DNA serves to carry information from the parent cell to the daughter cell and is only two nanometres wide. Synthesis is when the DNA is replicated – DNA is a double helix, each turn of the helix is ten base pairs, made up of nucleotides which consist of nitrogenous bases. The two visible peaks between the curvatures of the helix are dubbed the major and minor grooves and have alternating lengths.
Supported by a sugar phosphate backbone; the 3’ carbon of the ribose link to the adjacent deoxynucleotide 5’ carbon by phosphodiester bridges during polymerisation. During this synthesis helicase unzips the DNA and polymerase utilises triphosphate Okazaki fragments whilst synthesising the leading 5’ carbon stand - the lagging 3’ carbon strand with the use of primers. The bases pair up: adenine (A) to thymine (T) and guanine (G) and cytosine (C). A to T has two hydrogen bonds and G to C has three hydrogen bonds.
RNA has uracil instead of thymine. During synthesis DNA can only be replicated in a 3’ (phosphate) to 5’ (hydroxyl) carbon direction and serves as the coding template, the double banded structure is called reverse complimentary. DNA’s structure is stabilised by a thousands of hydrogen bonds, Van der Waals’s forces also contribute. 5’ to 3’ serves for RNA synthesis coding.
Bases can exist in two tautometric forms, the standard enol from and rare keto form. Tautomers are a type of isomerism. Other types of isomerism include geometric isomerism, cis meaning on the same side and trans meaning across. Optical isomers are non-superimposable mirror image enantiomers. Tautometric isomerism leads to mispairing of bases. DNA’s structure is best retained at high humidity and low salt known as B-DNA. Denaturisation may occur at high temperatures, within alkali solution and in concentrated methanal (formaldehyde) or urea.
Various DNA structures may exist due to local-sequence dependant modulations of structure. Circular genomes occur in prokaryotic genomes and plasmids and well as viral, chloroplastic and mitochondrial DNA. However animal DNA is stored in chromosomes, DNA is wound around histone proteins to form nucleosomes. An entire chromosome forms during metaphase. The genetic code is made up of codons, which are triplets of bases.
