Red blood cells - structure and function

Question 1

What is the primary function of a RBC

Answer 1

To transport respiratory gases to and from the tissues

Question 2

How does a RBC travel through the microvascular system without mechanical damage

Answer 2

The RBC membrane is extremely tough yet flexible

Interactions between the membrane and cytoskeletal proteins determines strength and flexibility

Question 3

What does the outer part of the RBC membrane consist of

Answer 3

A hydrophilic portion containing glycolipids, glycoproteins and proteins

Question 4

What does the central part of the RBC membrane consist of

Answer 4

A hydrophobic layer containing proteins, cholesterol and phospholipids

Question 5

What does the inner part of the RBC membrane consist of

Answer 5

A hydrophilic layer of mesh-like cytoskeletal proteins to support the lipid bilayer

Question 6

Where is phosphatidyl situated in the RBC and why

Answer 6

On the inside of the cell membrane since macrophages can detect it

Question 7

Which phospholipids are on the outer layer

Answer 7

Uncharged phospholipids, phosphatidyl choline and sphingomyelin

Question 8

Which phospholipids are on the inner layer

Answer 8

Charged phospholipids, phosphatidyl ethanolamine and phosphatidyl serine

Question 9

What does an increase in free plasma cholesterol mean for RBC’s and why

Answer 9

It will result in an accumulation of cholesterol in the RBC membrane since membrane cholesterol exists in free equilibrium with plasma cholesterol

Question 10

What happens if a RBC has too much cholesterol

Answer 10

Acanthocytosis (spur cells) - Cells appear to have spikes on the cell membrane

Question 11

What happens if a RBC has too much cholesterol and phospholipid

Answer 11

Target cells - Cells look like a bullseye because of a disproportional increase in the ratio of surface membrane area to volume

Question 12

Where are integral membrane proteins found

Answer 12

Extend from the outer surface and transverse the entire membrane to the inner surface

Question 13

What are the 2 major integral membrane proteins

Answer 13

• Glycophorins (A,B and C)

- band 3 (anion transporters)

Question 14

What are some other integral membrane proteins

Answer 14

• Na+/ATPase
• Aquaporin 1
• Surface receptors e.g. TfR

Question 15

Where are peripheral proteins found

Answer 15

Limited to cytoplasmic surface of membrane and forms the RBC cytoskeleton

Question 16

What are the major peripheral proteins include

Answer 16

• Spectrin
• Ankyrin
• Protein 4.1
• Actin

Question 17

What are spectrin proteins and what are they made of

Answer 17

The most abundant peripheral protein

Composed of alpha and beta chains

Question 18

What do ankyrin proteins do

Answer 18

Primarily anchors lipid bilayer to membrane skeleton via interaction with spectrum and band 3

Question 19

What does protein 4.1 do

Answer 19

Links the skeleton to the membrane by means of its associations with glycophorin
Stabilises interaction of spectrin with actin

Question 20

What do actin proteins do

Answer 20

Responsible for contracting and relaxation of membrane

Strong cohesion between bilayer and membrane skeleton maintains surface area

Question 21

What is the function of spectrin proteins

Answer 21

Very important in RBC membrane integrity since it binds with other peripheral proteins to form the cytoskeleton network of microfilaments
Controls biconcave shape and deformability of cell

Question 22

How does the shape of the RBC relate to its function

Answer 22

1. Provides the optimum surface area to volume ratio for respiratory exchange
2. Provides elasticity allowing the passage through micro vessels

Question 23

What is hereditary elliptocytosis and how does it happen

Answer 23

RBC is permanently elliptical since there is a problem with ankyrin or spectrin

Question 24

What is hereditary spherocytosis and how does it happen

Answer 24

RBC cannot retain its shape since there is a problem with band 3 and actin and ankyrin/spectrin

Question 25

What requires energy to be maintained in the RBC

Answer 25

1. Cation pumps
2. Hb in reduced state
3. Reduced sulfhydryl groups in Hb and other proteins
4. RBC integrity and deformability

Question 26

What are the different RBC metabolic pathway

Answer 26

• Glycolytic pathway or Embden-Meyerhof pathway
• Pentose-phosphate pathway
• Methaemoglobin reductase pathway
• Luebering-rapoport shunt

Question 27

What does the glycolytic pathway do and how do it work

Answer 27

• Generates 90-95% of energy needed by RBCs
• Glucose is metabolised and generates two molecules of ATP
• Functions in the maintenance of RBC shape, flexibility and cation pumps

Question 28

Why is the pentose phosphate pathway needed and how does it work

Answer 28

RBC needs reduced glutathione (GSH) to protect from oxidative damage
This pathway provides the reducing power, NADPH
NADPH maintains GSH and protects Hb and membrane proteins

Question 29

What does the methaemoglobin reductase pathway do

Answer 29

Maintains iron in the ferrous (Fe2+) state

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

Question 30

What does the Luebering-rapoport shunt

Answer 30

It permits the accumulation of 2,3-diposphoglycerate

This is essential for maintaining normal oxygen tension, regulating haemoglobin affinity

Question 31

What features of the RBC help it to withstand life without structural deterioration

Answer 31

1. The geometry of the cell; SA to V ratio - facilitates deformation whilst maintaining a constant surface area
2. Membrane deformability - spectrin molecules undergo reversible change in conformation, some uncoiled and extended, others compressed and folded
3. Cytoplasmic viscosity determined by MCHC - as MCHC rises, viscosity rises exponentially