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Bio 169 2003 Exam 2
Name___________________________________
Biology 169 -- Exam 2
February 25, 2003
Answer each question, noting carefully the instructions for each.
Repeat: Read the instructions for each question before answering!!!
Be as specific and concise as possible in each answer,
noting the suggested length limits described for each problem.
Please print name on top of each page! (In case pages get separated.)
--------------------------------------------------------------------------------------------------------------------I certify that I have performed my work on this examination in full conformity with the provisions of
the Honor Code.
Signature___________________________________
1. (3 points) What important property of the cell cycle was shown by fusing cells in G1 or cells in
G2 with cells in S phase (1 or 2 sentences)?
S phase cells contain an activity can that can induce G1 but not G2 nuclei to replicate DNA. G2
nuclei are refractory to S phase induction because of the block to re-replication.
2. (3 points) Describe an important difference between the cyclin dependent kinases that control the
mammalian and yeast cell cycle (1 sentence).
The yeast cell cycle is run with only a single CDK, while mammalian cells use multiple, different
CDK proteins.
3. (4 points) S. pombe cdc2 mutants and S. cerevisiae cdc28 temperature sensitive mutants arrest at
different points in the cell cycle. At what point does each of these mutants arrest? Explain why they
arrest at different cell-cycle phases (2 sentences).
cdc28 mutant arrest in G1, and cdc2 mutants arrest in G2. The kinases act at both the G1-S and G2M transitions. Since ts alleles never cause complete loss of function at the restrictive temperature, the
interpretation of the result is that more CDC28 activity is needed during G1 relative to G2 in S.
cerevisiae, and more CDC2 activity is needed during G2 relative to G1 in S. pombe.
4. (3 points) What activity prevents the re-initiation of origins of replication during S and G2 phase,
and at what time during the cell cycle is this activity removed (2 sentences)?
CDK activity (e.g. CDC28 in S. cerevisiae), which is removed during mitosis because of cyclin
destruction.
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Bio 169 2003 Exam 2
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5. (2 points) Human genes that regulate the cell cycle were first isolated by (circle one):
a. Biochemical purification
b. Complementation of yeast mutants
c. Complementation of Xenopus mutants
d. Positional cloning
6. (3 points) Describe the difference between a centromere and a kinetochore, and the role they play
together during the cell cycle (2 sentences).
The centromere is a DNA sequence necessary for chromosome movement during mitosis, and the
kinetochore is the protein complex that forms at the centromere to which spindle microtubules attach.
Both are needed for segregation of chromosomes during mitosis and meiosis, and a chromosome can
have one and only one centromere.
7. (2 points) Circle all of the following true statements about eukaryotic S phase.
a. There is a single origin of replication in the genome.
b. All chromosomes must have at least one origin of replication.
c. Each chromosome is replicated twice during S phase of a mitotic cell cycle.
d. There are multiple origins of replication in the genome.
8. (5 points) Investigators found that cyclin B concentration rises and falls in synchrony with mitotic
events and MPF activity. However, correlation is not causality. How did they show that cyclin B was
responsible for these cell cycle events (4-5 sentences)?
A “cycling” extract was made from a frog egg that was activated to start early development. mRNA
was depleted from this extract using low level of RNAse. Such an extract does not cycle. cyclin B
mRNA was added back to this depleted extract (after inactivating the RNAse), and it began cycling
again.
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Bio 169 2003 Exam 2
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9. (2 points) Circle any of the following statements that are consistent with the
known action of the p21 family of cdk inhibitors (i.e. there could be more
than one).
a. over expression arrests mammalian cells in G1 phase
b. prevent the transcription of cdk genes
c. simultaneously bind cyclin and cdk
d. interact only with unbound cdk proteins
10. (2 points) Mitotic cyclin levels in early Xenopus embryos are regulated by (circle
the best answer):
a. phosphorylation
b. synthesis and degradation of their mRNAs
c. ubiquitination by APC during mitosis
d. transcription by MPF
11. (2 points) Circle any of the following statements that are consistent with the
known action of the S. pombe wee1 protein (i.e. there could be more than one).
a. phosphorylates cdc2 on Tyr15
b. phosphorylates cdc2 on Thr 161
c. inhibits the kinase activity of cdc2 protein
d. dephosphorylates and activates CAK kinase
e. dephosphorylates Tyr15 of cdc2
13. (2 points) The restriction point in mammalian cells is equivalent to (circle one):
a. the anaphase stage of M phase
b. START in S. cerevisiae
c. the point at which the spindle forms
d. G2-M control in S. pombe
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Bio 169 2003 Exam 2
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12. (2 points each) For each of the following situations in S. pombe, indicate whether a “wee”
phenotype, characterized as small cells with a shortened G2 phase, or a G2 arrest phenotype would
occur (write either “wee” or “G2 arrest” on the line provided). For temperature sensitive alleles (ts),
assume the phenotype was scored at the restrictive temperature.
ts mutation of cdc2
___G2 arrest____________
ts mutations of cdc13
___G2 arrest___________
ts mutation of cdc25
___G2 arrest___________
a wee1 mutation
____wee___________
expression of a cdc2 mutant that
cannot be phosphorylated on Tyr 15 ____wee___________
expression of a cdc2 mutant that
cannot be phosphorylated on Thr 161 ____G2 arrest___________
over expression of cdc25
____wee___________
a dominant, hyperactive cdc2 allele ____wee___________
14. (1 point) Name one stimulus for quiescent (G0) cells to re-enter the cell cycle?
_growth factor___________
Name 3 molecular events that occur within cells during G1 after such stimulation (“passage through
the restriction point” is not what I’m looking for) (2 points each).
1) ____cyclin D transcription is induce by the RAS/MAPK pathway_________________
2) ____RB protein becomes hyperphosphorylated__________________________________
3) ____The transcription of genes regulated by E2F increases______________________
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Bio 169 2003 Exam 2
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15. (2 points each) Assume that a wild type mammalian cell in G0 takes 8 hours to enter S phase
after addition of growth factors, and that the Restriction Point occurs 5 hours before the beginning of
S phase. Indicate by writing “YES” or “NO” whether a cell will divide at least once or not in each of
the following experimental situations.
Continuous incubation in cell culture medium containing serum
______Yes_________
Incubation in medium containing serum for 6 hours,
followed by incubation in medium lacking serum
______Yes_________
Incubation in medium containing serum for 3 hours,
followed by incubation in medium lacking serum
_______No________
Incubation in medium containing serum for 3 hours,
followed by incubation in medium lacking serum for 30 min,
followed by continuous incubation in medium containing serum
_______Yes________
16. (2 points) Which causes cyclin D to be over expressed in mantle cell lymphoma (circle one)?
a.
gene amplification
b.
chromosome translocation
c.
point mutation
d.
mutation of both alleles to the recessive genotype
17. (1 point) E2F controls the transcription of genes encoding proteins that predominantly act in
which phase of the cell cycle? ___S phase_________________
18. (2 points) The components of the mammalian restriction point that when mutated lead to
cancer include all of the following except (circle one):
a. cyclin D
b. p16
c. Rb
d. cdc2
19. (2 points each) Name three criteria used to establish that the RB gene had been identified.
1)_____RB mRNA is not expressed in some retinoblastoma tumors____________
2)_____expression of RB can suppress the growth of RB mutant cell lines__________
3)expression of RB can suppress the formation of tumors in nude mice caused by RB mutant cells
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Bio 169 2003 Exam 2
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20. (3 points) Why did Bob Weinberg think that Ted Dryja’s strategy for cloning the RB gene would
fail (2 sentences)?
Dryja was cloning random pieces of chromosome 13 and analyzing their expression in
retinoblastomas. That is tantamount to “looking for a needle in a haystack”.
21. (2 points each) Indicated whether the following situations would tend to promote cell cycle
progression, inhibit cell cycle progression, or do nothing (use those words).
A cell with a mutant E2F that cannot bind to DNA
______inhibit______________
A cell with a mutant pRB that cannot bind to E2F
______promote___________
A cell with a mutant p16 protein that cannot bind to cdk4
______promote____________
A cell with a mutant cdk4 that cannot bind to cyclin D
_______inhibit_____________
Expression of a mutant pRB that cannot be phosphorylated by cyclin D/cdk4
________inhibit____________
Expression of a hyper-stable cyclin D protein
________promote___________
A deletion of the RB gene
________promote____________
A deletion of both the RB gene and the cyclin D gene
________promote___________
A deletion of both the RB gene and the E2F1 gene
________inhibit___________
Over expression of the p16 gene in an RB mutant cell
________nothing___________
Over expression of the p16 gene in a normal cell
________inhibit___________
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