[FMS] CBS - Haemoglobin Flashcards
what is the structure of adult haemoglobin HbA
Hb is a tetramer : 2 identical beta globin subunits and 2 identical alpha globin subunits
Hb is dimer of a dimer (α1β1)(α2β2)
Why is oxygen a key component of ATP generation?
final electron acceptor in oxidative phosphorylation
which has higher affinity? Mb or Hb
AFFINITY: Mb > Hb
becuase Mb is fully saturated at a lower oxygen level (partial pressure of oxygen: pO2)
how many bonds can fe2+ bind with in Hb, and to what specifically?
Fe2+ (ferrous) ion can bond with six ligands:
- four by nitrogen atoms of haem group
- fifth by attachment to specific histidine of globin
- sixth is available for the reversible attachment of oxygen
2 forms of Hb
Oxyhaemoglobin (oxyHb)
Deoxyhaemoglobin (deoxyHb)
what prevents the oxygen from oxidising Fe2+ to Fe3+
Hydrophobic residues found in interior of globin prevents oxygen from oxidising the Fe2+ to Fe3+
what type of Fe ion can’t bind to oxygen, and what is it called?
Haem with Fe3+ is unable to bind oxygen
This is met-haemaglobin (metHb)
name of the oxygen saturation curve for Hb
sigmoid shape (S)
what kind of binding does the oxygen saturation curve for Hb show?
cooperative binding and an example allostery.
^ Allostery occurs when the binding of oxygen to one globin changes the shape of the binding site of another globin.
what needs to be high in order for Hb to be fully saturated?
When pO2 (partial pressure of oxygen) is high cooperative binding allows Hb to be fully saturated.
2 forms of globin subunits
Each globin subunit can exist in two forms (states):
T (tense)
R (relaxed)
what does T (tense) and R (relaxed) mean in terms of affinity
T (tense) conformation with low affinity for oxygen.
R (relaxed) conformation with high affinity for oxygen.
when oxygen binds to a1 what happens, and what happens to the affinity of B1?
Binding of oxygen to α1 changes the conformation of α1
⬇
Binding of oxygen to α1 changes β1 to R state.
⬇
THEREFORE β1 has increased affinity for oxygen.
what is the bohr effect?
Ability of haemoglobin to bind oxygen decreases as the [H+] increases.
Ability of haemoglobin to bind oxygen decreases as the pH decreases.
THEREOFRE H+ and Ph effects how Hb binds to oxygen
which part of the body releases most oxygen?
- peripheral tissues release most O2 (away from lungs)
what happens when theres a loss of the bohr effect?
hyperventilation
how does loss of bohr effect lead to hyperventilation
- more expiration of CO2
- CO2 level in plasma reduced = hypocapnia
- less H2CO3
- [H+] drops / pH increases
- No protons = Bohr effect does not operate
- Less O2 released to peripherical tissues
what are the 3 types of Hb
why does HbF have higher affinity than HbA?
so in placenta HbF is able to be saturated in preference to HbA .
order of affinities for Mb, HbA, HbF
what is BPG
2, 3 - bisphosphoglycerate (BPG) is allosteric regulator of oxygen binding of haemoglobin.
how is BPG generated
BPG is generated by metabolising tissues.
where does BPG bind to, and in what state?
BPG is negatively charged so binds to positively charged pocket but ONLY IN T-STATE!! (deoxyHb).
is BPG positively or negatively charged
- BPG negatively charged
when BPG binds to Hb what happens to its affinity?
Binding of BPG LOWERS the affinity of Hb for oxygen.
is SCD a dominant or recessive disease?
- recessively inherited
how is SCD characterised?
characterised by formation of sickle shaped cells
what mutation causes SCD
mutation of beta-globin from GLU to VAL on the 6th position on surface
GLU is acidic, hydrophilic but VAL is hydrophobic and polar
difference in shape between HbA and HbS
In HbA glutamic acid is stabilised by hydrogen bonds with aqueous environment
In HbS to prevent valine being in an aqueous environment two haemoglobins aggregate together
^ This aggregation continues to form polymers
what does the sickle shaped cells do? why are they bad?
Sickle shaped cells can be trapped in capillaries and lyse
low fe2+ intake in the diet leads to what disease?
anaemia
high levels of plasma glucose cause what disease?
diabetes type 1
what disease is caused by an imbalance of globin chain production.
Hereditary haemolytic anaemia
what disease is caused by deficient beta-globin production
beta-thalassaemia
what disease is caused by deficient alpha-globin production
alpha-thalassaemia
what disease is caused by the mutations of developmental expression of gamma gene
Hereditary persistence of fetal haemoglobin (HPFH)
what is the name of the ring in the heme group structure
prophoryin ring
defects in heme synthesis leads to what disease?
Porphyria
Mb is fully saturated at a ___ oxygen level
lower
DO HAEMOGLOBIN QUIZ ON KEATS THEN RESUME FLASHCARDS
https://keats.kcl.ac.uk/mod/quiz/view.php?id=7540248
try the Hb quiz on keats and come back
https://keats.kcl.ac.uk/mod/quiz/attempt.php?attempt=4370706&cmid=6619916
What state is oxyHb in at physiological pH?
OxyHb is more acidic (pKa 6.8) and at physiological pH it is dissociated.
How can oxygen be stored?
In striated muscles bound to myoglobin (Mb)
What are globins?
Globins are around 150 amino acids in length consisting of alpha helices.
They also include a haem group buried within a hydrophobic pocket.
What side of the haem group faces the surface of the globin?
The hydrophilic side of the haem group faces the surface of the globin.
What is carbon dioxide converted to?
Most carbon dioxide is converted to carbonic acid by carbonic anhydrase in erythrocytes.
- The carbonic acid then dissociates into bicarbonate (HCO3- and H+).
- Bicarbonate is then exported via Cl-/HCO3- channel.
Some carbon dioxide reversibly binds to Hb to form carbaminoheamoglobin.
What is the effect on haemoglobin as [H+] increases?
Ability of haemoglobin to bind to oxygen decreases as the [H+] increases.
What is the effect on haemoglobin as the pH decreases?
The ability of haemoglobin to bind to oxygen decreases as the pH decreases.
What does the impact of oxygen saturation have on H+ binding of haemoglobin in lungs?
- Increase in [H+] within the erythrocytes shifts the dissociation of bicarbonate towards carbonic acid.
- HCO3- + H+ → H2CO3
- Increase in carbonic acid shifts the equilibrium of carbonic anhydrase towards carbon dioxide.
- H2CO3 → H2O + CO2 (reversible reaction)
- Carbon dioxide is expired.
What is the percentage of HbA and HbF at birth?
20% HbA and 80% HbF.
What is the oxygen binding curve of HbA in absence of BPG similar to.
Myoglobin (Mb).
in transport of CO2 how much is dissolved in blood
10%
in transport of CO2 how much is converted to bicarbonate
60%
in transport of CO2 how much is bound to Hb
30%
Which is a better buffer oxy or deoxy for the H+ produced in metabolism?
DEOXY IS BETTER - It is less dissociated (more protonated) than oxyhaemoglobin at the pH of blood
