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AP Biology Unit 6: Gene Expression and Regulation

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Unit 6: Gene Expression and Regulation

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Question 1

During DNA replication, which enzyme synthesizes new DNA strands by adding nucleotides complementary to the template strand?

A.HelicaseB.DNA polymeraseC.PrimaseD.Ligase

Question 2

In gel electrophoresis of DNA fragments, a researcher loads four samples and observes that one fragment migrated the farthest from the well. What does this indicate about that fragment?

A.It has the highest molecular weight and is the largest fragmentB.It is the smallest fragment in the sampleC.It has the most negative charge and is most attracted to the positive electrodeD.It contains more guanine-cytosine base pairs than the other fragments

Question 3

Scientists use bacterial transformation to introduce a gene of interest into E. coli using a plasmid vector. The plasmid contains an ampicillin resistance gene (amp^R) and a lacZ gene (which turns colonies blue on X-gal plates) into which the gene of interest has been inserted. If transformation is successful and the insert disrupts lacZ, which of the following correctly describes the transformed bacteria?

A.Ampicillin sensitive, white colonies on X-gal platesB.Ampicillin resistant, white colonies on X-gal platesC.Ampicillin resistant, blue colonies on X-gal platesD.Ampicillin sensitive, blue colonies on X-gal plates

Question 4

A point mutation changes a codon from UUU (phenylalanine) to UUA (leucine) in a translated protein. Which of the following best describes this mutation?

A.Silent mutation, because the protein is unchangedB.Missense mutation, because one amino acid is substituted for anotherC.Nonsense mutation, because a stop codon is introducedD.Frameshift mutation, because a nucleotide is inserted or deleted

Question 5

The lac operon in E. coli is repressed under which of the following conditions?

A.Lactose present, glucose absentB.Lactose absent, glucose presentC.Lactose present, glucose presentD.Lactose absent, glucose absent

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Question 6

During transcription in eukaryotes, which of the following modifications occurs to pre-mRNA before it exits the nucleus?

A.Introns are translated into regulatory peptides before being removedB.Addition of a 5′ cap, a 3′ poly-A tail, and splicing of intronsC.Reverse transcription to produce a complementary DNA (cDNA) copyD.Translation of the first exon to begin protein synthesis in the nucleus

Question 7

A ribosome is reading an mRNA strand and reaches the codon 5′-UAA-3′. What happens at this point in translation?

A.A tRNA carrying the amino acid tyrosine enters the A siteB.A release factor binds the A site, and the completed polypeptide is releasedC.The ribosome shifts back one nucleotide and re-reads the codonD.mRNA is degraded immediately to recycle the nucleotides

Question 8

Researchers studying gene regulation find that a eukaryotic gene is highly expressed in liver cells but completely silenced in neurons despite both cell types having identical genomic DNA. Which combination of mechanisms could best explain this tissue-specific expression pattern?

A.Different DNA sequences in liver vs. neuron genomes encoding different versions of the geneB.Liver-specific activator transcription factors and neuron-specific DNA methylation silencing the gene's promoterC.Alternative splicing that produces a functional protein only in liver cellsD.Ribosomes in neurons are unable to translate liver-specific mRNAs

Question 9

Polymerase chain reaction (PCR) requires a template, primers, dNTPs, and a heat-stable DNA polymerase (Taq). Which of the following is the correct sequence of steps in one PCR cycle?

A.Annealing → Denaturation → ExtensionB.Denaturation → Annealing → ExtensionC.Extension → Denaturation → AnnealingD.Denaturation → Extension → Annealing

Question 10

In the central dogma of molecular biology, which of the following correctly describes the typical flow of genetic information?

A.Protein → RNA → DNAB.DNA → RNA → ProteinC.RNA → DNA → ProteinD.DNA → Protein → RNA

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Question 11

CRISPR-Cas9 is used to introduce a double-strand break in a gene. In most mammalian cells, the break is repaired by non-homologous end joining (NHEJ). Which of the following best describes a likely molecular outcome of NHEJ repair?

A.The break is repaired precisely using the sister chromatid as a template, restoring the original sequenceB.Small insertions or deletions (indels) are introduced at the cut site, often causing frameshift mutationsC.The entire chromosome containing the cut is degraded to prevent genome instabilityD.The Cas9 protein becomes integrated into the genome at the cut site

Question 12

Transcription factors bind to specific DNA sequences in the promoter or enhancer regions of eukaryotic genes. A mutation abolishes the binding of an activator transcription factor to an enhancer 10,000 bp upstream of the gene's transcription start site. Which of the following best predicts the effect on gene expression?

A.No effect, because enhancers must be adjacent to the promoter to functionB.Gene expression decreases or is abolished because the activator can no longer stimulate RNA polymerase II recruitmentC.Gene expression increases because the enhancer normally inhibits the geneD.The mutation affects only transcription in embryonic cells because enhancers are only active during development

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