RBC structure and function

Question 1

Structure of red blood cells [5 marks]

Answer 1

• No nucleus, mitochondria or ER
• Cytoplasm rich in haemoglobin
• Biconcave
• Flexible membrane
• High surface area to volume ratio

Question 2

Function of red blood cells [1 mark]

Answer 2

To carry oxygen and carbon dioxide to and from tissue.

Question 3

What lipids does the outer hydrophilic portion consist of? [2 marks]

Answer 3

• Phosphatidylcholine
• Sphingomyelin

BOTH UNCHARGED

Question 4

What lipids does the inner hydrophobic portion consist of? [2 marks]

Answer 4

• Phosphatidylethanolamine
• Phosphatidylserine

BOTH CHARGED

Question 5

What does increased cholesterol in red blood cells cause?

Answer 5

Acanthocytosis (spiked cells)

Question 6

What does an increase in cholesterol and phospholipids and a decrease in haemoglobin cause? [1 mark]

Answer 6

Target cells

Question 7

What are the integral proteins in red blood cells? [5 marks]

Answer 7

• Glycophorin (A, B and C)
• Band 3
• Na+/k+ ATPase
• Aquaporin 1
• Transferrin Receptor

Question 8

What is the peripheral protein Spectrin and what does it do? [4 marks]

Answer 8

• Most abudant
• Made up of alpha and beta chains
• Binds with other peripheral proteins to form the cytoskeletal network of microfilaments
• Controls biconcave shape and deformability of cell.

Question 9

What is the peripheral protein Ankyrin and what does it do? [1 mark]

Answer 9

Anchors lipid bilayer to membrane skeleton via spectrin and band 3 interaction

Question 10

What is the peripheral protein Protein 4.1 and what does it do? [4 marks]

Answer 10

• Links cytoskeleton to the membrane via glycophorin

- Stabilises interaction of spectrin with actin

Question 11

What is the peripheral protein Actin and what does it do? [1 mark]

Answer 11

It’s responsible for contraction and relaxation of the membrane.

Question 12

What is the function of the membrane? [3 marks]

Answer 12

• Provides shape
• Provides deformability, elasticity
• Regulates intracellular cation concentration

Question 13

What causes hereditary elliptocytosis? [2 marks]

Answer 13

• Mutations in genes destabilise the cytoskeleton of erythrocyte
• So they can’t maintain their shape

Question 14

What causes hereditary spherocytosis? [2 marks]

Answer 14

• Mutations in genes for spectrin or ankyrin means that they can’t link with actin
• This makes erythrocytes more likely to lyse in water

Question 15

What allows red blood cells to stay alive without structural deterioration? [3 marks]

Answer 15

• Surface area to volume ratio
• Membrane deformability
• Cytoplasmic viscosity determined by Mean Corpuscular Haemoglobin Concentration (higher MCHC = higher viscocity)

Question 16

Haemoglobin structure [4 marks]

Answer 16

• Globular
• 2 alpha globin chain, 2 beta globin chain
• Haem is a complex of protoporphyrin IX and Fe2+ (Fe2+ in centre with 4 nitrogen)

Question 17

Why do red blood cells need metabolic pathways?

Answer 17

• To maintain cation pumps
• To maintain Hb in reduced state
• To maintain reduced sulfhydryl groups in Hb
• To maintain RBC integrity and deformability

Question 18

Glycolytic pathway

Answer 18

• Glucose is metabolised to generate 2 ATP
• Generates 90-95% of energy needed
• Maintain RBC shape, flexibility and cation pumps

Question 19

Hexose monophosphate stunt (a.k.a. pentose phosphate)

Answer 19

• Provides the reducing power NADPH
• Maintains glutathione in the reduced form
• Red blood cells use reduced glutathione to protect it against oxidative damage

Question 20

Methaemoglobin Reductase pathway

Answer 20

• Maintain iron in Fe2+

- Without the enzyme, methaemoglobin with Fe3+ accumulate and it can’t carry oxygen

Question 21

Luebering Rapoport shunt

Answer 21

Permits the accumulation of 2,3-DPG which is essential for maintaining normal oxygen tension, regulating haemoglobin affinity