Question 1

Which experiment provided the first strong evidence for the 'one gene-one enzyme' hypothesis, and what organism was used?

Accepted Answer

The experiment with Neurospora crassa (bread mold) using X-ray mutagenesis to identify mutants unable to grow on minimal medium.

Question 2

A patient with alkaptonuria has dark urine due to a defect in a metabolic pathway. Which concept does this disorder best illustrate?

Accepted Answer

Genes control metabolic pathways by encoding specific enzymes.

Question 3

In the arginine biosynthetic pathway, a Class II mutant of Neurospora crassa can grow only when citrulline or arginine is supplied. Which enzyme is defective in this mutant?

Accepted Answer

Enzyme B (converts ornithine to citrulline)

Question 4

Which of the following best describes the process of transcription?

Accepted Answer

Synthesis of RNA from a DNA template by RNA polymerase II in the 5' → 3' direction.

Question 5

Given the DNA template strand 3'-TAC TTC ACC CGT-5', what is the corresponding mRNA sequence?

Accepted Answer

$$5'-AUG AAG UGG GCA-3'$$

Question 6

Using the mRNA sequence $$5'-AUG AAG UGG GCA-3'$$ and the genetic code, what is the resulting amino acid sequence?

Accepted Answer

Met-Lys-Trp-Ala

Question 7

Which modification occurs at the 5' end of eukaryotic mRNA during RNA processing, and what is its function?

Accepted Answer

Addition of a modified guanine nucleotide (5' cap) to protect mRNA from degradation and aid ribosome attachment.

Question 8

What is the main difference between gene expression in prokaryotes and eukaryotes?

Accepted Answer

Prokaryotes couple transcription and translation, while eukaryotes modify RNA before translation.

Question 9

Which type of mutation results in a premature stop codon and usually produces a nonfunctional protein?

Accepted Answer

Nonsense mutation

Question 10

A frameshift mutation is most likely caused by which of the following genetic changes?

Accepted Answer

Insertion or deletion of nucleotides not in multiples of three

Question 11

Why is the genetic code considered nearly universal among organisms?

Accepted Answer

The same codons specify the same amino acids in almost all organisms tested.

Question 12

Which of the following best explains why bacteria can produce human insulin when given the human insulin gene?

Accepted Answer

The universality of the genetic code allows bacteria to translate human genes into the correct protein.

Question 13

During translation, which site on the ribosome does the incoming aminoacyl-tRNA first bind?

Accepted Answer

A site (Aminoacyl-tRNA site)

Question 14

Which post-translational modification is most likely to target a protein for secretion from the cell?

Accepted Answer

Addition of a signal peptide at the N-terminus

Question 15

A mutation in the gene encoding ornithine transcarbamylase (OTC) results in OTC deficiency. Which metabolite would you expect to accumulate in the patient's blood?

Accepted Answer

Ornithine

Question 16

Which of the following best describes alternative splicing?

Accepted Answer

The process by which different combinations of exons are joined to produce multiple polypeptides from one gene.

Question 17

Which of the following is a silent mutation?

Accepted Answer

A nucleotide change that does not alter the amino acid sequence due to redundancy in the genetic code.

Question 18

Which of the following is NOT a function of the 3' poly-A tail added during RNA processing?

Accepted Answer

Initiating translation by binding to the ribosome

Question 19

Which of the following best describes the relationship between genes and proteins according to the 'one gene-one polypeptide' hypothesis?

Accepted Answer

Each gene encodes a single polypeptide, but some proteins are composed of multiple polypeptides from different genes.

Gene Expression: From Gene to Protein (Chapter 17) – Study Notes

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