Structure and function of Red blood cells Flashcards
What aspects of the red blood cells structure enable it to carry out it’s function?
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
What are the consequences of the red blood cell structure?
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
What is the structure of the red blood cell membrane?
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
Red cells need energy to maintain specific ion concentrations gradient and keep water out. True/false?
True
The sodium-potassium pump keeps ion concentrations correct, keeps systems working in the cell and keeps water out however it requires ATP (energy)
What type of protein is haemoglobin?
A tetrameric globular protein, with one haem group attached to each globulin chain.
What is the most common type of haemoglobin structure in adults?
HbA - has 2 alpha and 2 beta chains (97% of people)
Apart from HbA, what other haemoglobin structures can be present in adults?
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.
What is the description of a haem group?
Haem group is Fe2+ in a flat porphyrin ring.
How many oxygen molecules bind to one Fe2+ (haem group)?
1 oxygen molecule bind to 1 Fe2+
Oxygen can bind to Fe3+. True/false?
False
Oxygen CANNOT bind to Fe3+
What are the functions of haemoglobin?
Delivers oxygen to the tissues
Acts as a buffer to H+
Transport of CO2
How many O2 molecules are present per haemoglobin?
4 O2molecules per Hb
What is the sequence for destruction of a red blood cell?
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)
What are the challenges potentially faced by red blood cells?
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
Why is the formation of free radicals bad?
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)
How is carbon dioxide transported?
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
What is glutathione?
Glutathione protects us from hydrogen peroxide by reacting with it to form water and an oxidised glutathione product (GSSG).
This maintains the redox balance.
What are the system requirements for oxygen transport by haemoglobin?
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
What does a red blood cell need?
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)
What is the bohr effect?
Hemoglobin’s lower affinity for oxygen secondary to increases in the partial pressure of carbon dioxide and/or decreased blood pH.
What is the haldane effect?
Oxygenation of blood in the lungs displaces carbon dioxide from haemoglobin, increasing the removal of carbon dioxide.
