The document discusses the structure and functions of the cell membrane, also known as the plasma membrane, which separates the interior of the cell from its external environment. It details the chemical composition, including lipids, proteins, and carbohydrates, as well as various models used to describe the membrane, such as the fluid mosaic model. The cell membrane plays crucial roles in regulating material passage, maintaining ion distribution, and facilitating cell communication and recognition.

1. CELL MEMBRANE
BY
AKANSHA SINGH
M.SC. PREVIOUS
BAREILLY COLLAGE BAREILLY..

2. OUTLINES
• What is cell membrane
• Chemical compositions
• Structure of cell membrane
• Models of cell membrane
• Functions of cell membrane

3. WHAT IS CELL MEMBRANE ?
• The cell membrane ( also called the plasma membrane or plasmalemma )is a biological
membrane separating the interior cell from the outside environment.
• It appears in thin sections with the electron microscope as a triple layered structure about
7.5 nanometers thick
• The term cell membrane was coined by C.Nageli and Cramer in 1855.
• In1895 ,Charles Overton suggested that plasma membrane is composed of lipids.
• In 1925 , E. Gorter and G.Grendel proposed that plasma membrane is composed of
Phospholipid bilayer.

4. •

5. CHEMICAL COMPOSITION
1. Lipids- four major classes of lipids are commonly present in the plasma membrane:
Phospholipid ( most abundant), spingolipids , glycolipid and sterols (eg.Cholesterol).All
of them are amphipathic . Cholesterol is abundant in mammalian cell and is absent in
prokaryotic cells.
2. Proteins- plasma membrane contains about 50% protein.Amount and type is variable.
3. Carbohydrates- they are present only in the plasma membrane and are present
exterior ( glycoproteins) or polar end of Phospholipid at the external surface of
plasma membrane.

6. PHOSPHOLIPIDS
• Phospholipid molecule has a polar head and non polar tails.
• The polar head is charged and Hydrophilic (water Loving) facing outward ,contains a
PO4 group and glycerol.
• The non polar tails are Hydrophobic ( hates water) facing inward contains 2 fatty
acid chains that are non polar.

8. MEMBRANE CHOLESTEROL
• The amount of Cholesterol may vary with the type
of membrane.
• Plasma membranes have nearly one Cholesterol
per Phospholipid molecule.

9. MEMBRANE COMPONENTS

10. MEMBRANE PROTEIN
1. Transmembrane protein:These extend through the lipid bilayer projecting out on
either side of membrane
2. Peripheral protein:These are present on both outer and inner surfaces of lipid bilayer
and are loosely connected to it either by covalent or non covalent interactions.

11. MODELS OF CELL MEMBRANE
1.SANDWICH MODEL
1. In 1935 , Danielli and Davson Studied triglycerides lipid bilayer over a water surface.
2.They found that they arranged themselves with the polar heads facing outward.
3. It always formed droplets ( oil in water) and the surface tension was much higher than
of cell .
Drawback:
It can’t explain the actual process of transportation.

13. UNIT MEMBRANE MODEL
• Robertson (1959) described trilaminar structure of PM consisting of two parallel outer
dense layer which corresponds to the two protein layer and a middle light colour layer of
30-35A thickness corresponding to the hydrocarbon chains of the lipids.
• He demonstrate that the bio membranes present inside the cells and around various cell
organelles exhibits trilaminar structure.

14. UNIT MEMBRANE MODEL

15. FLUID MOSAIC MODEL
• Given by Singer and Nicolson in 1972.
• According to this model ,biological membranes are quasi fluid structure.
• Plasma membrane is Formed of “protein iceberg’s in a sea of lipids.
• Lipid molecules show 2 types of movement-
• 1. Transition movements – Molecules of one lipid layer can change position in the same
layer.
• 2. Flip flop Movement- Here molecules of 2 lipid bilayer interchange their position..

16. • Proteins are globular and are of two types .
• 1. Extrinsic/ Peripheral protein-
• These are 30% of total proteins .
• They act as permeases.
• They are loosely attached so can be easily separated ex- ATPase,Acetylcholine asterase.
• 2. Integral / Intrinsic protein-
• These are 70% of total plasma protein.
• These are partially or fully embedded in lipid bilayer so can’t be separated.
.

18. FUNCTIONS OF CELL MEMBRANE
• Regulation of the passage of material.
• Maintenance of differential distribution of ions.
• Response to environment.
• Contact with neighboring cells.
• Cell recognition.
• Communication between neighboring cells.
• Cellular Adhesion .
• Protection.
• Excretion.

19. THANKYOU….