2 - DNA replication, cell cycle & mitosis Flashcards
What is semi-conservative DNA replication?
Each strand forms the template for a new strand of DNA.
DNA replication requires..
Template stand.
Oligonucleotide primer.
Supply of dNTPs.
DNA helicase does what?
Energy from ATP is used to break H bonds in DNA to separate strands.
DNA polymerase does what?
Add deoxynucleotide tri-phosphates (dNTPs) to the 3’ end of a DNA molecule.
DNA synthesis goes in what direction?
5’ - 3’ direction
What drives the reaction?
The release of energy from the hydrolysis of the tri-phosphate.
Drugs used as chain terminators are called?
Nucleoside analogs. (No -OH group on carbon 3 so no nucleotides can be added).
Name 4 nucleoside analogs
ddC - H on C3
AZT - N3 on C3
Acyclovir - Guanine base
Cytosine arabinose - Chemotherapy drug
What is the origin of replication?
Discrete points on the DNA molecule where replication begins.
What direction are strands synthesised in what direction?
5 to 3.
What is the replication fork?
The site of DNA synthesis, it moves along during the process.
How is the leading strand synthesised?
Continuously in 5 - 3 direction.
How is the lagging strand synthesised?
Discontinuously in 5 - 3 direction, making okazaki fragments.
How is a new chain started?
An RNA primer
How is an RNA primer made?
Synthesised by an RNA polymerase called primase.
About 10 bases long
The primer is extended by a DNA Polymerase until the last RNA primer is reached.
Its removed later.
How is the RNA primer used on the leading strand?
Only 1 is required, at the replication origin.
How are okazaki fragments joined?
- Primer is removed
- DNA polymerase then synthesises DNA through the RNA primer region. (Repair DNA polymerase)
- Two adjacent strands of DNA are joined together.
How is the RNA primer removed?
A ribonuclease removes the RNA primer using a 5′ to 3′ exonuclease activity.
How are the 2 adjacent strands joined together?
DNA ligase joins them using ATP.
What is a sliding clamp?
Makes sure DNA polymerase doesn’t fall off DNA strand.
What does a single strand DNA binding protein do?
Make sure no H bonds are reformed.
How accurate is DNA replication?
1 error per 10^9 base pairs.
How is DNA proof read?
DNA Polymerase has 3’ to 5’ exonuclease activities for proof reading.
Replication of E.coli genome.
- There is only 1 origin called Ori C.
- There are 2 replication forks in opposite directions.
- They move in opposite directions and meet at the other side of the circular chromosome.
This is called Bi-directional replication.
