In a pcr reaction, a few seconds at high temperature disrupts the that hold the two strands of dna together, so every molecule of dna unwinds and becomes single-stranded.

Hydrogen Bonds

Explanation:

In the polymerase chain reaction (PCR) the temperature rises to 90 ° C - 95 ° C, to break the hydrogen bonds, which are the types of bonds responsible for pairing the two strands of DNA, this process is known as denaturation of DNA.

The DNA is extremely stable, due to a large number of bonds (hydrogen bonds) that form between the two strands. If the temperature decreases, these bonds will begin to recompose, until the DNA returns to its original state

yes it is weird but true

that is wrong, its not thymus.