Naked extracellular DNA (eDNA), most of it released by cell death, is nearly ubiquitous in the environment. Its concentration in soil may be as high as 2 μg/L, and its concentration in natural aquatic environments may be as high at 88 μg/L. [106] Various possible functions have been proposed for eDNA: it may be involved in horizontal gene transfer; [107] it may provide nutrients; [108] and it may act as a buffer to recruit or titrate ions or antibiotics. [109] Extracellular DNA acts as a functional extracellular matrix component in the biofilms of several bacterial species. It may act as a recognition factor to regulate the attachment and dispersal of specific cell types in the biofilm; [110] it may contribute to biofilm formation; [111] and it may contribute to the biofilm's physical strength and resistance to biological stress. [112] Several artificial nucleobases have been synthesized, and successfully incorporated in the eight-base DNA analogue named Hachimoji DNA. Dubbed S, B, P, and Z, these artificial bases are capable of bonding with each other in a predictable way (S–B and P–Z), maintain the double helix structure of DNA, and be transcribed to RNA. Their existence could be seen as an indication that there is nothing special about the four natural nucleobases that evolved on Earth. [70] [71] On the other hand, DNA is tightly related to RNA which does not only act as a transcript of DNA but also performs as molecular machines many tasks in cells. For this purpose it has to fold into a structure. It has been shown that to allow to create all possible structures at least four bases are required for the corresponding RNA, [72] while a higher number is also possible but this would be against the natural principle of least effort.

Thorpe JH, Gale BC, Teixeira SC, Cardin CJ. "RCSB PDB – 1M6G: Structural Characterisation of the Holliday Junction TCGGTACCGA". www.rcsb.org . Retrieved 27 March 2023. Clue to chemistry of heredity found". The New York Times, June 1953. First American newspaper coverage of the discovery of the DNA structure Gusfield D (15 January 1997). Algorithms on Strings, Trees, and Sequences: Computer Science and Computational Biology. Cambridge University Press. ISBN 978-0-521-58519-4. Jeffreys AJ, Wilson V, Thein SL (1985). "Individual-specific 'fingerprints' of human DNA". Nature. 316 (6023): 76–79. Bibcode: 1985Natur.316...76J. doi: 10.1038/316076a0. PMID 2989708. S2CID 4229883. Rothemund PW (March 2006). "Folding DNA to create nanoscale shapes and patterns" (PDF). Nature. 440 (7082): 297–302. Bibcode: 2006Natur.440..297R. doi: 10.1038/nature04586. PMID 16541064. S2CID 4316391.Collins A, Morton NE (June 1994). "Likelihood ratios for DNA identification". Proceedings of the National Academy of Sciences of the United States of America. 91 (13): 6007–11. Bibcode: 1994PNAS...91.6007C. doi: 10.1073/pnas.91.13.6007. PMC 44126. PMID 8016106.

Berne C, Kysela DT, Brun YV (August 2010). "A bacterial extracellular DNA inhibits settling of motile progeny cells within a biofilm". Molecular Microbiology. 77 (4): 815–29. doi: 10.1111/j.1365-2958.2010.07267.x. PMC 2962764. PMID 20598083.Franklin RE, Gosling RG (6 March 1953). "The Structure of Sodium Thymonucleate Fibres I. The Influence of Water Content" (PDF). Acta Crystallogr. 6 (8–9): 673–77. doi: 10.1107/S0365110X53001939. Archived (PDF) from the original on 9 January 2016. Mandelkern M, Elias JG, Eden D, Crothers DM (October 1981). "The dimensions of DNA in solution". Journal of Molecular Biology. 152 (1): 153–61. doi: 10.1016/0022-2836(81)90099-1. ISSN 0022-2836. PMID 7338906. Zhang D, Keilty D, Zhang ZF, Chian RC (March 2017). "Mitochondria in oocyte aging: current understanding". Facts, Views & Vision in ObGyn. 9 (1): 29–38. PMC 5506767. PMID 28721182. Further information: DNA damage (naturally occurring), Mutation, and DNA damage theory of aging A covalent adduct between a metabolically activated form of benzo[ a]pyrene, the major mutagen in tobacco smoke, and DNA [82]

a b Doherty AJ, Suh SW (November 2000). "Structural and mechanistic conservation in DNA ligases". Nucleic Acids Research. 28 (21): 4051–58. doi: 10.1093/nar/28.21.4051. PMC 113121. PMID 11058099.a b Piovesan A, Pelleri MC, Antonaros F, Strippoli P, Caracausi M, Vitale L (2019). "On the length, weight and GC content of the human genome". BMC Res Notes. 12 (1): 106. doi: 10.1186/s13104-019-4137-z. PMC 6391780. PMID 30813969.

Cell division is essential for an organism to grow, but, when a cell divides, it must replicate the DNA in its genome so that the two daughter cells have the same genetic information as their parent. The double-stranded structure of DNA provides a simple mechanism for DNA replication. Here, the two strands are separated and then each strand's complementary DNA sequence is recreated by an enzyme called DNA polymerase. This enzyme makes the complementary strand by finding the correct base through complementary base pairing and bonding it onto the original strand. As DNA polymerases can only extend a DNA strand in a 5′ to 3′ direction, different mechanisms are used to copy the antiparallel strands of the double helix. [105] In this way, the base on the old strand dictates which base appears on the new strand, and the cell ends up with a perfect copy of its DNA.

Summary: Features of DNA and RNA

Schoeffler AJ, Berger JM (December 2005). "Recent advances in understanding structure-function relationships in the type II topoisomerase mechanism". Biochemical Society Transactions. 33 (Pt 6): 1465–70. doi: 10.1042/BST20051465. PMID 16246147.