Question

At the very beginning of translation, the first tRNA molecule

Select one:
a. connects an amino acid to its anticodon.
b. attaches to the P site of the ribosome.
c. attaches directly to the DNA codon.
d. binds to the ribosome's A site.

Answer 1

At the start of translation, the first tRNA molecule attaches to the P site of the ribosome, where it matches the mRNA's AUG start codon with its UAC anticodon and carries methionine.

Step-by-step explanation:

At the very beginning of translation, the first tRNA molecule attaches to the P site of the ribosome. This is the initiation phase of protein synthesis. The initiator tRNA carries methionine and has an anticodon that is complementary to the AUG start codon on the mRNA. Once the small ribosomal subunit has bound to the mRNA, the initiator tRNA with the anticodon UAC aligns with the AUG codon in the P site, and the large ribosomal subunit joins to complete the initiation complex.

As the translation process continues, subsequent tRNA molecules, carrying their specific amino acids and with anticodons matching the mRNA codons, bind to the A site of the ribosome. The amino acids are then linked together by peptide bonds, a reaction catalyzed by the ribosome's peptidyl transferase activity, to form a growing polypeptide chain. The ribosome moves along the mRNA molecule, and as it does so, tRNAs enter the A site, transfer their amino acid to the chain at the P site, and then exit through the E site.