1. A certain protein contains a relatively large number of arginine and lysine r
ID: 213541 • Letter: 1
Question
1. A certain protein contains a relatively large number of arginine and lysine residues on its surface. Which of the following can be predicted about the purification of this protein if it were present in a buffer with a pH of 7?
a) The protein would elute very early during sizes-exclusion chromatography.
b) The protein would bind to an anion exchange resin.
c) The protein would bind to a cation exchange resin.
d) The protein would bind to a GST column.
e) The protein would migrate very quickly through SDS-PAGE.
2. Which of the following amino acids is LEAST likely to be found on the surface of a protein?
a) lysine
b) tryptophan
c) glutamine
d) serine
e) aspartate
3. Experiments on denaturation and renaturation in the enzyme ribonuclease (RNase) by Dr. Anfinsen have shown that:
a) Folding of denatured RNase into the native, active conformation, requires the input of energy in the form of heat.
b) The completely unfolded RNase enzyme, with all disufide bonds broken, is still enzymatically active as long as there is no urea present.
c) The primary amino acid sequence of RNase is sufficient to determine its specific tertiary structure.
d) The order of cysteines in RNase does not matter, as long as the correct weak interactions can form between the other amino acids as a result of urea removal.
e) Proteins cannot self-assemble into a functional conformation after they have been denatured.
4. Five DNA polymerases have been identified in the bacterium E. coli. Two of them (DNA polymerases IV and V) lack a 3'-5' exonuclease activity. What is the function of the 3'-5' exonuclease activity present in many DNA polymerases?
a) The 3'-5' exonuclease function allows the cell to generate dNMPs, which can be converted to dNTPs and then used for synthesis of essential DNA when nutrients are low
b) The 3'-5' exonuclease is a proofreading function, eliminating mismatched nucleotides incorrectly inserted into the growing DNA strand.
c) The 3'-5' exonuclease removes DNA and RNA primers.
d) The 3'-5' exonuclease creates blunt ends so ligase can join DNA fragments.
e) The 3'-5' exonuclease creates 3' extensions after double-strand breaks are detected, which in turn promote strand invasion as part of the double-strand break repair mechanism.
5. The term "semidiscontinuous DNA replication" indicates:
a) implementation of multiple replication forks.
b) the insertion of DNA to replace the RNA primers during lagging-strand synthesis.
c) the mechanisms of leading- (continuous) and lagging- (discontinuous) strand synthesis.
d) the mechanisms of leading- (discontinuous) and lagging- (continuous) strand synthesis.
e) the presence of several chromosomes that are replicated separately.
Explanation / Answer
Answer 1
Option C is correct i.e the protein would bind to a cation exchange resin.
Answer 2
Tryptophan is least likely to be found on protein surfaces.
Answer 3
Option C is correct i.e the primary amino acid sequence of RNase is sufficient to determine its specific tertiary structure.
Answer 4
Option B is correct i.e the 3'-5' exonuclease is a proofreading function, eliminating mismatched nucleotides incorrectly inserted into the growing DNA strand.
Answer 5
Option C is correct i.e the mechanisms of leading (continous) and lagging (discontinuous) strand synthesis.
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