The red blood cell

Question 1

Give a description of the RBC

Answer 1

• aNUCLEATED
• no ribosome = no protein synthesis
• no mitochondria
• Energy is derived from anaerobic glycolysis

Question 2

Give a description of the hemoglobin

Answer 2

• tetramer
• 4 glycoproteins: 2 alpha and 3 beta chains
• Each globin monomer carries a haem group in an area called the haem pocket

Question 3

If haem binds to O2, what is the function of the globin chains

Answer 3

*Free haem binds to O2 to form ferric haem therefore the function of the globin chains it to :
> reducing its strength
> Maintaining the ferrous state
> allowing dissociation of the oxygen
>The globin also prevents the binding of other potential ligands

Question 4

Discuss the transition of the globins to quaternary structure?

Answer 4

*After 2-3 haems have been oxygenated, the entire tetramer changes the chape to form apha1beta1 and alpha2beta2

Question 5

What causes the transition from a tense state to a relaxed state and what is the advantage of this

Answer 5

• Binding of the first O2 to the haem leads to strain in the molecule because of the flattening of the haem
• After the second O2 bond, the strain leads to the movement of one alpha-beta dimer relative to the other.
• This is achieved by H bonds and releasing H+

> > > The oxygen affinity of haemoglobin increases by a factor of 500

Question 6

How does pH affect the O2 affinity of hemoglobin

Answer 6

pH: the Bohr affinity > the lower the pH, the lower the O2 affinity

*This depends on the H bonds which stabilizes the deoxy form releasing as they break

> Active tissues tend to lower the pH and so this decrease in O2 affinity leads to increased O2 delivery

Question 7

How does temperature affect the O2 affinity of hemoglobin?

Answer 7

• As deoxy-Hb binds to O2, energy is released from the breaking H bonds
• An increase in energy in the form of temperature drives the equilibrium to deoxy-Hb and favours the release of oxygen

Question 8

HoDw does CO2 affect the O2 affinity of Hb?

Answer 8

• The reaction is catalyzed by carbonic anhydrase
• CO2 + H2O < = > HCO3 occurs in the tissues .
• As the tense state reforms, H+ is bound to Hb and this drives the reaction to form HCO3
• In the lung, as O2 binds the H+ is released from Hb and reacts with HCO3 to form CO2 + H2O.

Co2 is blown off

Question 9

describe the membrane of the red blood cell

Answer 9

• RBC has no internal structure and thus the membrane is very flexible but cannot be stretched.
• Biconcave disc which is not fixed but has a maximum surface to area volume ratio
• The cell must become cup-shaped to pass through the smallest capillaries

Question 10

What is the function of 2,3DpG

Answer 10

*This stabilizes the tense form of Hb by binding to the ga between the dimers present in an oxygenated state.
Fetus Hb does not bind to 2,3DPG

Question 11

What is the methemoglobin

Answer 11

2% of Hb is auto-oxidised each day be converting Fe2+ > Fe3+

*Fe2+ is regenerated by using NADH produced from glycolysis and cytochrome bs

Question 12

Whatis a Glutathione (GSH)?

Answer 12

*This mops up oxidants in the RBC cytosol preventing them Hb / sulphur containing groups in membrane and enzymes.

Two GSH are combined to frm GSSG
GSSG must be reduced to GSH
GSSG + NADPH + H+&raquo_space; 2GSH + NADP +

Question 13

What is the function of Hexose monophosphate shunt?

Answer 13

NADPH is generated by an HMP shunt to accelerate baseline capacity in the face of oxidase stress. The G6PD is the rate-limiting step