Question

List the major molecules that make up typical Gram-positive and Gram-negative cell walls and note which molecules are unique to each type of cell wall. How do these molecules contribute to the functions of the cell wall?

Answer 1

Molecules of the bacterial cell wall:

A. Gram Positive Cell Wall :-

1. Peptidoglycan - NAM and NAG

2. Ribitol- and Glycerol- teichoic acids and Lipoteichoic acids

B. Gram Negative Cell Wall :-

1. Peptidoglycan

2. Phospholipids

3. LPS - lipopolysaccharides

*peptidoglycan maintains the structure of the cell wall. It is responsible for forming the basic cell wall structure in bacteria. Gram Positive bacteria have a thick layer of peptidoglycan in their cell wall whereas Gram Negative bacteria have a thin layer of peptidoglycan in their cell wall.

* Teichoic acids are only present in the Gram Positive cell wall. They are responsible for linking the peptidoglycan layer to the cytoplasmic membrane. They also serve an antigenic function. They give the overall negative charge to Gram Positive cell wall.

*LPS is a large molecule unique to Gram Negative bacterial cell wall, consisting of a lipid and a polysaccharide composed of O-antigen, outer core and inner core joined by a covalent bond. The highly charged nature of lipopolysaccharides confer an overall negative charge to the gram -negative cell wall. The chemical structure of the outer membrane lipopolysaccharides is often unique to specific bacterial strains and is responsible for many of the antigenic properties of these strains.