What is the role of ribosome in protein synthesis?
1 Answer
Ribosome acts as a platform where codons written on mRNA are read. Ribosome also catalyses formation of peptide bond between two amino acids.
Explanation:
'Translation' of mRNA into proteins take place on robosomes. mRNA first attaches to small subunit of ribosome towards its 5' end and then the large subunit comes and join.
mRNA carries a series of triplet codons on it: each codon represents a particular amino acid. At a time two such codons are exposed on surface of a ribosome. Or you may say two codons become available for attachment with respective anticodons and this association between codon and anticodon can take place only on ribosomal surface . Anticodon is complementary to codon. Anticodon is part of a tRNA molecule and each tRNA carries an amino acid specific for the codon to which the tRNA can bind. (First codon from where translation starts is always AUG . First tRNA to become associated with ribosome, thus, always carries amino acid methionine.)
Ribosomal subunits are made of many molecules of proteins and few strands of RNA (called rRNA). When two tRNAs carrying two amino acids remain attached to two consequetive codons on ribosome, a peptide bond between the amino acids is formed. Peptide bond formation is catalysed by peptidyl transferase, a ribozyme, i.e. rRNA molecule present in large ribosomal subunit.
After formation of peptide bond first tRNA becomes dislodged, and two interconnected amino acids hang from the second tRNA.
This will be followed by a movement of ribosome along mRNA to expose the next codon on its surface. Another tRNA (specific to new exposed codon) will come and its anticodon will bind to mRNA. Another peptide bond formation can take place and thus, a chain of amino acids (called popypeptide chain) could be formed on ribosome.
