The document discusses the structure and functions of the cell membrane. It begins by defining the cell and cell membrane. The cell membrane, also called the plasma membrane, is a biological membrane separating the interior of a cell from the outside environment. It has a double layered structure of phospholipids and embedded proteins. The cell membrane serves protective, selective permeability, absorptive, excretory, gas exchange, and shape maintenance functions. It discusses various transport mechanisms like passive transport, active transport, ion channels, and vesicular transport that allow movement of substances across the membrane.

2. CELL MEMBRANE
STRUCTURE
Anas K P
2nd yr PBBSc
GCNT

3. Objectives
 Define cell and cell membrane
 Functions of cell membrane
 Transport mechanisms of cell membrane

4. CELLS
Basic living unit of all organisms.
 Determine the form and functions of the human body.
 Are specialized to perform specific functions.
 Organelles inside the cell perform specific functions.
CELL MEMBRANE
The cell membrane (also called the plasma membrane) is a
biological membrane separating the interior of a cell from the
outside environment.
 It appears in thin sections with the electron microscope as a
double layered structure about 7.5 – 10 nanometers thick.
 It contain almost proteins called membrane proteins.

5. Structure of cell membrane
Lipid Bilayer - 2 leyers of phospholipids
a. Phosphate head is polar ( water loving )
b. Fatty acid tail is non polar ( hydro phobic )
c. Protein embedded in membrane
Chemical composition
1. Lipids : Four major classes of lipids are commonly present
in the plasma membrane ; Phospholipids ( most abundant )
, Spingolipids , Glycolipids , and Sterols ( eg : Cholesterol)
2. Proteins :
 Plasma membrane contains about 50% protein. Amount
and type is variable.

6.  Myelin cells contains about 25% protein internal membrane
of chloroplast and mitochondria contains 50% proteins.
 Protein of plasma membrane are of two type ectoproteins
and endoproteins .
 Plasma membranes contain structural proteins , transport
proteins and enzymes.
3 Carbohydrates :
They are present only in the plasma membrane and are
present exterior ( glycoprotein's ) or polar end of
phospholipids at the external surface of plasma membrane.

7. Phospholipids :
 Phospholipids (PL) molecule has a polar head and non
polar tails.
 The polar head is charged and hydrophilic ( loves water )
facing outward , contains a - PO4 group and glycerol.
 The non polar tails are hydrophobic ( water hates ) facing
inward contain 2 fatty acid chains that are nonpolar .
 When Phospholipids placed in water form bilayer.

9. Functions of cell membranes:
 Protective function
 Selective permeability
 Absorptive function
 Excretory function
 Exchange of gases
 Maintenance of shape and size of the cells

10. Transport Mechanisms
 The permeability of substances across cell membranes is
dependent on their solubility in lipids and not on their
molecular size.
 Water soluble compounds are generally impermeable and
require carrier mediated transport.
 Transport mechanisms classified into :
1. Passive Transport
> Simple diffusion
> Facilitated diffusion
> Osmosis
> Bulk flow
> Filtration

11. 2. Active Transport
3. Ion Channels
> Ligand Gated Channels
> Voltage Gated Channels
4. Vascular Transport
> Exocytosis
> Endocytosis
5. Uniport , Symport and Antiport

12. Transport Mechanisms
Passive Transport
a. Simple diffusion
b. Facilitate
diffusion
c. Osmosis
d. Bulk flow
e. Filtration
Active
Transport
Ion Channels
a. Ligand Gated
b. Voltage
Gated
Vascular
Transport
a. Exocytosis
b.
Endocytosi
s
Uniport
Symport
&
Antiport

13. Passive Transport :
A. Simple Diffusion
 Solute and gases enter into the cells passively.
 They are driven by the concentration gradient.
 Simple diffusion occurs from higher to lower concentration.
 The rate of entry is proportional to the solubility of that
solute.
 This does not require any energy , but it is a very slow
process.

14. B. Facilitated Diffusion :
 It is a carrier mediated process
 Structurally similar solutes can competitively inhibit
the entry of the solute.
 This mechanism does not require energy , but the
rate of transport is more rapid than diffusion
process.
 It is dependent on concentration gradient.
 Hormones regulate the number of carrier
molecule.
 Examples of facilitated transport of glucose across
membrane is by glucose transporters.

16. C. Osmosis :
 Osmosis is the process of moving water across a
semi permeable membrane towards ion or solute rich region
in a solution.
 Lower concentration to higher concentration through
semi permeable membrane.

17. Ion Channels :
 Membranes have special devices called ion channels for
quick transport of electrolyte such as Ca++, K+, Na+ and Cl-
.
 These are selective ion conductive pores.
 Ion channels are specialized protein molecules that span
the membrane.
 Cation conductive channels generally remains closed but in
response to stimulus , they open allowing rapid flux ion
down the gradient.
 This may compared to opening of the gate of a cinema
house, when people rush to enter. Hence this regulation is
named as “Gated”.

18.  Based on the nature of stimuli that trigger the opening of
the gate they are classified into :-
1. Ligand Gated Channels : Acetylcholine receptor is an
example for ligand gated ion channel.
2. Voltage Gated channels : The channel is usually closed
in the ground state. The membrane potential change
switches the ion channel to open.
Voltage gated Sodium channels and voltage gated
potassium channels are the common examples

19. Active Transport :
A. The salient features of active transport are :-
 This form of transport requires energy . About 40% of total
expenditure in a cell is used for the active transport system.
 It requires specialized integral protein called transporters.
The transporters are susceptible to inhibition by specific
organic or inorganic compounds.
B. Cell has low intracellular sodium; but concentration of
potassium inside the cell is very high
 This is maintained by the sodium- potassium activated
ATPase, generally called Sodium pump
 The ATPase as an integral protein of the membrane.

20.  The hydrolysis of one molecule of ATP can result in
expulsion of 3 Na+ ions and influx of 2K+ ion .
 The ion transport and ATP hydrolysis are tightly coupled.

21. Vesicular Transport :
It is the transport of membrane bounded bounded substances
moving across plasma membrane classified to :-
1. Endocytosis
2. Exocytosis
Endocytosis:
It is a process by which the large number of particles are
taken with forming the vesicle into the cell.
It is classified into :-
1. Phagocytosis
It is a process by which the large number of particles
are engulfed in to the cell.

22. 2. Pinocytosis
It is a process by which the large number of particles
which are soluble in water are taken into the cell.

23. Exocytosis
Exocytosis is a process in which an intracellular vesicles
(membrane bounded sphere) moves to the plasma
membrane and fused the substance into the Extra cellular
fluids.

24. Uniport , symport and Antiport :
Uniport System
 Movement of a single substance
 It requires no energy from the cell
 Eg :
Simple diffusion
Facilitated diffusion
Symport System
 Transport of two substances using the energy produced by
concentration difference developed by primary active
transport.
 Substances are moving in the same direction.
 Eg : Transport of amino acid , glucose transport

25. Antiport System
 In this process , the two substances move across the
membrane in opposite directions .
 Eg: Sodium pump or chloride bicarbonate exchange in RBC

27. Recapitulation
 What is cell ?
 What is structure of cell membrane ?
 What are the functions of cell membrane ?
 What are the type of transport mechanisms ?
Assignment
What is cell organelles and briefly explain the cell organelles ?

28. Bibliography
 Vasudevan D M , S Sreekumari , Kannan vaidyanathan,
Textbook of Biochemistry for Dental students , 2nd edition
2011, Jaypee brothers medical publishers (P)Ltd, Page No:
1-6.
 Nicholas sperelakis , Cell Physiology source book , 3rd
edition, Academic press , Page No: 65-77.