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Structure of the cell membrane
 The membrane is a phospholipid bi-layer (i.e.
two layers of phospholipid molecules.
 The phosphate ‘head’ of the phospholipid
molecules are hydrophilic (attracted to water),
and form the outer and inner boundaries of
the membrane.
 The lipid ‘tail’ of the phospholipid molecules
are hydrophobic (repelled by water), and form
the inner layer of the membrane.
 The phospholipid bi-layer also contains the
steroid compound cholesterol, which maintains
the stability of the membrane.
 A variety of protein and carbohydrate molecules
are embedded in the membrane.
The cell membrane
Drawing by Mariana Ruiz Villarreal
Functions of the cell membrane
The cell membrane:
 Isolates the cell from the surrounding tissue fluid
 determines what substances enter and leave the cell
 contains a variety of receptors that respond to
substances in the cell’s environment e.g. hormones,
antigens.
What determines the rate of diffusion?
There 4 factors:
1. The steepness of the concentration gradient. The bigger the
difference between the two sides of the membrane the quicker
the rate of diffusion.
2. Temperature. Higher temperatures give molecules or ions more
kinetic energy. Molecules move around faster, so diffusion is
faster.
3. The surface area. The greater the surface area the faster the
diffusion can take place. This is because the more molecules or
ions can cross the membrane at any one moment.
4. The type of molecule or ion diffusing. Large molecules need
more energy to get them to move so they tend to diffuse more
slowly. Non-polar molecules diffuse more easily than polar
molecules because they are soluble in the non polar phospholipid
tails.
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Diffusion through the membrane
 Because the cell membrane is fatty,
most water soluble substances
cannot diffuse through it.
 Exceptions include oxygen & carbon
dioxide.
Membrane proteins
 A variety of proteins are embedded
in the bi-layer.
 These serve various functions
including the movement of
substances in and out of the cell.
Membrane transport proteins
Membrane proteins that aid the
movement of substances in and out
of the cell include:
Channel proteins (ion channels) –
open channels that allow simple
diffusion.
 Carrier proteins that allow facilitated
diffusion (e.g. glucose) and active
transport (specific membrane pumps).

Membrane transport
 Transport processes are either
passive or active.
 Passive processes require no
cellular energy and include
diffusion, osmosis & facilitated
diffusion.
 Active processes require ATP and
include specific membrane pumps
and phagocytosis/pinocytosis.
Simple diffusion (left) & facilitated
diffusion
Diagram created by LadyofHats
Diffusion through a membrane
Cell membrane
Inside cell
Outside cell
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Diffusion through a membrane
Cell membrane
diffusion
Inside cell
Outside cell
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Diffusion through a membrane
Cell membrane
Inside cell
Outside cell
EQUILIBRIUM
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Molecules that diffuse through cell
membranes
1.
Oxygen – Non-polar
so diffuses very
quickly.
1.
Carbon dioxide –
Polar but very small
so diffuses quickly.
2.
Water – Polar but
also very small so
diffuses quickly.
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Osmosis
‘The diffusion of water from an area
of high concentration of water
molecules (high water potential) to
an area of low concentration of
water (low water potential) across a
partially permeable membrane.’
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Facilitated diffusion
 Large polar molecules such as
glucose and amino acids, cannot
diffuse across the phospholipid
bilayer. Also ions such as Na+ or
Cl- cannot pass.
 These molecules pass through
protein channels instead.
Diffusion through these channels
is called FACILITATED
DIFFUSION.
 Movement of molecules is still
PASSIVE just like ordinary
diffusion, the only difference is,
the molecules go through a
protein channel instead of
passing between the
phospholipids.
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Cell markers and receptors
Various protein and carbohydrate molecules exposed on
the surface of the membrane:
 act as markers – these indicate to cells of the immune
system whether a cell is norm or abnormal (see MHC
proteins).
 serve as receptors that interact with substance in the
cell’s environment and initiate specific cellular
responses e.g. receptors sensitive to the hormone
insulin alter the rate of glucose intake.
 WHO estimates that more than 346 million people




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worldwide have diabetes. This number is likely to more
than double by 2030 without intervention.
346 million people worldwide have diabetes1.
In 2004, an estimated 3.4 million people died from
consequences of high blood sugar.
More than 80% of diabetes deaths occur in low- and
middle-income countries.
WHO projects that diabetes deaths will increase by two
thirds between 2008 and 2030.
Healthy diet, regular physical activity, maintaining a
normal body weight and avoiding tobacco use can prevent
or delay the onset of type 2 diabetes.
 World Diabetes Day (14 November 2013)[2]
World Diabetes Day raises global awareness of
diabetes - its escalating rates around the world
and how to prevent the illness in most cases. Started
by the International Diabetes Federation (IDF) and
WHO, the Day is celebrated on 14 November to mark
the birthday of Frederick Banting who, along with
Charles Best, was instrumental in the discovery of
insulin in 1922, a life-saving treatment for
diabetes patients
 Physiology of the Pancreas:-
The pancreas is composed of two major types of
tissues, ----------(1) the acini, which secrete digestive juices into the
duodenum,
(2) the islets of Langerhans, which secrete insulin and
glucagon directly into the blood
 I. Type I or IDDM:-Insulin Dependent Diabetes
Mellitus
II. Type II or NIDDM:-Non-Insulin
Dependent Diabetes Mellitus
III. MRDM:-Malnutrition Related Diabetes Mellitus
IV. IGT:-Impaired Glucose Tolerance
V. Gestational Diabetes:-Occur during pregnancy
 Type I or IDDM (Insulin Dependent Diabetes
Mellitus):The cells in the pancreas that make insulin are destroyed,
causing a severe lack of insulin.
 This is thought to be the result of the body attacking and
destroying its own cells in the pancreas - known as an
autoimmune reaction.
 It is an auto-immune disease where the body's immune
system destroys the insulin-producing beta cells in the
pancreas. This type of diabetes, also known as juvenileonset diabetes, accounts for 10-15% of all people with the
disease. It can appear at any age, although commonly under
40. People with type 1 diabetes must inject themselves with
insulin.
 Type II or NIDDM:-Non-Insulin Dependent Diabetes Mellitus
Type 2 diabetes is the most common form of diabetes, affecting 85-90%
of all people with the disease. This is characterised by insulin resistance
and relative insulin deficiency. The disease is strongly genetic in origin
but lifestyle factors such as excess weight, inactivity, high blood
pressure and poor diet are major risk factors for its development. Type
2 diabetes may be treated by dietary changes, exercise and/or tablets.
Insulin injections may later be required.
 The receptors on cells in the body that normally respond to the action
of insulin fail to be stimulated by it - this is known as insulin
resistance. In response to this more insulin may be produced,
and this over-production exhausts the insulin-manufacturing
cells in the pancreas;
1. There is simply insufficient insulin available
2.The insulin that is available may be abnormal and therefore
doesn't work properly.