Chap 9- Hemoglobin, an allosteric protein Flashcards
(18 cards)
Cooperative effect
enhanced activity resulting from cooperation between subunits of an allosteric molecule. The significance of the cooperative effect in allosteric proteins is evident in hemoglobin.
myoglobin def
a single polypeptide chain, consisting largely of alpha helices that are linked to one another by turns in the polypeptide chain to form a globular structure.
WHat are the two forms of myoglobin?
1.deoxymyoglobin- oxygen-free form
2. oxymyoglobin- a form having a bound oxygen molecule.
What is a heme group and what does it do?
It is a bound prosthetic group that when is present, gives myoglobin and hemoglobin the ability to bind oxygen. It also gives muscle and blood their red colour.
Contains an organic component, protoporphyrin, and a central iron atom.
what is the proximal histidine?
the histidine residue that occupies the fifth coordination site of iron in heme.
distal histidine def
a second histidine that resides on the opposite side of the heme from the proximal histidine. it prevents the oxidation of the heme iron to Fe3+, which cannot bond oxygen.
how many subunits are in human hemoglobin A?
4 total, 2 alpha subunits and 2 beta subunits.
Is the cooperative binding of oxygen by hemoglobin best described by the concerted or the sequential model?
Neither, it is a combined model. It is concerted in that hemoglobin with three sites occupied with oxygen is almost always in the quaternary structure associated with R state. hemoglobin with only one of the four sites remains primarily in the T quaternary structure. But, this molecule binds three times as stringly as does a fully deoxygenated hemoglobin.
what allosteric regulator is used to regulate the amount of oxygen released into the tissues?
2,3-biphosphoglycerate. It is a highly anionic compound, present in red blood cells at around the same concentration as hemoglobin. reduced oxygen affinity so that 66% of oxygen is released instead of only 8%, if it were absent.
what is the Bohr Effect
When oxygen binding is regulated by hydrogen ions and carbon dioxide that are byproducts of aerobic energy metabolism and in-turn, enhance oxygen release.
how does carbon dioxide concentration affect oxygen affinity?
as the concentrstion of csrbon dioxide increases in tissues, the amount of oxygen released approaches 90%. Carbon dioxide stabilizes deoxyhemoglobin by reacting with the terminal amino groups to form carbamate groups, which are negatively charged.
how do cells that need the most oxygen get oxygen?
They use the end-products of oxygen-dependent metabolism to signal their need for more oxygen.
What causes sickle cell anemia?
A single amino acid substitution in one hemoglobin chain. Hemoglobin molecules bind together to form large fibrous aggregates that extend across the cell, deforming the red cells.
what causes thalassemia?
thalassemia is caused by the loss or substantial reduction of a single hemoglobin chain.
what is the physiological significance of the cooperative binding of oxygen by hemoglobin?
the cooperativity allows hemoglobin to become saturated in the lungs, where oxygen pressure is high. when the hemoglobin moves to tissues, the lower oxygen pressure induces it to release oxygen and deliver it where its needed. Thus, the cooperative release favors a more complete unloading of oxygen in the tissues.
when crystals of deoxyhemoglobin are exposed to oxygen, the crystals shatter. Why?
Deoxyhemoglobin is in the T state. the presence of oxygen disrupts the R-T equilibrium in favor of the R state, The structural changes aee significant enough to cause the crystal to come apart.
Describe the role of 2,3-biphosphoglycerate in the function if hemoglobin
The presence of 2,3-BPG shifts the equilibrium toward the T state. 2,3-BPG binds only to the center cavity of deoxyhemoglobin (T state). The size of the center cavity decreases on the change to the R form, expelling the 2,3-BPG and thus facilitating the formation of the R state.
What effect does an increased concentration of 2,3BPG have on the oxygen binding curve for hemoglobin? explain why this is good for functioning at high altitude.
A higher concentration of 2,3BPG would shift the oxygen-binding curve to the right. the rightward shift of the curve would promote the dissociation of oxygen in the tissues and would therby increase the percentage of oxygen delivered to the tissues.
