Lecture Three - DNA replication Flashcards
What does semi-conservitive replication mean?
It means that during replication, the daughter DNA created is made half from the existing parent strand, and half from a newly created strand of DNA.
At which stage of the cell cycle does replication occur?
In the S stage, which stands for DNA synthesis.
How is replication similar and different in prokaryotes and eukaryotes?
Prokaryotes:
DNA organised into circular structures called plasmids.
The plasmid is replicated in both directions, until the replicating strands meet at the other side of the plasmid, and the new DNA plasmid separates.
Single origin of replication.
Eukaryotes:
DNA organised into linear chromosomes.
Replication occurs along the leading and lagging strand.
Can have multiple origins of replication.
What happens when a new nucleotide is added to a replicating DNA strand?
The nucleotide originally has three phosphate groups attached.
When the nucleotide attaches, two of the phosphate groups break off.
Are both strands used in transcription and replication?
No.
In replication, both strands of DNA are used for replication.
In transcription, only the template strand is used.
How does the replication of the leading and lagging strnd work?
The leading strand is replicated going in the 5’ -> 3’ direction continuously.
The lagging strand also replicates in the 5’-> 3’ direction, but this moves towards the replication fork (due to the antiparallel nature of DNA).
This means that the lagging stand is replicated in fragments (Okazaki fragments).
DNA polymerase I seals the gaps between each fragment.
Ligase sticks the two strands of DNA together.
What happens to the end of the DNA stand that has been replicated, and how is this problem fixed?
The end of the DNA molecule is shorter than the length it should be, due to the 5’ -> 3’ direction of replication.
Telomerase solves the shortening of the daughter strand.
It adds DNA to the end of the molecule, thus completing the DNA molecule, and making it the same length as its parent DNA molecule.
What is cloning?
Making an identicle copy.
What are recombinant proteins?
Proteins that are being produced in an organism that is not its host organism.
