1. Universities Press
Rafi M D: Textbook of Biochemistry for Medical Students (2nd Edn)
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2. Universities Press
Rafi M D: Textbook of Biochemistry for Medical Students (2nd Edn)
Biological Membranes:
Structure and Function
3. Universities Press
Rafi M D: Textbook of Biochemistry for Medical Students (2nd Edn)
Lipids
The major membrane lipids are phospholipids.
These are amphipathic molecules containing
both hydrophilic or polar (water soluble) and
hydrophobic or non-polar (water insoluble)
groups.
The cell membrane also contains equal
amounts of cholesterol.
COMPOSITION OF MEMBRANES
Membranes are made of a double layer of lipid
molecules containing proteins which are
embedded in them.
4. Universities Press
Rafi M D: Textbook of Biochemistry for Medical Students (2nd Edn)
● Proteins in membranes occur in two
different ways. Some proteins are located in
the interior of the membrane and are called
integral membrane proteins.
● Others are located in the outer surface of
the membranes and are known as peripheral
membrane proteins.
● Transmembrane proteins serve as:
a) Channels b) Carriers
c) Pumps d) Receptors
Proteins
5. Universities Press
Rafi M D: Textbook of Biochemistry for Medical Students (2nd Edn)
The extracellular surface of the plasma
membrane contains small amounts of
carbohydrate structures known as glycocalyx.
CARBOHYDRATES
6. Universities Press
Rafi M D: Textbook of Biochemistry for Medical Students (2nd Edn)
Membranes are organised into a structure
known as the fluid mosaic model. It is called
so because membrane proteins float in a sea
of lipids. This model of the cell membrane
was proposed by Singer and Nicholson in
1972
FLUID MOSAIC STRUCTURE
7. Universities Press
Rafi M D: Textbook of Biochemistry for Medical Students (2nd Edn)
FLUID-MOSAIC MODEL OF
MEMBRANE STRUCTURE
8. Universities Press
Rafi M D: Textbook of Biochemistry for Medical Students (2nd Edn)
Transport Across Biological Membranes
Passive Transport
Here, substances move across the cell
membrane without any energy expenditure by
the cell. It includes diffusion and osmosis.
1.Diffusion
Simple Diffusion
Facilitated Diffusion
2.Osmosis
MEMBRANE FUNCTION
9. Universities Press
Rafi M D: Textbook of Biochemistry for Medical Students (2nd Edn)
When substances are transported against
their chemical and electrical gradient
requiring energy, the process is called
active transport. The main types are
1. Primary active transport
2. Secondary active transport
3. Carrier transport
4. Vesicular transport
ACTIVE TRANSPORT
10. Universities Press
Rafi M D: Textbook of Biochemistry for Medical Students (2nd Edn)
1. Primary Active Transport
i) Sodium–potassium (Na+–K+) pump
ii) Calcium (Ca2+) pump
iii) Potassium–hydrogen (K+–H+) pump
2. Secondary Active Transport
11. Universities Press
Rafi M D: Textbook of Biochemistry for Medical Students (2nd Edn)
3. Carrier Type Transport
Uniporters
Symporters
Antiporters
Carrier type processes
12. Universities Press
Rafi M D: Textbook of Biochemistry for Medical Students (2nd Edn)
Many substances are transported across the
cell membrane by endocytosis and exocytosis.
i) Endocytosis: pinocytosis, phagocytosis
4. Vesicular Transport or Transcytosis
Sequence of events in endocytosis
13. Universities Press
Rafi M D: Textbook of Biochemistry for Medical Students (2nd Edn)
Sequence of events in exocytosis
ii) Exocytosis
