DNA Replication Flashcards
What is the error level of DNA replication
1 nucleotide per 1 billion
How long does DNA replication take?
Cell division occurs in less than 24 hours. DNA replication is a third of that time
Replication origins
The place where DNA replication begins.
There are specific nucleotide sequences that designate these.
Eukaryotes have multiple sites and prokaryotes only have one.
What is the Y shaped region of the replicating DNA called?
Replication Fork
Why is DNA replication semiconservative?
The two strands separate and then have new complimentary strands made on top of them. Since half of the DNA is original, it’s semi-conservative.
What enzyme unwinds the DNA during replication?
Helicase
How is the unpaired DNA stabilized as it’s unwound?
Single-strand binding proteins bind to the DNA to stabilize it.
How is tension in the DNA relieved as it’s unwound?
DNA gyrase ( a type of Topoisomerase) binds to the DNA ahead of the replication fork helping to relieve DNA torsion before helicase gets to it.
After DNA is unwound, how does transcription start?
Primase forms a one primer of RNA on the leading strand and multiple primers on the lagging strand that DNA polymerase can use to start its part in transcription. This primer is about 5 - 10 base pairs long and pairs RNA with the original template DNA.
How is DNA added to the template DNA?
DNA is added in the 5’ to 3’ direction by DNA Polymerase III. It uses the RNA primers to attach and start adding free nucleotides to the DNA one base pair at a time. The leading strand has its DNA generated continuously. The lagging strand has to do it in fits and starts since DNA polymerase III can only work in the 5’ to 3’ direction. It forms okazaki fragments between all the RNA primers
DNA Polymerase I replaces the RNA of the primers with DNA
What is the exonuclease activity of DNA polymerase I and DNA polymerase III?
DNA polymerase I has exonuclease activity in the 3’ - 5’ and 5’ - 3’ direction. It moves both backward during transcription to fix its own errors and moved forward for other types of DNA repair
DNA polymerase III has exonuclease activity in the 3’ - 5’ direction only. If it sees it made a mistake in pairing, it will go backward in the 3’ - 5’ direction to remove the wrongly paired base.
How are DNA segments stitched together after replication?
Ligase binds the backbones of DNA together on the lagging and leading strands after DNA polymerase 1 replaces the RNA with DNA.
What is lost after each DNA replication
A small nucleotide loss on each end of the chromosome called the telomere.
What is the telomere?
A repetitive section of DNA at the end of each chromosome
There are no genes here.
It protects the cell because a little bit of it is lost after each dna replication.
If only a small nub is left of the telomere, apoptosis (cell death) occurs.
What is telomerase?
It is a reverse transcriptase enzyme, that carries its own RNA, in eukaryotic germ cells that catalyzes the lengthening of the telomeres and restores them to their original length.
If this didn’t occur, the new zygote would have shorter telomeres and a shorter life overall.
about 90% of all cancer cells have high levels of telomerase. This makes them virtually immortal through all their rapid replications.
