Question 1

A double-stranded DNA molecule is separated into two single strands. One strand is found to be 38% adenine and thymine. What percentage of guanine is present in the entire original double-stranded molecule?

Accepted Answer

31%

Question 2

Given a DNA sequence with a TATA box, which of the following best describes the function of the TATA box in eukaryotic transcription?

Accepted Answer

It serves as a promoter element for transcription initiation.

Question 3

If the raw transcript of a gene starts at nucleotide 36 and ends at nucleotide 346, how many nucleotides are present in the transcript? Use the formula $$	ext{Total nucleotides} = 	ext{End} - 	ext{Start} + 1.$$

Accepted Answer

$$346 - 36 + 1 = 311$$

Question 4

Which sequence is most likely to be recognized as a poly-adenylation signal in eukaryotic mRNA processing?

Accepted Answer

AAUAAA

Question 5

A mutation in the lac operon produces a repressor protein that cannot bind to the operator region (I mutation). What is the expected effect on gene expression?

Accepted Answer

The operon is constitutively expressed.

Question 6

Which of the following best describes the Kozak sequence in eukaryotic translation?

Accepted Answer

It is a consensus sequence that enhances translation initiation.

Question 7

A partial diploid E. coli cell has the genotype $$I^s O^+ Z^+ / I^+ O^c Z^+. $$What is the expected expression pattern of the lac operon?

Accepted Answer

Constitutive expression

Question 8

If a mutation occurs in the promoter region (P’ mutation) of the lac operon, what is the most likely outcome?

Accepted Answer

RNA polymerase cannot recognize the promoter, so no transcription occurs.

Question 9

A DNA sequence contains two exons and one intron. If the exon portion of the 5’ splice site sequence starts at nucleotide 63 and ends at nucleotide 93, how many codons are present in this region? Use the formula $$	ext{Number of codons} = \frac{	ext{End} - 	ext{Start}}{3}.$$

Accepted Answer

$$\frac{93 - 63}{3} = 10$$

Question 10

Which of the following best describes the function of the 5’ splice site in eukaryotic mRNA processing?

Accepted Answer

It marks the boundary where the intron is removed from the pre-mRNA.

Question 11

A mutation in the lac operon produces a defective (non-functioning) β-galactosidase enzyme (Z mutation). What is the expected effect on lactose metabolism?

Accepted Answer

Lactose cannot be metabolized even if the operon is expressed.

Question 12

If the exon portion of the 3’ splice site sequence starts at nucleotide 146 and the stop codon begins at nucleotide 311, how many codons are present in this region? Use the formula $$	ext{Number of codons} = \frac{311 - 146}{3}.$$

Accepted Answer

$$\frac{311 - 146}{3} = 55$$

Question 13

Which of the following sequences is most likely to be found at the 5’ splice site of a eukaryotic gene?

Accepted Answer

[A/C]GGU[Pu]AGUA

Question 14

In the context of the lac operon, what does 'constitutive expression' mean?

Accepted Answer

The operon is always expressed and cannot be turned off.

Question 15

Which of the following is a correct description of the transcriptional start site sequence in eukaryotes?

Accepted Answer

It is located about 20-25 nucleotides downstream of the TATA box.

Question 16

A partial diploid E. coli cell has the genotype $$I^+ P^+ O^c Z^+ / I^+ P^+ O^+ Z^+. $$What is the expected expression pattern of the lac operon?

Accepted Answer

Constitutive expression

Question 17

Which of the following best describes the effect of an $$I^s$$ mutation in the lac operon?

Accepted Answer

The repressor cannot be removed from the operator, so the operon is always repressed.

Question 18

Which of the following is a plausible consequence of a mutation in the poly-adenylation signal sequence (AAUAAA) of a eukaryotic gene?

Accepted Answer

The mRNA may not be properly cleaved and polyadenylated, leading to instability.

Question 19

Which of the following best describes the relationship between the percentage of adenine and thymine in one strand of DNA and the percentage of guanine in the double-stranded molecule?

Accepted Answer

The percentage of guanine equals half of the remaining percentage after subtracting A+T from 100%.

Genetics Study Guide: DNA Structure, Gene Expression, and the Lac Operon

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