VPB 112: General Veterinary Biochemistry (1+1)

Ribosomal RNA

RIBOSOMAL RNA (r RNA)

• The ribosomal RNA accounts for 80% of the total cellular RNA.
• On the ribosomes the m RNA and t RNA molecules interact to form protein.
• All ribosomes contain 2 sub units of unequal size.
• Ribosomal RNA is found in association with a number of different proteins as components of ribosome.
• Prokaryotic ribosomes are smaller than eukaryotic ribosome.
• The intact prokaryotic ribosome is 70S ribosome (S- Svedberg unit, a measure of sedimentation rate). The intact eukaryotic ribosome is 80S.
• The prokaryotic ribosome 70S comprises 3 types: 16S, 23S and 5S rRNA. 16S r RNA, complexes with proteins and forms the 30S ribosomal subunit (smaller subunit), while 23S and 5S r RNAs complex with proteins and form the 50S ribosomal subunit (larger). The 30S and 50S ribosomal subunits join to form the 70S ribosome.
• The Eukaryotic ribosomes contain four types of r RNA molecules of 18, 28, 5, and 5.8S. 18S r RNA is complexed with proteins to form the 40S ribosomal subunit and the 28, 5 and 5.8S r RNAs are complexed with proteins to form the 60S ribosomal subunit. The 40 and 60S ribosomal subunits combine to form the 80S ribosome.

Functions of ribosomal RNA

• The binding of m RNA to ribosome.
• In the formation of peptide bond, catalyzed by the larger subunit.
• The 70S ribosome contains 2 functional sites termed as A site and the P site. Aminoacyl – t RNA binds at the A site and peptidyl – t RNA binds at the P site. These sites are made of portions from both smaller and larger subunits.
• The enzyme that catalyses the peptide bond formation (Peptidyl transferase) occurs in the large subunit.