BOTANY Higher Secondary Second Year - Textbooks Online

3.8. Structure of RNA and its types
The Ribonucleic acid is otherwise known as RNA. This is universally
present in all organisms except in DNA viruses. It is made up of nucleotides
called ribonucleotides. There are four types of nucleotides having four
different nitrogenous bases. But sugar and phosphate are common for all
nucleotides. The four nucleotides are adenine, cytosine, guanine and
uracil. The RNA plays an important role in protein synthesis. Now we
will know more about their types and their role in the biology of an
organism.
Types of RNA
There are three major types of RNA which occur in all organisms.
They are messenger RNA (mRNA), transfer RNA (tRNA) and ribosomal
RNA (rRNA).
Messenger RNA
As the name suggests mRNA carries the genetic information from
DNA to the ribosomes. Genetic informations on the DNA are transcribed
into the mRNA by a process called transcription. Here the “message” is
translated into action i.e. based on the genetic information different types
of proteins are synthesised. The type of gene that is involved in protein
synthesis depends upon their length, kinds and sequence of nucleotides.
It is about 3 to 5 per cent of the RNA content of the cell. The mRNA is
always single stranded. The mRNA is produced as a complementary
copy of the DNA, which is involved in protein synthesis.
Transfer RNA
Aminoacid
Transfer RNA is also known as
soluble RNA (sRNA). The tRNA is a
small molecule compared with other
types of RNAs. It amounts to about
15 per cent of total RNA of the cell.
The tRNA molecule performs a
number of functions. The most
important one is to act as a carrier of
aminoacid to the site of protein
synthesis. There are about more than
20 types of tRNAs. Each tRNA is
137
D arm
(D=Dihydrouridine)
Extra arm
Anticodon
arm
acceptor arm
T ψ C arm
(T=Thymine
ψ = Pseudouridine
C = Cytocine)
Fig. 3.10 Structure of tRNA