Structure and Function of Red Blood Cells Flashcards
cellular properties of RBCs?
no nucleus (so they are more deformable and more room for Hb molecules)
no mitochondria
full of Hb to carry oxygen
high surface area/volume ratio to allow gas exchange
flexible to squeeze through capillaries
consequences of no nucleus in RBCs?
cant divide or replace damaged proteins so have limited life span
consequences of no mitochondria in RBCs?
limited glycolysis for energy generation (no krebs cycle)
consequrnce of RBCs being full of Hb?
high oncotic pressure
oxygen rich environment (oxidation risk)
consequence of high surface area/volume ratio?
need to keep water our
consequence of RBCs being flexible?
specialised membrane required that can go wrong
describe the RBC membrane?
complex
not just a lipid bilayer
has protein spars and protein anchors
makes it flexible
describe the structure of Hb?
tetrameric globular protein
2 alpha and 2 beta chains
heme group is Fe2+ in a flat porphyrin ring (one heme group per subgroup)
one oxygen molecule binds to one Fe2+ (oxygen does not bind to Fe3+)
function of Hb?
deliver oxygen to tissues
act as buffer for H+
CO2 transport
where does RBC production take place?
in the bone marrow as a result of proliferation and differentiation of Haematopoietic stem cells
what regulates RBC production?
erythropoietin
summarise RBC production regulation
hypoxia sensed by kidney > erythropoietin produced > erythropoietin stimulates RBC production > erythropoietin levels drop
describe RBC destruction
normally occurs in spleen (and liver)
aged RBCs taken up by macrophages (taken out of circulation)
RBC contents are recycled
how are RBC contents 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
describe the process of the breakdown of heme to bilirubin?
heme > porphyrin > biliverdin > bilirubin
how do RBCs get energy and why?
only glycolysis (dont have a mitochondria for krebs cycle)
why is the lack of mitochondria a problem for RBCs?
glycolysis is low energy yielding
lots of oxygen about so oxygen free radicals are easily generated
free radicals can oxidise Fe2+ to Fe3+ which doesn’t transport oxygen
free radicals also damage proteins which cant be repaired or replaced
describe the reactive oxygen species formed in RBCs?
superoxide and hydrogen peroxide
have unpaired free electrons
capeable of interacting with other molecules proteins, DNA etc) and damaging their structure
what is glutathione?
protects us from hydrogen peroxide by reacting with it to form water and an oxidised glutathione product (GSSG)
what is the rate limiting enzyme in the process of glutathione?
glucose 6 phosphate dehydrogenase (G6PD)
how can glutathione (GSF) be replenished?
replenished by NADPH which is in turn generated by the hexose monophosphate shunt
how does RBC prevent oxidation of Fe2+ to Fe3+?
NADH
how does CO2 get from the tissues to the lungs?
10% dissolved in solution
30% bound directly to Hb as carbamino-haemoglobin
other 60% gets there as bicarbonate and the red cell has an important rle in generating that bicarbonate
how much oxygen can bind to one Hb?
4 O2 molecules per Hb
(one oxygen is bound to the Fe2+ in the heme group)
1g Hb will hold 1.34 ml of oxygen when fully saturated
subunits in foetal Hb?
2 alpha
2 gamma
how does Hb bind oxygen?
allosteric effect
the dissociation curve for Hb does not follow michaelis menten kinetics but it is sigmoidal
as one oxygen binds to a subunit the Hb shape changes which alters how easy it is for the next O2 to bind to another subunit in the Hb which changes the shape again
how is oxygen dissociation different in different Hb molecules
foetal Hb saturates more at the same pO2 so effectively takes more O2 from the maternal circulation
in muscles the monomeric myoglobin (which otherwise is a similar structure to Hb) takes O2 from RBCs and has different kinetics
small molecules can alter the shape of the oxygen dissociation curve as they interact with Hb, how do H+, CO2 and 2,3 BPG affect the curve?
shifts it to the right
this results in more O2 delivered to the tissues
