2. 2
WHAT IS CELL WALL?
▶ A cell wall is a structural layer surrounding some types of cells, just outside the cell
membrane.
It can be tough, flexible, and sometimes rigid. It provides the cell with both structural
support and protection, and also acts as a filtering mechanism.
▶ Cell walls are present in most prokaryotes (except mollicute bacteria), in algae,
fungi and eukaryotes including plants but are absent in animals.
▶ Bacterial cell walls are made of peptidoglycan , peptidoglycan is a primary
component of
bacterial cell wall.
▶ While cellulose was the primary component of plant cell wall.
▶ PEPTIDOGLYCAN: unique macromolecule composed of a repeating framework of
3. 3
CHEMICAL NATURE OF BACTERIAL CELL WALL
▶ Peptidoglycan is a made up of 2 amino sugars.
▶ 1.N-acetyl glucosamine [NAG]
▶ 2.N- acetylmuramic acid [NAM]
▶ NAM attached 4 amino acid chain. The four amino acids that compose the
tetrapeptide are: L-
alanine, D-glutamine, L-lysine or meso-diaminopimelic acid (DPA),
4. GRAM POSITIVE BACTERIA CELL WALL:
▶ 20-80 nm thick peptidoglycan
▶ Includes teichoic acids and lipoteichoic acids.- function in cell wall maintainance
enlargement during the cell division;move cation across the cell envelope; stimu
immune response.
▶ Some cell have periplasmic space between the cell membrane
They lack an outer membrane.
They have a slim layer of the cytoplasmic lipid layer.
5. GRAM NEGATIVE BACTERIA CELL WALL
▶ Inner and outer membranes and periplasmic space between
them
contains a thin peptidoglycan Layer
▶ Outer membrane contains lipopolysaccharides[LPS].
▶ Lipid portion endotoxin may become toxic when released during infection.
▶ Contain porin protein in upper layer – regulate molecules entering and leaving cell.
▶ Peptidoglycan layer 10 nm thickness.
6.
7. 7
COMPARI SON OF GRAM POSI T I V E AND
GRAM NEGAT I V E BAC T ERI A CEL L - WAL L
8. MICROSCOPIC IMAGES OF GRAM
POSITIVE AND GRAM NEGATIVE
• gram negative bacteria.[100X oil immersion]
