Term
| How do myoglobin and hemoglobin differ structurally? |
|
Definition
Myoglobin is a single chain with a single O2 binding site
Hemoglobin consists of 4 chains, each with its own single O2 binding site |
|
|
Term
| What are the basic functions of hemoglobin? |
|
Definition
Hemoglobin
1)transports O2 to tissue
2)transports C02 from the tissue to lungs |
|
|
Term
| What is the basic function of myoglobin? |
|
Definition
| Myoglobin accepts O2 from hemoglobin in muscle |
|
|
Term
| What role does the gamma subunit of hemoglobin play during fetal development? |
|
Definition
Before birth the gamma subunit of hemoglobin has a much higher affinity for O2 than the beta subunit.
The gamma subunit is in higher amounts in the fetus so this allows transfer of O2 from the mother to the fetus in the womb. |
|
|
Term
|
Definition
Heme is the prosthetic group that is responsible for the actual transport of O2
It's the part of the hemoglobin molecule that actually binds O2 |
|
|
Term
| What are the properties of heme important for O2 binding? |
|
Definition
The iron molecule is special because it can bind 6 separate molecules.
The iron must be in its Fe2+ state or else it would bind O2 too tightly and hemoglobin would no longer be useful for transport
The other molecules attached to Fe including the proteins protect iron from binding other things and keep it in the Fe2+ state |
|
|
Term
| What is the relation between myoglobin and the beta chain of hemoglobin? |
|
Definition
The structures are almost identical except for some slight differences at both the N-terminus and the C-terminus
They both contain the heme group which binds O2 |
|
|
Term
| What is non-cooperative binding? |
|
Definition
The binding of a ligand has NO effect on the binding of a second ligand
This happens in myoglobin because it only has one O2 binding site |
|
|
Term
| What is cooperative binding? |
|
Definition
The binding of a ligand to a binding site influences the binding of a second ligand to a different binding site.
This happens in hemoglobin |
|
|
Term
| What is the equation for binding of O2 to myoglobin? |
|
Definition
Mb + O2 <-> MbO2
Keq = [MbO2]/[Mb][O2] |
|
|
Term
| Why is the O2 saturation curve of myoglobin hyperbolic while the O2 saturation curve of hemoglobin is more sigmoidal? |
|
Definition
| Myoglobin has non-cooperative binding (and only one O2 binding site) and hemoglobin has cooperative binding (and 4 O2 binding sites) |
|
|
Term
| Why is the difference in O2 saturation curves in myoglobin versus hemoglobin important? |
|
Definition
The differences in saturation curves point to the affinity differences of O2 for myoglobin compared to hemoglobin
O2 has a much higher affinity for myoglobin than hemoglobin which is why O2 gets transferred from hemoglobin to myoglobin in the muscles |
|
|
Term
| How does cooperative binding work in hemoglobin? |
|
Definition
Without any attached O2 hemoglobin is considered to be in the taut state. In this state all of the binding sites are less accessible.
When one O2 molecule binds to the first binding site, the conformation of hemoglobin begins changing to the relaxed state. The relaxed state is more accessible to O2 and as more O2 bind the more it changes to the relaxed state. |
|
|
Term
| How is hemoglobin related to CO2? |
|
Definition
Although a large majority of the CO2 in the blood (~80%) is transported as bicarbonate the remaining 20% percent is transported as carbamate
The carbamate is transported on hemoglobin as it attached to the free amino groups in the protein |
|
|
Term
| How does binding of CO2 to hemoglobin affect binding of O2? |
|
Definition
Carbamate binding to hemoglobin stabilizes the taut formation thus decreasing the affinity for O2 in deoxyhemoglobin
This is necessary because CO2 is getting transported to the lungs and the body needs O2 to get transported in the opposite direction |
|
|
Term
| What effects does CO binding to hemoglobin have? |
|
Definition
CO has a much higher affinity for hemoglobin than O2 does
When CO binds to hemoglobin it causes it to revert to the R state (where O2 affinity is higher) thus causing the remaining O2 to be bound more tightly.
This prevents release of the O2 to the tissues.
The binding is not irreversible but it is very tight |
|
|
Term
|
Definition
The Bohr effect is where low pH (high acidity) will reduce the binding affinity of hemoglobin
The release of O2 is enhanced when the pH is lowered or when there is an increase in pC02.
Since deoxyhemoglobin is more basic than oxyhemoglobin, there is going to be an increase in deoxyhemoglobin when there's an increase in acidity. (shift of equilibrium favoring deoxyhemoglobin) |
|
|
Term
| How does the Bohr effect relate to O2 saturation curves? |
|
Definition
| Lowering the pH is going to decrease the affinity of O2 for hemoglobin and shift the curve to the right |
|
|
Term
| What effect does binding of 2,3-BPG to hemoglobin have? |
|
Definition
2,3-BPG binds to the T conformation of hemoglobin. It forms bonds with the beta chains that will stabilize only the T conformation
Since the T conformation has the lower oxygen affinity, BPG decreases the oxygen-binding affinity of hemoglobin |
|
|
Term
| How does 2,3-BPG bind to hemoglobin? |
|
Definition
| At physiological pH the phosphate groups of 2,3-BPG are negatively charged and 2,3-BPG binds to a positive cavity created by the two beta chains (positively charged AA's) |
|
|
Term
| What effect does 2,3-BPG have on the O2 saturation curve? |
|
Definition
| Since it decreases the O2 binding affinity of hemoglobin it shifts the curve to the right |
|
|
