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A base pair (bp) is a fundamental unit of double-stranded
nucleic acids Nucleic acids are biopolymer Biopolymers are natural polymer A polymer (; Greek ''poly- Poly, from the Greek :wikt:πολύς, πολύς meaning "many" or "much", may refer to: Businesses * China Poly Group Corporation, a Chinese busin ...
consisting of two
nucleobase Nucleobases, also known as ''nitrogenous bases'' or often simply ''bases'', are nitrogen-containing biological compounds that form nucleosides Nucleosides are glycosylamines that can be thought of as nucleotide Nucleotides are organic mo ...
s bound to each other by
hydrogen bond A hydrogen bond (or H-bond) is a primarily electrostatic Electrostatics is a branch of physics Physics is the that studies , its , its and behavior through , and the related entities of and . "Physical science is that department ...

hydrogen bond
s. They form the building blocks of the
DNA Deoxyribonucleic acid (; DNA) is a molecule A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon rings. A molecule is an electrically Electricity is the set of physical ...

DNA
double helix and contribute to the folded structure of both DNA and
RNA Ribonucleic acid (RNA) is a polymer A polymer (; Greek ''wikt:poly-, poly-'', "many" + ''wikt:-mer, -mer'', "part") is a Chemical substance, substance or material consisting of very large molecules, or macromolecules, composed of many Re ...

RNA
. Dictated by specific
hydrogen bond A hydrogen bond (or H-bond) is a primarily electrostatic Electrostatics is a branch of physics Physics is the that studies , its , its and behavior through , and the related entities of and . "Physical science is that department ...

hydrogen bond
ing patterns, "Watson–Crick" base pairs (
guanine Guanine () (symbol A symbol is a mark, sign, or word In linguistics, a word of a spoken language can be defined as the smallest sequence of phonemes that can be uttered in isolation with semantic, objective or pragmatics, practical me ...

guanine
cytosine Cytosine () (symbol A symbol is a mark, sign, or word In linguistics, a word of a spoken language can be defined as the smallest sequence of phonemes that can be uttered in isolation with semantic, objective or pragmatics, practical ...

cytosine
and
adenine Adenine (A, Ade) is a nucleobase 230px, Pyrimidine nucleobases are simple ring molecules. Nucleobases, also known as ''nitrogenous bases'' or often simply ''bases'', are nitrogen-containing biological compounds that form nucleosides Nucleos ...

adenine
thymine Thymine () (symbol A symbol is a mark, sign, or word In linguistics, a word of a spoken language can be defined as the smallest sequence of phonemes that can be uttered in isolation with semantic, objective or pragmatics, practical m ...

thymine
) allow the DNA helix to maintain a regular helical structure that is subtly dependent on its
nucleotide sequence A nucleic acid sequence is a succession of bases signified by a series of a set of five different letters that indicate the order of nucleotides Nucleotides are organic molecules consisting of a nucleoside and a phosphate. They serve as monom ...

nucleotide sequence
. The
complementary A complement is often something that completes something else, or at least adds to it in some useful way. Thus it may be: * Complement (linguistics), a word or phrase having a particular syntactic role ** Subject complement, a word or phrase addi ...
nature of this based-paired structure provides a redundant copy of the
genetic information A nucleic acid sequence is a succession of bases signified by a series of a set of five different letters that indicate the order of nucleotides Nucleotides are organic molecules consisting of a nucleoside and a phosphate. They serve as monom ...
encoded within each strand of DNA. The regular structure and data redundancy provided by the DNA double helix make DNA well suited to the storage of genetic information, while base-pairing between DNA and incoming nucleotides provides the mechanism through which
DNA polymerase A DNA polymerase is a member of a family of enzyme Enzymes () are s that act as s (biocatalysts). Catalysts accelerate . The molecules upon which enzymes may act are called , and the enzyme converts the substrates into different molecules ...

DNA polymerase
replicates DNA and
RNA polymerase In molecular biology Molecular biology is the branch of biology that seeks to understand the molecule, molecular basis of biological activity in and between Cell (biology), cells, including biomolecule, molecular synthesis, modification, m ...

RNA polymerase
transcribes DNA into RNA. Many DNA-binding proteins can recognize specific base-pairing patterns that identify particular regulatory regions of genes. Intramolecular base pairs can occur within single-stranded nucleic acids. This is particularly important in RNA molecules (e.g.,
transfer RNA Transfer RNA (abbreviated tRNA and formerly referred to as sRNA, for soluble RNA) is an adaptor molecule A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon rings. A molecule is an e ...
), where Watson–Crick base pairs (guanine–cytosine and adenine–
uracil Uracil () (symbol A symbol is a mark, sign, or word In linguistics, a word of a spoken language can be defined as the smallest sequence of phonemes that can be uttered in isolation with semantic, objective or pragmatics, practical mea ...

uracil
) permit the formation of short double-stranded helices, and a wide variety of non–Watson–Crick interactions (e.g., G–U or A–A) allow RNAs to fold into a vast range of specific three-dimensional
structures A structure is an arrangement and organization of interrelated elements in a material object or system A system is a group of Interaction, interacting or interrelated elements that act according to a set of rules to form a unified whole. A sy ...

structures
. In addition, base-pairing between
transfer RNA Transfer RNA (abbreviated tRNA and formerly referred to as sRNA, for soluble RNA) is an adaptor molecule A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon rings. A molecule is an e ...
(tRNA) and
messenger RNA In molecular biology, messenger ribonucleic acid (mRNA) is a single-stranded molecule of RNA that corresponds to the genetic sequence of a gene, and is read by a ribosome in the process of Protein biosynthesis, synthesizing a protein. mRNA i ...
(mRNA) forms the basis for the
molecular recognition through hydrogen bonds The term molecular recognition refers to the specific interaction between two or more molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunneling microscopy image of pentacene molecules, which consist of linear cha ...
events that result in the nucleotide sequence of mRNA becoming
translated Translation is the communication of the meaning of a source-language text by means of an equivalent target-language text. The English language draws a terminological distinction (which does not exist in every language) between ''transla ...

translated
into the amino acid sequence of
protein Proteins are large biomolecule , showing alpha helices, represented by ribbons. This poten was the first to have its suckture solved by X-ray crystallography by Max Perutz and Sir John Cowdery Kendrew in 1958, for which they received a No ...

protein
s via the
genetic code The genetic code is the set of rules used by living cells Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Closed spaces * Monastic cell, a small room, hut, or cave in which a monk or rel ...

genetic code
. The size of an individual
gene In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mecha ...

gene
or an organism's entire
genome In the fields of molecular biology Molecular biology is the branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, M ...

genome
is often measured in base pairs because DNA is usually double-stranded. Hence, the number of total base pairs is equal to the number of nucleotides in one of the strands (with the exception of non-coding single-stranded regions of
telomere A telomere ( or , from and ) is a region of repetitive nucleotide Nucleotides are organic molecules , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compounds that contain carbon-h ...

telomere
s). The
haploid Ploidy () is the number of complete sets of chromosome A chromosome is a long DNA molecule with part or all of the genetic material of an organism. Most eukaryotic chromosomes include packaging proteins called histones which, aided by ...
human genome The human genome is a complete set of nucleic acid sequence A nucleic acid sequence is a succession of bases signified by a series of a set of five different letters that indicate the order of nucleotides Nucleotides are organic molecules c ...

human genome
(23
chromosome A chromosome is a long DNA molecule with part or all of the genome, genetic material of an organism. Most eukaryotic chromosomes include packaging proteins called histones which, aided by Chaperone (protein), chaperone proteins, bind to and ...

chromosome
s) is estimated to be about 3.2 billion bases long and to contain 20,000–25,000 distinct protein-coding genes. A
kilobase A base pair (bp) is a fundamental unit of double-stranded nucleic acids consisting of two nucleobases bound to each other by hydrogen bonds. They form the building blocks of the DNA double helix and contribute to the folded structure of both DNA ...
(kb) is a unit of measurement in
molecular biology Molecular biology is the branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, P ...
equal to 1000 base pairs of DNA or RNA. The total number of
DNA Deoxyribonucleic acid (; DNA) is a molecule A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon rings. A molecule is an electrically Electricity is the set of physical ...

DNA
base pairs on Earth is estimated at 5.0 with a weight of 50 billion
tonne The tonne ( or ; symbol: t) is a metric unit of mass equal to 1,000 kilogram The kilogram (also kilogramme) is the base unit of mass Mass is the physical quantity, quantity of ''matter'' in a physical body. It is also a meas ...
s. In comparison, the total
mass Mass is the quantity Quantity is a property that can exist as a multitude or magnitude, which illustrate discontinuity and continuity. Quantities can be compared in terms of "more", "less", or "equal", or by assigning a numerical value ...
of the
biosphere The biosphere (from Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is ap ...
has been estimated to be as much as 4  TtC (trillion tons of
carbon Carbon (from la, carbo "coal") is a with the C and 6. It is lic and —making four s available to form s. It belongs to group 14 of the periodic table. Carbon makes up only about 0.025 percent of Earth's crust. Three occur naturally, ...

carbon
).


Hydrogen bonding and stability

Top, a G.C base pair with three
hydrogen bond A hydrogen bond (or H-bond) is a primarily electrostatic Electrostatics is a branch of physics Physics is the that studies , its , its and behavior through , and the related entities of and . "Physical science is that department ...

hydrogen bond
s. Bottom, an A.T base pair with two hydrogen bonds. Non-covalent hydrogen bonds between the bases are shown as dashed lines. The wiggly lines stand for the connection to the pentose sugar and point in the direction of the minor groove.
Hydrogen bond A hydrogen bond (or H-bond) is a primarily electrostatic Electrostatics is a branch of physics Physics is the that studies , its , its and behavior through , and the related entities of and . "Physical science is that department ...

Hydrogen bond
ing is the chemical interaction that underlies the base-pairing rules described above. Appropriate geometrical correspondence of hydrogen bond donors and acceptors allows only the "right" pairs to form stably. DNA with high
GC-content In molecular biology Molecular biology is the branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, mo ...
is more stable than DNA with low GC-content. But, contrary to popular belief, the hydrogen bonds do not stabilize the DNA significantly; stabilization is mainly due to stacking interactions. The bigger
nucleobase Nucleobases, also known as ''nitrogenous bases'' or often simply ''bases'', are nitrogen-containing biological compounds that form nucleosides Nucleosides are glycosylamines that can be thought of as nucleotide Nucleotides are organic mo ...
s, adenine and guanine, are members of a class of double-ringed chemical structures called
purine Purine is a heterocyclic 125px, Pyridine, a heterocyclic compound A heterocyclic compound or ring structure is a cyclic compound that has atoms of at least two different chemical element, elements as members of its ring(s). Heterocyclic chemi ...

purine
s; the smaller nucleobases, cytosine and thymine (and uracil), are members of a class of single-ringed chemical structures called
pyrimidine Pyrimidine is an aromatic In chemistry Chemistry is the scientific Science () is a systematic enterprise that builds and organizes knowledge Knowledge is a familiarity or awareness, of someone or something, such as facts ...

pyrimidine
s. Purines are complementary only with pyrimidines: pyrimidine-pyrimidine pairings are energetically unfavorable because the molecules are too far apart for hydrogen bonding to be established; purine-purine pairings are energetically unfavorable because the molecules are too close, leading to overlap repulsion. Purine-pyrimidine base-pairing of AT or GC or UA (in RNA) results in proper duplex structure. The only other purine-pyrimidine pairings would be AC and GT and UG (in RNA); these pairings are mismatches because the patterns of hydrogen donors and acceptors do not correspond. The GU pairing, with two hydrogen bonds, does occur fairly often in
RNA Ribonucleic acid (RNA) is a polymer A polymer (; Greek ''wikt:poly-, poly-'', "many" + ''wikt:-mer, -mer'', "part") is a Chemical substance, substance or material consisting of very large molecules, or macromolecules, composed of many Re ...

RNA
(see
wobble base pair 225px, Wobble base pairs for inosine and guanine ">guanine.html" ;"title="inosine and guanine">inosine and guanine A wobble base pair is a pairing between two nucleotides in RNA molecules that does not follow Watson-Crick base pair rules. The fou ...
). Paired DNA and RNA molecules are comparatively stable at room temperature, but the two nucleotide strands will separate above a
melting point The melting point (or, rarely, liquefaction point) of a substance is the temperature Temperature ( ) is a physical quantity that expresses hot and cold. It is the manifestation of thermal energy Thermal radiation in visible light can b ...
that is determined by the length of the molecules, the extent of mispairing (if any), and the GC content. Higher GC content results in higher melting temperatures; it is, therefore, unsurprising that the genomes of
extremophile An extremophile (from Latin ' meaning "extreme" and Greek ' () meaning "love") is an organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual contiguous system that embodies the ...
organisms such as '' Thermus thermophilus'' are particularly GC-rich. On the converse, regions of a genome that need to separate frequently — for example, the promoter regions for often- transcribed genes — are comparatively GC-poor (for example, see
TATA box In molecular biology, the TATA box (also called the Goldberg–Hogness box) is a DNA sequence, sequence of DNA found in the Promoter (genetics), core promoter region of genes in archaea and eukaryotes. The bacterial homolog of the TATA box is c ...
). GC content and melting temperature must also be taken into account when designing primers for
PCR Polymerase chain reaction (PCR) is a method widely used to rapidly make millions to billions of copies (complete copies or partial copies) of a specific DNA sample, allowing scientists to take a very small sample of DNA and amplify it (or a pa ...

PCR
reactions.


Examples

The following DNA sequences illustrate pair double-stranded patterns. By convention, the top strand is written from the
5' end Directionality, in molecular biology Molecular biology is the branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecul ...
to the
3' end Directionality, in molecular biology and biochemistry Biochemistry or biological chemistry, is the study of chemical processes within and relating to living organisms. A sub-discipline of both chemistry and biology, biochemistry may be divide ...
; thus, the bottom strand is written 3' to 5'. :A base-paired DNA sequence: :: :: :The corresponding RNA sequence, in which
uracil Uracil () (symbol A symbol is a mark, sign, or word In linguistics, a word of a spoken language can be defined as the smallest sequence of phonemes that can be uttered in isolation with semantic, objective or pragmatics, practical mea ...

uracil
is substituted for thymine in the RNA strand: :: ::


Base analogs and intercalators

Chemical analogs of nucleotides can take the place of proper nucleotides and establish non-canonical base-pairing, leading to errors (mostly
point mutation A point mutation or substitution is a genetic mutation where a single nucleotide base is changed, inserted or deleted from a DNA or RNA sequence of an organism's genome. Point mutations have a variety of effects on the downstream protein product ...

point mutation
s) in
DNA replication In molecular biology Molecular biology is the branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, mo ...

DNA replication
and
DNA transcription Transcription is the process of copying a segment of DNA into RNA. The segments of DNA transcribed into RNA molecules that can encode protein Proteins are large biomolecules or macromolecules that are comprised of one or more long chains of ...
. This is due to their isosteric chemistry. One common mutagenic base analog is 5-bromouracil, which resembles thymine but can base-pair to guanine in its
enol Enols, or more formally, alkenols, are a type of reactive structure or chemical intermediate, intermediate in organic chemistry that is represented as an alkene (olefin) with a hydroxyl group attached to one end of the alkene double bond. The term ...

enol
form. Other chemicals, known as
DNA intercalators
DNA intercalators
, fit into the gap between adjacent bases on a single strand and induce
frameshift mutation A frameshift mutation (also called a framing error or a reading frame shift) is a genetic mutation Image:Darwin Hybrid Tulip Mutation 2014-05-01.jpg, A tulip flower exhibiting a partially yellow petal due to a mutation in its genes In biology ...

frameshift mutation
s by "masquerading" as a base, causing the DNA replication machinery to skip or insert additional nucleotides at the intercalated site. Most intercalators are large polyaromatic compounds and are known or suspected
carcinogen A carcinogen is any substance, radionuclide A radionuclide (radioactive nuclide, radioisotope or radioactive isotope) is a nuclide A nuclide (or nucleide, from atomic nucleus, nucleus, also known as nuclear species) is a class of atoms characte ...
s. Examples include
ethidium bromide Ethidium bromide (or homidium bromide, chloride salt homidium chloride) is an intercalating agent commonly used as a fluorescent tag In molecular biology and biotechnology, a fluorescent tag, also known as a fluorescent label or fluorescent pr ...

ethidium bromide
and
acridine Acridine is an organic compound and a nitrogen heterocycle with the formula C13H9N. Acridines are substituted derivatives of the parent ring. It is a planar molecule that is structurally related to anthracene with one of the central CH groups r ...

acridine
.


Unnatural base pair (UBP)

An unnatural base pair (UBP) is a designed subunit (or
nucleobase Nucleobases, also known as ''nitrogenous bases'' or often simply ''bases'', are nitrogen-containing biological compounds that form nucleosides Nucleosides are glycosylamines that can be thought of as nucleotide Nucleotides are organic mo ...
) of
DNA Deoxyribonucleic acid (; DNA) is a molecule A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon rings. A molecule is an electrically Electricity is the set of physical ...

DNA
which is created in a laboratory and does not occur in nature. DNA sequences have been described which use newly created nucleobases to form a third base pair, in addition to the two base pairs found in nature, A-T (
adenine Adenine (A, Ade) is a nucleobase 230px, Pyrimidine nucleobases are simple ring molecules. Nucleobases, also known as ''nitrogenous bases'' or often simply ''bases'', are nitrogen-containing biological compounds that form nucleosides Nucleos ...

adenine
thymine Thymine () (symbol A symbol is a mark, sign, or word In linguistics, a word of a spoken language can be defined as the smallest sequence of phonemes that can be uttered in isolation with semantic, objective or pragmatics, practical m ...

thymine
) and G-C (
guanine Guanine () (symbol A symbol is a mark, sign, or word In linguistics, a word of a spoken language can be defined as the smallest sequence of phonemes that can be uttered in isolation with semantic, objective or pragmatics, practical me ...

guanine
cytosine Cytosine () (symbol A symbol is a mark, sign, or word In linguistics, a word of a spoken language can be defined as the smallest sequence of phonemes that can be uttered in isolation with semantic, objective or pragmatics, practical ...

cytosine
). A few research groups have been searching for a third base pair for DNA, including teams led by Steven A. Benner, Philippe Marliere,
Floyd E. Romesberg Floyd E. Romesberg is an American biotechnologist, biochemist, and geneticist formerly at Scripps Research Scripps Research, previously known as The Scripps Research Institute (TSRI), is a nonprofit American medical research Medical rese ...
and Ichiro Hirao. Some new base pairs based on alternative hydrogen bonding, hydrophobic interactions and metal coordination have been reported. In 1989 Steven Benner (then working at the Swiss Federal Institute of Technology in Zurich) and his team led with modified forms of cytosine and guanine into DNA molecules ''in vitro''. The nucleotides, which encoded RNA and proteins, were successfully replicated ''in vitro''. Since then, Benner's team has been trying to engineer cells that can make foreign bases from scratch, obviating the need for a feedstock. In 2002, Ichiro Hirao's group in Japan developed an unnatural base pair between 2-amino-8-(2-thienyl)purine (s) and pyridine-2-one (y) that functions in transcription and translation, for the site-specific incorporation of non-standard amino acids into proteins. In 2006, they created 7-(2-thienyl)imidazo ,5-byridine (Ds) and pyrrole-2-carbaldehyde (Pa) as a third base pair for replication and transcription. Afterward, Ds and 4- -(6-aminohexanamido)-1-propynyl2-nitropyrrole (Px) was discovered as a high fidelity pair in PCR amplification. In 2013, they applied the Ds-Px pair to DNA aptamer generation by ''in vitro'' selection (SELEX) and demonstrated the genetic alphabet expansion significantly augment DNA aptamer affinities to target proteins. In 2012, a group of American scientists led by Floyd Romesberg, a chemical biologist at the
Scripps Research Institute Scripps Research, previously known as The Scripps Research Institute (TSRI), is a nonprofit American medical research Medical research (or biomedical research), also known as experimental medicine, encompasses a wide array of research, exten ...
in San Diego, California, published that his team designed an unnatural base pair (UBP). The two new artificial nucleotides or ''Unnatural Base Pair'' (UBP) were named
d5SICS d5SICS is an artificial nucleoside containing 6-methylisoquinoline-1-thione-2-yl group instead of a base. It Base pair#Unnatural base pair (UBP), pairs up with dNaM in a hydrophobic interaction. It was not able to be removed by the error-correctin ...

d5SICS
and
dNaM dNaM is an artificial nucleobase Nucleobases, also known as ''nitrogenous bases'' or often simply ''bases'', are nitrogen-containing biological compounds that form nucleosides Nucleosides are glycosylamines that can be thought of as nucleo ...

dNaM
. More technically, these artificial
nucleotide Nucleotides are organic molecules , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen chemical bond, bonds. Due to carbon's ability to Catenation, ...

nucleotide
s bearing hydrophobic
nucleobase Nucleobases, also known as ''nitrogenous bases'' or often simply ''bases'', are nitrogen-containing biological compounds that form nucleosides Nucleosides are glycosylamines that can be thought of as nucleotide Nucleotides are organic mo ...
s, feature two fused
aromatic rings forms of benzene (top) combine to produce an average structure (bottom) In chemistry, aromaticity is a property of cyclic compound, cyclic (ring (chemistry), ring-shaped), plane (geometry), planar (flat) structures with pi bonds in Resonance (che ...
that form a (d5SICS–dNaM) complex or base pair in DNA. His team designed a variety of ''in vitro'' or "test tube" templates containing the unnatural base pair and they confirmed that it was efficiently replicated with high fidelity in virtually all sequence contexts using the modern standard ''in vitro'' techniques, namely and PCR-based applications. Their results show that for PCR and PCR-based applications, the d5SICS–dNaM unnatural base pair is functionally equivalent to a natural base pair, and when combined with the other two natural base pairs used by all organisms, A–T and G–C, they provide a fully functional and expanded six-letter "genetic alphabet". In 2014 the same team from the Scripps Research Institute reported that they synthesized a stretch of circular DNA known as a
plasmid A plasmid is a small, extrachromosomal DNA Extrachromosomal DNA (abbreviated ecDNA) is any DNA that is found off the chromosome A chromosome is a long DNA molecule with part or all of the genetic material of an organism. Most eukaryo ...
containing natural T-A and C-G base pairs along with the best-performing UBP Romesberg's laboratory had designed and inserted it into cells of the common bacterium '''' that successfully replicated the unnatural base pairs through multiple generations. The
transfection Transfection is the process of deliberately introducing naked or purified nucleic acids into eukaryotic Eukaryotes () are organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any indi ...

transfection
did not hamper the growth of the ''E. coli'' cells and showed no sign of losing its unnatural base pairs to its natural
DNA repair DNA repair is a collection of processes by which a cell identifies and corrects damage to the DNA Deoxyribonucleic acid (; DNA) is a molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunneling microscopy image of pentacene mol ...

DNA repair
mechanisms. This is the first known example of a living organism passing along an expanded genetic code to subsequent generations. Romesberg said he and his colleagues created 300 variants to refine the design of nucleotides that would be stable enough and would be replicated as easily as the natural ones when the cells divide. This was in part achieved by the addition of a supportive that expresses a nucleotide triphosphate transporter which efficiently imports the triphosphates of both d5SICSTP and dNaMTP into ''E. coli'' bacteria. Then, the natural bacterial replication pathways use them to accurately replicate a
plasmid A plasmid is a small, extrachromosomal DNA Extrachromosomal DNA (abbreviated ecDNA) is any DNA that is found off the chromosome A chromosome is a long DNA molecule with part or all of the genetic material of an organism. Most eukaryo ...
containing d5SICS–dNaM. Other researchers were surprised that the bacteria replicated these human-made DNA subunits. The successful incorporation of a third base pair is a significant breakthrough toward the goal of greatly expanding the number of
amino acid Amino acids are organic compound In , organic compounds are generally any s that contain - . Due to carbon's ability to (form chains with other carbon s), millions of organic compounds are known. The study of the properties, reactions, a ...

amino acid
s which can be encoded by DNA, from the existing 20 amino acids to a theoretically possible 172, thereby expanding the potential for living organisms to produce novel
protein Proteins are large biomolecule , showing alpha helices, represented by ribbons. This poten was the first to have its suckture solved by X-ray crystallography by Max Perutz and Sir John Cowdery Kendrew in 1958, for which they received a No ...

protein
s. The artificial strings of DNA do not encode for anything yet, but scientists speculate they could be designed to manufacture new proteins which could have industrial or pharmaceutical uses. Experts said the synthetic DNA incorporating the unnatural base pair raises the possibility of life forms based on a different DNA code.


Length measurements

The following abbreviations are commonly used to describe the length of a D/R: * bp = base pair(s)—one bp corresponds to approximately 3.4 (340 pm) of length along the strand, and to roughly 618 or 643 daltons for DNA and RNA respectively. * kb (= kbp) = kilo base pairs = 1,000 bp * Mb (= Mbp) = mega base pairs = 1,000,000 bp * Gb = giga base pairs = 1,000,000,000 bp. For single-stranded DNA/RNA, units of
nucleotide Nucleotides are organic molecules , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen chemical bond, bonds. Due to carbon's ability to Catenation, ...

nucleotide
s are used—abbreviated nt (or knt, Mnt, Gnt)—as they are not paired. To distinguish between units of
computer storage Computer data storage is a technology consisting of computer components and Data storage device, recording media that are used to retain digital data (computing), data. It is a core function and fundamental component of computers. The cent ...
and bases, kbp, Mbp, Gbp, etc. may be used for base pairs. The
centimorgan In genetics Genetics is a branch of biology concerned with the study of genes, genetic variation, and heredity in organisms.Hartl D, Jones E (2005) Though heredity had been observed for millennia, Gregor Mendel, Moravia, Moravian scientist an ...
is also often used to imply distance along a chromosome, but the number of base pairs it corresponds to varies widely. In the human genome, the centimorgan is about 1 million base pairs.


See also

* List of Y-DNA single-nucleotide polymorphisms * Non-canonical base pairing *
Chargaff's rules Chargaff's rules state that DNA from any species of any organism should have a 1:1 protein stoichiometry ratio (base pair rule) of purine Purine is a heterocyclic compound, heterocyclic aromatic organic compound that consists of two rings (pyri ...


References


Further reading

* (See esp. ch. 6 and 9) * * *


External links


DAN
webserver version of the EMBOSS tool for calculating melting temperatures {{DEFAULTSORT:Base Pair Nucleobases Molecular genetics Nucleic acids