CELL MEMBRANE

M. Pharm Ⅱ semester
Dept. of Pharmaceutics

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CONTENTS:
 Structure of cell

 Plasma membrane

 Lipid bilayer

 Fluid mosaic model

Membrane protein

 Functions of membrane protein

 Functions of cell membrane.

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STRUCTURE OF CELL

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Plasma Membrane

cytoplasm

plasma
membrane

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Structure of cell membrane

 For a drug to be absorbed and distributed into organs
and tissues and eliminated from the body, it must pass
through one or more biological membranes/barriers at
various locations.

 Such a movement of drug across the membrane is
called as ‘drug transport’.

 The membrane is like a ‘mayonnaise sandwich’.

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PLASMAMEMBRANE

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 The cellular membrane consists of a double layer of
amphiphilic phospholipids molecules arranged in such a
fashion that their hydrocarbon chains are oriented
inwards to form the hydrophobic or lipophilic phase and
their polar heads oriented to form the outer and inner
hydrophilic boundaries of the cellular membrane that
face the surrounding aq. Environment.

Globular protein molecules are associated on either side
of these hydrophilic boundaries.

 The bio-membrane acts like a semipermeable barrier
permitting rapid and limited passage of some compounds
while restricting others.

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# THE LIPID BILAYER :
The basic structural framework of the plasma membrane is the lipid
bilayer, two back to back layers made up of three types of lipid
molecules—–

# Phospholipids (75% of the membrane lipid)

# Cholesterol ( About 20%)

# Glycolipid (About 5%)

The bilayer arrangement occurs because the lipids are
Amphipathic molecule which means they have both polar and
nonpolar parts.

The polar head is hydrophilic.

The nonpolar parts is hydrophobic.

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Phospholipids

 Has a hydrophilic
(water loving head)

 Hydrophobic (water
fearing) Tail

 Made up mostly of
carbon (black)&
Hydrogen (light blue)

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Phospholipid bi-layer
 The cell membrane is made

up of 2 layers of
phospholipids.

 The Hydrophilic heads face
out.

 The Hydrophobic tails face
inward

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Other Membrane components

Cholesterol makes the cell membrane more stiff and

less permeable.

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Fluid Mosaic Model

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➢Singer and Nicolson developed the fluid mosaic model

➢The phospholipids molecules orient themselves in the
bilayer with their hydrophilic heads facing outward. In this
way the heads face a watery fluid on either side – cytosol on
the inside and extracellular fluid on the outside.

➢Cholesterol molecules are weakly amphipathic. It is attached
with the polar heads of the phospholipids and glycolipids.

➢Cholesterol may increase or decrease fluidity depending
on other factors, such as the fatty acid composition of the
other lipids found in the membrane.

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MEMBRANE PROTEIN

It categorized into:
1) Integral protein.
2) Peripheral protein.
3) Glycoprotein.

Integral Protein: It extends into or through the lipid bilayer
among the fatty acid tails and are firmly embedded in it. Most
integral proteins are transmembrane proteins, which means
that they span the entire lipid bilayer and protrude into both the
cytosol and extracellular fluid.

They are Amphipathic. The hydrophilic ends protrude into either
the watery extracellular fluid or the cytosol.

The hydrophobic regions extends among the fatty acid tails.

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Peripheral Protein:

Are firmly embedded in the membrane. They are
attached more loosely with the polar heads of the
membrane lipids or with the integral Proteins.

Glycoprotein:

It acts as cell identity marker.

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MEMBRANE PROTEIN

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TRANSPORT PROTEINS – regulate the movement of
water-soluble molecules through the cell membrane.

RECEPTOR PROTEINS –recognizes and binds to specific
molecules. Often trigger some response by the cell such as
endocytosis or cell division.

RECOGNITION PROTEINS – identifies the cell as
belonging to a specific species or organ. Helps immune
system tell invading cells from cells belonging to the
organism.

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Outside of cell

Some proteins cross Some proteins adhere one cell
the entire membrane. to another.

Some proteins penetrate the
bilayer only partially.

Peripheral proteins do not penetrate the
bilayer at all.

Inside of cell

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FUNCTION OF THE MEMBRANE PROTEIN.

1.Integral membrane proteins acts as ion channels.

2.Integral membrane proteins acts as transporters.

3.Integral membrane proteins acts as receptors.

4.Integral membrane proteins acts as Linkers.

5.Integral membrane proteins acts as enzymes.

6.Glycoproteins acts as cell identity marker.

7.pheripheral proteins acts as enzymes and linkers.

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Some functions of membrane proteins

1. Hydrophillic channel
Proteins of adjacent

selective for substance
cells hooked together

2. Actively pump to form a junction
substances

Sequential steps in a
Glycoproteins serve

pathway carried out by
as tags recognized

ordered enzymes in
by other cells

membrane

Chemical messenger binds to
protein causing a conformation
change that relays message to 1. Maintain cell shape

inside the cell and protein location

2. Coordinate extra-
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Cell Membranes Show Selective Permeability

oxygen, carbon glucose and other large,

dioxide, and other polar, water-soluble

small, nonpolar molecules; ions (e.g.,

molecules; some H+, Na+, K+, Ca++,

water molecules Cl–); water molecules

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The Cell membrane functions to:

 Control what goes in and out of a cell.

 Anchors the cytoskeleton to help provide shape.

 Attaches to a substrate outside of the cell or to other cells to help
form tissues

 Controls the transportation of substances across the membrane by
using proteins as carriers and channels

 Contains receptors that allow cells to communicate through chemical
messages

 Contains recognition proteins which help identify the cell, so the
immune system does not attack it.

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REFERENCE
 Principles of anatomy and physiology 12th

edition by G.J.TORTORA & B.H.DERRICKSON
page no: 61 to 100

 https://en.wikibooks.org/wiki/Structural_Bi
ochemistry/Membrane_Proteins

 https://en.wikipedia.org/wiki/Cell_membra
ne

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