Question 1

Which experiment provided the foundational evidence for the 'One Gene-One Enzyme' hypothesis?

Accepted Answer

Beadle and Tatum's X-ray mutagenesis of Neurospora crassa

Question 2

A mutation in the DNA sequence causes the insertion of a single nucleotide. What is the most likely consequence for the resulting protein?

Accepted Answer

A frameshift mutation, altering all downstream amino acids

Question 3

Why is a triplet code necessary to encode all 20 amino acids?

Accepted Answer

A doublet code only allows for $$4^2 = 16$ combinations, which is insufficient

Question 4

Which of the following best describes the difference between the coding strand and the template strand during transcription?

Accepted Answer

The coding strand has the same sequence as mRNA (except T is replaced by U)

Question 5

In the Beadle and Tatum experiment, what was the significance of mutants that could only grow on supplemented medium?

Accepted Answer

They had lost the ability to synthesize certain amino acids or vitamins

Question 6

Which statement about the genetic code is correct?

Accepted Answer

It is degenerate, so multiple codons can specify the same amino acid

Question 7

A patient with sickle-cell anemia has hemoglobin with a single amino acid substitution. Which change is responsible for this disease?

Accepted Answer

Glutamic acid replaced by valine

Question 8

What is the role of alternative splicing in eukaryotic gene expression?

Accepted Answer

It allows a single gene to encode multiple polypeptides

Question 9

Which codon acts as the start codon in mRNA translation?

Accepted Answer

AUG

Question 10

If a gene sequence is $$5'-ATG GGC TCG-3' ($$coding strand), what is the corresponding mRNA sequence?

Accepted Answer

$$5'-AUG GGC UCG-3'$$

Question 11

Which experimental approach was used by Nirenberg and Matthaei to determine codon assignments?

Accepted Answer

Cell-free systems with synthetic RNA homopolymers

Question 12

A frameshift mutation is most likely to occur due to which of the following?

Accepted Answer

Insertion or deletion of one or two bases

Question 13

Why did the 'One Gene-One Enzyme' hypothesis need to be revised to 'One Gene-One Polypeptide'?

Accepted Answer

Because not all proteins are enzymes

Question 14

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

Accepted Answer

It is nearly universal, with minor variations in some organisms

Question 15

If three nucleotides are deleted from a gene, what is the expected effect on the reading frame?

Accepted Answer

Only one amino acid is missing, but the reading frame is preserved

Question 16

Which property of the genetic code helps minimize the impact of point mutations?

Accepted Answer

Degeneracy

Question 17

A scientist synthesizes an RNA molecule with the sequence $$5'-UUUUUUUUUU-3'. $$When added to a cell-free system, which amino acid is incorporated?

Accepted Answer

Phenylalanine

Question 18

What is the function of stop codons in the genetic code?

Accepted Answer

Terminate polypeptide synthesis

Question 19

Which of the following best explains how cell-free systems contributed to deciphering the genetic code?

Accepted Answer

They allowed direct observation of protein synthesis from synthetic RNAs

Question 20

A mutation changes the codon $$5'-GAA-3' to$$ $$5'-GAG-3'. $$Both codons specify glutamic acid. What type of mutation is this?

Accepted Answer

Silent mutation

Gene Expression II: The Genetic Code and Protein Synthesis

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