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. 2002 Oct 29;167(9):1032-3.

Genetics 101: polymerase chain reaction

Alison Sinclair  1
Affiliations

Genetics 101: polymerase chain reaction

Alison Sinclair. CMAJ. .

Erratum in

  • CMAJ. 2003 Mar 4;168(5):544
No abstract available

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Figures

None
Fig. 1: PCR schematic showing the amplification of the target sequence of DNA (green) from the template DNA (blue). In cycle 1, primers bind to each strand of the template (blue) and DNA polymerase synthesizes 2 new complementary strands (red). There is no signal to stop synthesis, so the daughter strand lengthens until the strands are separated for the next cycle. At the beginning of cycle 2, half the strands are the original template (blue) that synthesize strands of undefined length. However, each strand produced in the first cycle binds the primer directing synthesis in the opposite direction. Synthesis proceeds to a defined end point — the beginning of the strand. The product of this synthesis is a strand of DNA of defined length bounded by the 2 primers (green) and containing the sequence of interest. At the beginning of cycle 3, one-quarter of the strands are the original template (blue). One-half of the strands are single stranded with one defined end (red). Each of these will produce a daughter strand with 2 defined ends (green). One-quarter have 2 defined ends, and each of these will also produce a daughter strand with 2 defined ends (green). With further cycles the original template (blue) cannot increase in number. The strands with one undefined and one defined end (red) can only be synthesized from the original template strands and will increase arithmetically. However the number of strands that have 2 primer-defined ends, and therefore a defined length, will increase exponentially (cycle 4 and beyond).
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Comment in

  • Viral genomes.
    Walsh SR. Walsh SR. CMAJ. 2003 Mar 4;168(5):544. CMAJ. 2003. PMID: 12615744 Free PMC article. No abstract available.

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