Structure and function of Red blood cells

Question 1

What aspects of the red blood cells structure enable it to carry out it’s function?

Answer 1

Full of haemoglobin to carry oxygen

No nucleus makes it more deformable, and more room for Hb molecules

No mitochondria either

High Surface area/volume ratio to allow for gas exchange

Flexible to squeeze through capillaries

Question 2

What are the consequences of the red blood cell structure?

Answer 2

Full of haemoglobin means high oncotic pressure, oxygen rich environment (oxidation risk)

No nucleus means can’t divide, can’t replace damaged proteins - limited cell lifespan

No mitochondria means limited to glycolysis for energy generation (no Krebs’ cycle)

High Surface area/volume ratio means need to keep water out

Flexible means it has a specialised membrane required that can go wrong

Question 3

What is the structure of the red blood cell membrane?

Answer 3

It is a complex structure that is not just a lipid bilayer.

Areas of protein anchors and “spars” make it flexible.

If a protein is mutated then this can have consequences for deformability and shortened red cell surivival

Question 4

Red cells need energy to maintain specific ion concentrations gradient and keep water out. True/false?

Answer 4

True

The sodium-potassium pump keeps ion concentrations correct, keeps systems working in the cell and keeps water out however it requires ATP (energy)

Question 5

What type of protein is haemoglobin?

Answer 5

A tetrameric globular protein, with one haem group attached to each globulin chain.

Question 6

What is the most common type of haemoglobin structure in adults?

Answer 6

HbA - has 2 alpha and 2 beta chains (97% of people)

Question 7

Apart from HbA, what other haemoglobin structures can be present in adults?

Answer 7

HbA2 - (2.5% of people) - functional haemoglobin with 2 alpha and 2 delta chains.

HbF - foetal haemoglobin, 2 alpha and 2 gamma chains, seen in <1% of adult population.

Question 8

What is the description of a haem group?

Answer 8

Haem group is Fe2+ in a flat porphyrin ring.

Question 9

How many oxygen molecules bind to one Fe2+ (haem group)?

Answer 9

1 oxygen molecule bind to 1 Fe2+

Question 10

Oxygen can bind to Fe3+. True/false?

Answer 10

False

Oxygen CANNOT bind to Fe3+

Question 11

What are the functions of haemoglobin?

Answer 11

Delivers oxygen to the tissues

Acts as a buffer to H+

Transport of CO2

Question 12

How many O2 molecules are present per haemoglobin?

Answer 12

4 O2molecules per Hb

Question 13

What is the sequence for destruction of a red blood cell?

Answer 13

Normally occurs in spleen (and liver) - average red cell lifespan 120 days

Aged red cells taken up by macrophages i.e. taken out of the circulation

Red cell contents are recycled

Globin chains recycled to amino acids

Heme group broken down to iron and bilirubin

Bilirubin taken to liver and conjugated

Then excreted in bile (colours faeces and urine)

Question 14

What are the challenges potentially faced by red blood cells?

Answer 14

No mitochondria - only glycolysis for energy no Krebs’ cycle

Glycolysis- a low energy yielding process

Lots of oxygen about - oxygen free radicals are easily generated

Question 15

Why is the formation of free radicals bad?

Answer 15

Can oxidise Fe2+ to Fe3+ which doesn’t transport oxygen

Free radicals damage proteins ~(remember we can’t repair/replace proteins as no machinery to do so -so once they’re damaged that’s it)

Question 16

How is carbon dioxide transported?

Answer 16

Only 10% is dissolved in solution

Around 30% is bound directly to Hb as carbamino-Hb

The other 60% gets there as bicarbonate and the red cell has an important role in generating that bicarbonate

Question 16

What is glutathione?

Answer 16

Glutathione protects us from hydrogen peroxide by reacting with it to form water and an oxidised glutathione product (GSSG).

This maintains the redox balance.

Question 17

What are the system requirements for oxygen transport by haemoglobin?

Answer 17

Hb needs to be able to bind oxygen easily when there is a lot about (ie lungs where pO2 is high)

Needs to hold on to it as the pO2 drops a little (ie in transport in blood vessels)

Needs to then release 02 in the tissues where the pO2 is low

Cope with extra demand when stressed and have spare capacity in the system to cope when anaemic

Question 18

What does a red blood cell need?

Answer 18

Energy i.e. ATP

A way to keep Fe2+ from becoming Fe3+ (ie stop it oxidising)

To prevent oxidative damage to enzymes from free radicals

A way of buffering CO2 for transport

A way of holding onto oxygen in transport and dumping it in hypoxic environments

A way of improving tissue oxygen delivery when it needs it most (when anaemic or when high demand for oxygen - metabolic acidosis, high CO2 concentrations, anaemia)

Question 19

What is the bohr effect?

Answer 19

Hemoglobin’s lower affinity for oxygen secondary to increases in the partial pressure of carbon dioxide and/or decreased blood pH.

Question 20

What is the haldane effect?

Answer 20

Oxygenation of blood in the lungs displaces carbon dioxide from haemoglobin, increasing the removal of carbon dioxide.