AP Biology: Gene Expression and Regulation Practice Questions
Test yourself on AP Biology: Gene Expression and Regulation with 12 original AP Exams practice questions. Pick an answer to see instant feedback and a full explanation.
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1. A mutation prevents RNA polymerase from binding efficiently to a bacterial promoter. Which outcome is most likely?
Explanation. A promoter is a DNA region where RNA polymerase and associated factors begin transcription. If RNA polymerase cannot bind efficiently, fewer RNA transcripts are made from that gene. Ribosomes translate mRNA; they do not bind directly to DNA promoters.
2. In a repressible operon, a corepressor binds to a repressor protein and activates it. What does the activated repressor usually do?
Explanation. In a repressible operon, the corepressor helps the repressor bind the operator. This blocks RNA polymerase from transcribing the operon's structural genes. Splicing, translation, and reverse transcription are different processes.
3. The lac operon is most strongly expressed when which conditions are present?
Explanation. Lactose leads to inactivation of the lac repressor, allowing transcription. Low glucose raises cAMP, which helps CAP bind near the promoter and increases transcription. If the promoter is deleted, RNA polymerase cannot initiate normal transcription.
4. Why can two specialized cells in the same multicellular organism have different proteins even though they contain the same genome?
Explanation. Cell specialization depends largely on differential gene expression. Cells can contain the same DNA but transcribe and translate different genes because of regulatory proteins, chromatin state, signaling, and developmental history.
5. A transcription factor binds an enhancer far from a eukaryotic gene's promoter. How can it still affect transcription of that gene?
Explanation. Eukaryotic DNA can bend and loop, allowing proteins bound at distant enhancers to interact with promoter-associated proteins. This can increase or sometimes regulate transcription without requiring the enhancer to sit directly beside the promoter.
6. Histone acetylation near a gene is often associated with increased transcription. Which explanation best fits this pattern?
Explanation. Adding acetyl groups to histone tails can reduce tight interactions between histones and DNA, producing a more open chromatin structure. Open chromatin is generally more accessible for transcription factors and RNA polymerase.
7. DNA methylation at a gene's regulatory region often reduces transcription. Which mechanism is most consistent with this effect?
Explanation. DNA methylation can silence genes by making regulatory DNA less accessible or by recruiting proteins that promote compact chromatin. It does not alter mRNA bases or cause ribosomes to translate DNA.
8. A eukaryotic pre-mRNA is alternatively spliced in two tissues. What is a likely result?
Explanation. Alternative splicing combines exons in different patterns, allowing one gene to produce multiple mRNA isoforms and potentially different protein variants. The chromosome itself is not edited by the splicing event.
9. A microRNA pairs with a complementary sequence on a target mRNA. Which outcome is most likely?
Explanation. MicroRNAs are small regulatory RNAs that can bind target mRNAs and reduce protein production by blocking translation or promoting mRNA breakdown. This is post-transcriptional regulation.
10. A point mutation changes a codon but the same amino acid is added during translation. What kind of mutation is this?
Explanation. Because the genetic code is redundant, some codon changes still specify the same amino acid. That is a silent mutation at the protein-sequence level. A nonsense mutation creates a stop codon, and a frameshift changes the reading frame.
11. A mutation creates an early stop codon in the coding sequence of a gene. What is the most direct expected effect?
Explanation. An early stop codon is a nonsense mutation. During translation, the ribosome stops prematurely, often producing a shortened protein that may not function normally.
12. During early development, a gradient of a regulatory protein causes different cells to activate different target genes. What does this example illustrate?
Explanation. Development often depends on spatial signals and concentration gradients. Cells exposed to different amounts of a regulatory protein can activate different transcriptional programs, leading to different cell fates.
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FAQ
What should I know about gene regulation for AP Biology?
Focus on how cells control when genes are transcribed, how RNA is processed, how translation is regulated, and how protein activity can be changed after translation. Know examples such as operons, transcription factors, chromatin modification, alternative splicing, and microRNAs.
How are prokaryotic and eukaryotic gene regulation different?
Prokaryotes often regulate groups of related genes in operons, especially at transcription initiation. Eukaryotes regulate genes at many layers, including chromatin structure, enhancers, transcription factors, RNA processing, mRNA stability, translation, and protein modification.
What mistakes should I avoid on AP Biology gene expression questions?
Do not mix up DNA, RNA, and protein roles. Promoters and enhancers are DNA regulatory sequences, transcription makes RNA, splicing edits pre-mRNA, and translation makes protein. Also remember that regulation can happen before, during, or after transcription and translation.