DNA replication Flashcards
What is step 1 in DNA replication?
The Parent DNA molecule starts to ‘unzip’ at one end by an enzyme called helicase.
What does the enzyme primase do?
This enzyme makes a small piece of RNA called a primer which marks the starting point of the new DNA strand.
What does DNA polymerase do?
DNA polymerase can only add DNA bases in one direction. From the 5’ prime end to the 3’ prime end.
How is the leading DNA strand made?
The leading strand is made continuously. An RNA primer starts off the strand, and then DNA polymerase adds bases one by one in the 5’ to 3’ direction.
How is the lagging DNA stand made?
The lagging strand can only be made in a series of small chunks because it runs in the 3’ 5’ direction. These chunks are called Okazaki fragments.
How are Okazaki fragments made in the lagging strand and what happens to the RNA primers?
Each fragment is started by an RNA primer. Then DNA polymerase adds a short row of DNA bases in a 5’ to 3’ direction. The next RNA primer is added further down the lagging strand. Then another Okazaki fragment is made, connecting the two RNA primers. Then the enzyme, exonuclease removes all RNA primers from both strands of DNA. Then a DNA polymerase fills in the gaps left behind with DNA.
What does DNA ligase do?
The DNA ligase finishes the process of DNA replication by sealing up the fragments of DNA in both strands to form two continues strands.
How long does it take a cell to completely copy its DNA?
It takes 8 hours for a cell to copy its DNA.
Why is DNA replication semi-conservative?
DNA replication is semi-conservative because each DNA molecule is made up of one old, conserved strand of DNA and one new one.
How many DNA strands are in a chromosome?
There is one long DNA strand in a chromosome.
What results after DNA replication?
DNA replication results in the formation of two identical copies of each chromosome, (sister chromatids attached at the centromere).
What is the point where the DNA strand splitting starts called?
Replication fork.
