Friday, October 9, 2015

Cell wall and membrane structure of prokaryotes (Part II)

4)Fimbriae and Pili
- Both made up of pilin
 
-
Fimbriae
Pili
Differences
Shorter
Longer
Help the cell to adhere to surface
Join bacterial cells for DNA transfer
Distributed evenly around the cell ( from several to hundreds)
Only one or two per cell
Similarities
·       Made up of protein pilin
·       Shorter and thinner than flagella

 
 
 
No.
Characteristics
Cilia
1
Definition
Cilia are short, hair like appendages extending from the surface of a living cell.
Flagella are long, threadlike appendages on the surface of a living cell.
2
Number
Numerous
Less in Number
3
Length
Short and hair like organelle (5-10µ)
Long wipe like organelle (150µ)
4
Occurrence
Occurs throughout the cell surface.
Presence at one end or two ends or all over the surface.
5
Cross section
Nexin arm present.
Nexin arm absent
6
Density
Many (hundreds) per cell
Few (less than 10) per cell
7
Beating
Cilia beat in a coordinated rhythm either simultaneously (synchronous) or one after the other (metachronic).
They beat independent of each other.
8
Motion
Rotational, like a motor, very fast moving
Wave-like, undulating, sinusoidal, slow movement compared to cilia
9
Found in
Eukaryotic cells
Eukaryotic and prokaryotic cells
10
Energy Production
Cilia use ‘kinesin’ which has an ATPase activity that produces energy to perform the movement.
Flagella are powered by the proton-motive force by the plasma membrane.
11
Functions
Helps in locomotion, feeding circulation, aeration, etc.
Help mainly in locomotion only.
12
Examples
Cilia present in Paramecium
Flagella present in Salmonella
Difference between flagella and cilia

 
5) Cell wall
Anything that is fit can pass through cell wall
- Function:
  • Contributes to pathogenicity (teichoic acid and peptidoglycan)
  • Classification into gram positive or gram negative
  • Prevent rupture of bacteria cell
  • Provide shape to bacteria
  • Anchor for surface appendages ( flagella, cilia, pili)
  • Withstand osmotic pressure

S.N.
Characteristics
Gram Positive
Gram Negative
1
Gram Reaction

Retain crystal violet dye and stain blue or purple

Can be decolorized to accept counterstain (safranin) and stain pink or red
2
Cell Wall
Cell Wall is 20-30 nm thick.
Cell Wall is 8-12 nm thick.
3
Cell Wall
The wall is Smooth.
The wall is wavy.
4
Peptidoglycan Layer
Thick (multilayered)
Thin (single-layered)
5
Teichoic Acids
Present in many (contribute to pathogenicity)
Absent
6
Periplasmic Space
Absent
Present
7
Outer Membrane
Absent
Present
8
Porins
Absent
Occurs in Outer Membrane
9
Lipopolysaccharide (LPS) Content
Virtually None
High (contribute to pathogenicity)
10
Lipid and Lipoprotein Content
Low (acid-fast bacteria have lipids linked to peptidoglycan)
High (because of presence of outer membrane)
11
Mesosomes
Quite Prominent
Less Prominent
12
Flagellar Structure
2 rings in basal body
4 rings in basal body
13
Toxin Produced
Exotoxins
Endotoxins or Exotoxins
14
Resistance to Physical Disruption
High
Low
15
Cell Wall Disruption by Lysozyme
High
Low (requires pretreatment to destabilize outer membrane)
16
Susceptibility to Penicillin and Sulfonamide
High
Low
17
Susceptibility to Streptomycin, Chloramphenicol and Tetracycline
Low
High
18
Inhibition by Basic Dyes
High
Low
19
Susceptibility to Anionic Detergents
High
Low
20
Resistance to Sodium Azide
High
Low
21
Resistance to Drying
High
Low