ribonucleic acid

ribonucleic acid /ri·bo·nu·cle·ic ac·id/ (-noo-kle´ik) RNA, a nucleic acid found in all living cells, constituting the genetic material in the RNA viruses, and playing a role in the flow of genetic information; it is a linear polymer which on hydrolysis yields adenine, guanine, cytosine, uracil, ribose, and phosphoric acid and which may contain extensive secondary structure. For specific types of RNA, see under RNA.

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ri·bo·nu·cle·ic acid (rb-n-klk, -kl-)

n.

RNA.

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ribonucleic acid (RNA)

[rī′bōno̅o̅klē′ik]

Etymology: ribose + L, nucleus, nut kernel, acidus, sour

a nucleic acid, found in both the nucleus and cytoplasm of cells, that plays several roles in the translation of the genetic code and the assembly of proteins. Kinds of RNA include messenger RNA, ribosomal RNA, and transfer RNA. See also deoxyribonucleic acid.

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ribonucleic acid (RNA),

n a nucleic acid, found in both the nucleus and cytoplasm of cells, that transmits genetic instructions from the nucleus to the cytoplasm. RNA functions in the assembly of proteins.

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ribonucleic acid

nucleic acids present in all living cells which are particularly involved in cellular protein synthesis and replace DNA as a carrier of genetic information in some viruses; abbreviated RNA. RNA is similar in composition to DNA with two exceptions: the sugar in RNA is ribose (in DNA it is deoxyribose) and in RNA the pyrimidine uracil replaces the thymidine of DNA. The structure of RNA varies from helical to uncoiled linear strands of varying lengths, depending on the number of nucleotides forming the strand. This variance in structure is evident in the different types of RNA. For example, transfer RNA (tRNA) contains only about 75 nucleotides, while some mRNAs may contain thousands of nucleotides. Messenger RNA (mRNA) receives its name from its function of carrying the genetic code from DNA in the nucleus of the cell to the cytoplasm, where proteins are synthesized. The transfer of the genetic code from DNA to mRNA is called transcription. Molecules of mRNA migrate to the cytoplasm and bind to ribosomes, to form polyribosomes. RNA moves along the ribosomes and its information content as codons (three nucleotides) is translated into a particular sequence of amino acids, i.e. a protein or polypeptide. Stop codons, UAA, UAG and UGA, terminate translation of mRNA. Transfer RNA (tRNA) called also soluble RNA, brings about the transfer of specific amino acid molecules to the growing protein molecules during the synthesis of proteins. Each of the 20 common amino acids found in protein molecules has a corresponding type of tRNA. Thus, a specific tRNA carries the appropriate amino acid to its appropriate place in the nascent chain of the protein molecule being synthesized. tRNA has a triplet of nucleotides called the anticodon which is able, by base pairing to the codon triplet in mRNA as it moves along the ribosomes, to place the amino acids in the specific order characteristic of the particular protein. See also trna. Ribosomal RNA (rRNA) is so called because it is found as a major structural component of ribosomes are the cytoplasmic organelle required for linking of amino acids into protein molecules.

Large amounts of RNA are also found in the nucleus of cells. One class of nuclear RNA, called heterogeneous RNA (hnRNA), represents primary RNA transcripts, i.e. before processing including splicing of introns, to form mRNA. A second class of nuclear RNA is called small nuclear RNA (snRNA) one species of which, called small nuclear ribonucleoprotein (snRNP), is believed to play an important role in the processing of hnRNA to mRNA. In the splicing reaction RNA itself acts as an 'enzyme' in that it is able to cut and religate other RNA molecules.