Question

1) Incoming aminoacyl-tRNA binds at the A site, where the codon is read. The decoding center of 16S rRNA ensures the proper choice of aminoacyl-tRNA in the A site. 2) Peptide bond formation: the peptidyl-tRNA is transferred from the tRNA that's holding it to the -NH2 group of the new aa. 3) Translocation of the (one residue longer) peptidyl-tRNA to the P site - to make room for a new aminoacyl-tRNA at the A site, coupled with movement of the ribosome one codon down.

A. Translation initiation
B. Translation elongation
C. Translation termination
D. Transcription initiation

Answer 1

During translation elongation, a charged tRNA binds to the A site of the ribosome, a peptide bond is formed, and the ribosome moves one codon along the mRNA. Termination occurs when the ribosome encounters a stop codon, leading to the release of the polypeptide.

Step-by-step explanation:

During the elongation stage of translation, a charged tRNA binds to mRNA in the A site of the ribosome; a peptide bond is catalyzed between the two adjacent amino acids, breaking the bond between the first amino acid and its tRNA; the ribosome moves one codon along the mRNA; and the first tRNA is moved from the P site of the ribosome to the E site and leaves the ribosomal complex.

Termination of translation occurs when the ribosome encounters a stop codon, which does not code for a tRNA. Release factors cause the polypeptide to be released, and the ribosomal complex dissociates.

Elongation proceeds with charged tRNAs entering the A site and then shifting to the P site followed by the E site with each single-codon "step" of the ribosome. Ribosomal steps are induced by conformational changes that advance the ribosome by three bases in the 3' direction. The energy for each step of the ribosome is donated by an elongation factor that hydrolyzes GTP. Peptide bonds form between the amino group of the amino acid attached to the A-site tRNA and the carboxyl group of the amino acid attached to the P-site tRNA.