Question 1

Which of the following best describes the role of the Shine-Dalgarno sequence in bacterial translation initiation?

Accepted Answer

It is a purine-rich sequence in the mRNA that base pairs with the 3' end of the 16S rRNA to position the ribosome at the start codon.

Question 2

A mutation changes the third base of a codon from C to U, but the same amino acid is incorporated into the polypeptide. Which concept explains this phenomenon?

Accepted Answer

Third-base wobble, which allows flexible pairing at the third codon position.

Question 3

During translation elongation in bacteria, which factor is responsible for delivering charged tRNAs to the A site of the ribosome?

Accepted Answer

EF-Tu

Question 4

Which of the following statements about the genetic code is correct?

Accepted Answer

It is a triplet code, with each codon consisting of three nucleotides.

Question 5

A patient is found to have a mutation that deletes a single nucleotide from the coding region of a gene. What is the most likely consequence at the protein level?

Accepted Answer

A frameshift mutation will occur, altering the reading frame and likely producing a nonfunctional protein.

Question 6

Which of the following best explains why methionine is not always the first amino acid in mature eukaryotic proteins?

Accepted Answer

Posttranslational processing removes the N-terminal methionine after translation.

Question 7

Which of the following is a function of aminoacyl-tRNA synthetase?

Accepted Answer

It catalyzes the attachment of the correct amino acid to its corresponding tRNA using ATP.

Question 8

In eukaryotic translation initiation, what is the role of the Kozak sequence?

Accepted Answer

It helps the ribosome identify the correct AUG start codon for translation initiation.

Question 9

Which of the following best describes the structure of a fully assembled eukaryotic ribosome?

Accepted Answer

It consists of a 40S small subunit and a 60S large subunit, forming an 80S ribosome.

Question 10

A researcher is studying a bacterial operon that produces a polycistronic mRNA. Which of the following is true about translation of this mRNA?

Accepted Answer

Each coding region has its own start and stop codon, and ribosomes can initiate translation at multiple sites.

Question 11

Which of the following best explains why the genetic code is described as 'degenerate'?

Accepted Answer

Most amino acids are specified by more than one codon.

Question 12

Which of the following is a direct result of the universality of the genetic code?

Accepted Answer

Bacteria can be engineered to produce human proteins, such as insulin.

Question 13

Which of the following best describes the process of translation termination in eukaryotes?

Accepted Answer

A single release factor, eRF1, recognizes all three stop codons and promotes release of the polypeptide.

Question 14

A scientist observes that a polypeptide is cleaved into two separate functional proteins after translation. Which posttranslational process does this represent?

Accepted Answer

Proteolytic cleavage, as seen in the maturation of insulin from proinsulin.

Question 15

Which of the following equations correctly represents the energy requirement for charging a tRNA with its amino acid?

Accepted Answer

$$\mathrm{Amino\ acid} + \mathrm{tRNA} + \mathrm{ATP} \xrightarrow{\mathrm{aminoacyl{-}tRNA\ synthetase}} \mathrm{aminoacyl{-}tRNA} + \mathrm{AMP} + \mathrm{PP_i}$$

Question 16

Which of the following is a real-world example of the importance of the signal hypothesis in protein targeting?

Accepted Answer

Secreted proteins, such as antibodies, are synthesized with an N-terminal signal sequence that directs them to the endoplasmic reticulum.

Question 17

Which of the following best describes the function of the P site in the ribosome during translation?

Accepted Answer

It holds the tRNA to which the growing polypeptide chain is attached.

Question 18

A mutation in the gene encoding EF-G in bacteria would most directly affect which step of translation?

Accepted Answer

Translocation of the ribosome along the mRNA.

Question 19

Which of the following experimental results provided conclusive evidence that the genetic code is nonoverlapping?

Accepted Answer

Single nucleotide substitutions caused only single amino acid changes in the protein.

9. The Molecular Biology of Translation

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