AP Biology / Gene Expression and Regulation
Lesson
Not every gene is on in every cell
Regulation saves energy and makes cell types.
Learning goals
- Explain why two cells with the same DNA can make different proteins.
- Give a simple example of a regulatory switch.
Explanation
A liver cell and a neuron share a genome in one body, yet they transcribe different sets of genes. Transcription factors, enhancers, packing of DNA, and later RNA processing all act as switches and dimmers. Development is largely a story of turning the right genes on at the right time.
In bacteria, a classic classroom switch is an operon that stays off when a nutrient is absent and turns on when the nutrient appears. Eukaryotes use more layers. The shared idea is economy and identity: do not build a protein you do not need.
Key terms
- Gene regulation. Control of whether, when, and how much a gene is expressed.
- Mutation. A change in a DNA sequence, which may or may not change a phenotype.
Common mistakes
- Saying specialized cells “lose the genes” they do not use.
- Treating all mutations as harmful.
Practice
Original Marlow Works items. Check the answer explanation after you try.
A cell’s surface-area-to-volume ratio is important because it affects:
Original Marlow Works item — not a College Board question.
Take your time—this is practice, not a test.
Answer explanation
If a transcription factor for a muscle gene is missing, what happens to the DNA sequence of that gene?
Answer. The sequence can still be intact; it may simply not be transcribed in that cell.
Regulation changes expression, not necessarily the stored information.
Related resources
External links with reuse status. Marlow Works is independent and does not copy restricted exam or textbook material.
Official / link only
AP Biology course page
Official eight-unit framework, science practices, and lab resources.
College Board · All rights reserved · accessed 2026-10-01
Open sourceReference only — do not copy
OpenStax Biology 2e
Biology reference with commercial-use restrictions on the current publisher page.
OpenStax · CC BY-NC-SA 4.0 with additional restrictions · accessed 2026-10-01
Link only unless permission is obtained.
Open source