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Volume I · MMXXVI AP Biology
Library› AP Biology› Unit 6: Gene Expression and Regulation
⁂   AP Biology · Unit 6

6. Gene Expression and Regulation

12–16% of the AP exam. 9 key topics. 4 common errors analyzed.

12–16% exam weight 20 instructional periods

Unit 6: Gene Expression and Regulation

Unit 6 covers gene expression and regulation — a core component of the AP Biology curriculum. Master these concepts to build the mechanistic vocabulary the FRQ rubrics demand.

Key topics in this unit

  1. DNA structure: double helix, antiparallel strands, complementary base pairing
  2. DNA replication: semiconservative model, leading and lagging strand synthesis, key enzymes (helicase, primase, DNA polymerase, ligase)
  3. Transcription: RNA polymerase, promoter recognition, mRNA synthesis, termination
  4. Translation: ribosome structure, tRNA-codon matching, polypeptide elongation and termination
  5. Gene regulation in prokaryotes: lac operon model (inducible), trp operon (repressible)
  6. Gene regulation in eukaryotes: transcription factors, enhancers, silencers, chromatin remodeling
  7. Post-transcriptional regulation: 5' cap and poly-A tail, splicing (introns/exons), miRNA, siRNA
  8. Epigenetic mechanisms: DNA methylation and histone acetylation/methylation effects on gene expression
  9. Biotechnology applications: PCR, gel electrophoresis, CRISPR-Cas9, bacterial transformation, recombinant DNA technology

Common errors — what the rubric penalizes

These are the most frequently penalized mistakes on AP exam FRQs and MCQs. Review each before your next practice session.

Common error

Confusing the template strand with the coding strand during transcription — the mRNA sequence matches the coding (non-template) strand (with U replacing T), not the template strand

Common error

Misapplying the lac operon model: the repressor is active (binds operator) when lactose is absent, and inactive (cannot bind operator) when lactose (allolactose) is present

Common error

Conflating prokaryotic gene regulation (single operon, no nuclear membrane, immediate translation) with eukaryotic regulation (nucleus, post-transcriptional processing, chromatin-level control)

Common error

Stating that histone acetylation always silences gene expression — acetylation loosens chromatin (activates transcription); methylation context-dependently activates or silences

Study checklist

  • Can you list all key topics from memory without this page?
  • Have you worked through at least one FRQ-style question per topic?
  • Can you explain each common error above — and why the correct answer differs?
  • Have you reviewed the relevant College Board CED section and formula sheet entries?
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Our worked solutions and practice questions are original instructional content created by Tian2 AP. They are aligned to the concepts and skills described in College Board’s Course and Exam Description and are not reproductions of, or affiliated with, College Board’s official materials.