Structure of the Cell Membranes

Question 1

What is the structure of the cell-surface membrane?

Answer 1

-Basic structure known as plasma membrane
-Phospholipids form a bilayer with hydrophilic heads facing outward and hydrophobic tails facing inwards
-Carrier proteins and protein channels are embedded into the phospholipid bilayer
-Cholesterol molecules occur within the phospholipid bilayer
-Glycolipids and Glycoproteins are attached to carbohydrates and extrinsic proteins respectively

Question 2

What are the functions of the following within the cell surface membrane:
-Phospholipid bilayer
-Carrier proteins and protein channels
-Cholesterol
-Glycolipids
-Glycoproteins

Answer 2

=Phospholipid bilayer
-Allows lipid-soluble substances to enter and leave the cell
-Prevents water-soluble substances entering and leaving the cell

=Carrier proteins and protein channels
-Allow for water-soluble substances to be transported into the cell
-Allows active transport to occur via carrier proteins
-Provide structural sipport

=Cholesterol
-Makes the membranes less fluid at higher temperatures
-Prevents leakage of water and dissolved ions from the cell
-Reduce lateral movement of molecules including phospholipids

=Glycolipids
-Act as recognition sites
-Maintain the stability of the membrane
-Help cells to attach to one another and so form tissues

=Glycoproteins
-Act as recpgnition sites
-Allows cells to recognise one another (e.g. lymphocytes)

Question 3

Why is the fluid-mosaic model referred to as ‘fluid’ and ‘mosaic’?

Answer 3

FLUID: Individual phospholipid molecules can move relative to one another. This gives the membrane a flexible structure that is constantly changing in shape.

MOSAIC: Proteins that are embedded in the phospholipid bilayer vary in shape, size and pattern.