Editing DNA synthesis (section)

{{Short description|Replication of DNA}}
[[File:DNA molecular structure, showing individual nucleotides and bonds.jpg|upright=1.25|thumb|right|Structure of double-stranded DNA, the product of DNA synthesis, showing individual nucleotide units and bonds.]]
'''DNA synthesis''' is the natural or artificial creation of [[deoxyribonucleic acid]] (DNA) molecules. DNA is a [[macromolecule]] made up of [[nucleotide]] units, which are linked by [[covalent bonds]] and [[hydrogen bonds]], in a repeating structure. DNA synthesis occurs when these nucleotide units are joined to form DNA; this can occur artificially (''in vitro'') or naturally (''in vivo''). Nucleotide units are made up of a nitrogenous base (cytosine, guanine, adenine or thymine), pentose sugar (deoxyribose) and phosphate group. Each unit is joined when a covalent bond forms between its phosphate group and the pentose sugar of the next nucleotide, forming a sugar-phosphate backbone. DNA is a complementary, double stranded structure as specific base pairing (adenine and thymine, guanine and cytosine) occurs naturally when hydrogen bonds form between the nucleotide bases.

There are several different definitions for DNA synthesis: it can refer to [[DNA replication]] - DNA biosynthesis (''in vivo'' DNA amplification), [[polymerase chain reaction]] - enzymatic DNA synthesis (''in vitro'' DNA amplification) or [[gene synthesis]] - physically creating [[synthetic DNA|artificial gene sequences]]. Though each type of synthesis is very different, they do share some features.
Nucleotides that have been joined to form [[polynucleotide]]s can act as a DNA template for one form of DNA synthesis - PCR - to occur. DNA replication also works by using a DNA template, the DNA double helix unwinds during replication, exposing unpaired bases for new nucleotides to hydrogen bond to. Gene synthesis, however, does not require a DNA template and genes are assembled ''de novo''.

DNA synthesis occurs in all [[eukaryote]]s and [[prokaryote]]s, as well as some [[virus]]es. The accurate synthesis of DNA is important in order to avoid mutations to DNA. In humans, mutations could lead to diseases such as cancer so DNA synthesis, and the machinery involved ''in vivo'', has been studied extensively throughout the decades. In the future these studies may be used to develop technologies involving DNA synthesis, to be used in data storage.