Q: A eukaryotic mRNA is being translated. Which sequence is most important for efficient recognition of the start codon by the ribosome?

The Kozak sequence ($$\text{GCCRCCAUGG})$$

Question 1

Which of the following best describes the function of the Shine–Dalgarno sequence in prokaryotic translation initiation?

Accepted Answer

It acts as a ribosome-binding site by base-pairing with the 16S rRNA, positioning the ribosome at the correct start codon.

Question 2

A mutation changes the codon GAG to GTG in the β-globin gene. What is the molecular consequence of this mutation in hemoglobin?

Accepted Answer

Glutamic acid is replaced by valine, resulting in hemoglobin S and sickle cell disease.

Question 3

Which of the following post-translational modifications is primarily responsible for targeting proteins for degradation by the proteasome?

Accepted Answer

Ubiquitination

Question 4

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

Accepted Answer

EF-Tu

Question 5

Which of the following statements about tRNA is FALSE?

Accepted Answer

tRNAs are directly translated into proteins during translation.

Question 6

A eukaryotic mRNA is being translated. Which sequence is most important for efficient recognition of the start codon by the ribosome?

Accepted Answer

The Kozak sequence ($$	ext{GCCRCCAUGG})$$

Question 7

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

Accepted Answer

Most amino acids are encoded by more than one codon.

Question 8

A mutation inserts a single nucleotide into the coding region of a gene. What is the most likely effect on the resulting protein?

Accepted Answer

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

Question 9

Which of the following is a function of the poly-A tail in eukaryotic mRNA?

Accepted Answer

It enhances translation initiation and mRNA stability.

Question 10

Which of the following best describes the role of aminoacyl-tRNA synthetases in translation?

Accepted Answer

They catalyze the attachment of amino acids to their corresponding tRNAs using ATP.

Question 11

Which of the following is a direct consequence of a stop codon entering the A site of the ribosome during translation?

Accepted Answer

A release factor binds, triggering hydrolysis of the polypeptide from the tRNA.

Question 12

Which of the following post-translational modifications is most important for stabilizing the structure of extracellular proteins such as antibodies?

Accepted Answer

Formation of disulfide bonds

Question 13

A protein destined for secretion from a eukaryotic cell is synthesized with a signal sequence. What is the fate of this signal sequence?

Accepted Answer

It is recognized by the signal recognition particle (SRP) and is usually cleaved off after the protein enters the ER.

Question 14

Which of the following best describes the quaternary structure of a protein?

Accepted Answer

The arrangement and interaction of multiple polypeptide chains in a functional protein complex.

Question 15

Which of the following is a key difference between prokaryotic and eukaryotic translation?

Accepted Answer

Eukaryotic mRNAs are capped and polyadenylated, while prokaryotic mRNAs are not.

Question 16

Which of the following best explains the importance of the 'wobble' position in the genetic code?

Accepted Answer

It allows a single tRNA to recognize multiple codons for the same amino acid, increasing efficiency.

Question 17

A scientist is studying a protein that is rapidly degraded in the cell. Which post-translational modification is most likely responsible for this rapid degradation?

Accepted Answer

Polyubiquitination linked through lysine-48 (K48)

Question 18

Which of the following is a real-life example of how a single amino acid substitution can affect protein function and lead to disease?

Accepted Answer

Sickle cell anemia, caused by a substitution of valine for glutamic acid in hemoglobin.

Question 19

Which of the following best describes the function of protein domains?

Accepted Answer

They are distinct structural and functional units within a protein that can confer specific activities such as DNA binding or dimerization.

Translation and Post-Translational Modifications in Genetics

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