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Double stranded DNA forms a helical structure and is found in this form in the nucleus of a eukaryotic cell. It is comprised of a sense and antisense strand that are complementary to each other and these bind to each other according to Watson-Crick base pairing rules. The nucleotide bases that make up DNA are guanine, cytosine, adenine and thymine. These bases are abbreviated to G, C, A and T respectively. Guanine always forms three hydrogen bonds with cytosine and adenine always forms two hydrogen bonds with thymine. Therefore the [G] = [C] and [A] = [T]. The G-C triple hydrogen bond requires more energy to break than the A-T double hydrogen bond. moreDouble stranded DNA is split into single stranded DNA in the cell during processes such as DNA replication and transcription of DNA into mRNA. For a cell to fit all of its DNA into the nucleus, it must compress it down into chromosomes.

A single stranded DNA molecule can be made into a DsDNA molecule during DNA replication in the cell, by DNA polymerase III.

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