Biochemistry - Cardiology Block (III) Flashcards
Why is hemoglobin a necessary component of efficient oxygen transport within the body?
O2 is relatively insoluble
(as are all nonpolar gases)
Which is more soluble in blood (and any aqueous solution), polar or nonpolar gases?
Polar gases
At what pH is O2 / hemoglobin binding increased, high or low?
High pH
At what pH is O2 / hemoglobin binding decreased, high or low?
Low pH
Which of the following affect myoglobin affinity for O2?
pH
2,3-DPG
CO2
None of them
(myoglobin not regulated by pH or modifying molecules as hemoglobin is)
Hemoglobin is made up of how many subunits?
Myoglobin is made up of how many subunits?
4;
1
What are the two contributing portions of a heme molecule?
The protoporphyrin IX ring
+
Fe2+ (ferrous iron)
How many bonds can a single ferrous iron atom make?
To what structure(s) is one ferrous iron atom bound in a single heme molecule?
6;
4 bonds to the protoporphyrin IX ring,
1 bond to a posterior histidine (from helix F),
1 potential bond to oxygen
Binding of O2 to the ferrous iron in a heme molecule leads to _______ movement of what amino acid also bound to the ferrous iron?
Lateral;
histidine
Ferrous iron is notated as ___?
Is this an oxidized or reduced form of Fe?
Fe2+;
reduced (as opposed to oxidized, ferric iron –> Fe3+)
True/False.
Ligand binding to molecules such as hemoglobin is all of the following: specific, reversible, and transient.
True.
What is the Kd in regards to ligands for a molecule like myoglobin?
The concentration [L] of the ligand (mM) at which 50% of the available binding sites are occupied (on average)
A ligand with high affinity for its substrate protein (e.g. hemoglobin) will have what type of Kd, high or low?
Low
A Kd in ligand binding is equivalent to what type of constant in Michaelis-Menten kinetics?
Km
- (low Kd = high affinity;*
- high Kd = low affinity)*
What does sigma represent in the attached graph?
(Note: the graph shows myoglobin O2 binding in relation to partial pressure of O2)
θ = binding sites filled
(in this case, by O2)
Which is indicative of high ligand affinity in a graph comparing binding sites to partial pressure of the gas in question, a right shift or a left shift?
Left shift
A right shift in a graph showing hemoglobin-O2 binding would indicate what type of affinity, high or low?
Low
The hemoglobin-O2 binding curve is ___________, indicating cooperativity.
The myoglobin-O2 binding curve is ___________, indicating no cooperativity.
Sigmoidal;
hyperbolic
The myoglobin-O2 binding curve is hyperbolic, indicating no __________.
The hemoglobin-O2 binding curve is sigmoidal, indicating __________.
Cooperativity;
cooperativity
In the T state, the Fe2+ in heme is where?
Pulled out of the plane of the protoporphyrin IX ring
(low affinity for O2)
In the R state, the Fe2+ in heme is where?
In-plane with the protoporphyrin IX ring
(high affinity for O2)
The histidine that binds the heme group Fe2+ is attached to which hemoglobin subunit, α or β?
α
(from helix F)
In which hemoglobin state (tense or relaxed) is the Fe2+ pulled out of plane with the protoporphyrin ring (by histidine)?
Tense (T)
In which hemoglobin state (tense or relaxed) is the Fe2+ pulled into plane with the protoporphyrin ring (by histidine)?
Relaxed (R)
How many O2 molecules can bind one hemoglobin molecule?
4
What type of bonds allow for hemoglobin conformational change from T to R and back?
How many of these bonds?
Ionic bonds;
8 (2 intrachain; 6 interchain)
For each single O2 molecule that binds hemoglobin, how many ionic bonds are broken (of the 8 involved in conformational change)?
2
Describe which concentration changes in the following would likely lead to a right shift (decreased affinity) in hemoglobin-O2 binding:
H+
2,3-BPG
CO2
CO
H+ - Increased
2,3-BPG - Increased
CO2 - Increased
CO - Decreased
How does increased [H+] lead to increased O2 unloading from hemoglobin?
Decreased pH leads to stronger ionic interactions between hemoglobin subunits (favoring the T state)
Describe which concentration changes in the following would likely lead to a left shift (increased affinity) in hemoglobin-O2 binding:
H+
2,3-BPG
CO2
CO
H+ - Decreased
2,3-BPG - Decreased
CO2 - Decreased
CO - Increased
In what direction does a high CO concentration shift the hemoglobin-O2 binding curve?
To the left
(high CO increases Hb-O2 binding)
Does 2,3-BPG increase or decrease O2 binding to hemoglobin?
Decrease
(causes O2 unloading)
Describe the three methods by which CO2 is transported in the blood and what percentage of CO2 follows each method.
Dissolved in the blood (10%)
As carbaminohemoglobin (~20%)
As bicarbonate (~70%)
How much of CO2 is simply dissolved in the blood?
10%
How much of CO2 is transported as carbaminohemoglobin?
~20%
How much of CO2 is transported as bicarbonate?
~70%
Where does CO2 bind hemoglobin to form carbaminohemoglobin?
The amino-terminal end of each subunit
What two effects does CO have on O2-hemoglobin interactions?
- It replaces O2
(binds with 250x the affinity of O2)
- It causes a left shift and decreased O2 unloading
(stabilizes the R state)
How does CO poisoning manifest?
How does severe CO poisoning manifest?
How can CO poisoning be treated?
Flu-like syndromes (headache, nausea, vertigo);
seizures, coma and death;
pure oxygen delivery (can be hyperbaric)
Ingestion of nitrates (e.g. bismuth nitrate or from well water) or oxidixing medications can have what effect on hemoglobin?
What is this condition called in infants?
How is it treated (in general)?
Oxidation of Fe2+ to Fe3+
(methemoglobinemia);
blue-baby syndrome;
methylene blue
Prolonged periods of time spent at high altitudes will have what two effects on the blood?
Increased 2,3-BPG;
increased Hb and RBCs
How are γ Hb subunits different from β Hb subunits?
(I.e. how are infant hemoglobin (α2γ2) different from adult hemoglobin (α2β2)?)
Less affinity for 2,3-BPG
(specifically, 2 serine residues are replaced with 2 histidine granules)
Why does fetal Hb (α2γ2) have a higher affinity for O2 than adult Hb (α2β2)?
γ subunits has less affinity for 2,3-BPG than β subunits
What is the mechanism of the Bohr effect?
As acidity increases, protons attach to hemoglobin histidines
—> cause a conformational change in Hgb and O2 unloading
What enzyme combines CO2 and H2O to form carbonic acid and a proton?
Which is the predominant tissue in which this reaction take place?
Carbonic anhydrase;
erythrocytes
How much of CO2 is transported in the blood as bicarbonate?
How much of CO2 is transported in the blood as dissolved CO2?
How much of CO2 is transported in the blood bound to Hgb as carbaminohemoglobin?
~70%
~10%
~20%
Which has a stronger affinity for Hgb, O2 or CO?
How much stronger is its affinity?
CO
250x
True/False.
A single bound CO destabilizes the R state of Hgb.
False.
It stabilizes the Hgb
Sickle cell anemia results due to what genetic defect?
Glutamate6 change to valine6 in both β-hemoglobin chains
True/False.
A single mutation in the gene coding for the sixth glutamic acid in β-hemoglobin is all it takes to result in sickle cell anemia.
False.
The disorder is autosomal recessive. A mutation in both genes (SS, homozygous) is necessary.
Sickle cell anemia results from a mutation in the __ glutamic acid in β-Hgb to ________.
Hemoglobin C disease results from a mutation in the __ glutamic acid in β-Hgb to ________.
6th, valine;
6th, lysine
True/False.
Sickle cell vasocclusive crises can affect any organ system.
True.
What inheritance pattern does sickle cell anemia follow?
Autosomal recessive
What is the first-line treatment for the disorder shown here?
Via what mechanism does it function?
Hydroxyurea;
increasing HgbF concetrations
HgbS is most likely to form fibers and sickle RBCs when it is in what state?
What are the implications?
The deoxygenated state;
hypoxic conditions (e.g. exercise, high altitudes) can exacerbate the condition
Through what mechanism does hydroxyurea improve the signs/symptoms of sickle cell anemia?
HgbF levels increase;
HgbF gets incorporated into HgbS chains and halts their continued polymerization
Is sickle cell anemia a hemolytic anemia?
Yes.
The sickle cells are rigid and inflexible and become jammed and/or lysed in capillary beds
Besides hydroxyurea, what other treatments exist for sickle cell anemia in certain situations?
Blood transfusions,
prophylactic antibiotics,
pain management,
bone marrow transplants
The glutamic acid that is changed to valine in sickle cell anemia is at what amino acid position and in which hemoglobin chain?
The glutamic acid that is changed to lysine in hemoglobin C disease is at what amino acid position and in which hemoglobin chain?
6, β-Hgb;
6, β-Hgb
What treatments are typically needed for hemoglobin C disease?
None;
it is basically a much less severe form of sickle cell anemia
(glutamic acid6 –> lysine6 instead of valine)
What form of HbS (Sickle cell hemoglobin) is protective against malaria?
The heterozygous form
During weeks 3 - 8 of embryonic development, what organ is producing erythrocytes?
What kind of hemoglobin is produced? What two subunits are used?
Yolk sac;
hemoglobin E (HbE), ε2ζ2 (epsilon, zeta)
At week 9 of embryonic development, which organ takes over erythrocyte production?
What kind of hemoglobin is produced? What two subunits are used?
The liver;
hemoglobin F (HbF), α2γ2
What are the three main types of hemoglobin found in adults?
In what percentages?
Adult Hb (HbA) α2β2 >95% of adult Hb
Adult Hb (HbA2) α2δ2 <3% of adult Hb
Fetal Hb (HbF) α2γ2 <3% of adult Hb
What are the two forms of adult hemoglobin?
HbA α2β2 (>95%)
HbA2 α2δ2
What type of hemoglobin predominates in the embryonic period?
What type of hemoglobin predominates in the fetal period?
What type of hemoglobin predominates in the adult period?
What type of hemoglobin is present in adults but never predominates at any stage?
HbE ε2ζ2
HbF α2γ2
HbA α2β2
HbA2 α2δ2