Q: During eukaryotic translation initiation, which sequence is recognized by the ribosome to identify the correct start codon?

Kozak sequence ($$\text{ACCAUGG})$$

Question 1

Which enzyme is responsible for editing the HIV genome by deaminating cytosine to uracil, thereby causing G-to-A hypermutation and impairing viral DNA synthesis?

Accepted Answer

APOBEC3G

Question 2

What is the primary function of the HIV protein Vif in the viral life cycle?

Accepted Answer

Counteracts APOBEC3G to prevent hypermutation

Question 3

During mRNA processing in eukaryotes, which regions are removed to produce mature mRNA?

Accepted Answer

Introns

Question 4

A frameshift mutation occurs when nucleotides are inserted or deleted in numbers not divisible by three. What is the most likely consequence of such a mutation?

Accepted Answer

The reading frame shifts, resulting in a completely different amino acid sequence downstream.

Question 5

In sickle cell anemia, a single nucleotide mutation in the HBB gene changes the codon for glutamic acid (GAG) to valine (GTG). Which type of mutation is this?

Accepted Answer

Missense mutation

Question 6

The genetic code is described as 'degenerate but unambiguous.' What does this mean?

Accepted Answer

Multiple codons can encode the same amino acid, but each codon specifies only one amino acid.

Question 7

If an extraterrestrial organism has five nucleotides and uses doublet codons, what is the maximum number of different amino acids that could be encoded?

Accepted Answer

25

Question 8

Which of the following is considered a 'silent mutation'?

Accepted Answer

A base substitution that does not change the amino acid encoded.

Question 9

What is the minimum number of tRNAs required to recognize all six codons for leucine, considering the wobble hypothesis?

Accepted Answer

Two

Question 10

Which enzyme links amino acids to their corresponding tRNAs, forming a high-energy ester bond?

Accepted Answer

Aminoacyl-tRNA synthetase

Question 11

During eukaryotic translation initiation, which sequence is recognized by the ribosome to identify the correct start codon?

Accepted Answer

Kozak sequence ($$	ext{ACCAUGG})$$

Question 12

Kanamycin is an antibiotic that allows diverse tRNAs with any anticodons to bind in the A site of bacterial ribosomes. What effect does this have on bacterial translation?

Accepted Answer

It causes incorporation of incorrect amino acids into a polypeptide.

Question 13

A nonsense mutation is one that causes:

Accepted Answer

Premature termination of translation

Question 14

Which of the following mechanisms can counteract the effects of a premature stop codon (nonsense mutation) in eukaryotic cells?

Accepted Answer

Nonsense-mediated decay

Question 15

What is the role of molecular chaperones such as Hsp70 and Hsp60 in cells?

Accepted Answer

They guide proper folding of polypeptides and guard against improper interactions.

Question 16

Which of the following best describes the signal peptide mechanism for membrane and secreted proteins?

Accepted Answer

A hydrophobic N-terminal sequence is recognized by SRP and directs cotranslational import into the ER.

Question 17

Which ribosomal site is responsible for holding the tRNA carrying the growing polypeptide chain during translation?

Accepted Answer

P site

Question 18

According to the wobble hypothesis, which base in the tRNA anticodon can pair with U, C, or A in the mRNA codon?

Accepted Answer

Inosine

Question 19

Which of the following enzymes does NOT use a template for adding nucleotides?

Accepted Answer

Poly A polymerase

Question 20

A mutation in the stop codon of a gene results in translation reading through the boundary of the open reading frame (ORF). What is the cellular response in eukaryotes?

Accepted Answer

Translation is stalled and an RNA degrading enzyme binds the empty A site, degrading the defective mRNA via nonstop decay.

Gene Expression and the Genetic Code: From Transcription to Translation and Mutation

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