DNA Replication
Chain terminator drugs are incorporated into DNA but lack a ___ in their chemical structure which prevents incorporation of additional ___ in the DNA or RNA polymer being synthesized.
3'-OH, nucleotides
5 steps of DNA synthesis
1. Identify origins of replication 2. Unwind dsDNA: helicase 3. Initiate (primer synthesis) and elongate 4. Ligate new DNA on lagging strand 5. Reassemble into chromatin
3 key events in the maturation of okazaki fragments
1. removqal of RNA primers w endonuclease 2. filling in the gap by DNA polymerase 3. sealing of "nick" by DNA ligase in an ATP-requiring rxn
___ synthesizes a short RNA primer onto which ___ adds an additional short stretch of DNA. The reason an RNA primer is first synthesized is due to the fact that only RNA polymerizing enzymes can join ___ in the absence of ____.
primase enzyme, DNA polymerase alpha, 2 nucleotides, a DNA polymer
With each nucleotide addition to a DNA polymer, the chemical moiety __ is released.
pyrophosphate
Replicative complex
unwind dna, recruit necessary machinery to copy the DNA (primase enzyme, DNA polymerase enzyme, Topoisomerase I - prevents overwinding ahead of replication fork). ORC no longer required, replaced by RPA (replication protein A)
final step of okazaki fragment maturation involves which enzyme
DNA ligase
Elongation
DNA pol delta/epsilon synthesizes DNA, PCNA is a "clamp" holding DNA pol onto the DNA
If a dividing cell is treated with a drug that inhibits topoisomerase, what would result?
Inhibition of DNA replication and cell cycle arrest
Pre-replicative Complex
Origin Recognition Complex (ORC) binds to ori DNA at late M1/early G1 and then cdt1 and cdt6 recruit/load the MCM helicase onto the ori. after MCM helicase is added, cdt1 and cdt6 are released
DNA replication occurs in the _____ phase of cell cycle
S phase, 6-12 hours
Inhibitors of telemorase are touted by some as potential anti-aging drugs for what reason?
Telomeres shorten in most somatic cells with each cell division
How is replication licensed only once per cell cycle?
Cdc6 inhibited during S phase, Cdt1 degraded during S phase, Geminin inhibits Cdt1 and is most abundant in S and G2
An experimenter forces very high levels of cdc6 and cdc1 expression in a otherwise normal cell line. Which of the following would you expect to occur?
Cells will replicate DNA more than once per cell cycle
Hayflick limit
after approx 50 cell divisions, telomeres shorten enough to be "senescent"
Acyclovir (Zovirax) is known as a ____ since it lacks a ___ with which incoming nucleotides can form a phosphodiester bond.
chain terminator, 3'-OH
telemorase
enzyme that adds nucleotides to telomeres after replication, abundant in cancer cells and stem cells. most differentiated somatic cells have lower/absent telemorase
The cdt1 inhibitor ___ rises during __ phase to ensure only a single round of licensing per cell cycle
geminin, S
Reassembly into chromatin after replication
histones removed by chaperones ahead of the fork
Okazaki fragments
lagging strand is synthesized discontinuously, 1000bp long, each has RNA primer, joined together by DNA ligase, and endonuclease involved to cut off RNA flap
