- It is the process of polymerisation of amino acids to form a polypeptide based on the sequence of codons in mRNA.
- It takes place in ribosomes. Ribosome consists of structural RNAs and about 80 types of proteins.
- Ribosome also acts as a catalyst (23S rRNA in bacteria is the enzyme- ribozyme) for the formation of peptide bond (peptidyl transferase enzyme in large subunit of ribosome).
- Translation includes 4 steps:
- Charging of tRNA
1. Charging (aminoacylation) of tRNA
· Formation of peptide bond needs energy obtained from ATP.
· For this, amino acids are activated (amino acid + ATP) and linked to their cognate tRNA in presence of aminoacyl tRNA synthetase. Thus, the tRNA becomes charged.
· In this, small subunit of ribosome binds to mRNA at the start codon (AUG).
· Now large subunit binds to small subunit to form initiation complex.
· Large subunit consists of aminoacyl tRNA binding site (A site) and peptidyl site (P site).
· The initiator tRNA (which carries methionine) binds on P site. Its anticodon (UAC) recognises start codon AUG.
· Second aminoacyl tRNA binds to the A site of ribosome. Its anticodon binds to the second codon on the mRNA and a peptide bond is formed between first and second amino acids in presence of peptidyl transferase.
· First amino acid and its tRNA are broken. This tRNA is removed from P site and second tRNA from A site is pulled to P site along with mRNA. This is called translocation.
· These processes are repeated for other codons in mRNA.
· During translation, ribosome moves from codon to codon.
· When a release factor binds to stop codon, the translation terminates.
· The polypeptide and tRNA are released from the ribosomes.
· The ribosome dissociates into large and small subunits.
A group of ribosomes associated with a single mRNA for translation is called a polyribosome (polysomes).
An mRNA has additional sequences that are not translated (untranslated regions or UTR). UTRs are present at both 5’-end (before start codon) and 3’-end (after stop codon). They are required for efficient translation process.
- Topic 1: The DNA
- Topic 2: The Search for Genetic Material
- Topic 3: Properties of Genetic Material, RNA World
- Topic 4: DNA Replication
- Topic 5: Transcription
- Topic 6: Genetic Code, Types of RNA
- Topic 7: Translation (Protein Synthesis)
- Topic 8: Regulation of Gene Expression, Operon Concept
- Topic 9: Human Genome Project (HGP)
- Topic 10: DNA Fingerprinting