4.2 Flashcards
1
Q
model for semi-conservative replication
A
DNA splits and two new DNA strands are formed each with one side from the original
2
Q
evidence for semi-conservative replication
A
DNA with heavy nitrogen (N15) mixed in a lighter nigtrogen (N14) medium made a lighter DNA
After one round of replication, DNA was 50% heavy N, after two rounds, DNA containing only light N appeared
we have now used fluorescent labels to replicate this data
3
Q
prokaryote replication
A
- one origin of replication
- starts from 3’ to 5’ on template
- both strands are simultaneously template strands
- leading strand: one primer, continuous build 5’ to 3’ towards replication fork
- lagging strand: multiple primers, builds fragments of 5’ to 3’ (Okazaki fragments) away from replication fork
4
Q
replication complex
A
- helicase unwinds DNA duplex
- DNA polymerase extends RNA primer
- Topoisomerase II bind upstream of unwinding site (untangle DNA)
5
Q
lagging strand
A
- RNA primase lays down primer
- DNA polymerase extends to make fragment
(repeat those two steps) - different DNA polymerase removes connective primers and replaces with DNA
- DNA ligase joins two fragments
6
Q
proofreads DNA
A
DNA polymerase will remove incorrect nucleotide and won’t continue until correct one is added
7
Q
eukaryotic replication
A
- multiple origins of replication
- requires primer
- always reads in 3-5, builds in 5-3
- also had lagging + leading strands
- successive replication of lagging strands yields shorter DNA sequences
- telomeres prevent DNA erosion
8
Q
telomeres
A
- nucleotide sequence made up of repetitions of one short nucleotide sequence (in humans it’s TTAGGG)
- serves as a buffer zone so that coding genes are protected from DNA erosion
- does still get shorter over time (except for in gametes and stem cells, they have telomerase)
9
Q
telomerase
A
reverse transcriptase enzyme that catalyzes the lengthening of telomere strands
