Nucleic acid | Definition, Function, Structure, & Types

chemical compound

printPrint

Please select which sections you would like to print:

verifiedCite

While every effort has been made to follow citation style rules, there may be some discrepancies.Please refer to the appropriate style manual or other sources if you have any questions.

Select Citation Style

Feedback

Thank you for your feedback

Our editors will review what you’ve submitted and determine whether to revise the article.

What are nucleic acids?

Nucleic acids are naturally occurring chemical compounds that serve as the primary information-carrying molecules in cells. They play an especially important role in directing protein synthesis. The two main classes of nucleic acids are deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).

What is the basic structure of a nucleic acid?

Nucleic acids are long chainlike molecules composed of a series of nearly identical building blocks callednucleotides. Eachnucleotideconsists of a nitrogen-containing aromatic base attached to a pentose (five-carbon)sugar, which is in turn attached to aphosphategroup.

What nitrogen-containing bases occur in nucleic acids?

Each nucleic acid contains four of five possible nitrogen-containingbases:adenine(A),guanine(G),cytosine(C),thymine(T), anduracil(U). A and G are categorized aspurines, andC, T, and U are calledpyrimidines. All nucleic acids contain the bases A, C, and G; T, however, is found only in DNA, while U is found in RNA.

When were nucleic acids discovered?

Nucleic acids were discovered in 1869 by Swiss biochemist Friedrich Miescher.

nucleic acid, naturally occurring chemical compound that serves as the main information-carrying molecule of the cell and that directs the process of protein synthesis, thereby determining the inherited characteristics of every living thing. Nucleic acids are further defined by their ability to be broken down to yield phosphoric acid, sugars, and a mixture of organic bases (purines and pyrimidines).

The two main classes of nucleic acids are deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). DNA is the master blueprint for life and constitutes the genetic material in all free-living organisms and most viruses. RNA is the genetic material of certain viruses, but it is also found in all living cells, where it plays an important role in certain processes, such as the making of proteins.

Nucleotides: building blocks of nucleic acids

Basic structure

Nucleic acids are polynucleotides—that is, long chainlike molecules composed of a series of nearly identical building blocks called nucleotides. Each nucleotide consists of a nitrogen-containing aromatic base attached to a pentose (five-carbon) sugar, which is in turn attached to a phosphate group.

Each nucleic acid contains four of five possible nitrogen-containing bases: adenine (A), guanine (G), cytosine (C), thymine (T), and uracil (U). A and G are categorized as purines, and C, T, and U are collectively called pyrimidines. All nucleic acids contain the bases A, C, and G; T, however, is found only in DNA, while U is found in RNA.

The pentose sugar in DNA (2′-deoxyribose) differs from the sugar in RNA (ribose) by the absence of a hydroxyl group (―OH) on the 2′ carbon of the sugar ring. Without an attached phosphate group, the sugar attached to one of the bases is known as a nucleoside. The phosphate group connects successive sugar residues by bridging the 5′-hydroxyl group on one sugar to the 3′-hydroxyl group of the next sugar in the chain. These nucleoside linkages are called phosphodiester bonds and are the same in RNA and DNA.

Biosynthesis and degradation

Nucleotides are synthesized from readily available precursors in the cell. The ribose phosphate portion of both purine and pyrimidine nucleotides is synthesized from glucose via the pentose phosphate pathway. The six-atom pyrimidine ring is synthesized first and subsequently attached to the ribose phosphate. The two rings in purines are synthesized while attached to the ribose phosphate during the assembly of adenine or guanine nucleosides. In both cases the end product is a nucleotide carrying a phosphate attached to the 5′ carbon on the sugar. Finally, a specialized enzyme called a kinase adds two phosphate groups using adenosine triphosphate (ATP) as the phosphate donor to form ribonucleoside triphosphate, the immediate precursor of RNA. For DNA, the 2′-hydroxyl group is removed from the ribonucleoside diphosphate to give deoxyribonucleoside diphosphate. An additional phosphate group from ATP is then added by another kinase to form a deoxyribonucleoside triphosphate, the immediate precursor of DNA.

During normal cell metabolism, RNA is constantly being made and broken down. The purine and pyrimidine residues are reused by several salvage pathways to make more genetic material. Purine is salvaged in the form of the corresponding nucleotide, whereas pyrimidine is salvaged as the nucleoside.

Get Unlimited Access

Try Britannica Premium for free and discover more.

Nucleic acid | Definition, Function, Structure, & Types | Britannica (2024)