Download DOC

Quiz #3 key
BE 109 SP 03 MON/WED
4/9/03
Name_____________________
Write your name on this quiz and then answer the following questions in three sentences
or LESS. You have fifteen minutes to answer ten questions.
1. When you input the mRNA sequence of your gene of interest into Ambion’s website,
what nucleotide pattern does it look for to come up with a list of candidate siRNA
sequences?
Ambion’s algorithm searches for the AA(N19) pattern of nucelotides.
2. Why is it important to maintain DNA replication fidelity? Is it acceptable to have a
one in a million error rate?
DNA replication fidelity protects us from spontaneous mutations due to
replication errors. In each cell division, 1.2x10^10 base pairing decisions must be
made. A 1 in a million error rate would therefore unacceptable.
3. What are some of the causes of DNA damage?
Many exogenous (e.g. cigarette smoke, food, sunlight, pollution, chemicals) and
endogenous (e.g. oxidation products) agents cause DNA damage. Many answers
are possible.
4. How does having defects in DNA repair pathways affect human health?
Makes people highly prone to cancer. Li-Fraumeni syndrome, ataxia
telangiectasia, and Seckel syndrome are also possible answers.
5. What general category of DNA repair are EXO1 and AAG involved in?
Excision repair.
6. What is the specific role of exonuclease-1 in this type of DNA repair? That is, which
step does it accomplish?
After a mismatch is identified and a nick introduced, EXO1 cuts out a section of
the DNA strand containing the mismatched base.
7. How do E. coli distinguish between parental and newly replicated strands when
performing DNA mismatch repair? For instance, if a T was wrongly paired with a G, how
does the cell know which base to replace?
DNA strand methylation. For a short period after replication, the newly replicated
strand is unmethylated, while the parental strand is not. The DNA repair
machinery is able to remove the mismatched base from the new strand.
8. ATR, ATM, and p53 are all involved in pathways that allow the cell to do what in
response to DNA damage signals?
DNA damage signals activate ATR/ATM, which pass the signal on to p53 and
others. Downstream effectors halt the cell cycle so that DNA repair can occur, or
in some cases, apoptosis.
9. Why has it been difficult to produce an ATR knockout mouse? Hint: what is the
phenotype of ATR knockout cells?
ATR-/- is embryonic lethal. The mice die before being born. ATR-/- cells are
unable to grow.