Compositions of cell wall

Question 1

Composition of cell wall

Answer 1

• peptidoglycan/murein
• NAGA-NAMA
  N- acetylglucosamine (NAG)
  N-acetylmuramic acid(NAM)
  When these repeating unit forms layer over layer, they form peptidoglycan

IN nag- OH-H
IN nam- 0H-CH3-CH-C=O-0H

Question 2

The cell wall of gram-positive bacteria

Answer 2

• Layers of peptidoglycan forming a thick, rigid structure (70%-80%)
• Teichoic acids- alcohol(glycerol/ribitol) and phosphate
  lipoteichoic acid- spans the peptidoglycan layer and is linked to the plasma membrane
  wall teichoic acid- linked to the peptidoglycan layer.
• because of the -ve charge (from the phosphate group) teichoic acids may bind and regulate the movement of cations (+ve ions) into and out of the cell

Question 3

Gram-negative cell wall

Answer 3

• very few layers of peptidoglycans and an outer membrane
• Peptidoglycan is bonded to lipoproteins in the outer membrane and is in the periplasm
• a gel-like fluid between the outer membrane and the plasma membrane
  -They do not contain techoic acid

Question 4

What is the outer membrane of the gram-negative cell

Answer 4

Consists of :
- lipopolysaccharides (LPS)
- lipoproteins
- phospholipids

Question 5

Lipopolysaccharides (LPS)

Answer 5

of the outer membrane is a large complex molecule that contain lipid and carbohydrates
Consist of three component:
-lipid A
-core of polysaccharide
-an 0 polysaccharide

Question 6

What is endospore and give example

Answer 6

• an endospore is a special resistant, dormant structure formed within a cell that protects a bacterium from adverse environmental condition

When essential nutrients are depleted, they will form a specialized “resting cell” cells

• bacillus and clostridium (gram positive)

during the process of sporulation, where the bacteria forms into a spore, they enter a stage called dormancy or dormant.

Question 7

What kind of staining is performed on endospore and why?

Answer 7

The Schaeffer Fulton endospore stain.
Unlike simple methods and gram staining, dyes do not penetrate the wall of the endospore

Question 8

What are spirochetes?

Answer 8

• They are group of bacterias
• The best known spirochetes is Treponema pallidum, which is the causative agents of syphilis

Question 9

What is axial filament?

Answer 9

• Spirochetes more by means of axial filament or endoflagella, bundle of fibres that arise at the end of cell beneath an outer sheath and spiral around the cell.
• They are made up of a protein called flagellin
• The rotation of the filament produces a movement of the outer sheath that propels the spirochetes in a spiral notion
• Type of movement that is similar to the way a corkscrew moves through a cork.

Question 10

What are fimbriae and pili ?

Answer 10

Gram negative bacteria have hair like appendages that are shorter, straighter and thinner for the attachment and transfer of DNA.
These structures consist of a protein called pilin arranged helically around a central core

Question 11

Explain about fimbriae

Answer 11

• It can occur at the poles of the bacterial cell or can be evenly distributed over the entire surface of the cell.
• They are present from few to several hundred per cell.
• They have a tendency to adhere to each other and to surface.
• Neisseria gonnorhea is the causative agent of gonorrhoea.

Question 12

What are pili ?

Answer 12

• They are usually longer than fimbriae
• They number only one or two per cell.
• Pili are involved in motility and DNA transfer
• Such pili are called conjugation (sex) Pili

note : no movement just transfer of materials

Question 13

What are the external structures to the cell wall?

Answer 13

• Glycocalyx
• Flagella
• Axial filaments
• Fimbriae
• Pili

Question 14

What is glycocalyx?

Answer 14

• Many prokaryotes secrete on their surface a substance called glycocalyx.
• Glycocalyx (meaning sugar coat) surround the cell.
• It is a viscous (sticky), gelatinous polymer that is external to the cell wall
• Composed of polysaccharide, polypeptide or both.
• It is made inside the cell and secreted to the cell surface
  1) - Substance organised and is firmly attached to the cell wall- capsule
  The presence of a capsule is determined by using negative staining or the Manewals method
  2) Substance is unorganised and only loosely attached to the cell wall- slime layer.

Question 15

Advantages of glycocalyx

Answer 15

• B. anthracis cause anthrax (D-glutamic acid)
• Streptococcus pneumoniae causes pneumonia
  Capsules often protect pathogenic bacteria from phagocytosis by the cells of the host and evade the immune system
• Glycocalyx, extracellular polymeric substance(