1. Which non-covalent interaction is primarily responsible for stabilizing a hel
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Question
1. Which non-covalent interaction is primarilyresponsible for stabilizing a helices, ß sheets, and ß
turns?
a. Hydrophobic interactions.
b. Ion-pairing.
c. Hydrogen bonding.
d. Stacking of aromatic rings.
e. Van der Waals interactions.
2.Which is not associated with the formation of oligomers?
a. Increased stability compared to the dissociated subunits.
b. The formation of active sites between adjacent subunits.
c. Contact between the subunits that allows for changes in
quaternary structure when ligands bind. This can control
biological activity.
d. Increased efficiency by synthesizing smaller subunits
rather than a single chain the same size as the oligomer.
e. An enhanced ability to adopt F and ? angles outside the
common ranges.
3. Would you expect myoglobin that is injected
intravenously to perform the same function as
hemoglobin? Explain.
a. No, myoglobin cannot release oxygen as well to the
tissues.
b. No, because the heme of myoglobin binds oxygen at a
different coordination site.
c. No, because 2,3-BPG completely inhibits the binding of
oxygen to myoglobin.
d. Yes, in the blood myoglobin adopts a similar quaternary
structure as hemoglobin and binds oxygen with positive
cooperativity.
e. Yes, because both bind oxygen very easily in the lungs.
Explanation / Answer
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1. C. Hydrogen bonding.
--> The main chain amide groups are involved in H-bonding with others that are further apart. Amide peptide bonds are polar, i.e. not hydrophobic, not ions, not aromatic rings. There may be some Van deer Waals interactions, but the Hydrogen bonds are numerous and much stronger.
2. e. An enhanced ability to adopt F and ? angles outside the common ranges.
--> Statement (a) is correct as oligomers typically spontaneously form in solution. Statement (b) is correct too. For example, the HIV protease is a dimereric enzyme where the active site is formed exactly at the interface between the two subunits and thus making the statement (b) correct. Statement (c) is correct as there is communication between subunits in an oligomer that has cooperativity: ligand binding in one subunit influences ligand binding in the other subunits. Statement (d) is also correct as the cell can synthesize more efficiently a lot of smaller chains that rearrangement themselves in oligomers, than synthesizing a few way too long chains. Statement (e). is very curious. Given the first four statements are all correct, then I presume the statement (e) is incorrect.
3. a. No, myoglobin cannot release oxygen as well to the tissues.
--> Hemoglobin is a tetramer where the subunits show cooperativity of oxygen binding; That makes the oxygen delivery very efficient and sensitive. Myoglobin is a monomeric (one chain) protein where it has no such cooperatively. So myoglobin cannot release oxygen as well to the tissue.
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