Nucleic acids are biopolymers, or small biomolecules, essential to all
known forms of life. They are composed of nucleotides, which are
monomers made of three components: a 5-carbon sugar, a phosphate group
and a nitrogenous base. If the sugar is a compound ribose, the polymer
RNA (ribonucleic acid); if the sugar is derived from ribose as
deoxyribose, the polymer is
DNA (deoxyribonucleic acid).
Nucleic acids are the most important of all biomolecules. They are
found in abundance in all living things, where they function to create
and encode and then store information in the nucleus of every living
cell of every life-form organism on Earth. In turn, they function to
transmit and express that information inside and outside the cell
nucleus—to the interior operations of the cell and ultimately to the
next generation of each living organism. The encoded information is
contained and conveyed via the nucleic acid sequence, which provides
the 'ladder-step' ordering of nucleotides within the molecules of RNA
Strings of nucleotides are bonded to form helical
backbones—typically, one for RNA, two for DNA—and assembled into
chains of base-pairs selected from the five primary, or canonical,
nucleobases, which are: adenine, cytosine, guanine, thymine, and
uracil; note, thymine occurs only in
DNA and uracil only in RNA. Using
amino acids and the process known as protein synthesis, the
specific sequencing in
DNA of these nucleobase-pairs enables storing
and transmitting coded instructions as genes. In RNA, base-pair
sequencing provides for manufacturing new proteins that determine the
frames and parts and most chemical processes of all life forms.
2 Occurrence and nomenclature
3 Molecular composition and size
6.1 Deoxyribonucleic acid
6.2 Ribonucleic acid
6.3 Artificial nucleic acid
7 See also
11 Further reading
12 External links
Nuclein were discovered by
Friedrich Miescher in 1869.
Richard Altmann discovered that nuclein has acidic properties,
and it became called nucleic acid
In 1938 Astbury and Bell published the first X-ray diffraction pattern
In 1953 Watson and Crick determined the structure of DNA.
Experimental studies of nucleic acids constitute a major part of
modern biological and medical research, and form a foundation for
genome and forensic science, and the biotechnology and pharmaceutical
Occurrence and nomenclature
The term nucleic acid is the overall name for
DNA and RNA, members of
a family of biopolymers, and is synonymous with polynucleotide.
Nucleic acids were named for their initial discovery within the
nucleus, and for the presence of phosphate groups (related to
phosphoric acid). Although first discovered within the nucleus of
eukaryotic cells, nucleic acids are now known to be found in all life
forms including within bacteria, archaea, mitochondria, chloroplasts,
viruses, and viroids. (note: there is debate as to whether viruses
are living or non-living). All living cells contain both
DNA and RNA
(except some cells such as mature red blood cells), while viruses
DNA or RNA, but usually not both. The basic
component of biological nucleic acids is the nucleotide, each of which
contains a pentose sugar (ribose or deoxyribose), a phosphate group,
and a nucleobase. Nucleic acids are also generated within the
laboratory, through the use of enzymes (
and by solid-phase chemical synthesis. The chemical methods also
enable the generation of altered nucleic acids that are not found in
nature, for example peptide nucleic acids.
Molecular composition and size
Nucleic acids are generally very large molecules. Indeed, DNA
molecules are probably the largest individual molecules known.
Well-studied biological nucleic acid molecules range in size from 21
nucleotides (small interfering RNA) to large chromosomes (human
chromosome 1 is a single molecule that contains 247 million base
In most cases, naturally occurring
DNA molecules are double-stranded
RNA molecules are single-stranded. There are numerous
exceptions, however—some viruses have genomes made of
RNA and other viruses have single-stranded DNA
genomes, and, in some circumstances, nucleic acid structures with
three or four strands can form.
Nucleic acids are linear polymers (chains) of nucleotides. Each
nucleotide consists of three components: a purine or pyrimidine
nucleobase (sometimes termed nitrogenous base or simply base), a
pentose sugar, and a phosphate group. The substructure consisting of a
nucleobase plus sugar is termed a nucleoside.
Nucleic acid types
differ in the structure of the sugar in their nucleotides–DNA
contains 2'-deoxyribose while
RNA contains ribose (where the only
difference is the presence of a hydroxyl group). Also, the nucleobases
found in the two nucleic acid types are different: adenine, cytosine,
and guanine are found in both
RNA and DNA, while thymine occurs in DNA
and uracil occurs in RNA.
The sugars and phosphates in nucleic acids are connected to each other
in an alternating chain (sugar-phosphate backbone) through
phosphodiester linkages. In conventional nomenclature, the carbons
to which the phosphate groups attach are the 3'-end and the 5'-end
carbons of the sugar. This gives nucleic acids directionality, and the
ends of nucleic acid molecules are referred to as 5'-end and 3'-end.
The nucleobases are joined to the sugars via an N-glycosidic linkage
involving a nucleobase ring nitrogen (N-1 for pyrimidines and N-9 for
purines) and the 1' carbon of the pentose sugar ring.
Non-standard nucleosides are also found in both
usually arise from modification of the standard nucleosides within the
DNA molecule or the primary (initial)
RNA transcript. Transfer RNA
(tRNA) molecules contain a particularly large number of modified
Double-stranded nucleic acids are made up of complementary sequences,
in which extensive Watson-Crick base pairing results in a highly
repeated and quite uniform double-helical three-dimensional
structure. In contrast, single-stranded
DNA molecules are
not constrained to a regular double helix, and can adopt highly
complex three-dimensional structures that are based on short stretches
of intramolecular base-paired sequences including both Watson-Crick
and noncanonical base pairs, and a wide range of complex tertiary
Nucleic acid molecules are usually unbranched, and may occur as linear
and circular molecules. For example, bacterial chromosomes, plasmids,
mitochondrial DNA, and chloroplast
DNA are usually circular
DNA molecules, while chromosomes of the eukaryotic
nucleus are usually linear double-stranded
DNA molecules. Most RNA
molecules are linear, single-stranded molecules, but both circular and
branched molecules can result from
RNA splicing reactions. The
total amount of pyrimidine is equal to the total amount of purines.
The diameter of the helix is about 20A.
Nucleic acid sequence
RNA molecule differs from another primarily in the sequence
Nucleotide sequences are of great importance in
biology since they carry the ultimate instructions that encode all
biological molecules, molecular assemblies, subcellular and cellular
structures, organs, and organisms, and directly enable cognition,
memory, and behavior (see Genetics). Enormous efforts have gone into
the development of experimental methods to determine the nucleotide
sequence of biological
RNA molecules, and today
hundreds of millions of nucleotides are sequenced daily at genome
centers and smaller laboratories worldwide. In addition to maintaining
the GenBank nucleic acid sequence database, the National Center for
Biotechnology Information (NCBI, https://www.ncbi.nlm.nih.gov)
provides analysis and retrieval resources for the data in GenBank and
other biological data made available through the NCBI web site.
Main article: DNA
Deoxyribonucleic acid (DNA) is a nucleic acid containing the genetic
instructions used in the development and functioning of all known
living organisms. The
DNA segments carrying this genetic information
are called genes. Likewise, other
DNA sequences have structural
purposes, or are involved in regulating the use of this genetic
information. Along with
RNA and proteins,
DNA is one of the three
major macromolecules that are essential for all known forms of life.
DNA consists of two long polymers of simple units called nucleotides,
with backbones made of sugars and phosphate groups joined by ester
bonds. These two strands run in opposite directions to each other and
are, therefore, anti-parallel. Attached to each sugar is one of four
types of molecules called nucleobases (informally, bases). It is the
sequence of these four nucleobases along the backbone that encodes
information. This information is read using the genetic code, which
specifies the sequence of the amino acids within proteins. The code is
read by copying stretches of
DNA into the related nucleic acid
a process called transcription. Within cells
DNA is organized into
long structures called chromosomes. During cell division these
chromosomes are duplicated in the process of
providing each cell its own complete set of chromosomes. Eukaryotic
organisms (animals, plants, fungi, and protists) store most of their
DNA inside the cell nucleus and some of their
DNA in organelles, such
as mitochondria or chloroplasts. In contrast, prokaryotes (bacteria
and archaea) store their
DNA only in the cytoplasm. Within the
chromosomes, chromatin proteins such as histones compact and organize
DNA. These compact structures guide the interactions between
other proteins, helping control which parts of the
Main article: RNA
Ribonucleic acid (RNA) functions in converting genetic information
from genes into the amino acid sequences of proteins. The three
universal types of
RNA include transfer
RNA (tRNA), messenger RNA
(mRNA), and ribosomal
RNA (rRNA). Messenger
RNA acts to carry genetic
sequence information between
DNA and ribosomes, directing protein
RNA is a major component of the ribosome, and
catalyzes peptide bond formation. Transfer
RNA serves as the carrier
molecule for amino acids to be used in protein synthesis, and is
responsible for decoding the mRNA. In addition, many other classes of
RNA are now known.
Artificial nucleic acid
Nucleic acid analogue
Artificial nucleic acid analogues have been designed and synthesized
by chemists, and include peptide nucleic acid, morpholino- and locked
nucleic acid, glycol nucleic acid, and threose nucleic acid. Each of
these is distinguished from naturally occurring
RNA by changes
to the backbone of the molecules.
Comparison of nucleic acid simulation software
History of biochemistry
History of molecular biology
Nucleic acid methods
Nucleic acid structure
Nucleic acid thermodynamics
Quantification of nucleic acids
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Nucleic Acids Research journal
Nucleic Acids Book (free online book on the chemistry and biology of
Types of nucleic acids
precursor, heterogenous nuclear
Small Cajal Body RNAs
Trans-acting small interfering
Molecular and cellular biology portal