Question

Why the first denaturation cycle is long than the pther denaturation?

Answer 1

Explanation:

The denaturation step is longer because what you are usually dealing with is purified genomic DNA many thousands of base pairs long. ... Last cycle yes, you extend it to ensure as much of the single stranded DNA you have left over is turned into double stranded, but not the first.

Answer 2

Melting temperature refers to the temperature at which DNA strands dissociate from each other and become single stranded (or more correctly when 50% of a DNA duplex is single stranded and 50% double stranded). During your denaturation cycle, the DNA strands are 'melted' from each other, and the primer is also dissociated from the template.