Download CellMembranes - Mexico Central School District

Also called the plasma membrane because many cells in the
body are in direct contact with the fluid portion of the
blood - plasma

Is found in all organisms, prokaryotic and eukaryotic

Regulates what enters and leaves the cell
Maintains the proper internal chemical composition of the cell –
gives the cell what it needs and gets rid of cellular waste

Helps the cell communicate with other cells

Provides protection for the cell

Supports the cell - helps give it shape
1. Lipids
2. Proteins
Structure:
Two layers of special lipid (fat) molecules called
phospholipids, placed on top of each other.

HYDROPHILIC HEAD
“water loving”
-Attracted to the water
-Also called POLAR

HYDROPHOBIC TAIL
“water fearing”
-Not attracted to the water
-Also called NON-POLAR
A Phospholipid
AS Biology. Foundation. Cell
membranes and Transport
6
Hydrophilic heads – face the watery regions
inside and outside the cell.
Animation
Hydrophobic tails - face each other in a
water-free region.
FUNCTION:
1. Provides the overall structure for the plasma
membrane.
 Like a film of oil – the membrane is “fluid”
2.
Allows some small molecules and atoms to
pass through the membrane.
Structure:


1 Cholesterol per Phospholipid!
Not found in plants or prokaryotes
Function:



They immobilize part of the phospholipid molecule.
This keep the membrane fluid, but not too fluid - It
keeps the membrane from turning to mush!
Without cholesterol a cell would need a cell wall.
Structure:
A sugar (carbohydrate)
attached to a lipid
Function:
1. Recognition sites – allows cells to recognize…
 other cells from the same organism:
- Organ donation
- Blood transfusions
2. Protection against harsh conditions (temp, pH)
Structure:
Extends into and completely through the Phospholipid Bilayer,
from the outer surface to the inner surface.
Structure:
This type of protein is found on the outer surface or inner surface
of the bilayer only. Peripheral proteins do not span the membrane.
They are found on the periphery of the membrane.
Function:
1.
Channel Protein/Transport Protein: The protein itself is a
channel or grove that substances can move through to go into
or out of the cell.
2.
Receptor Proteins: Receptors will bind a specific substance for
transport into the cell.
EX: Hormones (chemical messages)
Almost every cell has insulin receptors. When you eat a meal your
pancreas secretes insulin into your blood stream. The insulin
binds insulin receptors. Some intercellular signaling happens and
eventually a Glucose transporter is sent to the cell surface so that
the glucose from the food you just ate can get into your cells.
Structure:
A sugar (carbohydrate)
attached to a protein
Function:
1. Recognition sites – allows cells to recognize…
 other cells from the same organism:
- Organ donation
- Blood transfusions
2. Protection against harsh conditions (temp, pH)
FLUID- because individual phospholipids and proteins
can move around freely within the layer, like it’s a
liquid.
MOSAIC- because of the pattern produced by the
scattered protein molecules when the membrane is
viewed from above.