6.6.4 Translation/Elongation: The Initiation of Elongation

Question 1

note

Answer 1

• Translation occurs in three stages: initiation, elongation, and termination. During initiation, the 5’ cap on the messenger RNA (mRNA) strand signals the attachment of the small subunit of the ribosome.
  • During initiation, the cell expends energy in the form of GTP.
  • During elongation, amino acids are added one by one to form a polypeptide chain. Elongation occurs through codon recognition, peptide-bond formation, and translocation. The addition of each amino acid involves the aid of protein elongation factors

Question 2

Codon recognition

Answer 2

• The picture shows an incoming aminoacyl tRNA bearing the anticodon sequence “UUU.” It binds to the
  mRNA codon containing the sequence “AAA.” Codon recognition occurs in the A site of the large ribosomal subunit

Question 3

Peptide-bond formation

Answer 3

• The illustration on the left depicts the new amino acid being joined to the existing polypeptide strand with
  the help of an RNA ribozyme. The bond that forms between the two amino acids is a peptide bond. An rRNA molecule of the large ribosomal subunit, functioning as a ribozyme, catalyzes the formation of the peptide bond.

Question 4

Translocation.

Answer 4

• After the peptide bond forms, the entire polypeptide strand is moved to the tRNA in the A site. During translocation, the tRNA in the A site moves to the P site. The tRNA in the P site moves into the E site and is released from the ribosome.

Question 5

Which of the following statements concerning translation / elongation is false?

Answer 5

• The incoming amino acid joins the polypeptide chain on the P site

Question 6

During elongation the ribosome moves along the mRNA in the ____ direction in _____-base steps.

Answer 6

• 3′ ; 3

Question 7

In eukaryotes, which component is not directly involved in translation?

Answer 7

• DNA

Question 8

Which of the following is directly translated into protein?

Answer 8

• messenger RNA