Genomic stability and tumorigenesis (L12) Flashcards
What does Topoisomerase do and what are the differences b/w Topoisomerase I and II?
Topoisomerase prevents overwinding in DNA.
I cleaves one strand via a tyrosine residue w/o using ATP
II cleaves both strands using ATP and induces negative supercoiling.
Name an inhibitor of each Topoisomerase I and II.
What are they used for?
Camptothecin inhibits Top. I by preventing re-ligation of the nicked DNA strand;
Etoposide inhibits Top. II by preventing religation of DNA double strand.
They are used for lung, ovarian, testicular/breast, and prostate cancer.
Why does ciprofloxacin, used to treat infections, not affect the human cells?
Ciprofloxacin inhibits DNA gyrase which is a topoisomerase found ONLY in prokaryotes.
Name 4 topoisomerase II inhibitors used for bacterial infections (like urinary and respiratory).
- Novobiocin (blocks ATP binding)
- Nalidixic acid (DNA gyrase)
- Ciprofloxacin (DNA gyrase)
- Norfloxacin (DNA gyrase)
Describe the process of priming for DNAP in E. coli.
Primase synthesizes an RNA primer that anneals to a single strand of DNA, DNAP III will come and new DNA for the rest of that strand.
DNAP I will alter remove the RNAP and DNA ligase will fill in that last little gap.
Primase is a ___ Dependent ___ polymerase.
DNAP III is a ___ dependent ___ polymerase.
Telomerase is a ___ dependent ___ polymerase.
DNA; RNA
DNA; DNA
RNA; DNA
What does DNA ligase do in DNA replication?
Joins okazaki fragments together.
What AA is in the active site for DNA ligase?
Lysine
What are the functions of the 3 main bacterial polymerases and in which direction do they have EXOnuclease activity?
DNAP I: fills gap after RNA primer removal, removes RNA primer w/ RNaseH, DNA repair; exonuclease 5’>3’ AND 3’>5’
DNAP II: DNA repair; exonuclease 3’>5’
DNAP III: Replication (synthesis of DNA); exonuclease 3’>5’
In eukaryotes, how does the origin of replication differ?
Which is the main DNAP for eukaryotes and what exonuclease activity does it have?
there are several point of origins, each of which have bi-directional synthesis (which is semi-conservative).
DNAP delta has 3’>5’ exonuclease activity
What are the 4 phases of the cell cycle and what happens in each one?
G1: growth and metabolism
S: DNA replication
G2: Preparation for cell division
M: Mitosis
(G0):Non dividing stage
What do telomerases do?
They extend the 3’ overhang using a built in RNA sequence as a template to synthesize new DNA nucleotides 5’>3’, then DNAP can come and fill in the important overhang sequence
How does doxorubicin work?
It is an anticancer drug that intercalates b/w stacked bp’s thus inhibiting DNA replication and transcription
How does 5-Fluorouracil work?
It is an analog of U or T, and is converted in the body to 5-FdUMP, which binds tightly to thymidylate synthase (the enzyme that synthesizes dUMP>dTMP). Thus Thymine nu’s can’t be generated for DNA synthesis.
How does acycloguanosine work?
It is an anti-viral drug that imitates guanosine and is incorporated into DNA which halts replication b/c it can’t be paired with anything.
Describe the effect of mutagenic tautomers.
The imino tautomer of Adenine can pair w/ Cytosine, eventally leading to a transition from A-T to C-G.
NOTE: Tautomer forms of bases are rare but still occasionally happen (99:1 equilibrium ratio of normal to tautomeric form).
What happens when you treat DNA w/ nitrous acid?
It converts Adenine to Hypoxanthine which pairs to cytosine, inducing a transition from A-T to G-C
Nitrosamine, a dietary mutagen metabolites methylate guanine (which will pair to Thymine).
Name 4 places it is found.
- Latex products (eg balloons)
- nitrite in food products after entering stomach
- fryed foods (enhanced from high temp)
- pickling-salt (a preservative in Japan)
What is ethidium bromide and how is it a mutagen?
It is an acridine dye and induces FRAMESHIFT mutations by intercalating into the DNA, leading to the incoroporation of an additional base.
Benzo[a]pyrene is not carcinogenic until____.
Where is a common place it is found?
Until it is oxidized w/in cells. It is found w/ the burning of tobacco which will coat the airways and lungs.
What is the difference in effect b/w UV light and ionizing radiation?
UV causes pyrimidine dimers, ionizing radiation causes double strand breaks.
How do melanomas appear?
They are dark brown growths that result from nonrepair of pyrimidine dimers caused by UV light.
What’s the difference b/w base and nucleotide excision repair?
Base excision repair replaced one BASE by using glycosylase to cleave the glycosidic bond.
Nucleotide excision repair removes several NUCLEOTIDES at once and uses DNAP to fill in the gap and ligase to bind it.
Describe Burkitt’s lymphoma.
MYC, a proto-oncogene, is translocated from chromosome 8 to the immunoglobin heavy chain gene locus on chromosome 14. Thus, the MYC gene will be heavily transcribed in B cells resulting in enhanced cell proliferation, commonly leading to many neuroblastomas.
Xeroderma pigmentosum is a result of a defect in ____
the nucleotide excision repair mechanism, so thymine dimers are not repaired efficiently.
A defect in mismatch repair proteins can lead to
Hereditary Nonpolyposis Colorectal Cancer
