Key Points of DNA Translation Process

ACT 1 - Initiation 

• The smaller Subunit of Ribosome charged with tRNA and the amino acid Methionine encounters mRNA
• They attach and start to scan for the start signal 
• The small subunit ribosome finds the starting sequence (AUG), the codon (triplet) for amino acid Methionine
• The large subunit of ribosome joins the small subunit to form the complete ribosome 
• Ribosomal subunit for Prokaryotic cells - 50 S and 30 S
• Ribosomal subunit for Eukaryotic cells - 60 S and 40 S

Act 2 - Elongation 

• A new tRNA + amino acid enter the A site of the ribosome 
• Anti-codon matches with mRNA codon basepairs, ribosome can link the 2nd amino acid together 
• tRNA shifts from A site to P site, P site to E site and leaves the ribosome without any amino acid
• The ribosome itself moves one triplet forward and a new tRNA + amino acid will enter the ribosome
• Procedure is repeated 

Act 3 - Termination 

• When ribosome reaches 1 of the 3 stop codons (UGA, UAG and UAA), there are no corresponding tRNAs
• Termination proteins bind to the ribosome and stimulate the release of the amino acid chain (polypeptide chain) 
• Large and small subunit dissociate as ribosome released from mRNA