Introduction to DNA replication Flashcards
Describe the relationship between the partner strands of DNA in a double helix.
A strand is exactly complementary to the nucleotide sequence of it’s partner strand
In general what happens to the DNA in replication?
The 2 strands separate
Each strand acts as a template for the production of a new complementary strand
DNA replication is semi-conservative, what does this mean?
Each of the 2 daughter molecule will have one of the old parent strands and 1 newly made strand
What is the referred to as the replication machine?
The group of proteins and enzymes that carry out DNA replication
When during the cell cycle does replication take place?
In the S phase of the cycle
Before mitosis
Each new double strand consists of one parental strand and one new daughter strand, what is this known as?
Semiconservative replication
What must first be done to DNA before replication can occur?
Helix must be opened to expose the separate strands
What starts the process of DNA replication?
Initiator proteins start the process
What do initiator proteins do?
They bind to DNA strands, pry them apart and break the hydrogen bonds
What is the position where the DNA helix is first opened?
The Origin of Replication
What is the Origin of Replication?
The position in DNA where the helix is first opened
What is a replication “bubble”?
Where the two separate strands open up from the origin of replication
What direction does replication occur in?
Replication proceeds in both directions from each origin until entire molecule is copied
How many origins does a human genome have?
10,000 origins
How many origins does a bacterial genome have?
1
What is found at each end of a replication bubble?
A replication fork
What is a replication fork?
2
A Y-shaped region found at each end of a replication bubble
This is where the new strands of DNA are elongating
How do the replication forks move?
2 forks move away from the origin in either directions
DNA replication occurs in two directions, what is this called?
Bidirectional
What catalyses the elongation of a new strand of DNA at a replication fork?
DNA polymerases
How many polymerases do eukaryotes use?
At least 11
How many polymerases do prokaryotes use?
2, Pol 1 and pol II
What do polymerases do?
Catalyse the elongation of a new strand of DNA at the replication fork
What end of the DNA are nucleotides added onto?
The 3 prime end of the new strand
What direction does DNA polymerase work in?
The 5’ to the 3’ direction
What direction can DNA elongate in?
5’ to 3’
Starts at 5’
Works towards 3’
New nts added to 3’ end
What is the leading strand?
2
The new strand in the 5’ to 3’ direction strand (complementary to the 3’ to 5’ parent strand)
The strand that can be synthesised continuously
How is the lagging strand synthesised?
Synthesised discontinuously as a series of Okazaki fragments
What joins the Okazaki fragments together?
DNA ligase
What does DNA ligase do?
Joins the sugar-phosphate backbones of the Okazaki fragments together
What direction is the leading strand replicated in relation to the replication fork?
Replicated in 5’ to 3’ direction
5’ at origin towards 3’ of fork
Adding on nts at the 3’ end of new strand continuously
