Page 25 - MNU microbiology theoritical 2025

General Microbiology & Immunology (PM 401) Second level Semester 4 2024/2025

3- Cell envelope

• The bacterial envelope can be a three-layered structure

- Capsules and slime layer

- Cell wall

- Plasma membrane
- Outer membrane in Gram negative

bacteria.

- All cells have a plasma membrane, which is the essential and definitive
characteristic of a "cell".

- Nearly all prokaryotes have a cell wall to prevent cell damage.

Glycocalyx (Capsules and slime layer)

• Some bacteria may have additional cell envelope structures exterior to the cell

wall

• Many bacteria envelop themselves with a gel-like layer

Most are composed of polysaccharides, and are commonly referred to as a

glycocalyx

1- Capsule:

• Structure Rigid, tightly organized glycocalyx, a

polysaccharide layer that completely envelopes the cell Ex:

Streptococcus pneumoniae

• Function

- Offers protection from a variety of different threats to the cell,

General Microbiology & Immunology (PM 401) theoretical handbook Page 14