Biology Reference
In-Depth Information
Figure 8.1
(
Continued
) B) The process of amplification has low efficiency in the early cycles and some of
the products produced lack defined ends. At the start, a single molecule (two strands) is denatured by
heating and primer a and b, respectively, anneal to homologous sequences on strand 2 and 1. As shown
above, amplification in cycle 1 extends some distance along the original DNA template strands. During
cycle 2, the DNA is once again heated to denature it, and old and new strands can serve as templates for
DNA synthesis. Note the DNA is synthesized from the 5
′
to the 3
′
direction. The primers are indicated by
the small rectangles; the sequences homologous to the primers are designated at a' and b'. Once again in
cycle 2, extension of some new strands occurs beyond the a' or b' sequences. However, for the first time
