Translation of mRNA into a Polypeptide

Vocabulary terms and definitions covering the molecular mechanisms of mRNA translation, including initiation, elongation, and termination.

Translation

The second stage of protein synthesis where an mRNA sequence is translated into a polypeptide chain.

Initiator tRNA

An aminoacyl-tRNA with the anticodon $UAC$ that is bonded to the amino acid methionine ($met$) and binds to the start codon $AUG$.

Small Ribosomal Subunit

The part of the ribosome that forms a complex with $met$-tRNA and binds to the $5'$-cap of mRNA to begin scanning.

Scanning

The process where the $met$-tRNA and ribosomal complex slides down mRNA in the $5'$ to $3'$ direction until the start codon is recognized.

Start Codon

The mRNA sequence $AUG$ where translation begins and the reading frame is established.

Large Ribosomal Subunit

The part of the ribosome that binds to the small ribosomal subunit to form a functioning ribosome once the start codon is recognized.

P-site (Peptidyl site)

The ribosomal site where the initiator $met$-tRNA is initially positioned and where the tRNA carrying the growing polypeptide chain moves during elongation.

A-site (Aminoacyl site)

The ribosomal site that accepts new aminoacyl-tRNAs with matching anticodons for the next codon in the mRNA sequence.

E-site (Exit site)

The ribosomal site where empty tRNAs move to be ejected from the ribosome.

Peptidyl Transferase

The enzyme/activity that cleaves the amino acid from the tRNA in the P-site and forms a peptide bond with the amino acid on the tRNA in the A-site.

$$GTP$$

The energy source used ($GTP \rightarrow GDP + P_i$) to facilitate the cleavage of amino acids and the formation of peptide bonds.

Translocation

The phase where the ribosome moves down the mRNA to the next codon, shifting the tRNA with the polypeptide chain to the P-site and the empty tRNA to the E-site.

Stop Codon

A specific mRNA sequence that, when reached at the A-site, signals the termination of translation.

Protein Release Factor

A factor that causes the ribosomal subunits to break away, releasing the mRNA and the completed polypeptide chain upon reaching a stop codon.