DNA replication Flashcards
When does DNA replication occur?
S phase of interphase
What are the three stages of DNA replication?
Initiation
Elongation
Termination
What happens in inititation?
Origin of replication is recognised
DNA polymerase is recruited
DNA primase starts the process
What does DNA primase do?
Adds primers
form beginning of the new strand of DNA
What is a primer?
Short single stranded sections of DNA/RNA
Why is DNA primase required for DNA replication?
Because DNA polymerase can only extend already existing DNA strands
can’t form new ones from scratch
What happens in elongation?
DNA polymerase reads DNA template strand
extends new DNA strand
Which direction does DNA polymerase read the DNA template strand in?
3’ to 5’
Which direction does DNA polymerase extend the new DNA strand in?
5’ to 3’
What does DNA helicase do?
Unwinds DNA
moving the replication fork along
What happens to DNA polymerase when the replication fork moves along? Why?
One DNA polymerase moves to the replication fork
so it can continue reading the DNA template strand 3’ to 5’
and extending the new DNA strand 5’ to 3’
What is formed as a result of DNA polymerase always moving to the replication fork as it moves along?
Fragments of DNA
called okozaki fragments
What does DNA ligase do in elongation?
Join together the okozaki fragments
forming the lagging strand
What happens in termination?
Two replication forks meet in the middle
giving rise to separate DNA fragments
DNA ligase joins them together
What does DNA replication produce?
Two molecules of DNA
What is each molecule of DNA produced by DNA replication made up of?
One old template strand
One newly formed strand
What is the structure of a chromosome before DNA replication?
One DNA molecule
What is the structure of a chromosome after DNA replication?
Made up of two chromatids
joined together by centrosome in middle
What is a chromatid?
One DNA molecule
What reaction occurs when a new nucleotide is added to the new DNA strand?
(dNMP)n + dNTP —–> (dNMP)n+1 + PPi
