Molecular biologists use several shorthand terms when referring to nucleic acid

Nucleic acid

Nucleic acids are biological molecules essential for life, and include DNA and RNA . Together with proteins, nucleic acids make up the most important macromolecules; each is found in abundance in all living things, where they function in encoding, transmitting and expressing genetic information...

 molecules, such as DNA

DNA

Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...

 and RNA

RNA

Ribonucleic acid , or RNA, is one of the three major macromolecules that are essential for all known forms of life....

, collectively referred to as nucleic acid nomenclature.

The most common is the representation of the base pair

Base pair

In molecular biology and genetics, the linking between two nitrogenous bases on opposite complementary DNA or certain types of RNA strands that are connected via hydrogen bonds is called a base pair...

s as letters—an adenine

Adenine

Adenine is a nucleobase with a variety of roles in biochemistry including cellular respiration, in the form of both the energy-rich adenosine triphosphate and the cofactors nicotinamide adenine dinucleotide and flavin adenine dinucleotide , and protein synthesis, as a chemical component of DNA...

 nucleotide

Nucleotide

Nucleotides are molecules that, when joined together, make up the structural units of RNA and DNA. In addition, nucleotides participate in cellular signaling , and are incorporated into important cofactors of enzymatic reactions...

 is abbreviated as A, guanine

Guanine

Guanine is one of the four main nucleobases found in the nucleic acids DNA and RNA, the others being adenine, cytosine, and thymine . In DNA, guanine is paired with cytosine. With the formula C5H5N5O, guanine is a derivative of purine, consisting of a fused pyrimidine-imidazole ring system with...

 as G, cytosine

Cytosine

Cytosine is one of the four main bases found in DNA and RNA, along with adenine, guanine, and thymine . It is a pyrimidine derivative, with a heterocyclic aromatic ring and two substituents attached . The nucleoside of cytosine is cytidine...

 as C, thymine

Thymine

Thymine is one of the four nucleobases in the nucleic acid of DNA that are represented by the letters G–C–A–T. The others are adenine, guanine, and cytosine. Thymine is also known as 5-methyluracil, a pyrimidine nucleobase. As the name suggests, thymine may be derived by methylation of uracil at...

 as T, and in RNA, uracil

Uracil

Uracil is one of the four nucleobases in the nucleic acid of RNA that are represented by the letters A, G, C and U. The others are adenine, cytosine, and guanine. In RNA, uracil binds to adenine via two hydrogen bonds. In DNA, the uracil nucleobase is replaced by thymine.Uracil is a common and...

 as U.

Additionally, the positions of the carbon

Carbon

Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...

s in the ribose

Ribose

Ribose is an organic compound with the formula C5H10O5; specifically, a monosaccharide with linear form H––4–H, which has all the hydroxyl groups on the same side in the Fischer projection....

 sugar that forms the backbone of the nucleic acid chain are numbered, and are used to indicate the direction of nucleic acids (5'->3' versus 3'->5'), see directionality

Directionality (molecular biology)

Directionality, in molecular biology and biochemistry, is the end-to-end chemical orientation of a single strand of nucleic acid. The chemical convention of naming carbon atoms in the nucleotide sugar-ring numerically gives rise to a 5′-end and a 3′-end...

.

Expanded letter code

In addition to the conventional GATC symbols, there is an expanded letter code to indicate a position within a sequence that may be flexible when defining sequences.

Letter	Nucleotide(s) included
A	A
T	T
G	G
C	C
R	G or A
Y	T or C
M	A or C
K	G or T
S	G or C
W	A or T
H	A or C or T
B	G or T or C
V	G or C or A
D	G or T or A
N	G or T or A or C

For example, if the sequences known to bind protein X are known to be AAAAAAGAAA, AAAAAACAAA, AAAAAATAAA, and AAAAAAAAAA, this can be expressed as AAAAAANAAA.

Triple Helix Base Pairing

Watson and Crick base pairs are indicated by a "•" or a "-" or a "." (example: A•T, or poly(rC)•2poly(rC)).

Hoogsteen triple helix

Triple helix

In geometry, a triple helix is a set of three congruent geometrical helices with the same axis, differing by a translation along the axis. Structures in the form of a triple helix include:* collagen helix...

 base pairs are indicated by a "*" or a ":" (example: C•G*G+, or T•A*T, or C•G*G, or T•A*A).

See also

• DNA replication
  DNA replication
  DNA replication is a biological process that occurs in all living organisms and copies their DNA; it is the basis for biological inheritance. The process starts with one double-stranded DNA molecule and produces two identical copies of the molecule...
  
  
• Nucleotide
  Nucleotide
  Nucleotides are molecules that, when joined together, make up the structural units of RNA and DNA. In addition, nucleotides participate in cellular signaling , and are incorporated into important cofactors of enzymatic reactions...