Agricultural Uses
Ribonucleic acid (RNA) is a generic term for a group of
natural polymers, consisting of long chains of alternating
phosphate and D-ribose units, with bases adenine,
guanine, cytosine and uracil bonded to the 1 position of
the ribose. Ribonucleic acid is universally present in
living cells and has a functional genetic specificity due to
the sequence of bases along the polyribonucleotide chain.
The following four types of RNA are known:
(i) Messenger RNA: It is synthesized in the living
cell by the action of an enzyme that carries out the
polymerization of ribonucleotides on a DNA template
region which carries the information for the primary
sequence of amino acids in a structural protein. It is a
ribonucleotide copy of the deoxynucleotide sequences in
the primary genetic material.
(ii) Ribosomal RNA: It exists as a part of a functional
limit within living cells, called the ribosome, a particle
containing protein and ribosomal RNA in roughly 1:2
parts by weight, having a particle weight of about 8
million. Messenger RNA combines with ribosomes to
form polysomes containing ribosome units, usually 5 ,
complexed to the messenger RNA molecule. This
aggregate structure is the active template for protein
synthesis.
(iii) Transfer RNA: It is the smallest and best
characterized RNA. Its molecules contain about 80
nucleotides per chain. There are at least twenty separate
kinds, correspondingly related to each of the 20 amino
acids naturally occurring in proteins. Transfer RNA must
have at least two kinds of specificity. (i) It must recognize
(or be recognized by) the proper amino acid activating
enzyme so that the proper amino acid will be transferred
to its free 2' or 3' -OH group. (ii) It must be recognized as
the proper triplet on the messenger RNA-ribosome
aggregate. Having these properties, transfer RNA
accepts or forms an intermediate transfer RNA amino
acid that finds its way to the polysome, complexes at a
triplet coding for the activated amino acid, and allows
transfer of the amino acid into peptide linkage.
(iv) viral RNA: It is isolated from bacterial viruses,
and animals and may be considered as a polycistronic
messenger RNA. It has a molecular weight of 1 to 2
million. Generally, there is one molecule of RNA per
infective virus particle. The RNA of RNA virus can be
separated from its protein component and is also
infective, bringing about the formation of complete
virus.
