Structure and Function of Red Blood Cells

Question 1

cellular properties of RBCs?

Answer 1

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

Question 2

consequences of no nucleus in RBCs?

Answer 2

cant divide or replace damaged proteins so have limited life span

Question 3

consequences of no mitochondria in RBCs?

Answer 3

limited glycolysis for energy generation (no krebs cycle)

Question 4

consequrnce of RBCs being full of Hb?

Answer 4

high oncotic pressure

oxygen rich environment (oxidation risk)

Question 5

consequence of high surface area/volume ratio?

Answer 5

need to keep water our

Question 6

consequence of RBCs being flexible?

Answer 6

specialised membrane required that can go wrong

Question 7

describe the RBC membrane?

Answer 7

complex
not just a lipid bilayer
has protein spars and protein anchors
makes it flexible

Question 8

describe the structure of Hb?

Answer 8

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+)

Question 9

function of Hb?

Answer 9

deliver oxygen to tissues
act as buffer for H+
CO2 transport

Question 10

where does RBC production take place?

Answer 10

in the bone marrow as a result of proliferation and differentiation of Haematopoietic stem cells

Question 11

what regulates RBC production?

Answer 11

erythropoietin

Question 12

summarise RBC production regulation

Answer 12

hypoxia sensed by kidney > erythropoietin produced > erythropoietin stimulates RBC production > erythropoietin levels drop

Question 13

describe RBC destruction

Answer 13

normally occurs in spleen (and liver)
aged RBCs taken up by macrophages (taken out of circulation)
RBC contents are recycled

Question 14

how are RBC contents recycled?

Answer 14

globin chains recycled to amino acids
heme group broken down to iron and bilirubin
bilirubin taken to liver and conjugated then excreted in bile

Question 15

describe the process of the breakdown of heme to bilirubin?

Answer 15

heme > porphyrin > biliverdin > bilirubin

Question 16

how do RBCs get energy and why?

Answer 16

only glycolysis (dont have a mitochondria for krebs cycle)

Question 17

why is the lack of mitochondria a problem for RBCs?

Answer 17

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

Question 18

describe the reactive oxygen species formed in RBCs?

Answer 18

superoxide and hydrogen peroxide
have unpaired free electrons
capeable of interacting with other molecules proteins, DNA etc) and damaging their structure

Question 19

what is glutathione?

Answer 19

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

Question 20

what is the rate limiting enzyme in the process of glutathione?

Answer 20

glucose 6 phosphate dehydrogenase (G6PD)

Question 21

how can glutathione (GSF) be replenished?

Answer 21

replenished by NADPH which is in turn generated by the hexose monophosphate shunt

Question 22

how does RBC prevent oxidation of Fe2+ to Fe3+?

Answer 22

NADH

Question 23

how does CO2 get from the tissues to the lungs?

Answer 23

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

Question 24

how much oxygen can bind to one Hb?

Answer 24

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

Question 25

subunits in foetal Hb?

Answer 25

2 alpha

2 gamma

Question 26

how does Hb bind oxygen?

Answer 26

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

Question 27

how is oxygen dissociation different in different Hb molecules

Answer 27

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

Question 28

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?

Answer 28

shifts it to the right

this results in more O2 delivered to the tissues