Question 1

Which experiment led to the discovery that the codon UUU codes for phenylalanine during translation?

Accepted Answer

Marshall Nirenberg's in vitro translation using synthetic poly-U mRNA

Question 2

What is the role of aminoacyl-tRNA synthetase in translation?

Accepted Answer

It attaches the correct amino acid to its corresponding tRNA using ATP hydrolysis.

Question 3

Which of the following best describes the relationship between a tRNA anticodon and an mRNA codon?

Accepted Answer

They are complementary and antiparallel.

Question 4

A mutation in the gene encoding the mitochondrial rRNA makes it more similar to bacterial rRNA. What is a likely consequence if a patient is treated with streptomycin?

Accepted Answer

Increased risk of mitochondrial protein synthesis inhibition, possibly leading to side effects such as hearing loss.

Question 5

Which site on the ribosome does the incoming aminoacyl-tRNA first bind during elongation?

Accepted Answer

A site

Question 6

What is the main catalytic component responsible for peptide bond formation during translation?

Accepted Answer

The rRNA of the large ribosomal subunit (23S in prokaryotes, 28S in eukaryotes)

Question 7

Which of the following equations correctly represents the endergonic reaction catalyzed by aminoacyl-tRNA synthetase?

Accepted Answer

$$\mathrm{Amino\ acid} + \mathrm{tRNA} + \mathrm{ATP} \rightarrow \mathrm{Aminoacyl{-}tRNA} + \mathrm{AMP} + 2\mathrm{P_i}$$

Question 8

Why can bacteria simultaneously transcribe and translate the same mRNA molecule, but eukaryotes cannot?

Accepted Answer

Eukaryotic transcription and translation are separated by the nuclear envelope.

Question 9

Which of the following is a post-translational modification that can regulate protein activity?

Accepted Answer

Phosphorylation by protein kinases

Question 10

A mutation changes the Shine-Dalgarno sequence in a bacterial mRNA. What is the most likely effect?

Accepted Answer

The ribosome cannot recognize the start codon, reducing translation initiation.

Question 11

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

Accepted Answer

Multiple codons can specify the same amino acid.

Question 12

During translation elongation, what is the correct order of events?

Accepted Answer

Codon recognition, peptide bond formation, translocation

Question 13

Which of the following statements about ribosomes is TRUE?

Accepted Answer

The Svedberg unit (S) measures the rate of sedimentation, which depends on size, shape, and density.

Question 14

A patient is given a drug that inhibits the activity of protein phosphatases. Which process would be directly affected?

Accepted Answer

Removal of phosphate groups from proteins

Question 15

Which of the following best describes the directionality of protein synthesis on the ribosome?

Accepted Answer

Proteins are synthesized from the N-terminus to the C-terminus, reading mRNA 5' to 3'.

Question 16

Which of the following is a function of the signal recognition particle (SRP) during translation in eukaryotes?

Accepted Answer

It directs ribosomes to the endoplasmic reticulum for synthesis of secretory proteins.

Question 17

Which of the following is an example of a ribozyme?

Accepted Answer

The rRNA in the large ribosomal subunit that catalyzes peptide bond formation

Question 18

If a tRNA has the anticodon sequence 5'-GAA-3', which mRNA codon will it recognize?

Accepted Answer

5'-CUU-3'

Question 19

Which of the following best explains why polyribosomes (polysomes) are advantageous for cells?

Accepted Answer

They allow multiple copies of a protein to be synthesized from a single mRNA simultaneously.

Question 20

A protein destined for the mitochondria is synthesized in the cytosol. What sequence ensures its correct localization?

Accepted Answer

A mitochondrial targeting signal

LEC 22:Translation: The Molecular Mechanism of Protein Synthesis

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