The method in DNA heating and cooling can be used to separate the DNA strands lengthwise and make them single-stranded. When DNA is heated to just below boiling (90 degrees Celsius to 95 degrees Celsius), the two strands separate, revealing the information contained in their bases. With the nucleotides exposed, DNA can be easily identified, replicated, or transcribed. If heat-denatured DNA is then slowly cooled, complementary nucleotides will hydrogen-bond with one another, and the strands will renature or regain their familiar double stranded form.
The method in Restriction Endonucleases (or restriction enzymes), an enzyme present naturally in bacteria that can be used to cleave DNA at specific locations (palindromes), uses enzymes called endonucleases to break the phosphodiester bonds bonds between adjacent nucleotides on both strands of DNA, leading to a break in the DNA strand.