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AP® Biology Unit 6 Review and Practice Test: Gene Expression and Regulation

Struggling with AP® Biology Unit 6 prep? We have got you covered. UWorld provides a thorough coverage of Gene Expression and Regulation, where our AP experts break down concepts like DNA, RNA, protein synthesis, genotype and phenotype, cell specialization, and more. So, whether you need help with AP Bio Unit 6 FRQs and MCQs, or simply want to understand concepts in detail, choosing UWorld can lead you to a 5.

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Try These AP Biology Unit 6 Practice Test Questions

Study with UWorld for AP Biology: Gene Expression and Regulation. Our AP Bio Unit 6 MCQs mimic the difficulty of the real exam, so you are fully prepared. Each question comes with detailed step-by-step explanations, helping you understand the right and wrong behind every answer choice.
Try these sample practice questions with detailed answer explanations:
Gene Expression and Regulation Practice Tests

Question

Some small interfering RNAs (siRNAs) are known to regulate gene expression in eukaryotic cells. In an experiment, two groups of eukaryotic cells were each stimulated to take up different siRNA molecules (siRNA 1 or siRNA 2). Both of these siRNAs are known to affect gene expression. A third group of cells was stimulated to take up control siRNAs, which were engineered to have no effect on gene expression. After 72 hours, the mRNA levels for three genes were measured in each group. The graph below shows the results of this experiment.

Which of the following statements about these siRNA molecules is best supported by the results presented in the graph?

A. siRNA 1 binds and causes the degradation of Gene B mRNA; siRNA 2 binds and causes the degradation of Gene A mRNA.
B. siRNA 1 binds and causes the degradation of Gene A mRNA; siRNA 2 binds and causes the degradation of Gene B mRNA.
C. Both siRNA 1 and siRNA 2 bind the mRNA molecules produced from all three genes.
D. Both siRNA1 and siRNA 2 have identical nucleotide sequences.

Explanation

When genes are transcribed into mRNA transcripts, regulation of gene expression occurs post-transcriptionally (ie, at the level of the transcript). MicroRNAs (miRNAs) and small interfering RNAs (siRNAs) are small, noncoding elements that perform post-transcriptional regulation. These small RNAs often form complexes with specific proteins and bind complementary nucleotide sequences on target mRNA molecules, causing mRNA degradation or inhibition of translation.

In this question, two groups of eukaryotic cells were each stimulated to take up different siRNA molecules that affected gene expression. A third group of cells took up control siRNA that did not affect expression. The graph shows that, compared to cells with control siRNAs, cells that took up siRNA 1 exhibited decreased Gene A mRNA levels, whereas cells that took up siRNA 2 exhibited decreased Gene B mRNA levels.

Therefore, siRNA 1 binds and degrades Gene A mRNA, whereas siRNA 2 binds and degrades Gene B mRNA (Choice A).

(Choice C) siRNA 1 only decreased Gene A mRNA levels and siRNA 2 only decreased Gene B mRNA levels. In addition, neither siRNA 1 nor siRNA 2 affected Gene C expression compared to control cells. Therefore, siRNA 1 and siRNA 2 do not bind mRNA produced from all three genes to regulate their expression.

(Choice D) siRNA 1 and siRNA 2 decrease mRNA expression for different genes ( Genes A and B ), indicating that the nucleotide sequence complementary to the target mRNA is different (not identical) in each siRNA molecule.

Things to remember:
Small interfering RNAs (siRNAs) are small, noncoding RNA molecules that bind target mRNA molecules, often causing mRNA degradation.

Question

In a gene expression study, scientists extracted RNA samples from eukaryotic cells. These initial samples contained all types of RNA found within the cells. They then added a specialized solution containing microscopic magnetic beads to the RNA samples. These beads consisted of synthetic pieces of single-stranded DNA made up of repeated thymine nucleotides. These thymine nucleotides are able to form hydrogen bonds with mature mRNA molecules that have been modified in the nucleus. Once bound to mRNA, the beads were collected using a specialized magnet, allowing mature mRNA to be isolated from the initial RNA samples. Which of the following best describes how these beads most likely bound the mRNA molecules?

A. The thymine nucleotides of the beads formed hydrogen bonds with the nucleotides in the poly-A tails of the mRNA molecules.
B. The thymine nucleotides of the beads formed hydrogen bonds with many different types of nucleotides in the coding regions of the mRNA molecules.
C. The thymine nucleotides of the beads formed hydrogen bonds with all three nucleotides of the universal start codons (AUG) in the mRNA molecules.
D. The thymine nucleotides of the beads formed hydrogen bonds with the GTP caps of the mRNA molecules.

Explanation

During eukaryotic gene expression, genes are initially transcribed into pre-messenger RNA (pre-mRNA) molecules in the nucleus. Prior to translation, pre-mRNA undergoes a series of modifications to form mature mRNA, including the splicing (ie, removal) of noncoding introns as well as the addition of a 3' poly-adenine (poly-A) tail and a 5' GTP cap.

Specifically, both the poly-A tail and GTP cap allow mature mRNA to exit the nucleus and enter the cytoplasm for translation. Once in the cytoplasm, the poly-A tail and GTP cap help prevent mRNA degradation and allow ribosomes to recognize and bind mRNA.

In this question, magnetic beads were added to eukaryotic RNA samples. These beads contained single-stranded DNA pieces made up of repeated thymine (T) nucleotides that bound mature mRNAs. Because all mature mRNAs have poly-A tails, the thymine nucleotides of the beads likely formed complementary hydrogen bonds with the adenine nucleotides of the mRNA poly-A tails.

(Choice B) In base pairing, thymine always pairs with adenine. Therefore, thymine nucleotides would not form hydrogen bonds with many different nucleotide types in mRNA coding regions.

(Choice C) All mRNA molecules have a universal start codon (AUG) where translation begins. Although one thymine nucleotide could bond with the adenine (A) in the start codon, thymine would not be complementary to uracil (U) or guanine (G).

(Choice D) Although all mature mRNAs have GTP caps, this region does not contain nucleotides complementary to thymine.

Things to remember:
In eukaryotic cells, pre-mRNA transcribed in the nucleus is modified to produce mature mRNA. Modifications include splicing (removing) introns and adding a 3' poly-A tail and 5' GTP cap.

Question

miR-1 is a small, noncoding nucleic acid that is single-stranded in nature and has ribose-containing nucleotides. miR-1 has been found in animal heart muscle cells (cardiomyocytes), which contract to facilitate the pumping action necessary to circulate blood throughout the body. Scientific research has proven that miR-1 posttranscriptionally regulates the production of HSP60, a protein known to prevent damage to other proteins in high-heat environments. Which of the following would best describe how miR-1 acts to regulate HSP60 expression in cardiomyocytes?

A. miR-1 is read by ribosomes to generate HSP60 proteins.
B. miR-1 pairs with proteins to form the ribosomes that will translate HSP60 proteins.
C. miR-1 binds to complementary sequences on HSP60 mRNA, inhibiting its translation into proteins.
D. miR-1 transfers incorrect codons to the ribosome, resulting in permanently shortened HSP60 proteins.

Explanation

When genes are transcribed into messenger RNA (mRNA) transcripts, gene expression can be regulated at the level of the transcript. This kind of posttranscriptional regulation can be carried out by many elements, including small, noncoding RNA molecules such as microRNAs (miRNAs) and small interfering RNAs (siRNAs).

miRNAs bind to complementary sequences on target mRNAs to inhibit target gene expression. miRNA exerts its gene-silencing effects by forming a complex with a specific protein. The miRNA component of the protein-miRNA complex then binds to the complementary region of the target mRNA to either degrade the target mRNA or to block ribosome access to the target mRNA (prevents translation). In this way, miRNAs control which genes are expressed and which genes are not.

In this question, miR-1 most likely binds to complementary sequences on HSP60 mRNA, thereby inhibiting its translation into protein. Therefore, miR-1 posttranscriptionally regulates the expression levels of HSP60 in cardiomyocytes.

The following RNAs have other functions:

  • (Choice A) mRNA carries the protein-coding message in DNA within the nucleus to the ribosome in the cytoplasm. This occurs because eukaryotic DNA does not leave the nucleus.

  • (Choice B) Ribosomal RNA (rRNA), along with associated proteins, forms ribosomes.

  • (Choice D) Transfer RNA (tRNA), functions during translation and transfers the correct amino acid to the ribosome; this new amino acid is added to a growing polypeptide chain.

Things to remember:
MicroRNAs are small, noncoding RNA molecules that bind to complementary sequences on target mRNA to degrade the target mRNA or block it from being translated by the ribosome.

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Frequently Asked Questions (FAQs)

Following are the topics covered in AP Bio Unit 6: Gene Expression and Regulation:

  1. DNA and RNA Structure 
  2. DNA Replication 
  3. Transcription and RNA
  4. Translation 
  5. Regulation of Gene Expression
  6. Gene Expression and Cell Specialization
  7. Mutations
  8. Biotechnology
Start your overall prep at least 2-3 months before your exam and create a study schedule that works for you. Use a quality prep like UWorld, which comes with a comprehensive study guide, an extensive question bank, digital study tools such as flashcards and notebooks, and a performance tracking dashboard, to get a thorough coverage of all the concepts and achieve your desired score.
You can use Khan Academy for basic understanding of concepts or UWorld’s free trial to get an idea of our AP Bio Unit 6 coursework and teaching methodology. Once you are satisfied with the free trial, switch to the full subscription to utilize all the study resources.
AP Bio Unit 6 consists of two types of questions: Multiple-Choice (MCQs) and Free-Response (FRQs). While the MCQs test your understanding of key concepts, the FRQs require you to apply your knowledge to experimental scenarios.
Practice as much as you can. Look at past year sample FRQs to get an idea about the difficulty level of questions. Please note that this winter, UWorld is launching AP Bio Unit 6 FRQs with an AI-powered scoring system to help you understand what AP graders actually look for in your answers.
AP Biology Unit 6: Gene Expression and Regulation accounts for 12-16% of the exam weight and requires around 18-20 AP class periods to cover the contents.
UWorld provides an excellent Unit 6 AP Bio study guide, including thorough coverage of the content, colorful, well-labelled images and Check-for-Understanding questions. You can buy our study guide on Amazon or directly on UWorld’s website.
Yes, UWorld lets you do custom practice to focus solely on Unit 6. This topic-wise practice helps in reviewing topics as many times as you want until you understand them completely and feel confident about taking the exam.
The important terms to remember for AP Bio Unit 6 include operon, transcription factor, mRNA, RNA polymerase, repressor, promoter, enhancer, epigenetic modification and more. You can use UWorld’s study guide to get the full glossary of the key terms and important concepts.
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