1.2 - Replication of DNA Flashcards
Explain why DNA replication is described as semi-conservative?
It has one new and one original strand
Why is DNA replication required?
Before mitosis to ensure that both daughter cells get an identical copy of the genetic information from the parent cell.
What is required in order for DNA replication to take place?
DNA polymerase and ligase (enzymes), DNA nucleotides, primers, template DNA, ATP
Which bonds are broken to separate the two strands of DNA?
Hydrogen bonds
Why can DNA only be replicated in one direction?
Because DNA polymerase can only add DNA nucleotides to the 3’ end of the new DNA strand which is forming.
What is meant by discontinuous synthesis of the lagging strand?
Strand is replicated in fragments
What is a primer?
a short strand of nucleotides which binds to the 3’ end of the template DNA strand allowing DNA polymerase to add nucleotides.
What is the function of a primer?
To provide a start point for DNA polymerase.
Why are there multiple replication forks on one strand of DNA?
To allow speedy replication.
Why is there a leading and lagging strand in DNA replication?
Parent strands are anti-parallel but DNA polymerase can only add DNA nucleotides to the 3’ end of the new DNA strand which is forming.
What is the first stage of enzyme control of DNA replication?
After the hydrogen bonds break, the DNA separates.
What is the second stage of enzyme control of DNA replication?
A DNA primer (a short stretch of complementary nucleotides) attaches to the start of the piece of DNA being copied
What is the third stage of enzyme control of DNA replication?
DNA polymerase then attaches free nucleotides to the 3’ end of the primer
What is the fourth stage of enzyme control of DNA replication?
This is a continuos process until leading strand is copied
What is the function of PCR?
To amplify a sequence of DNA.
What are the requirements of PCR?
Template DNA, heat-tolerant (taq) DNA polymerase, primers, free DNA nucleotides.
When is PCR used?
Crime scene analysis to identify suspects, paternity testing and diagnose genetic disorders.
Why is DNA heated in the first stage of PCR ?
To break the hydrogen bonds between the bases and separate the two strands.
Why is DNA cooled during the second stage of PCR?
To allow primers to bind/anneal to target sequences.
Why is heat-tolerant DNA polymerase used in PCR?
It doesn’t denature during the heating cycles.
Why is DNA heated back up for the third stage of PCR?
To allow heat-tolerant DNA polymerase to replicate the region of DNA.
What are the primers used in PCR?
they are short strands of nucleotides which are complimentary to specific target sequences at the two ends of the region of the DNA to be amplified.
What temperature does the first stage of PCR occur at?
92-98°C
What temperature does the second stage of PCR occur at?
50°C- 65°C
What temperature does the third stage of PCR occur at?
70-80°C
What is the difference between DNA polymerase and heat-tolerant polymerase?
DNA polymerase denatures at lower temperatures than heat-tolerant polymerase.
Which bonds are synthesised by DNA / heat-tolerant DNA polymerase?
Strong chemical bonds / covalent bonds between sugar and phosphates of adjacent nucleotides.
Which rule allows the molecules of DNA to be copied?
Complementary base pairing rule
List 3 uses of DNA amplified through PCR
- Solve crimes
- Settler paternity suits
- Diagnose genetic disorders
Why does the lagging strand have to be copied in fragments?
Because DNA polymerase can only add DNA nucleotides in a 5’ to 3’ direction
Why are two types of primer needed in PCR?
To flank the target region of DNA
