Why is the DNA polymerase used in PCR taken from Thermus aquaticus?

Thermus aquaticus lives in hot springs, so its polymerase is not denatured at 95 °C. The enzyme survives every heating step and need not be replaced each cycle.

What are primers, and why are they needed in PCR?

Primers are short single strands of DNA complementary to the ends of the target sequence. DNA polymerase can only add nucleotides to an existing strand, so primers start the copying.

How many copies of a DNA sequence are made from one molecule after 25 cycles of PCR?

About 3.4 × 10⁷ copies are made. The amount doubles each cycle, and 2²⁵ = 33,554,432.

CCEA A-Level Life and Health Sciences 0008

Experimental Techniques

Topic overview Standard solutions, titrations and qualitative tests Rates of reaction and organic preparations Physics measurements: oscillations, resistivity, lenses and critical angle Biological tests, colorimetry, chromatography and osmosis

Human Body Systems

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Genetics, Stem Cell Research and CloningA2 option

Topic overview DNA structure and the evidence for the double helix RNA, genes and the triplet code Genotype, phenotype and monohybrid inheritance Dihybrid crosses, epistasis and the chi-squared test DNA replication and the Meselson–Stahl experiment Meiosis and genetic variation Insulin, factor VIII and chymosin from genetically modified microbes Recombinant DNA technology and gene cloning Genetic engineering, food supply and ethics Gene therapy and cystic fibrosis Genetic disease, screening and counselling Genetic fingerprinting and gel electrophoresis Stem cells, therapeutic cloning and their ethics

MicrobiologyDouble Award

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Analytical Chemistry TechniquesDouble Award

Topic overview Volumetric analysis in industry and healthcare Applied titrations of vinegar, indigestion tablets and bleach Redox titration of iron tablets and evaluating titrations Principles of colorimetry Colorimetric analysis of copper ore, aspirin and iron Thin-layer chromatography and its uses Visualising chromatograms and identifying painkillers and pigments Calorimetry and combustion Molar enthalpy and bond energy calculations Qualitative tests for cations and gases

Enabling TechnologyDouble Award

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Genetics, Stem Cell Research and Cloning

Genetic fingerprinting and gel electrophoresis

3 things to know
A2 5

Overview

Why DNA identifies individuals, Jeffreys' genetic fingerprinting, the stages of PCR, primers, gel electrophoresis and DNA ladders, paternity, forensics, breeding and marker probabilities.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

Why can DNA be used to tell one individual from another?

Numbers

Who developed genetic fingerprinting, and when?

Process

Describe the three temperature stages of one PCR cycle.

Questions from this subtopic

Each one with the model answer underneath.

1
Why can DNA be used to tell one individual from another?
Model answer
The genome contains many non-coding sequences in which a short unit is repeated many times. The number of repeats varies so much that two unrelated people are very unlikely to share the same pattern.
2
Who developed genetic fingerprinting, and when?
Model answer
Alec Jeffreys developed genetic fingerprinting at the University of Leicester in 1984. Jeffreys noticed that repeated DNA sequences gave a pattern unique to each person.
3
Describe the three temperature stages of one PCR cycle.
Model answer
The DNA is heated to about 95 °C to separate the strands, then cooled to about 55 °C so primers bind. The temperature is raised to about 72 °C, where DNA polymerase copies each strand.
4
Why is the DNA polymerase used in PCR taken from Thermus aquaticus?
Model answer
Thermus aquaticus lives in hot springs, so its polymerase is not denatured at 95 °C. The enzyme survives every heating step and need not be replaced each cycle.
5
What are primers, and why are they needed in PCR?
Model answer
Primers are short single strands of DNA complementary to the ends of the target sequence. DNA polymerase can only add nucleotides to an existing strand, so primers start the copying.
6
How many copies of a DNA sequence are made from one molecule after 25 cycles of PCR?
Model answer
About 3.4 × 10⁷ copies are made. The amount doubles each cycle, and 2²⁵ = 33,554,432.

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