BACTERIAL CELL WALL

This slide describes about the gram positive and gram negative cell wall, And their shape

1. BACTERIAL CELL WALL NAME : NISHA R REG NO : BP211511 SUBJECT : GENERAL MICROBIOLOGY AND MICROBIAL DIVERSITY DATE : 15/11/2021 TITLE : BACTERIAL CELL WALL OF GRAM POSITIVE AND GRAM NEGATIVE BACTERIA SUBMITTED TO : Dr.P . SARANRAJ

2. GRAM POSITIVE BACTERIAL CELL WALL Cell wall is present outside the Cell membrane. Cell wall acts as a backbone of cell and gives shape and rigidity to the cell. Bacterial cell wall confers Osmotic protection from toxic substances and Gram staining characteristics. The cell walls of almost all the bacteria is made up of Peptidoglycan, also called murein or mucopeptide cell wall. It is found only in Prokaryotes The Peptidoglycan consists of two components viz., ( i ) Peptide portion which is composed of Amino acids connected by Peptide linkages and (ii) Glycan or Sugar portion.

3. The Glycan portion, which forms the backbone of Peptidoglycan, is composed alternating units of amino sugars N-acetyl-glucosamine (NAG) and N-acetyl-muramic acid (NAM) joined together by β-1,4 glycosidic linkages. The peptidoglycan chains are laterally liked by short chains of four amino acids which are attached to NAM residues. The four amino acids of this Tetrapeptide are D-alanine, L- alanina , D- glutamic acid and L-lysine. The Tetrapeptide chains are also interlinked by a Peptide bridge (Polypeptide linkage chains).

4. GRAM POSITIVE BACTERIAL CELL WALL

5. A Model Of The Constitution Of Gram Positive Bacterial Cell Wall

6. Teichoic acid, an acidic polymer consisting of a Carbohydrate (e.g., glucose), Phosphate and Alcohol is found in cell walls of Gram + ve bacteria. There are two classes of Teichoic acids. They are ( i ) Wall teichoic acid and (ii) Lipoteichoic acid. Teichoic acid has several functions such as binding metals, action as receptor sites for some viruses and maintaining cells at low pH to prevent degradation of cell walls by self-produced enzymes.

7. GRAM NEGATIVE BACTERIAL CELL WALL The cell walls of Gram negative bacteria are much more complex. The peptidoglycan layer of Gram negative bacteria is very thin making up only 10 % or less of the cell wall. The Outer membrane is a thin, bilayered structure consisting chiefly of Phospholipids, Proteins and Lipopolysaccharides (LPS).

8. The Outer membrane serves as a barrier to prevent the escape of important enzymes from the Periplasmic space. The permeability of Outer membrane to nutrients is provided by proteins called Porins which form channels in the membrane thought which substances of hydrophilic nature and low molecular weight can diffuse. The space between the Cytoplasmic membrane and the Outer membrane is called Periplasmic space. The Periplasmic space prevents the entry of various chemicals that could damage the cell. It also acts as main surface antigen in cell wall.

9.        GRAM NEGATIVE BACTERIAL CELL WALL