chapter 17b

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What is the primary function of the A site in the ribosome?

To hold the growing peptide chain
To facilitate the exit of tRNAs without amino acids
To synthesize proteins in a two-step sequence
To bind an aminoacyl-tRNA with a codon-anticodon match (correct)

During the three-step sequence of protein synthesis, what occurs in the second step?

The A site is available for another tRNA to bind
The tRNA in the E site exits
The ribosome moves down the mRNA by one codon
A peptide bond forms between the amino acid on the A-site tRNA and the polypeptide on the P-site tRNA (correct)

What is the direction of amino acid addition during protein synthesis?

Amino acids are added randomly to the polypeptide
Amino acids are always added to the carboxyl end (C-terminus) of the polypeptide (correct)
Amino acids are added to the amino end (N-terminus) of the polypeptide
Amino acids are added to the middle of the polypeptide

What is the name of the site where tRNAs without amino acids exit the ribosome?

E site (D) Signup and view all the answers

How many phases does translation have?

Three phases (C) Signup and view all the answers

What is the role of the P site in the ribosome?

To hold the growing peptide chain (D) Signup and view all the answers

What occurs when the A site encounters a stop codon?

Termination of translation (A) Signup and view all the answers

What is unique about the initiator tRNA in eukaryotes?

It contains methionine (D) Signup and view all the answers

What is the function of a release factor?

To hydrolyze the bond linking the P-site tRNA to the polypeptide chain (C) Signup and view all the answers

What is a characteristic of ribosomes in both prokaryotes and eukaryotes?

They are ribozymes (A) Signup and view all the answers

What is the result of elongation?

Extension of the polypeptide chain (D) Signup and view all the answers

What is the difference in mRNA translation between prokaryotes and eukaryotes?

Prokaryotes translate polycistronic messages, while eukaryotes translate monocistronic messages (D) Signup and view all the answers

What is the role of aminoacyl-tRNA synthetases?

To catalyze the addition of amino acids to tRNAs (C) Signup and view all the answers

How many different tRNAs are there in most cells?

40 (A) Signup and view all the answers

What is the function of the small subunit of the ribosome?

To hold the mRNA in place (A) Signup and view all the answers

What is wobble pairing, as proposed by Francis Crick?

A nonstandard base pairing at the anticodon's third position (C) Signup and view all the answers

What is the site where peptide bonds are formed during translation?

Peptidyltransferase site (D) Signup and view all the answers

How many tRNAs line up within the ribosome during translation?

3 (C) Signup and view all the answers

What is the characteristic of translation in bacteria?

Transcription and translation occur simultaneously. (B) Signup and view all the answers

What is the main function of a polyribosome?

To translate mRNA into protein. (B) Signup and view all the answers

What is the role of the 3' end of tRNA?

It is the amino acid binding site. (D) Signup and view all the answers

What is the function of the loop at the opposite end of tRNA?

It contains the anticodon. (A) Signup and view all the answers

What is the purpose of aminoacyl-tRNA?

To transfer amino acids to the ribosome. (D) Signup and view all the answers

What is the difference between prokaryotic and eukaryotic translation?

Prokaryotes have simultaneous transcription and translation, while eukaryotes have separate transcription and translation steps. (B) Signup and view all the answers

What occurs at the start of the elongation phase of protein synthesis?

The initiator tRNA is in the P site and the E and A sites are empty (C) Signup and view all the answers

What is the function of elongation factors during protein synthesis?

To help move the ribosome during translocation (D) Signup and view all the answers

What is the net result of the three steps of translocation?

The ribosome moves forward on the mRNA, and the growing protein is transferred to the P site (A) Signup and view all the answers

What is the composition of the active site of the ribosome?

Entirely ribosomal RNA (B) Signup and view all the answers

What occurs during peptide bond formation?

The amino acid on the P-site tRNA is transferred to the amino acid on the A-site tRNA (B) Signup and view all the answers

What is the classification of the ribosome based on its active site?

Ribozyme (A) Signup and view all the answers