Cell Membrane- Membrane Proeins

Question 1

What are some examples of proteins undergoing conformational change?

Answer 1

Haemoglobin, voltage gated sodium channels, ligand gated sodium channels, GPCRs, ATPases, phosphokinases.

Question 2

What are the three modes of motion permitted?

Answer 2

Lateral- formation of proteins complexes. Rotational- F1/F0 ATPase. Conformational change- localised within protein structure.

Question 3

Protein density in cell membranes, by dry weight.

Answer 3

Typical cell= 60%, myelin sheath= 20%, mitochondria= 75%, RBC= 75%.

Question 4

Describe classification of membrane proteins.

Answer 4

There are 2 major groups: peripheral and integral proteins. Peripheral proteins split into the external membrane face and the internal membrane face.

Question 5

What are the different types of protein interactions?

Answer 5

Aggregation, Tethering (extracellular and intracellular), cell-cell interaction.

Question 6

What are the three main structural components of cortical cytoskeleton?

Answer 6

1. Transmembrane proteins. 2. Intermediate anchoring proteins connecting 1 and 3. 3. Long flexible/elastic force carrying proteins. 1-2-3 interact via electrostatic non-covalent bonds.

Question 7

Role of ankyrin.

Answer 7

Anchors bicarbonate/chloride exchanger (band 3.1) to spectrin.

Question 8

What is spectrin?

Answer 8

It forms a flexible and elastic double helical structure. At the end of heterotetramer, it complexes with band 4.1 - Adductin -Actin.

Question 9

Describe cortical cytoskeleton disruption.

Answer 9

Cytoskeletal protein mutations- a loss of RBC structural intergrity. Mutations in ankyrin/spectrin/band 3/band 4.1 causes a loss of functional RBC cytoskeleton: Hereditary Spherocytosis ‘rigid’ balloon like RBC -> loss of O2 carrying capacity, osmotically fragile, shortened lifespan of 10-40 days.