Plasma membrane

1. CELL MEMBRANE
The cell membrane also called the plasma membrane or
Plasmalemma-separating the interior of a cell from the
outside environment.
Outside cell
Cell interior
Plasma
membrane

2. Plasma membrane
• The plasma membrane separates the internal
environment of the cell from the external
environment.
• It regulates the entrance and exit of
molecules into and out of the cell.
• It helps the cell and the organism maintain a
steady internal environment.

3. History

4. • Ernest overtone (1980) recognized that boundary of
plants and animals cells was “impregnated” by lipid
material.
• Langmuir studied that if a lipid containing hydrophilic
groups is dissolved in highly volatile solvent and
several drops then carefully applied to the surface of
water, the lipid spreads out to form a thin
monomolecular film in which the hydrophilic parts of
each molecule project into the water surface and the
hydrophobic parts are directed up away from the
water.
History

5. • Gordel and Grendel proposed that cell
membrane formed by bimolecular lipid sheet.
• In 1935 they proposed that plasma
membrane itself might be composed of two
such lipid – protein bilayers- one facing the
interior of the cell and the other facing the
external surface of the cell

6. Robertson’s Unit Membrane
Model
In the late 1950s, Robertson proposed this
mode
 According to the him, the unit membrane
consisted of bimolecular lipid sandwich
between outer and inner layers of the
proteins organized in a pleated sheet
configuration.
 Such arrangement was presumed to be
basically the same in all the cells.

8. Fluid mosaic model
• The plasma membrane is a phospholipid bilayer in
which protein molecules are either partially or
wholly embedded.
• The phospholipid bilayer has a fluid consistency.
• The proteins are scattered either just outside or
within the membrane.
• This description of the plasma membrane is called
the fluid-mosaic model of membrane structure.

9. The Fluid Mosaic Model

10. The Fluid Mosaic Model
• The hydrophilic (water-loving) polar heads of the
phospholipid molecules face the outside and
inside where water is present.
• The hydrophobic (water-fearing) nonpolar tails
face each other.
• Cholesterol is another lipid found in animal
plasma membranes.
• Cholesterol stiffens and strengthens the
membrane, thereby helping to regulate its
fluidity.

11. Plasma membrane or cell
membrane components
Contents
1 plasma membrane structure and
function
2 plasma membrane permeability

12. Membrane proteins
• The proteins in a membrane consist of
peripheral proteins and integral proteins.
1. Peripheral protiens
• Peripheral proteins are associated with only
one side of the plasma membrane.
• Peripheral proteins on the inside of the
membrane are often held in place by
cytoskeletal filaments.

13. Membrane proteins

14. 2.Integral protiens
• Integral proteins span the membrane, and can
protrude from one or both sides.
• They are embedded in the membrane, but
they can move laterally, changing their
position in the membrane.

15. Functions of the Proteins
• The plasma membranes of various cells and
the membranes of various organelles each
have their own unique collections of proteins.
• The peripheral proteins often have a structural
role in that they help stabilize and shape the
plasma membrane.
They may also function in signaling pathways.

16. Types of integral proteins
• The integral proteins largely determine a
membrane’s specific functions.
• Integral proteins can be of the following types:
• Channel proteins
• Carrier proteins
• Cell recognition proteins
• Receptor proteins
• Enzymatic proteins

17. Channel proteins
• Channel proteins are involved in the passage
of molecules through the membrane. They
have a channel that allows a substance to
simply move across the membrane.
For example,
A channel protein allows hydrogen ions to flow
across the inner mitochondrial membrane.
Without this movement of hydrogen ions, ATP
would never be produced.

18. Example
Channel Protein
• Allows a particular
molecule or ion to
cross the plasma
membrane freely.
• Cystic fibrosis, an
inherited disorder,
is caused by a faulty chloride (Cl–)
channel; a thick
mucus collects in
airways and in
pancreatic and liver ducts.

19. Carrier proteins
• Carrier proteins are also involved in the
passage of molecules through the membrane.
They combine with a substance and help it to
move across the membrane.
• For example, a carrier protein transports
sodium and potassium ions across a nerve cell
membrane. Without this carrier protein, nerve
conduction would be impossible.

20. Carrier Protein
• Selectively interacts with a specific molecule or ion
so that it can cross the plasma membrane.
• The family of GLUT carriers transfers glucose in and
out of the various cell types of the body.
• Different carriers respond
differently to blood
levels of glucose

21. Cell recognition proteins
• Cell recognition proteins are glycoproteins
Among other functions, these proteins help the
body recognize when it is being invaded by
pathogens so that an immune reaction can
occur.

22. Cell Recognition
Protein
 The MHC (major
histocompatibility
complex) glycoproteins
are different for each
person, so organ
transplants are difficult
to achieve.
 Cells with foreign MHC
glycoproteins are
attacked by white blood
cells responsible for immunity.

23. Receptor proteins
• Receptor proteins have a shape that allows a
specific molecule to bind to it . The binding of
this molecule causes the protein to change its
shape and thereby bring about a cellular
response.
• The coordination of the body’s organs is
totally dependent on such signal molecules.
For example, the liver stores glucose after it is
signaled to do so by insulin.

24. Receptor Protein
Shaped in such a way that a
specific molecule can bind to it.
Some types of dwarfism result not
because the body does not produce
enough growth hormone, but because
the plasma membrane growth hormone
receptors are faulty and cannot interact
with growth hormone.

25. Enzymatic proteins
• Enzymatic proteins carry out metabolic
reactions directly.
• Without the presence of enzymes, some of
which are attached to the various membranes
of the cell.
• A cell would never be able to perform the
metabolic reactions necessary to its proper
function

26. • Enzymatic Protein
Catalyzes a specific reaction.
The membrane protein,
adenylate cyclase, is involved in
ATP metabolism.
• Cholera bacteria release a toxin
that interferes with the proper functioning of
adenylate cyclase, which eventually leads to severe
diarrhea.

27. Carbohydrates
• Both phospholipids and proteins can have
attached carbohydrate (sugar) chains.
• These molecules are called glycolipids and
glycoproteins, respectively.
• The carbohydrate chains occur only on the
outside surface .
• Peripheral proteins occur asymmetrically on
one surface or the other, the two halves of the
membrane are not identical..

28. Carbohydrates
• Certain plasma transporter proteins,
hormones, and enzymes are glycoproteins
and in these molecules carbohydrates are
important to physiological activity.
• The carbohydrates of glycolipids of the RBC
plasma membrane determine weather a
person blood type is A, B, AB, O

29. A person having blood type A has an enzyme that
adds an N-acetylgalactosamine to the end of the
chain.
A person blood type B has an enzyme that adds a
Galactose to the chain terminus.

30. People with blood type AB posses both
enzymes.
People with blood group O lack the enzymes
capable of attaching either terminal sugar

31. How Cells Talk to One Another
• Cell Signaling
• The cells of a multicellular organism “talk”
to one another by using signaling molecules,
sometimes called chemical messengers.
• Some messengers are produced at a distance
from a target tissue and, in animals, are carried
by the circulatory system to various sites around
the body.
• For example, the pancreas releases a hormone
called insulin.

32. (a) Some cells signal one
another by making direct
contact.
(b) In paracrine regulation, a local
regulator diffuses to target cells.
(c) Neurons transmit signals
across synapses.
(d) Many hormones are
transported in blood to target cells

33. Receptor: Binds to a signaling
molecule, becomes activated and
initiates a transduction pathway.
2. Transduction pathway: Series
of relay proteins that ends when
a protein is activated.
3. Response: Targeted protein(s)
bring about the response(s) noted
structural
protein
enzyme
gene
regulatory
protein
Targeted
protein:
Cellular
response
Altered shape
or movement
of cell
Altered
metabolism
or a function
of cell
Altered gene
expression and
the amount of
a cell protein
Cytoplasm
plasma
membrane

34. The Permeability of the
Plasma Membrane
charged molecules
and ions
H2O
noncharged
molecules
macromolecule
protein
phospholipid
molecule

35. Passive Transport Processes
Some of the transport process happens
"passively" without the cell needing to expend
any energy to make them happen. These
processes are called "passive transport
processes".
Passive transport processes includes
Osmosis
Diffusion
Facilitated diffusion

37. Active Transport
Active transport refers to a process in which a
substance is transported across a membrane by the
use of an integral membrane protein (or protein
complex) that has ATPase activity.
Example: Sodium-Potassium pumps
The sodium-potassium pump was discovered in the
1950’s by Jens Christian Skou. It marked an important
step forward in our understanding of how ions get into
and out of cells, and it has a particular significance for
excitable cells such as nervous cells, which depend on
it for responding to stimuli and transmitting impulses.

40. ENDOCYTOSIS

41. Exocytosis

44. Co-transport
Co-transport is the name of a process in which two substances are
simultaneously transported across a membrane by one protein, or
protein complex which does not have ATPase activity.
Different types of co-transport
Symport
 When both substances are transported in the same direction the
transport protein is known as a symport.
Antiport
 When the substances are transported in opposite directions the
transport protein is known as an antiport.