DNA
Deoxyribonucleic acid is a
nucleic acid that contains the genetic instructions for the
biological development of a cellular form of life or a
virus. All known cellular life and some viruses have DNAs. DNA is a long
polymer of
nucleotides that encodes the sequence of
amino acid residues in
proteins, using the
genetic code: each amino acid is represented by three consecutive nucleotides .
In
eukaryotic cells, such as those of
plants,
animals,
fungi and
protists, most of the DNA is located in the
cell nucleus, and each DNA molecule is usually packed into a
chromosome and shaped as a double
helix.
Encyclopedia
Deoxyribonucleic acid is a
nucleic acid that contains the genetic instructions for the
biological development of a cellular form of life or a
virus. All known cellular life and some viruses have DNAs. DNA is a long
polymer of
nucleotides that encodes the sequence of
amino acid residues in
proteins, using the
genetic code: each amino acid is represented by three consecutive nucleotides .
In
eukaryotic cells, such as those of
plants,
animals,
fungi and
protists, most of the DNA is located in the
cell nucleus, and each DNA molecule is usually packed into a
chromosome and shaped as a double
helix. By contrast, in simpler cells called prokaryotes, including the
eubacteria and
archaea, DNA is found directly in the
cytoplasm and is circular. The cellular
organelles known as
chloroplasts and
mitochondria also carry DNA. DNA is thought to have originated approximately 3.5 to 4.6 billion years ago.
DNA is responsible for the genetic propagation of most inherited traits. In humans, these traits range from hair color to disease susceptibility. The genetic information encoded by an organism's DNA is called its genome. During
cell division, DNA is
replicated, and during
reproduction is transmitted to offspring. The offspring's genome is a combination of the genomes of its parents. Lineage studies can be done because mitochondrial DNA only comes from the mother, and the Y chromosome only comes from the father.
In humans, the mother's mitochondrial DNA together with 23
chromosomes from each parent combine to form the genome of a zygote, the
fertilized egg. As a result, with certain exceptions such as
red blood cells, most human cells contain 23 pairs of chromosomes, together with mitochondrial DNA inherited from the mother.
Overview
DNA consists of a pair of
molecules, organized as strands running start-to-end and joined by
hydrogen bonds along their lengths. Each strand is a chain of chemical "building blocks", called
nucleotides, of which there are four types:
adenine ,
cytosine ,
guanine and
thymine . In other applications such as
text editors, even simple algorithms for this problem usually suffice, but DNA sequences cause these algorithms to exhibit near-worst-case behavior due to their small number of distinct characters.
Database theory has been influenced by DNA research, which poses special problems for storing and manipulating DNA sequences. Databases specialized for DNA research are called genomic databases, and must address a number of unique technical challenges associated with the operations of approximate matching, sequence comparison, finding repeating patterns, and homology searching.
In 1994,
Leonard Adleman of the
University of Southern California made headlines when he discovered a way of solving the directed Hamiltonian path problem, an
NP-complete problem, using tools from molecular biology, in particular DNA. The new approach, dubbed DNA computing, has practical advantages over traditional computers in power use, space use, and efficiency, due to its ability to highly parallelize the computation , although there is labor worth mentioning involved in retrieving the answers. A number of other problems, including simulation of various abstract machines, the boolean satisfiability problem, and the bounded version of the Post correspondence problem, have since been analyzed using DNA computing.
Due to its compactness, DNA also has a theoretical role in
cryptography, where in particular it allows unbreakable
one-time pads to be efficiently constructed and used.
In historical and anthropological study
Because DNA collects mutations over time, which are then passed down from parent to offspring, it contains information about processes that have occurred in the past, becoming in time ancient DNA. By comparing different DNA sequences, geneticists can attempt to infer the history of organisms.
If DNA sequences from different species are compared, then the resulting family tree, or phylogeny can be used to study the
evolution of these species. This field of phylogenetics is a powerful tool in evolutionary biology. If DNA sequences within a species are compared, population geneticists can glean information on the history of particular populations. This can be used in studies ranging from ecological genetics to
anthropology .
DNA has also been used to look at fairly recent issues of family relationships, such as establishing some manner of familial relationship between the descendants of Sally Hemings and the family of
Thomas Jefferson. This usage is closely related to the use of DNA in criminal investigations detailed above. Indeed, some criminal investigations have been solved when DNA from crime scenes has fortuitously matched relatives of the guilty individual.
References
;Citations
;General references
- Robert Olby; "The Path to The Double Helix: Discovery of DNA"; first published in October 1974 by MacMillan, with foreword by Francis Crick; ISBN 046681173; the definitive DNA textbook, revised in 1994, with a 9 page postscript.
- Ridley, Matt; Francis Crick: Discoverer of the Genetic Code first published in June 2006 in the USA and then to be in the UK September 2006, by HarperCollins Publishers; 192 pp, ISBN 006082333X
- Watson, James D. and Francis H.C. Crick. . Nature 171, 737 – 738, 25 April 1953.
- Watson, James D. DNA: The Secret of Life ISBN 0375415467.
- Watson, James D. . ISBN 0393950751
- Chomet, S. , DNA Genesis of a Discovery, Newman-Hemisphere Press, London, 1994.
- Delmonte, C.S. and Mann, L.R.B. . Current Science, 85 , 1564 – 1570, 10 December 2003.
- Miller, Kenneth R., and Levin, Joseph. Biology. Saddle River, New Jersey: Prentice Hall, 2002.
Further Reading
- Steven Rose, The Chemistry of Life, Penguin, ISBN 0140272739. A comprehensive introduction to biochemistry.
External links
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- Watch videos and participate in real-time chat with top scientists
- DNA from the Beginning Study Guide
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- DNA Articles and Information collected from various sources.
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