Chapter 7 Flashcards
What is hemoglobin?
Oxygen transport protein circulating in the blood
How many subunits are in hemoglobin?
4: Two alpha and two beta chains
What is myoglobin?
Oxygen storage protein in muscle cells
How many subunits are in myoglobin?
One
What holds heme structure in place?
F and H helix
What prevents Fe2+ from binding to unwanted molecules?
Valine and Phenylalanine
What is oxymyoglobin?
Bound to O2, bright red
What is deoxymyoglobin?
No O2 bound, purplish
What is metmyoglobin?
Fe2+ oxidized to Fe 3+, brownish
No longer binds to O2
What is the equation of fractional saturation for myoglobin?
Y(O2) = [MbO2]/ [Mb]+[MbO2]
What is the equation for the dissociation constant of myoglobin?
Kd = [Mb][O2]/[MbO2]
What does a low Kd value mean?
The structure is more likely to stay together
What does a high Y(O2) value for myoglobin mean?
There is a high [MbO2] compared to [Mb]
What does a high Kd value mean?
The structure is more likely to break apart
What is the equilibrium value (k)?
The point where there is 50% saturation
What is arterial O2 pressure?
100 torr
What is venous O2 pressure?
30 torr
What does a Y(O2) value of 1 mean?
All myoglobin/hemoglobin is saturated with oxygen
What is the hill equation?
Y(O2) = (pO2)^n / [(p50)^n + (pO2)^n]
What does the hill constant (n) describe?
Increases with cooperativity
How does O2 binding to hemoglobin affect cooperativity?
Positively (increases n)
How does oxygen not being bound affect the heme structure?
0.06 nm out of place
How does oxygen being bound affect the heme structure?
Fe2+ moves into the plane
This causes a series of conformational changes in hemoglobin
What is allosteric regulation?
Positive or negative regulators that bind to another site than the O2 binding site
What is the R state of allosteric regulation?
Relaxed (bound to O2)
What is the T state of allosteric regulation?
Taut (not bound to O2)
How does the state of hemoglobin affect O2 binding?
Hemoglobin T state requires higher O2 concentration to bind – the more heme structures bound to O2 the easier oxygen binds to the remaining heme structures
What is the Bohr Effect?
Decrease in O2 binding by H+
What is the effect on oxygen binding when pH is increased?
An increase in pH leads to more O2 binding described by the Bohr effect
High pH -> low [H+] -> higher O2 binding
What is the effect of CO2 formation on oxygen binding to Mb/Hg?
CO2 formation decreases O2 binding
What enzyme forms carbonic acid?
Carbonic anhydrase
Why is the formation of H2CO3 desired from CO2?
CO2 is not soluble but carbonic acid is
What is BPG?
Allosteric effect of hemoglobin
What is the function of BPG?
Stabilizes the hemoglobin T state, therefore requiring a higher pO2 for O2 binding
How does BPG work?
The negative charge interacts with 2-Lys, 4-His, and 2 N-termini
What is the difference between adult and fetal hemoglobin?
In fetal hemoglobin, there are gamma strands instead of beta strands
What causes sickle-cell anemia?
Substitution of valine from glutamic acid in the 6th position of beta-chain (E6V)
What does the E6V mutation of sickle-cell result in?
Hydrophobic pocket created in deoxy- state; allows for valine to bind to the pocket
