Enhancers, Accessibility and Combinatorial Control · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Far away, yet in touch

Science · Genetics & Evolution · ages 19-21
Name ______________________   Date ____________

  1. An enhancer works only when placed at an exact distance facing one way.

    Circle one:   True   False

  2. How does an enhancer thousands of bases away affect its promoter?

    • It slides along the DNA until it collides
    • It copies itself next to the promoter
    • The DNA loops so bound activators touch the promoter complex

  3. Why is the same enhancer active in neurons but silent in liver?

    • Its activators are present and its chromatin is open only there
    • Its DNA sequence changes between the two cell types
    • Promoters refuse all contact in liver cells

  4. What does mediator do at an active enhancer?

    • It unwinds the DNA double helix
    • It degrades unneeded transcription factors
    • It links bound activators to the promoter complex

  5. What does combinatorial control mean?

    • One master switch per gene decides everything
    • Each gene reads a pattern of factors, firing only for approved mixes
    • Genes ignore repressors and chromatin entirely

  6. A gene needs factors A and B together. A cell supplies only A. What happens?

    • The gene stays silent; one required activator is missing
    • The gene fires fully; one activator is enough
    • The gene deletes its own enhancer

  7. A mutation closes the chromatin over an enhancer but leaves its sequence intact. What happens?

    • The enhancer fires even stronger
    • Nothing changes; sequence is all that counts
    • The enhancer goes silent and its gene drops

  8. Sam says each gene has one master switch factor and nothing else matters. What is wrong?

    • He is right; find each gene's single switch
    • Genes read combinations, so one factor rarely decides alone
    • Repressors never matter, only activators do
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Answer key

For grown-ups. Fold this page away before handing over the rest.

Far away, yet in touch W1-mt_BTMCj6V6jD-s1

  1. False · Distance and orientation matter little; occupancy matters most.
  2. The DNA loops so bound activators touch the promoter complex · Looping brings far-apart sites together in space.
  3. Its activators are present and its chromatin is open only there · Identical DNA fires only where context allows.
  4. It links bound activators to the promoter complex · Mediator bridges the loop between enhancer and promoter.
  5. Each gene reads a pattern of factors, firing only for approved mixes · A handful of shared factors mixes into thousands of patterns.
  6. The gene stays silent; one required activator is missing · Approved combinations need every required piece present.
  7. The enhancer goes silent and its gene drops · Regulation lives in protein and chromatin context, not sequence alone.
  8. Genes read combinations, so one factor rarely decides alone · Shared factors mix differently per gene to set patterns.
Worksheet · LightMySky