Q: Which of the following equations correctly represents the energy cost of adding one amino acid to a growing polypeptide chain during elongation?

$$4 \times 7.3\ \mathrm{kcal/mol} = 29.2\ \mathrm{kcal/mol}$$

Question 1

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

Accepted Answer

Some amino acids are specified by more than one codon.

Question 2

A mutation in the gene encoding hemoglobin causes sickle-cell anemia. Which type of mutation is responsible for this disease?

Accepted Answer

A missense mutation that substitutes valine for glutamic acid.

Question 3

During translation in bacteria, what is the role of the Shine-Dalgarno sequence?

Accepted Answer

It base pairs with the 16S rRNA to position the start codon at the P site.

Question 4

Which of the following statements about the wobble hypothesis is correct?

Accepted Answer

It allows for flexibility in base pairing at the third position of the codon, reducing the number of tRNAs needed.

Question 5

A researcher introduces a single nucleotide insertion into the coding region of a gene. What is the most likely consequence for the resulting protein?

Accepted Answer

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

Question 6

Which of the following best describes the function of aminoacyl-tRNA synthetases?

Accepted Answer

They attach amino acids to their corresponding tRNAs using ATP hydrolysis.

Question 7

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

Accepted Answer

It enhances recognition of the start codon by the ribosome.

Question 8

Which of the following equations correctly represents the energy cost of adding one amino acid to a growing polypeptide chain during elongation?

Accepted Answer

$$4 	imes 7.3\ \mathrm{kcal/mol} = 29.2\ \mathrm{kcal/mol}$$

Question 9

A nonsense mutation introduces a premature stop codon in the middle of an mRNA. In eukaryotic cells, which process is most likely to occur as a result?

Accepted Answer

Nonsense-mediated decay will target the mRNA for degradation.

Question 10

Which of the following is a real-world example of posttranslational processing?

Accepted Answer

The removal of the N-terminal methionine from a newly synthesized eukaryotic protein.

Question 11

A patient is found to have a mutation that changes a codon from UAU (tyrosine) to UAA (stop). What type of mutation is this, and what is the likely effect?

Accepted Answer

Nonsense mutation; translation will terminate prematurely.

Question 12

Which of the following statements about ribosomes is correct?

Accepted Answer

Ribosomes contain rRNA that catalyzes peptide bond formation.

Question 13

A scientist is studying a bacterial operon that encodes three enzymes involved in the same metabolic pathway. Which type of mRNA is most likely produced from this operon?

Accepted Answer

Polycistronic mRNA

Question 14

Which of the following best describes the function of molecular chaperones such as Hsp70 and Hsp60?

Accepted Answer

They assist in the proper folding of newly synthesized polypeptides.

Question 15

A mutation in a tRNA gene allows it to recognize a stop codon and insert an amino acid. What is the term for this type of tRNA, and what is a potential risk if it is highly efficient?

Accepted Answer

Suppressor tRNA; it may lead to the production of many abnormal proteins and cell death.

Question 16

Which of the following scenarios would most likely result in a silent mutation?

Accepted Answer

A base substitution at the third position of a codon that does not change the encoded amino acid.

Question 17

Which of the following is true regarding the universality of the genetic code?

Accepted Answer

Most organisms use the same genetic code, but some exceptions exist in mitochondria and certain bacteria.

Question 18

A researcher observes that a viral mRNA is efficiently translated in human cells because it uses codons that match the most abundant human tRNAs. What is this phenomenon called?

Accepted Answer

Codon usage bias

Question 19

Which of the following best describes the process of protein splicing?

Accepted Answer

Removal of inteins from a polypeptide, followed by joining of exteins.

Question 20

A patient’s cells are found to accumulate insoluble protein aggregates, leading to neurodegenerative symptoms. Which molecular process is most likely defective?

Accepted Answer

Folding of polypeptides by molecular chaperones.

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