Page 78 - Genetics_From_Genes_to_Genomes_6th_FULL_Part3

372 Chapter 11 Analyzing Genomic Variation

Figure 11.10 PCR amplification of a target sequence. In the first PCR cycle of this example, a single molecule of double-stranded
genomic DNA is heated to denature it into single strands. The temperature is then lowered to allow these single strands to hybridize with the
two PCR primers. A heat-stable DNA polymerase now polymerizes new DNA onto the 3′ ends of each primer. In the second PCR cycle, the
DNA in the reaction tube is denatured and then hybridized to the same primers. Both the original DNA strands and those made in the first
cycle serve as templates in the second round. Each cycle of PCR thus doubles the amount of DNA in the target region. After the conclusion
of the third round of PCR, the 5′ ends of the majority of template strands are defined by the 5′ ends of the primers, fixing the length of the
accumulating PCR product.
PCR cycle 1:
5' 3' 5' 3'
5' 3'

3' 5'
3' 5' 3' 5'
(1) Denature strands (2) Base pairing of primers (3) Polymerization from primers along templates
PCR cycle 2:
5' 3' 5' 3'
5' 3'

5'
3' 5'
3' 5' 3' 5'

5' 3' 5' 3'
5' 3'

3' 5'
3' 5' 3' 5'
(1) Denature strands (2) Base pairing of primers (3) Polymerization from primers along templates

Exponential amplification
1
copy

2
copies

4
copies

8
copies

16
copies

32
copies

64
copies