Small RNAs and silencing after transcription · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Silenced after the message is made

Science · Genetics & Evolution · ages 20-21
Name ______________________   Date ____________

  1. What is the direct target in the post-transcriptional small-RNA pathway taught here?

    • The target gene's promoter DNA
    • The target gene's enhancer DNA
    • An mRNA paired with the guide

  2. What helps a guide RNA recognise a target mRNA?

    • Complementary guide-target pairing
    • High transcription at the target gene's promoter
    • The target message's total length rather than its local sequence

  3. Extensive guide-target pairing can allow an active slicing Argonaute to cleave the target mRNA.

    Circle one:   True   False

  4. Cleavage increases target mRNA decay at each abundance. Production stays fixed. Compared with the old steady state, what is the new steady-state abundance?

    • Unchanged, because production remains at its previous rate
    • Lower, because loss is faster
    • Higher, because faster turnover requires more messages

  5. A microRNA partly pairs with a target. Must the target's mRNA abundance remain unchanged during repression?

    • No; partial pairing can promote decay
    • Yes; mismatches prevent the target RNA from decaying
    • Yes; repression with mismatches affects translation alone

  6. mRNA stays at 100% of control, while protein abundance falls to 20%. What would measuring only mRNA miss?

    • The directly measured change in transcription initiation rate
    • The evidence proving that the guide cleaved the target
    • The reduction in protein abundance

  7. One guide represses mRNAs R and S. Only R's recognition site is altered, preventing recognition of R. The guide, S and indirect regulation remain unchanged. This site alteration alone should relieve the guide's repression of both messages.

    Circle one:   True   False

  8. A student says normal mRNA abundance proves normal protein production. Which correction is supported?

    • Translation can fall despite normal mRNA
    • Normal message abundance fixes translation rate per message
    • Normal mRNA shows that reduced protein must result from faster degradation
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Answer key

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

Silenced after the message is made W1-mt_1AozDyS1Mn-s1

  1. An mRNA paired with the guide · This pathway acts through guide pairing with mRNA, rather than direct recognition of a promoter or enhancer.
  2. Complementary guide-target pairing · Complementary pairing helps recognition. Other pairing features and target context also affect silencing.
  3. True · Cleavage is possible when suitable pairing and an active slicing Argonaute are both present.
  4. Lower, because loss is faster · With fixed production and faster decay, production and loss balance at a lower mRNA abundance.
  5. No; partial pairing can promote decay · Partial pairing can reduce translation and promote decay. It does not guarantee unchanged message abundance.
  6. The reduction in protein abundance · The mRNA measurement is unchanged but the protein measurement is lower. These data alone do not identify the cause.
  7. False · The alteration prevents recognition of R, not S. The unchanged guide can still recognise and repress S through its unchanged site.
  8. Translation can fall despite normal mRNA · Message abundance does not establish translation rate. Faster protein degradation is another possible cause of low protein abundance, not the only one.
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