Cell wall and membrane structure of prokaryotes (Part I)

1) Glycocalyx
- Gelatinous polysaccharides
- Protect from phagocytosis by allowing the bacterium to attach itself to inert (chemically inactive) surface like teeth or rocks
- Source of nutrient and energy to microbes (Example: Streptococcus mutans which colonizes the teeth ferment glucose in glycocalyx and acid by products contribute to tooth decay)
- Protect from dehydration
- If it is loosely attached to the cell wall, it is known as slime layer
- Capsules is firmly attached to the cell wall

2) Flagella

Arrangement of flagella

 

Structure of flagella

 

• Flagella consists of filament, hook and basal body.
• Flagella is made up of protein flagellin, which is arranged in several intertwined chain that form a helix around the hollow core.
• Hook is made up of 120 copies of a single protein, FlgE
• Basal body anchors the flagellum to the cell wall and plasma membrane
• Gram positive bacteria has two rings while gram negative bacteria has four rings as shown in diagram above.
• Flagella contributes to motility
• Motility can be directly observed under light microscope through hanging drop in cavity slide and wet mount preparation
• True motility show propelling action towards definite direction.
• False motility show zigzag movement and directionless. It might seems true movement due to bombardment of water molecules
• Movement towards nutrient, sunlight and magnetic force is known as chemotaxis, phototaxis and magnetotaxis repectively.
• During inoculation, motility of bacteria can be seen through turbidity (cloudiness) of medium
• One of the importance of bacterial locomotion is that it can help the bacteria to move away from unfavourable condition such as accumulation of chemicals



Difference between prokaryotes and eukaryotes flagella

 

 

Flagella and bacterial motility


3) Axial filaments
- Also known as endoflagella
- Wrap around the cell
- Present in spirochetes