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AP Course

AP Biology

Updated for the AP Biology framework effective fall 2025, with concept lessons, data reasoning, quizzes, and practice problems.

Explore life from molecules and cells to evolution and ecosystems through the official AP Biology unit sequence.

Lessons
Structure of Water and Hydrogen BondingElements of LifeIntroduction to MacromoleculesCarbohydratesLipidsNucleic AcidsProteinsCell Structure and FunctionCell SizePlasma MembraneMembrane PermeabilityMembrane TransportFacilitated DiffusionTonicity and OsmoregulationMechanisms of TransportCell CompartmentalizationOrigins of Cell CompartmentalizationEnzymesEnvironmental Impacts on Enzyme FunctionCellular EnergyPhotosynthesisCellular RespirationCell CommunicationIntroduction to Signal TransductionSignal Transduction PathwaysFeedbackCell CycleRegulation of Cell CycleMeiosisMeiosis and Genetic DiversityMendelian GeneticsNon-Mendelian GeneticsEnvironmental Effects on PhenotypeDNA and RNA StructureDNA ReplicationTranscription and RNA ProcessingTranslationRegulation of Gene ExpressionGene Expression and Cell SpecializationMutationsBiotechnologyIntroduction to Natural SelectionNatural SelectionArtificial SelectionPopulation GeneticsHardy–Weinberg EquilibriumEvidence of EvolutionCommon AncestryContinuing EvolutionPhylogenySpeciationVariations in PopulationsOrigins of Life on EarthResponses to the EnvironmentEnergy Flow Through EcosystemsPopulation EcologyEffect of Density on PopulationsCommunity EcologyBiodiversityDisruptions in Ecosystems
Quizzes
Practice Problems Lab design, data analysis, and FRQ practice resources can be added here.

AP Biology · Unit 6 · Topic 6.5

Regulation of Gene Expression

Information flows through regulated molecular steps, and changes in sequence or expression can alter phenotype.

1. Topic Lens

Regulation of Gene Expression is studied through gene expression and regulation. Connect the system boundary, interacting parts, and measurable evidence before applying a formula.

\[N_{aa}=\frac{N_{\text{coding nucleotides}}}{3}-1\]

2. Why the Formula Works

The relationship is built from definitions and conservation reasoning:

  1. Translation reads nonoverlapping nucleotide triplets called codons.
  2. One codon terminates translation and does not add an amino acid.
  3. For a coding region that includes the stop codon, divide by three and subtract one.
\[3N_{aa}+3=N_{\text{coding nucleotides}}\]

3. Detailed Visual Model

Pixel diagram for Regulation of Gene ExpressionOriginal schematic connecting Regulation of Gene Expression to Gene Expression and Regulation.
Regulation of Gene Expression: an original pixel-style model. Use it as a schematic, not a literal scale drawing.

4. Worked Example and Lab Link

A coding sequence contains 300 nucleotides including one stop codon. What is the maximum peptide length?

Answer: There are 100 codons; one is stop, so the peptide contains 99 amino acids.

Investigation idea: Translate original short DNA variants with a codon chart and compare silent, missense, and nonsense outcomes.

Common trap: Do not translate promoter or intron sequences, and remember that the stop codon encodes no amino acid.

Checkpoint · Topic 6.5

Explain how regulation of gene expression supports or limits this conclusion: There are 100 codons; one is stop, so the peptide contains 99 amino acids.

Official curriculum reference: College Board AP Biology course page. The explanation and worked example are independently written for this study site.