How does DNA unravel its double helix for duplicating?
DNA is supercoiled around structural proteins called histones this allows the separation of chromosomes during cell division to be ordered and avoid (hopefully) chromosomal mutations as occurs in Down’s syndrome. During DNA replication the enzyme helicase breaks the hydrogen bonds between the nucleotides at a replicating fork at the area for the gene to be transcribed or is the whole DNA molecule needs replicating semi-conservatively. This allows polymerase to work in both direction from 5′ to 3′ ends to create either mRNA or a daughter strand, this again keeps things ordered and prevents the knotty mess and hopefuly point mutations such as deletion. Ligase stitches the DNA molecule back together when transcription or replication is complete. The DNA length depends on the chromosome for example the Y chromosome is relatively short but chromosome 21 and 22 are very long.
