RNA RIBONUCLEIC ACID Ribonucleic acid is a nucleic
RNA
RIBONUCLEIC ACID �Ribonucleic acid is a nucleic acid containing ribose sugar. �It is found in large amount in the cytoplasm and at a lesser amount in the nucleus. �In the cytoplasm, it is mainly found in the ribosomes and the nucleus it is mainly found in the nucleolus. �RNA is formed of a single strand. It consists of several units called ribonucleotides. �Hence each RNA molecules is formed of several nucleotides.
Chemical composition �Each nucleotides is formed of three different molecules, namely phosphate, ribose sugar and nitrogen base. �The nitrogen bases are two types, namely purines and pyrimidines. �The purines present in the RNA are adinine and guanine. �The pyrimidines present in RNA are cytosine and uracil.
Types of RNA
Messenger RNA �carries genetic information for protein synthesis from the DNA to the cytoplasm. �The term m. RNA was coined by Jacob and monad in 1961. �The m. RNA carries the message in the form of triplet codes. �Based on the number of genes Monocistronic m. RNA Polycistronic m. RNA
Structure �single stranded, polynucleotide chain containing 500 to 1500 nucleotides. �One end of the m. RNA is called 5′ end and the other end is called 3′ end. �At the 5′ end a cap is found in most eukaryotes and animal viruses. �The cap is formed by the condensation of a guanylate residue. The cap helps the m. RNA to bind with ribosomes. Function �m. RNA carries the genetic information in the form of triplet code from the DNA. The code decides the type of protein to be synthesized.
Transfer RNA
� The t. RNA is a ribonucleic acid which transfers the activated amino acids to the ribosomes to synthesize proteins. Structure of t. RNA � It is made up of 73 to 95 nucleotide units called ribonucleotides. � The polynucleotide chain of t. RNA is folded on itself and attain the shape of a cloverleaf. � The 3′ and 5′ of t. RNA lie side as a result of folding. � The 3′ end always ends in CCA base sequence. This is the site for the attachment of activated amino acid. � The 5′ end terminates in G or C. � The t. RNA has 5 arms. They are: Amino acid acceptor arm D-arm Anticodon arm Variable arm T ψ C arm
Ribosomal RNA � Ribosomal RNA is a ribonucleic acid present in the ribosomes and hence it is called ribosomal RNA. � It is also called insoluble RNA. It constitutes about 80% of the cellular RNA. � The helical regions are connected by intervening single strand regions. � In the helical regions, most of the base pairs are complementary. � They are jointed by hydrogen bonds. In the unfolded single strand regions, the base pairs are not complementary. � Because of this nature, in the r. RNA, the purine and pyrimidine bases have no equality. � In some regions, the single strand is twisted upon itself to form a double helix. � The r. RNA are classified into 7 types according to their sedimentation coefficient are the following: � 28 Sr. RNA, 23 Sr. RNA, 18 Sr. RNA, 16 Sr. RNA, 55 Sr. RNA, 5. 8 Sr. RNA, 5 Sr. RNA.
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