BIOCHEM C785 EXAM QUESTIONS AND CORRECT
ANSWERS, WITH COMPLETE SOLUTION.
Your model has three disulfide bonds. Which bond stabilizes tertiary structure?
Which bond stabilizes quaternary structure? Explain your response.
Amino acids 6 and 11 in the A-chain form a disulfide bond. Since this disulfide bond
involves two amino acids in the same polypeptide chain, it stabilizes tertiary structure.
The disulfide bond involving amino acid 7 of the A-chain and amino acid 7 of the B-
chain is helping hold two separate polypeptide chains together. Thus, it stabilizes
quaternary structure. Similarly, the disulfide bond that involves amino acid 20 of the A-
chain and amino acid 19 of the B-chain stabilizes quaternary structure since it is holding
the two separate polypeptide chains together.
Which of the following are involved in stabilizing the secondary structure of
insulin?
Hydrogen bonds between portions of the backbone of the polypeptide chain
If the primary structure of insulin had glycine at position 6 in the A-chain instead
of cysteine, which level(s) of protein structure would most likely be affected?
Replacing cysteine at position 6 with glycine would impact tertiary structure. Cysteine is
the only amino acid that can form disulfide bonds, so the bond between amino acids 6
and 11 of the A-chain would not be able to form.
When Stephen calls to ask whether he can still use the insulin he left in his hot
car, what would you tell him about the effect of the heat on the insulin? What
might have happened to the insulin in the hot car?
The high temperatures in his car may have damaged his insulin. The heat disrupts
hydrogen bonds and hydrophobic interactions, denaturing proteins like insulin. Even if
the insulin is cooled, it may not refold properly.
The next time Stephen comes to the office, he remembers that the high
temperatures in his car can damage his insulin. He wants to know more about
how this happens. Using your model, you demonstrate the kinds of changes to
insulin you expect to see in hot temperatures. You untape portions of the model,
showing the protein unraveling. Which of the following bonds will you leave
intact as you demonstrate the impact of heat on insulin's structure?
Disulfide bonds
The amyloid 𝛃 that is 42 amino acids long is more hydrophobic than the version
that is 40 amino acids in length. In healthy individuals, amyloid 𝛃 tends to remain
soluble and does not aggregate together. Which of the following is likely true of
healthy individuals?
They have more amyloid 𝛃 that is 40 amino acids long than amyloid 𝛃 that is 42 amino
acids long.
Hydrophobic things tend to aggregate. Since the version of amyloid 𝛃 that is 42 amino
acids in length is hydrophobic, it is likely that healthy individuals have less of this
version and more of the version that is only 40 amino acids long.
ANSWERS, WITH COMPLETE SOLUTION.
Your model has three disulfide bonds. Which bond stabilizes tertiary structure?
Which bond stabilizes quaternary structure? Explain your response.
Amino acids 6 and 11 in the A-chain form a disulfide bond. Since this disulfide bond
involves two amino acids in the same polypeptide chain, it stabilizes tertiary structure.
The disulfide bond involving amino acid 7 of the A-chain and amino acid 7 of the B-
chain is helping hold two separate polypeptide chains together. Thus, it stabilizes
quaternary structure. Similarly, the disulfide bond that involves amino acid 20 of the A-
chain and amino acid 19 of the B-chain stabilizes quaternary structure since it is holding
the two separate polypeptide chains together.
Which of the following are involved in stabilizing the secondary structure of
insulin?
Hydrogen bonds between portions of the backbone of the polypeptide chain
If the primary structure of insulin had glycine at position 6 in the A-chain instead
of cysteine, which level(s) of protein structure would most likely be affected?
Replacing cysteine at position 6 with glycine would impact tertiary structure. Cysteine is
the only amino acid that can form disulfide bonds, so the bond between amino acids 6
and 11 of the A-chain would not be able to form.
When Stephen calls to ask whether he can still use the insulin he left in his hot
car, what would you tell him about the effect of the heat on the insulin? What
might have happened to the insulin in the hot car?
The high temperatures in his car may have damaged his insulin. The heat disrupts
hydrogen bonds and hydrophobic interactions, denaturing proteins like insulin. Even if
the insulin is cooled, it may not refold properly.
The next time Stephen comes to the office, he remembers that the high
temperatures in his car can damage his insulin. He wants to know more about
how this happens. Using your model, you demonstrate the kinds of changes to
insulin you expect to see in hot temperatures. You untape portions of the model,
showing the protein unraveling. Which of the following bonds will you leave
intact as you demonstrate the impact of heat on insulin's structure?
Disulfide bonds
The amyloid 𝛃 that is 42 amino acids long is more hydrophobic than the version
that is 40 amino acids in length. In healthy individuals, amyloid 𝛃 tends to remain
soluble and does not aggregate together. Which of the following is likely true of
healthy individuals?
They have more amyloid 𝛃 that is 40 amino acids long than amyloid 𝛃 that is 42 amino
acids long.
Hydrophobic things tend to aggregate. Since the version of amyloid 𝛃 that is 42 amino
acids in length is hydrophobic, it is likely that healthy individuals have less of this
version and more of the version that is only 40 amino acids long.
