Help with multipe choice questions please? No guessing if possible please. 12. I
ID: 3167094 • Letter: H
Question
Help with multipe choice questions please? No guessing if possible please.
12.
In which level of protein structure would you see ?-helices and ?-sheets?
primary
secondary
tertiary
D. quaternary
13.
All of the following are true about mutations EXCEPT:
Can occur spontaneously
Are changes in DNA
Can be induced through exposure to mutagens
Are nonrandom
15.
Which of the following is used to repair double-strand breaks?
Base-excision repair
Nonhomologous end joining
NER
Direct repair
19.
Which of the following is used to repair photodimers?
Nonhomologous end joining
Direct repair
Base-excision repair
NER
20.
Gaps in DNA are best repaired by which of the following repair mechanisms?
Nucleotide excision repair
Direct repair
Base excision repair
Recombinational repair
A.primary
B.secondary
C.tertiary
D. quaternary
13.
All of the following are true about mutations EXCEPT:
A.Can occur spontaneously
B.Are changes in DNA
C.Can be induced through exposure to mutagens
D.Are nonrandom
Explanation / Answer
12) Option 'B' is the correct answer.
Alpha helix and beta sheets are secondary structures of proteins. These structures are formes by hydrogen bonding between peptide chains to stabilize the secondary structure. Protein secondary structure is the three dimensional form of local segments of proteins. Secondary structure is formally defined by the pattern of hydrogen bonds between the amino hydrogen and carboxyl oxygen atoms in the peptide backbone.
13) Option 'D' is the correct answer.
Mutations are random, changes in DNA that may be either spontaneous or non-spontaneous, caused by exposure to mutagens such as UV light or chemicals like ethidium bromide etc. Naturally occuring mutations are always random, although arficially induced mutations may be site-directed and hence maight be non-random in nature.
15) Option 'B' isthe correct answer.
Non-homologous end joining is used to repair double stranded breaks in DNA. In NHEJ, DNA Ligase IV, a specialized DNA ligase that forms a complex with the cofactor XRCC4, directly joins the two ends. To guide accurate repair, NHEJ relies on short homologous sequences called microhomologies present on the single-stranded tails of the DNA ends to be joined. If these overhangs are compatible, repair is usually accurate
19) Option 'B' is the correct answer.
The mechanism of repairing UV-induced pyrimidine dimers is direct reversal of the dimerization reaction. The process is called photoreactivation because energy derived from visible light is utilized to break the cyclobutane ring structure. The original pyrimidine bases remain in DNA, now restored to their normal state.
20) Option 'D' is the correct answer.
Recombinational repair is used for repairing the gaps in DNA. Recombinational repair depends on the fact that one strand of the parental DNA was undamaged and therefore was copied during replication to yield a normal daughter molecule. The undamaged parental strand can be used to fill the gap opposite the site of damage in the other daughter molecule by recombination between homologous DNA sequences
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