The plasma membrane is a 5-10 nm thick bilayer that acts as the boundary of the cell. It is made of phospholipids, proteins, carbohydrates, and cholesterol. The fluid mosaic model describes the plasma membrane as a fluid bilayer with integral and peripheral proteins embedded within. Integral proteins span the membrane while peripheral proteins are attached to either surface. Glycoproteins and glycolipids on the outer surface contain carbohydrates that protect and lubricate the cell. The plasma membrane performs critical functions like protection, ATP synthesis, communication, transport, and endocytosis/exocytosis.

1. Dr. P.
Saranraj
Plasma Membrane
Structure and Function

2. Plasma Membrane
Also called as Cytoplasmic Membrane
or Cell Membrane.
Act as a boundary of cell.
5 to 10 nm thick.
 Prokaryotes – Phospholipids and
Proteins; Eukaryotes – Carbohydrates
and Streols (Cholesterol)
Made up of Phospholipid Bilayer

3. Phospholipids Structure
 Amphipathic – Molecule having both:
Hydrophilic heads
Hydrophobic tails
 ~8 nm thick
Phospholipid

4. Fluid-Mosaic Model Structure
The dynamic arrangement of
Proteins and Phospholipids in
Plasma membrane is called as Fluid-
Mosaic Model Structure.
Discovered by Jonathan Singer and
Garth Nicholson.
Two types of Membrane proteins are
present (i) Peripheral Proteins and (ii)
Integral Proteins.

6. Peripheral Proteins
 Connected to the membrane and easily
removed by mild treatments.
 It lies at the inner and outer surface of
the membrane.
 They are soluble in aqueous solution and
make upto 20 to 30 % of total proteins.
 They may function as enzymes that
catalyze chemical reactions and act as a
mediators of changes in membrane shape
during movement.

7. Integral Proteins
 Integral proteins can be removed from the
membrane only after disrupting the lipid
bilayer (by using detergents).
 Not soluble in aqueous solutions and
forms above 70 – 80 % of Membrane
proteins.
 Most integral proteins penetrate the
membrane completely and are called
Transmembrane proteins.

8. Glycoproteins & Glycolipids
 Many of the proteins and some of the lipids
on the outer surface of the plasma
membrane have carbohydrates attached to
them.
 Proteins attached to carbohydrates are
called Glycoproteins.
 Lipids attached to carbohydrates are called
Glycolipids.
 Both glycoproteins and glycolipids helps to
protect the cell and lubricate the cells

9. Plasma Membrane Functions
Protection
ATP Synthesis by Electron Transport
Chain (ETC)
Communication (Cell to cell
interaction)
Transport of substances
Pigments and enzymes responsible
for Photosynthesis are present in Cell
membrane.
Exocytosis and Endocytosis