SPEC POINT 2.2

Question 1

Why are cell membranes vital structures?

Answer 1

They create an enclosed space separating the internal cell enviornment from the external cell environment

Question 2

What is the structure of a cell membrane?

Answer 2

Phospholipid bilayer containing proteins, cholesterol, glycoproteins and glycolipids

Question 3

What are phospholipids made up of?

Answer 3

1. a molecule of glycerol
2. a phosphate group (head)
3. 2 fatty acid tails (lipid tail)

Question 4

List the evidence for the fluid-mosaic model of biological membranes:

Answer 4

1. TWO LAYERS OF PHOSPHOLIPIDS - area of total lipid from red blood cells was double that of red blood cell cell membrane
2. PROTEIN IN CELL MEMBRANE - electron micrographs show electron dense layer in membranes
3. PROTEINS ARE DISTINCT AND INDEPENDENT STRUCTURES, THAT SPAN THE MEMBRANE - freeze fracture electron micrographs show distinct globular structures that span membrane/these disappear when protein is removed from cell before procedure
4. PHOSPHOLIPIDS ARE MOBILE AND NOT IN STATIC POSITIONS - differently labelled proteins from two different cells end up mixed together when the cells are fused (showing that they can move)

Question 5

How do the phospholipids contribute to the structure of the cell membrane?

Answer 5

Due to the hydrophilic phosphate head of the molecule, it attracts other polar molecules like water. The fatty acid tails are non polar and are therefore hydrophobic, this means the phospholipids become arranged so the tails have no contact with the water.

Question 6

What are models of membrane structure?

Answer 6

Interpretations of data which can change when scientific advances enable new discoveries. Models represent real life structures and processes

Question 6

What does the term ‘fluid mosaic’ mean in reference to cell membranes?

Answer 6

Fluid refers to the movement of the phospholipids in the plane of the membrane
Mosaic refers to the random association of proteins within the membrane

Question 6

Explain why a phospholipid bilayer (with no proteins in it) is a barrier to the movement of certain types of particle:

Answer 6

1. Phospholipid fatty acids are hydrophobic
2. They prevent the movement of charged, large or polar substances because these substances cannot interact with the hydrophobic fatty acid chains
3. The phospholipids are also very close together, so large molecules are also unable to freely diffuse across the membrane

Question 6

What is the role of proteins within the cell membrane?

Answer 6

Involved with cell transport and communication

Question 7

What is the difference between intrinsic and extrinisic proteins?

Answer 7

Intrinsic - embedded within the membrane, precise arrangement determined by hydrophillic and hydrophobic regions
Extrinsic - attached to the outer or inner surface of the membrane

Question 8

What is the difference between glycolipids and glycoproteins?

Answer 8

Glycolipids - lipids with carbohydrate attached

Glycoproteins - proteins with carbohydrate attached

Question 9

What is the location and function of glycolipids and glycoproteins in the cell membrane?

Answer 9

Location: present on surface of cell membrane
Function: aid cell to cell communication by attaching as cell markers or binding with substances at the cell surface

Question 10

What is the role of cholesterol within the cell membrane?

Answer 10

Found between the phospholipids where it regulates membrane fluidity by stopping the phospholipid tails from packing too closely together
It increases the mechanical strength and stability of membranes (at higher temps too) and without it membranes would break down and cells would burst