Lecture 2 Membrane Proteins

Question 1

Outline the biochemical evidence for membrane proteins

Answer 1

1) freeze fracture

2) membrane fractionation and gel electrophoresis

Question 2

Outline the functional evidence for membrane proteins

Answer 2

1) facilitated diffusion
2) ion gradients
3) specificity of cell responses

Question 3

What are the three ways membrane proteins may move ?

Answer 3

1) laterally ( from side to side )
2) conformational change , eg carrier proteins
3) rotate

Question 4

What is one difference in the mobility between phospholipids and membrane proteins ?

Answer 4

Membrane proteins cannot flip flop whereas phospholipds can.

Question 5

What are the two types of membrane proteins ?

Answer 5

1) integral proteins

2) peripheral membrane proteins

Question 6

What’s are features of peripheral membrane proteins

Answer 6

• • peripheral membrane proteins lie on the surface of membranes by hydrogen bond interactions or electrostatic.
• they can be removed by changes in pH Or ionic strength

Question 7

What are features of integral proteins

Answer 7

• interact with the hydrophobic regions of the bilayer.
• proteins cannot be removed by changes in ionic or pH strength
• they require detergents that compete for the hydrophobic regions in the bilayer

Question 8

How many membrane proteins contribute to the cytoskeleton?

Answer 8

• network of spectrum and actin molecules .
• spctrin winds together to form an anti parallel heterodimer where two of these then form head to head assosiations to form a heretotetramer.

Question 9

What are the ways membrane protein mobility may be restricted ?

Answer 9

L1) assosiations with other extra membranous proteins eg peripheral proteins such as the cytoskeleton.

2) membrane protein associations eg proteins aggregate together.
3) proteins tend to just Separate out into fluid or cholesterol poor regions.

Question 10

What are two examples of haemolytic anaemia ?

Answer 10

1) hereditary spherocytosis

2) hereditary ellipocytosis

Question 11

What is hereditary spherocytosis ?

Answer 11

• this is where spectrum levels may be depleted by 40-50 %

- the red blood cells become round and become less resistant to lysis during passage through capillaries.

Question 12

What is hereditary elliptocytosis ?

Answer 12

• this is where there is a common defect in the spectrin protein which results in the inability to form heterotetramers resulting in fragile elliptoid cells( become rugby ball shaped)