Page 190 - MNU microbiology theoritical 2025

General Microbiology & Immunology (PM 401) Second level Semester 4 2024/2025

2- Elongation
• Elongation is the stage where the amino acid chain gets longer.

• In elongation, the mRNA is read one codon at a time, and the amino acid

matching each codon is added to a growing

protein chain.

• At the start of translation, the tRNA with the

anticodon to AUG will bind to AUG. This

tRNA is bound to methionine, and the site it

occupies is the P site.

• A second tRNA with a different amino acid

will bind to the next codon on the mRNA

molecule at the A site.

• In step 2 of translation figure, the peptide

chain in the P site will attach to the amino acid

in the A site. Once this attachment occurs, the

ribosome will shift and move one position (3

bases, or 1 codon) forward along the mRNA

transcript.

• Now, the peptide chain with two amino acids

occupies the P site, while the A site becomes

empty.

• his shift allows the first, empty tRNA to drift

out via the E ("exit") site

• A new tRNA will bind to the A site, and the

process will repeat itself.

General Microbiology & Immunology (PM 401) theoretical handbook Page 179