structure and organization of nucleic acids

Question 1

steps in DNA replication

Answer 1

ORC activated during S phase
ORC binds origin of replication sites, initiating replication
DNA helicase binds origin of replication, breaks H bonds, unwinding DNA helix (uses ATP)
SSBs bind exposed single strands, preventing re-association and protecting from degradation
DNA polymerase α (primase) synthesizes RNA primer
DNA polymerase ε (leading) or δ (lagging) initiates synthesis in 5’-3’ direction
RNA primers are removed by ribonuclease
gap is filled by DNA polymerase
DNA ligase joins Okazaki fragments
topo II relieves supercoiling

Question 2

doxorubicin

Answer 2

anticancer drug
causes topo II poisoning of cancer cells
traps DNA topo II at replication site, increasing cleavage
results in permanent DS breaks –> apoptosis

Question 3

ciprofloxacin

Answer 3

quinolone antibiotic
acts as topo poison, similar to doxorubicin
increases level of DNA strand breaks
forms water-metal ion bridges via Ser81 and Glu85 in bacterial topoisomerase
mutations in Ser81 and Glu85 are most common reason for resistance
human topo lacks necessary AAs necessary to anchor bridges

Question 4

telomere

Answer 4

ends of linear chromosomes
repetitive noncoding sequences
TTAGGG x many
protect genetic information from being deleted during rounds of replication

Question 5

telomerase

Answer 5

maintains telomeres
has short RNA template that is complementary to DNA telomere sequence
reverse transcriptase activity (uses RNA template to generate DNA)
embryonic, stem cells, and cancer cells have high telomerase activity