in this notes we will study and learn about cell membrane parts of cell membrane different formation of cell membrane lipids present in cell membrane function of cell membrane

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TOPIC CELL MEMBRANE
NAME = USMAN AHMAD
SEMESTER = IST
SECTION = A
ASSIGNMENT SUB TO: MAM.SAMEENA PERVAZ
PROGRAM =PHARM D

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Cell;
Definition;
Cell Is define as structural and functional unit of living organism
Cell membrane;
Definition;
the outermost boundary of cell is called cell membrane
 The cell membrane consists of a lipid bi-layer that is semipermeable.
 The cell membrane regulate the transport of materials entering and exit the cell.
 It is mainly composed of protein.
STRUCTURE OF CELL MEMBRANE
 cell membrane is a fluid mosaic of proteins, lipids and carbohydrates.
 The cell It i impermeable to ions and water-soluble molecules crossing
membranes only through carriers, trans membrane channels and pumps.
 The trans membrane proteins nourish the cell with nutrients, regulate the internal
ion concentration and set up a trans membrane electrical potential. Change in a
single amino acid in one Cl− channel and cell membrane pump can lead to human
disease cystic fibrosis.
 On the basis of location of the membrane in the body, lipids can make up
anywhere from 20-80% of the membrane, the rest being proteins.

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 It is composed of a Phospholipds bi layer, which is two layers of Phospholipds
back-to-back. Phospholipds are lipids with a phosphate group associated with
them. The Phospholipds have one head and two tails where the head is polar
and water-loving or hydrophilic. Tails on the other hand are non polar and
water-fearing or hydrophobic.
FLUID MOSIC MODEL;
The biological model, which was devised by Seymour Jonathan Singer and Garth L.
Nicolson in 1972.
The fluid mosaic model explains various observations regarding the structure of
functional cell membranes. According to this biological model, there is a lipid
bilayer (two molecules thick layer consisting primarily of amphipathic Phospholipds)
in which protein molecules are embedded. The Phospholipds bi layer
gives fluidity and elasticity to the membrane
It is mainly made up of Phospholipds, proteins, cholesterol, and carbohydrate
Functions of the cell Membrane
1.A Physical Barrier

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 The cell membrane surrounds all cells and physically separates the
cytoplasm, which is the material that makes up the cell, from the
extracellular fluid outside the cell. This protects all the components of the
cell from the outside environment and allows separate activities to occur
inside and outside the cell.
 The cell membrane provides structural support to the cell. It tethers the
cytoskeleton, which is a network of protein filaments inside the cell.
2. Selective Permeability
 cell membranes are selectively permeable (or semi-permeable), meaning
that only certain molecules can pass through them. Water, oxygen, and
carbon dioxide can easily travel through the membrane. Generally, ions (e.g.
sodium, potassium) and polar molecules cannot pass through the membrane;
they must go through specific channels or pores in the membrane instead of
freely diffusing through. This way, the membrane can control the rate at which
certain molecules can enter and exit the cell.
3.Endocytosis and Exocytosis
Endocytosis is when a cell ingests relatively larger contents than the single ions
or molecules that pass through channels. Through endocytosis, a cell can take
in large quantities of molecules or even whole bacteria from the extracellular
fluid. Exocytosis is when the cell releases these materials. The cell membrane
plays an important role in both of these processes. The shape of the
membrane itself changes to allow molecules to enter or exit the cell. It also
forms vacuoles, small bubbles of membrane that can transport many
molecules at once, in order to transport materials to different places in the
cell.
4.Cell Signaling
Another important function of the membrane is to facilitate communication and
signaling between cells. It does so through the use of various proteins and

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carbohydrates in the membrane. Proteins on the cell “mark” that cell so that other
cells can identify it. The membrane also has receptors that allow it to carry out
certain tasks when molecules such as hormones bind to those receptors.
TRANSPORT IN CELL MEMBRANE;
Cell membranes surround each cell and some organelles, such as the nucleus and the
Golgi body. They are comprised of a Phospholipds bi-layer and this acts as
a semipermeable barrier that regulates what enters and exits the cell or
organelle. This is highly important as this is how cells can obtain molecules such as
oxygen and remove waste products like urea.
There are two main ways in which molecules are transported across the cell
membrane;
A.Passive transport
B.Osmosis
C.Simple Diffusion
D.Facilitated Diffusion
A. ACTIVE TRANSPORT;
DEFINITION;
It is the type of transport in which the movement of lower concentration
to higher concentration with use of energy(ATP) is called active transport
Example;
NA and k exchange in cell by use of ATP

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Types of active transport;
1. Endocytosis
2. Exocytosis
1. Endocytosis;
Endocytosis is a general term describing a process by which cells
absorb external material by engulfing it with the cell membrane. Endocytosis is
usually subdivided into pinocytosis and phagocytosis.
phagocytosis
membrane derived vesicle, known as phagosome. Phagocytes can ingest microbial
pathogens, but important Phagocytosis consists in recognition and ingestion of
particles larger than 0.5 μm into a plasma also apoptotic cells.
i. Pincocytosis:
Pinocytosis is an active, energy consuming process where extracellular
fluid and solutes are taken up into a cell via small vesicles. It is a type of endocytosis,
which refers to the uptake of substances by a cell. Phagocytosis and receptor-
mediated endocytosis are other types of endocytosis.

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Exocytosis;
Exocytosis is the fusion of secretory vesicles with the plasma membrane and results in
the discharge of vesicle content into the extracellular space and the incorporation of
new proteins and lipids into the plasma membrane.
Passive transport refers to transport across the cell membrane that does not require
energy from metabolic processes. Instead, this form of transport relies on the
natural kinetic energy of molecules and their random movement . There are three
modes of passive transport
A.Simple diffusion
B.Facilitated diffusion
C.Osmosis
A.Simple diffusion
Simple diffusion is the movement of molecules from a region of high concentration to
a region of low concentration until an equilibrium is reached.

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Example;
Oxygen can freely diffuse through the cell membrane using this form
of
passive transport.
Facilitated diffusion
Facilitated diffusion is the same as simple diffusion but this form of transport
uses membrane proteins, such as channel proteins and carrier proteins. Channel
proteins provide a hydrophilic channel for the passage of charged and polar molecules,
like ions. Meanwhile, carrier proteins change their conformational shape for the
transport of molecules.
Example
Glucose is an example of a molecule that is transported across the cell membrane
through facilitated diffusion.

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Osmosis
Osmosis is the movement of water molecules from a region of high water potential to
a region of lower water potential through a semipermeable membrane. This form of
transport looks very different between plant and animal cells as plant cells have cell
walls surrounding each cell.
EXAMPLE
Water is example of osmosis