The structure of cell membrane

1. GROUP FOUR
A PRESENTATION ON THE
STRUCTURE OF THE CELL
MEMBRANE

2. THE STRUCTURE OF
THE CELL
MEMBRANE

3. THE CELL MEMBRANE
• The cell membrane is a structure that separates the
interior of a cell from its outside environment.
• The cell membrane regulates what enters and exits the
cell so that it does not lose too many nutrients or take in
too many ions.
• It is selectively permeable in function.

4. STRUCTURE OF THE CELL MEMBRANE
• The fluid mosaic model of the cell membrane is how scientists
describe what the membrane looks like and functions.
• It was first proposed in 1972.
• According to this model, the membrane is a fluid structure with a
mosaic of components – primarily, proteins and cholesterol
embedded in or attached to a double layer (bilayer) phospholipid.
• The pattern of these molecules put together is known as mosaic.
• The molecules are constantly moving in two dimensions, a fluid
fashion, similar to icebergs floating in the ocean.
• The movement of the mosaic of molecules makes it impossible to
form a completely impenetrable barrier.

5. Structureofthecellmembrane.

6. PHOSPHOLIPDS
• The cell membrane is made up of a phospholipid bilayer.
• Phospholipids are lipids (fatty acid chains) with a phosphate
group attached to them.
• The phospholipids have one head and two tails.
• The head is polar and hydrophilic, or water-loving.
• The tails are nonpolar and hydrophobic, or water-fearing.

7. • The cell membrane is exposed to water
mixed with electrolytes and other
materials on the outside and the inside of
the cell.
• The phosphate heads in each phosphate
layer face the aqueous or watery
environment on either side and the tails
face away from the water between the
layers of the head, because they are
hydrophobic.
• This arrangement means that only small,
uncharged molecules can pass through
the membrane.
• The membrane is called semi-permeable,
meaning that some things can pass
through without assistance, while other
things cannot.

8. CHOLESTEROL
• Cholesterol is a type of steroid.
• The cholesterol molecules are randomly distributed across the
phospholipid bilayer, helping the bilayer stay fluid in different
environmental conditions.
• The cholesterol holds the phospholipid together so that they do not
separate too far, letting unwanted substances in, or compact tightly,
restricting movement across the membrane.

9. • Without cholesterol, the phospholipids in your cell membrane will
start to get closer when exposed to cold making it difficult for small
molecules like gases to squeeze in between the phospholipids like
they normally do.
• Without cholesterol, the phospholipids start to separate from each
other leaving large gaps.

10. PROTEINS
• The cell membrane is made up of two different types of
proteins: integral and peripheral proteins.
• Integral proteins are embedded into the phospholipid bilayer;
may or may not extend through both layers.
• They are helpful for transporting large molecules like glucose
across the cell membrane.
• Peripheral proteins are found on the inner or outer surface of
the phospholipid bilayer, but not embedded in the hydrophobic
core. They can be attracted to the ends of the integral proteins,
or not, and help in transport or communication between
neighbouring cells.

11. WHAT CAN GO THROUGH THE
CELL MEMBRANE
• The fluid mosaic model helps and explains how membranes
regulate the movement of substances in and out of the cell.
• Substances do not move across the barrier indiscriminately;
membranes are selectively permeable.
• The cell is able to take up many varieties of small molecules
and ions and exclude others.
• Substances that move through the cell membrane do so at
different rates.

12. • Movement of a molecule through a membrane depends on the interaction
of the molecule with the hydrophobic core of the membrane.
• Nonpolar molecules, such as hydrocarbons, CO2 and O2 are hydrophobic
and can dissolve in the lipid bilayer and cross easily, without the resistance
of membrane proteins.
• The hydrophobic core impedes the direct passage of ions and polar
molecules, which are hydrophilic.
• Proteins assist and regulate the transport of ions and polar molecules.
• These ions and polar molecules pass through transport proteins that span
the membrane, avoiding contact with the lipid bilayer.
• Each transport protein is specific for the substance that it translocates.
• Some transport proteins called channel proteins have a hydrophilic
channel that certain molecules and ions can use as a tunnel through the
membrane.
• The passage of water through the membrane can be greatly facilitated by
channel proteins known as aquaporins.

13. Channelproteins

14. THANK YOU.