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AP®BiologyCollege BoardExam QuestionsUnit 6: Gene Expression & RegulationGene Expression

Gene Expression (College Board AP® Biology)

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Gene Expression

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Gene Expression

1
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Researchers investigated the effect of diet on DNA methylation, a type of DNA modification during which methyl groups are added to DNA. They studied a group of genetically identical mice, exposing half of them to a high-fat diet and the other half to a normal diet for 12 weeks. They then measured the methylation levels of a gene associated with obesity in liver cells from both groups. The results are shown in Figure 1.

Bar chart showing DNA methylation levels in liver cells. High-fat diet has around 57% methylation, while normal diet has about 15%.
Figure 1: DNA methylation in mice fed a normal diet and mice fed a high-fat diet.

Which of the following conclusions is best supported by the data?

  • A high-fat diet causes mutation in obesity-associated genes in mice.

  • DNA methylation levels are not affected by dietary changes.

  • Increased DNA methylation leads to higher expression of obesity-associated genes.

  • Environmental factors can lead to epigenetic modifications.

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The lac operon is a group of genes found in in prokaryotes that regulates production of the enzyme β-galactosidase. Scientists studied the effect of glucose and lactose sugar on the lac operon in E. coli bacteria. They set up four experimental conditions:

  1. no glucose or lactose

  2. glucose only

  3. lactose only

  4. both glucose and lactose

They measured the levels of β-galactosidase enzyme produced by bacteria under each condition. Which of the following is the correct null hypothesis for this investigation?

  • The presence or absence of glucose and lactose has no effect on β-galactosidase enzyme production in E. coli.

  • β-galactosidase enzyme is only produced by E. coli in the absence of both glucose and lactose.

  • The presence or absence of glucose and lactose has an effect on β-galactosidase enzyme production in E. coli.

  • β-galactosidase enzyme production in E. coli increases in the presence of lactose, regardless of glucose availability.

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Gene expression can be affected by modification of histone proteins. Histones can be modified by the removal of acetyl groups, a process that is catalysed by a group of enzymes known as histone deacetylases (HDACs). Researchers investigated the role of histone acetylation in gene expression. They treated human fibroblast cells with a histone deacetylase inhibitor (HDACi) and measured the expression levels of various genes over several hours. The results for one gene are shown in Figure 2.

Line graph showing gene expression levels increasing from 2 to 12 over 10 hours after HDACi treatment, then stabilizing from 12 to 25 hours.
Figure 2. The effect of HDACi treatment on gene expression over time

Which of the following conclusions about histone acetylation and gene expression is best supported by the data?

  •  Higher levels of histone deacetylation lead to increased gene expression.

  • The level of histone acetylation has no effect on gene expression.

  • A higher level of histone acetylation is linked to increased gene expression.

  • After the addition of HDACi gene expression increases until 12 hours and then remains constant.

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Genes involved in tumor development are typically classified into two main categories: oncogenes and tumor suppressor genes. Which of the following correctly describes the role of tumor suppressor genes?

  • Promoting rapid cell division and growth.

  • Coding for proteins that slow the cell cycle and signal apoptosis.

  • Binding to enhancer sequences to increase the rate of transcription.

  • Silencing DNA to prevent gene expression.

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Plant cells use transcription factors in a similar way to animal cells. One transcription factor found in plant cells is known as PIF. When activated PIF binds to a promoter region, triggering transcription of the amylase gene and initiating seed germination. PIF is inhibited a repressor protein called DELLA. The activity of PIF is regulated by the plant hormone gibberellin in the process shown in Figure 3.

Diagram illustrating the process where gibberellin triggers the breakdown of della, freeing PIF to bind to the promoter, initiating transcription.
Figure 3. The interaction between gibberellin and the DELLA repressor protein.

Which of the following best explains how the application of gibberellin hormone can facilitate the germination of seeds?

  • Gibberellin promotes the binding of DELLA to the amylase gene, preventing transcription.

  • Gibberellin activates an enzyme that breaks down DELLA, allowing PIF to activate transcription of the amylase gene.

  • Gibberellin binds to an enzyme, allowing it to attach to the promoter of the amylase gene and initiate transcription.

  • Gibberellin directly breaks down DELLA, allowing PIF to bind to the promoter region of the amylase gene.

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