capsulated bacteria cause dental carries (Cavity) and UTI ( E. Coli).
It protect against lytic enzyme.
Inhibiting phagocytosis and contributes virulence of pathogenic bacteria.
4. Cytoplasmic membrane
Cytoplasmic membrane is present immediately below cell wall.
Beneath the cell wall separating, it form cell cytoplasm.
Cytoplasmic membrane act as osmotic barrier.
5-10nm thick elastic semi- permeable layer.
It composed of phospholipid and proteins.
It act as semi-permeable membrane controlling inflow and outflow of component to move.
Function of cytoplasmic
1. Act as permeability barrier to keep cytoplasmic material inside cell and substance into and out of cell.
2. Transport nutrient into cell and eliminate waste material.
3. Anchors DNA during replication
4. Energy storage
5. Functioning in DNA and cell wall synthesis.
Internal structure of cytoplasmic membrane
1. Cytoplasm
2. Cytoplasmic structure
a. Ribosomes
b. Cytoplasmic inclusions and vacoules
c. Nuclear material or nucleoid
d. Plasmid
e. Mesosomes
f. Bacterial spores
1. Endospore
2. Exospore
4. Cell wall
Cell wall is tough and rigid structure surrounding bacterium like a sheel.
Bacterial Cell wall contains network of peptidoglycan chains.
Types of cell walls of bacteria
Two types of cell walls of bacteria-
1. Gram-Negative cell wall
2. Gram-Positive cell wall
1. Cell wall of Gram Positive Bacteria
1. Peptidoglycan
Gram Positive Bacteria usually have much greater amount of peptidoglycan in their cell wall (16-80 nm) than gram negative bacteria (2 nm).
2. Teichoic acid
Gram positive cell wall contains teichoic acid. Teichoic acid helps to hold peptidoglycan chain together.
Teichoic acid absent in gram negative bacteria.
Teichoic acid act as surface antigen, protect bacteria from thermal injury of Gram Positive Bacteria.
2. Cell wall of Gram negative bacteria
Cell wall of Gram negative bacteria has no teichoic acid and thin peptidoglycan layer.
This is why, it loses crystal violet stain during gram staining.
Lipoproteins layer
Outer portion of cell wall consist of an outer membrane, not found in gram positive.
Lipoprotein layer connects peptidoglycan to outer membrane.
Outer membrane
Contain certain proteins named outer membrane proteins. These are target sites for phages, antibiotics.
Lipopolysaccharides (LPS)
LPS constitute endotoxin of gram-negative bacteria.
Lipopolysaccharide composed of -
1. Lipid A; Lipopolysacchaide layer consist of lipid A.
2. Polysaccharide; which attach to polysaccharide.
3. Polysaccharide O antigen; polysaccharide determines major surface antigen, O antigen.
4. The periplasmic space is space in between the inner and outer membranes, provide resistance to gram negative cells from antimicrobial agent dyes, disinfectant and lysozymes.
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