Structure Of Rna

STRUCTURE OF RNA

• RNA is a polymer of ribonucleotides held together by 3’-5’ phosphodiester bridges.
• Sugar present in RNA is ribose.
• RNA contains uracil.
• RNA is a single stranded
• Mainly seen in cytoplasm.
• It does not obey Chargaff’s rule.
• Types of RNA-

1. Messenger RNA (mRNA)- 5-10%
2. Transfer RNA (tRNA)- 10-20%
3. Ribosomal RNA (rRNA)- 50-80%

1. Messenger RNA (mRNA)-

• The mRNA is synthesized in the nucleus as heterogeneous nuclear RNA (hn RNA) processed into functional m RNA.
• mRNA carries information from the nucleus to the ribosome.
• 5’ end capped by 7 Methylguanosine triphosphate.
• 3’ end contains 20-250 polymer of adenylate residues.

2. Ribosomal RNA (rRNA)-

• Most abundant RNA & play an important role in protein synthesis and binding of mRNA to ribosomes.
• The eukaryotic ribosomes are composed of two major nucleoprotein complexes- 60S and 40S subunit.
• 28S, 18S and 5S are the major varieties.

3. Transfer RNA (tRNA)-

• It is the smallest tRNA having 73 to 93 nucleotide residues.
• L shaped tertiary structure.
• Clover leaf shape in the secondary structure.
• It transport amino acids in an activated form from cytosol to ribosome for protein synthesis.
• tRNA contain significant proportion of nucleosides with unusual bases are-

1. DihydroUridine
2. Pseudouridine
3. Inosine
4. Ribothymidine

• tRNA is the only RNA that can contain thymine.
• tRNA mainly contains 4 arms-

1. Acceptor arm- site of attachment of amino acid. Terminations in the sequence CCA at the 3¹ end.
2. Anticodon arm-
3. D arm

4. TψC arm

•  miRNA and siRNA– Main function- it cause inhibition of gene expression.
• P bodies- non translating mRNA form ribonucleoprotein particles and they accumulate in cytoplasmic organelle.
• Ribozymes- some ribosomes have intrinsic catalytic activity.
• It involves cleavage of nucleic acid.
• 2 types of ribozymes are-

1. Peptidyl transferase
2. Ribozymes involved in RNA splicing.

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