The Red Cell Membrane

Question 1

What is the normal arrangement of the phospholipids in the red cell membrane?

Answer 1

Outer membrane: Phosphatidylcholine and sphingomyelin

In the inner layer phosphatidyl ethanolamine and phosphatidylserine

Question 2

What molecules are important in the maintenance of the membrane?

Answer 2

Flippase
floppase
scramblase
they aim to prevent the exposure of PS to the outer layer

Question 3

What are the most significant RBC membrane proteins currently known about?

Answer 3

Blood group antigens
Transport proteins such as band 3 RhAG - o2 and co2
AQP1 and glut 1
Adhesive proteins and signalling receptors

Question 4

What happens if there is exposure of inner proteins to the outer membrane?

Answer 4

This triggers apoptosis and phagocytosis by macrophages

Question 5

Give examples of adhesive protein?

Answer 5

ICAM4 and Lu

Question 6

What are the mechanical and functional features of the red cell?

Answer 6

Mechanical: 
Strong and resistant to damage
Elastic and deformable
Elongates upto 250% its original dimensions (longitudinal only, otherwise can lyse cell)
Functional functions:
Ag presentation
Molecule transportation
maintenance of phospholipid dysequilibrium to evade macrophage phagocytosis

Question 7

What are some membrane transport proteins?

Answer 7

Band 3
AQ1
Glut1
Kidd antigen protein
RhAG
Na-K-ATPase
Ca ATPase
Na-K-2Cl co transporter
Na-cl co transporter
gardos

Question 8

What is the function of ankyrin complex?

Answer 8

it anchors the structure onto the spectrin proteins

Question 9

What is the action of the 4.1R complex?

Answer 9

cellular elongation

binds the duffy antigen and glut 1

Question 10

What is Spectrin composed of?

Answer 10

alpha and beta

filamentous triple helices of repeats of 106AAs

Question 11

What do the anchoring proteins bind to?

Answer 11

Actin

Adducting dermatin tropomyosin

Question 12

How is the biconcave disc maintained in the RBC?

Answer 12

Strong cohesion between the lipid bilayer and skeletal proteins stop membrane vesiculation
The integrity of the membrane is maintained by strong interactions in the skeletal proteins and phospholipids
Cation regulation is also important as maintains RBC volume

Question 13

What is cytoplasmic viscosity?

Answer 13

Ability of the cell to change shape

Question 14

What is cytoplasmic viscosity governed by?

Answer 14

Hb conc in the cell MCHC

Question 15

What do increases in cytoplasmic viscosity lead to?

Answer 15

Increases in viscosity hamper the abilty of the cell to squeeze through microcirculation whcih affects tissue oxygen delivery

Question 16

What causes a membrane to deform?

Answer 16

Spectrin repeats - more spectrin repeats - more folding and unfolding units

Question 17

In what diseases is the membrane/skeletal protein mutated?

Answer 17

Hereditary spherocytosis
Hereditary Elliptocytosis
Hereditary stomatocytosis
Hereditary ovalocytosis

Question 18

What is seen in hereditary spherocytosis?

Answer 18

Autosomal dominant
anaemia
jaundice
reticulocytosis
splenomegaly
gallstones
spherocytes in blood films

Question 19

What is the cause of the spherocytosis?

Answer 19

Membrane surface area loss occurs due to reduction in loss of cohesion of membrane component due to mutations in the vertical complexes

Question 20

What is the cause of hereditary elliptocytosis?

Answer 20

AD disease

Loss of CSM SA due to mutations in roteins important in horizontal adhesive proteins

Question 21

Hereditary stomatocytosis?

Answer 21

high cytoplasmic cation content gives rise to overhydrated cells that look like stomatocytes

Question 22

Hereditary ovalocytosis?

Answer 22

Single mutation in band 3 - loss of deformability common in SEasians

Question 23

Quick run down of the structure of the red cell membrane?

Answer 23

Lipid bilayar, with a network of skeletal proteins beneath the inner layer (e.g alpha spectrin)
-The membrane is studded with transmembrane proteins such as Band 3 (transport protein) and ICAM4 (Adhesion proteins`0
-It is highly elastic and deformable
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