Polymerase Chain Reaction (PCR)

Question 1

Outline the steps of PCR

Answer 1

• a DNA sample is mixed with a sample of free nucleotides, DNA polymerase (Taq polymerase) and primers
• the mixture is heated to 95 degrees to break the hydrogen bonds between the bases to make the DNA single stranded
• the mixture is then cooled to 50 degrees and the primers anneal to the strands of DNA (hydrogen bonds reform)
• DNA polymerase can now bind to the double stranded sections
• the temperature is then raised to 72 degrees (optimum)
• DNA polymerase then extends the double stranded section by adding free nucleotides to turn unwound DNA
• this cycle repeats until multiple copies of the DNA are made

Question 2

What is PCR?

Answer 2

PCR is used to create multiple copies of a section of DNA (known as amplification)

Question 3

What are the differences between natural DNA replication and PCR?

Answer 3

DNA Replication
- whole chromosomes
- no primer is required
- DNA helicase enzyme is used to separate strands
PCR
- short sequence only (few hundred bases)
- addition of primer to start sequence
- heating and cooling used to separate and bind strands