Download Exercices Week 1 -with answers File

Exercises for BMC-1
Week 1
September 15, 2014
1) You discover a new frog species and determine that Adenine makes up 27% of its
DNA content. What percentage of Guanine do you expect?
a) 24%; b) 27%; c) 48%; d) 50%; e) none of the above
(Answer: e, 27%x2=54%, leaving 46% to split between G and C, hence 23% for G)
2) Which of the following statements concerning DNA replication is incorrect?
a) DNA helicase unwinds the double-helix.
b) Single-stranded DNA-binding protein stabilizes the opened double-helix.
c) The sliding clamp keeps DNA polymerase on single-stranded DNA.
d) A single RNA primer is synthesized on the lagging strand.
e) Okazaki fragments are sealed by a DNA ligase.
(Answer: d)
3) Which of the following enzymes function mostly in lagging strand synthesis?
DNA primase, DNA helicase, single-stranded DNA-binding proteins, DNA ligase, DNA
polymerase
(Answer: DNA primase, DNA ligase)
4) You grow a single yeast cell in the presence of radioactive 32P. This cell undergoes
DNA replication, after which you immediately wash out the 32P. After cell division, do
both daughter cells contain radioactive DNA? What about the four grand daughters?
(Answer: yes, both daughters, but only two grand daughters, semi-conservative DNA
replication)
5) Gene A has 7 exons and 6 introns, whereas gene B has 3 exons and 2 introns. Can
the protein encoded by gene B be larger than that encoded by gene A?
(Answer: yes, the number of exons does not say anything about their size)
6) Gene X in the house fly contains a region A that is 93% identical to the corresponding
region A’ in the corresponding gene X’ in Drosophila, as well as a region B that is 62%
identical to the corresponding region B’ in the corresponding gene X’ in Drosophila.
Only one of the following statements is correct. Which one?
a) The house fly and Drosophila have diverged about 100 million years ago.
b) The house fly emerged more recently during evolution.
c) Regions A and A’ correspond to exons, regions B and B’ to introns.
d) Exons in the house fly are longer than in Drosophila.
e) Introns in the house fly are longer than in Drosophila.
(Answer: c, region A is under higher evolutionary pressure than those that are noncoding/intronic)
7) Genes that code for  and  tubulin vary very little during evolution. Explain why.
(Answer: changes that occur in the corresponding genes are almost invariably
deleterious, and thus not retained during evolution)
For questions 7-9: see the phylogenetic tree below.
8) How many years ago did species M and P diverge from their last common ancestor?
(Answer: 20 Million years ago)
9) One of the following statements is correct. Which one?
a) Species M is unrelated to species S.
b) Species Q is more closely related to species R than to species P.
c) Species O is the most closely related species to species M.
d) Species N is related to species M, but not to species S.
e) Species O is more closely related to species N than to species S.
(Answer: e)
10) Are M and N more or less closely related to each other than P and S?
(Answer: more, since P and S exhibit 2% nucleotide divergence)