Everything about Nucleic Acids totally explained
A
nucleic acid is a
macromolecule composed of chains of monomeric
nucleotide. In
biochemistry these
molecules carry
genetic information or form structures within
cells. The most common nucleic acids are
deoxyribonucleic acid (DNA) and
ribonucleic acid (RNA). Nucleic acids are universal in living things, as they're found in all cells and
viruses. Nucleic acid was first discovered by
Friedrich Miescher.
Artificial nucleic acids include
peptide nucleic acid (PNA),
Morpholino and
locked nucleic acid (LNA), as well as
glycol nucleic acid (GNA) and
threose nucleic acid (TNA). Each of these is distinguished from naturally-occurring DNA or RNA by changes to the backbone of the molecule.
Chemical structure
The term "nucleic acid" is the generic name for a family of
biopolymers, named for their role in the
cell nucleus. The
monomers from which nucleic acids are constructed are called
nucleotides.
Each nucleotide consists of three components: a nitrogenous
heterocyclic base, which is either a
purine or a
pyrimidine; a
pentose sugar; and a
phosphate group. Nucleic acid types differ in the structure of the sugar in their nucleotides - DNA contains 2-
deoxyriboses while RNA contains
ribose (where the only difference is the presence of a
hydroxyl group). Also, the nitrogenous bases found in the two nucleic acid types are different:
adenine,
cytosine, and
guanine are found in both RNA and DNA, while
thymine only occurs in DNA and
uracil only occurs in RNA. Other rare nucleic acid bases can occur, for example
inosine in strands of mature
transfer RNA.
Nucleic acids are usually either single-stranded or double-stranded, though structures with three or more strands can form. A double-stranded nucleic acid consists of two single-stranded nucleic acids held together by
hydrogen bonds, such as in the DNA double helix. In contrast, RNA is usually single-stranded, but any given strand may fold back upon itself to form secondary structure as in tRNA and rRNA. Within cells, DNA is usually double-stranded, though some
viruses have single-stranded DNA as their genome.
Retroviruses have single-stranded RNA as their genome.
The sugars and phosphates in nucleic acids are connected to each other in an alternating chain, linked by shared oxygens, forming a
phosphodiester bond. 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 polarity. The bases extend from a glycosidic linkage to the 1' carbon of the pentose sugar ring. Bases are joined through N-1 of pyrimidines and N-9 of purines to 1' carbon of ribose through N-β glycosyl bond.
Types of nucleic acids
Ribonucleic acid
» Main article: RNA
Ribonucleic acid, or RNA, is a nucleic acid polymer consisting of nucleotide monomers, which plays several important roles in the processes of translating genetic information from deoxyribonucleic acid (DNA) into proteins. RNA acts as a messenger between DNA and the protein synthesis complexes known as ribosomes, forms vital portions of ribosomes, and serves as an essential carrier molecule for amino acids to be used in protein synthesis.
Deoxyribonucleic acid
» Main article: DNA
Deoxyribonucleic acid (DNA) is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms. The main role of DNA molecules is the long-term storage of information and DNA is often compared to a set of blueprints, since it contains the instructions needed to construct other components of cells, such as proteins and RNA molecules. The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in regulating the use of this genetic information.
Nucleic acid components
Nucleobases
» Main article: Nucleobase
Nucleobases are
heterocyclic aromatic organic compounds containing
nitrogen atoms. Nucleobases are the parts of
RNA and
DNA involved in
base pairing.
Cytosine,
guanine,
adenine,
thymine are found predominantly in DNA, while in RNA
uracil replaces
thymine. These are abbreviated as C, G, A, T, U, respectively.
Nucleobases are
complementary, and when forming base pairs, must always join accordingly: cytosine-guanine, adenine-thymine (adenine-uracil when RNA). The strength of the interaction between cytosine and guanine is stronger than between adenine and thymine because the former pair has three hydrogen bonds joining them while the latter pair have only two. Thus, the higher the GC content of double-stranded DNA, the more stable the molecule and the higher the
melting temperature.
Two main nucleobase classes exist, named for the molecule which forms their skeleton. These are the double-ringed
purines and single-ringed
pyrimidines. Adenine and guanine are purines (abbreviated as R), while cytosine, thymine, and uracil are all pyrimidines (abbreviated as Y).
Hypoxanthine and
xanthine are mutant forms of adenine and guanine, respectively, created through
mutagen presence, through deamination (replacement of the amine-group with a hydroxyl-group). These are abbreviated HX and X.
Nucleosides
» Main article: Nucleoside
Nucleosides are
glycosylamines made by attaching a
nucleobase (often referred to simply as bases) to a
ribose or
deoxyribose (
sugar) ring. In short, a nucleoside is a base linked to sugar. The names derive from the nucleobase names. The nucleosides commonly occurring in DNA and RNA include
cytidine,
uridine,
adenosine,
guanosine and
thymidine. When a phosphate is added to a nucleoside (by
phosphorylated by a specific
kinase enzyme), a nucleotide is produced.
Nucleoside analogues, such as
acyclovir, are used as
antiviral agents.
Nucleotides and deoxynucleotides
» Main article: Nucleotide
A nucleotide consists of a nucleoside and one or more
phosphate groups. Nucleotides are the
monomers of
RNA and
DNA, as well as forming the structural units of several important
cofactors -
CoA,
flavin adenine dinucleotide,
flavin mononucleotide,
adenosine triphosphate and
nicotinamide adenine dinucleotide phosphate. In the
cell nucleotides play important roles in
metabolism, and signaling.
Nucleotides are named after the nucleoside on which they're based, in conjunction with the number of phosphates they contain, for example:
Further Information
Get more info on 'Nucleic Acids'.
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