Unit 1 Topic 4 - Polymerase Chain Reaction (PCR)

Question 1

State that PCR is used to amplify regions of DNA.

Question 2

List the requirements for PCR

Answer 2

1. DNA fragment to be copied
2. Free DNA nucleotides
3. Primers for specific target DNA sequences
4. Taq Polymerase - This is a heat tolerant DNA Polymerase (Will not denature at high temps)

Question 3

Describe the 3 stages in PCR

Answer 3

Stage 1 - 95°C - DNA strands are separated (denatured) = hydrogen bonds between bases break.
Stage 2 - 55°C - The primers anneal (bind) to the target sequences on the DNA
Stage 3 - 72°C - Taq Polymerase adds DNA nucleotides to the strands to replicate the region of DNA.

Question 4

Give the number of copies of DNA produced by each cycle of PCR.

Answer 4

Each cycle doubles the number of DNA fragments

Question 5

Identify each stage of PCR from a thermal cycling graph

Question 6

List the sources of DNA used in PCR

Answer 6

• body fluids such as blood, semen & Saliva
• Hair follicles, bones & teeth
• cells from embryos

Question 7

Describe the possible uses for PCR

Answer 7

1. DNA fingerprint - Identify an individual by blood or tissue at a crime scene as specific areas of DNA are known to vary between people.
2. Detecting Diseases - specific sequences of DNA can indicate genetic disorders in embryos or the presence of bacteria or viruses
3. Evolution - DNA samples from ancient DNA can be amplified for studies into palaeontology and evolutionary relationships between species.
4. Paternity Testing - Comparison of DNA from two possible fathers and a child.
5. Population studies - Similarities in DNA can show migration patterns over time.

Question 8

Describe the process of gel electrophoresis

Answer 8

This is a method of separating molecules such as DNA, RNA and proteins based on their size.