Red Blood Cells Structure And Function

Question 1

Describe the structure of red blood cells?

Answer 1

Lacks nucleus, mitochondria, ER
Essentially a bag of haemoglobin
Biconcave, 8 micron cells but able to deform + pass through 3 micron capillaries or reticuloendothelial system without fragmentation
Have flexible membrane with high surface to volume ratio

Question 2

Describe the structure of red cell membrane?

Answer 2

Semi-permeable lipid bilayer with proteins scattered throughout:
Outer hydrophilic portion composed of glycolipids, glycoprotein, proteins
Central hydrophobic layer containing proteins, cholesterol + phospholipids
Inner hydrophilic layer of mesh like cytoskeletal proteins to support lipid bilayer

Question 3

What is structure of RBC membrane lipid (40%)?

Answer 3

Asymmetric phospholipid distribution
Unesterified free cholesterol between
Uncharged phospholipid of outer layer=> phosphatidyl choline and sphingomyelin
Charged phospholipid of inner layer=> phosphatidyl ethanolamine + phosphatidyl serine

Question 4

What is structure of RBC membrane proteins (50%)?

Answer 4

Integral membrane proteins
2 major integral membrane proteins => glycophorins + Band 3
Other integral proteins=> Na+/K+ ATPase, aquaporin 1, surface of membrane + forms RBC cytoskeleton
Peripheral proteins=> limited to cytoplasmic surface of membrane + forms RBC cytoskeleton
Major peripheral proteins include spectrin, ankyrin, protein 4.1 + actin

Question 5

What is function of spectrin?

Answer 5

Most abundant peripheral protein
Composed of alpha + beta chains
Very important in RBC membrane integrity
Controls biconcave shape + deformability of cell

Question 6

What is function of ankyrin?

Answer 6

Primarily anchors lipid bilayer to membrane skeleton via interaction with spectrin + band 3

Question 7

What is function of protein 4.1?

Answer 7

May link cytoskeleton to membrane by means of its association with glycophorin
Stabilises interaction of spectrin with actin

Question 8

What is function of actin?

Answer 8

Responsible for contraction + relaxation of membrane

Question 9

What is function of red cell membrane?

Answer 9

Provides shape=> provides optimum SA to volume ratio for respiratory exchange
Provides deformability, elasticity=> allowing passage through capillaries
Regulated intracellular cation concentration

Question 10

What do we see when things go wrong in red cells?

Answer 10

Hereditary elliptocytosis
Hereditary spherocytosis
Abnormality in spectrin
Abnormality in spectrin + ankyrin

Question 11

What features allow RBC to withstand life without structural deterioration?

Answer 11

Geometry of cell: SA to volume ratio
Membrane deformability
As MCHC rises, viscosity rises exponentially

Question 12

Describe the structure of haemoglobin?

Answer 12

Is globular haemoprotein
Haem is complex of protoporyphrin, IX and ferrous iron (Fe2+)
Iron held in centre of haem molecule by bonds to 4 nitrogen of porphyrin ring
Has 4 polypeptide subunits => 2 a globin chains and 2 B globin chains

Question 13

Metabolism in RBC provide energy required for?

Answer 13

Maintenance of action pumps
Maintenance of reduced sulfhydryl groups in Hb and other proteins
Maintenance of RBC integrity + deformability

Question 14

What are key metabolic pathways for RBC?

Answer 14

Glycolytic pathway
Pentose phosphate pathway
Methaemoglobin reductase
Luebering Rapoport shunt

Question 15

Describe the importance of glycolytic pathway in RBC?

Answer 15

Generates 90-95% of energy needed for RBCs

Functions in maintenance of RBC shape, flexibility + cation pumps

Question 16

Describe the importance of pentose phosphate pathway in RBC?

Answer 16

Pentose phosphate shunt provides reducing power, NADPH
NADPH maintains glutathione in reduced form (GSH)
RBC uses GSH to protect it from oxidative damage

Question 17

Describe the importance of methaemoglobin reductase pathway in RBC?

Answer 17

Maintain iron in ferrous

In absence of this enzyme, methaemoglobin accumulates and it cannot carry oxygen

Question 18

Describe the importance of Luebering rapoport shunt in RBCs?

Answer 18

Biochemical pathway in mature erythrocytes involving the formation of 2.4 bisphosphoglucerate + which regulates oxygen release from haemoglobin + delivery to tissues
Permits accumulation of 2,3 DPG which is essential for maintaining normal oxygen tension regulating haemoglobin affinity