The cell membrane is composed of phospholipids, cholesterol, proteins, and carbohydrates. Phospholipids form a lipid bilayer that acts as a selectively permeable barrier. Cholesterol molecules maintain the integrity and fluidity of the membrane. Membrane proteins perform important functions like transporting molecules, acting as enzymes, and receiving signals. The fluid mosaic model describes the cell membrane as a fluid structure with components that can move freely within it.

1. The Cell Membrane
Composition
Mansoura University
Faculty Of Clinical Pharmacy
Department Of Biophysics
BY
Ahmed Jamal Abdel-Hameed
Abdel-Rhman Mohammed El-Amir
Mohammed Ahmed Kiwan
Ahmed Yasser Abdel-Hady
Abdel-Rhman Mossad El-Laket

2. What is the Cell Membrane ?
• The cell membrane is a dynamic and intricate
structure that regulates materials transported
across the membrane. The membrane is
selectively permeable (or semi-permeable)
meaning that certain molecules can cross the
membrane and others cannot.

3. It is a barrier that separates a cell from its
surrounding environment. This outer boundary
of the cell is also called the plasma membrane.
It is composed of four different types of
molecules:
• Phospholipids
• Cholesterol
• Proteins
• Carbohydrates and other molecules.

4. Fluid Mosaic Model
• The fluid mosaic model describes the structure of a cell
membrane. It indicates that the cell membrane is not solid. It
is flexible and has a similar consistency to vegetable oil, so all
the individual molecules are just floating in a fluid medium,
and they are all capable of moving sideways within the cell
membrane.

5. • Mosaic refers to something that contains many
different parts. The plasma membrane is a
mosaic of phospholipids, cholesterol
molecules, proteins and carbohydrates.

6. Phospholipids
• Phospholipids make up the basic structure of a
cell membrane. A single phospholipid molecule
has two different ends: a head and a tail. The
head end contains a phosphate group and is
hydrophilic. This means that it likes or is attracted
to water molecules. Watery fluids are found both
inside a cell (intracellular fluid) and outside a cell
(extracellular fluid). The hydrophobic tails of
membrane phospholipids are organized in a
manner that keeps them away from water.

7. • The tail end is made up of two strings of
hydrogen and carbon atoms called fatty acid
chains. These chains are hydrophobic, or do
not like to mingle with water molecules.
Structure of a phospholipid molecule

9. • The lipid bilayer is the barrier that keeps ions,
proteins and other molecules where they are
needed and prevents them from diffusing into
areas where they should not be. Lipid bilayers are
ideally suited to this role because, even though
they are only a few nanometers in width,[1] they
are impermeable to most water-soluble
(hydrophilic) molecules. Bilayers are particularly
impermeable to ions, which allows cells to
regulate salt concentrations and pH by
transporting ions across their membranes using
proteins called ion pumps.

10. Cholesterol
• Cholesterol is found in every cell of your body.
It is especially abundant in the membranes of
these cells, where it helps maintain the
integrity of these membranes, and plays a role
in facilitating cell signaling-- meaning the
ability of your cells to communicate with each
other so you function as a human, rather than
a pile of cells.

11. • Cholesterol molecules are important for
maintaining the consistency of the cell
membrane. They strengthen the membrane by
preventing some small molecules from crossing
it. Cholesterol molecules also keep the
phospholipid tails from coming into contact and
solidifying. This ensures that the cell membrane
stays fluid and flexible.

13. Cholesterol Maintains the Integrity of
the Cell Membrane
• Cholesterol is an amphipathic molecule, meaning,
like phospholipids, it contains a hydrophilic and a
hydrophobic portion. Cholesterol's hydroxyl (OH)
group aligns with the phosphate heads of the
phospholipids. The remaining portion of it tucks
into the fatty acid portion of the membrane.
• This helps slightly immobilize the outer surface of
the membrane and make it less soluble to very
small water-soluble molecules that could
otherwise pass through more easily.

14. Cholesterol Helps Maintain the
Fluidity of Cell Membranes
• While cholesterol adds firmness and integrity to
the plasma membrane and prevents it from
becoming overly fluid, it also helps maintain its
fluidity.
• At the high concentrations it is found in our cell's
plasma membranes (close to 50 percent,
molecule for molecule) cholesterol helps separate
the phospholipids so that the fatty acid chains
can't come together and crystallize.
• Therefore, cholesterol helps prevent extremes--
whether too fluid, or too firm.

15. Carbohydrates
• Plasma membranes also contain
carbohydrates, predominantly glycoproteins,
but with some glycolipids.
• It provides cushioning and protection for the
plasma membrane, and it is also important in
cell recognition.

17. Proteins
• The cell membrane has large content of
proteins, typically around 50% of membrane
volume. These proteins are important for cell
because they are responsible for various
biological activities.

18. • Some plasma membrane proteins are located
in the lipid bilayer and are called integral
proteins. Other proteins, called peripheral
proteins, are outside of the lipid bilayer.
Peripheral proteins can be found on either
side of the lipid bilayer: inside the cell or
outside the cell.

19. Proteins are Inserted into the Membrane
Transport proteins, or permeases, transport
molecules across the membrane. Aquaporins
are special protein channels used to move water
across the membrane.

20. • Membrane proteins can function as enzymes
to speed up chemical reactions, act as
receptors for specific molecules, or transport
materials across the cell membrane.

21. • The following short video sums up all
what we discussed regarding the Cell
Membrane Components.