Protein Targeting and the Signal Sequence · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.
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Address tags for new proteins

Science · Organisms & Life Processes · ages 18-20
Name ______________________   Date ____________

  1. Chains all start in the cytosol but jobs live elsewhere, so no sorting is needed. True or false?

    Circle one:   True   False

  2. What is a signal sequence?

    • A short address tag on a new chain
    • A sugar tag added later in the Golgi
    • The ribosome that builds the chain

  3. Deleting the signal from a secreted protein strands it in the cytosol. True or false?

    Circle one:   True   False

  4. A protein targeting sequence is swapped for another type. What happens?

    • Nothing changes wherever the new tag points
    • The protein follows the new tag
    • Translation stops at once

  5. What does the rough ER build?

    • Lipids only and no proteins at all
    • Cytosolic enzymes for the home market
    • Proteins for export or membranes

  6. How does translation of a secreted protein differ from a cytosolic one?

    • It runs straight through without any pause at all
    • It stops and starts over from scratch
    • It pauses at the signal, then ends on the ER

  7. Proteins without ER signals are secreted outside. True or false?

    Circle one:   True   False

  8. A cytosolic enzyme that gains an ER signal stays cytosolic. True or false?

    Circle one:   True   False

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Answer key

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

Address tags for new proteins W1-mt_wVFZq8cZgn-s1

  1. False · One birthplace with many workplaces demands sorting.
  2. A short address tag on a new chain · The short stretch flags the protein for the ER and its station.
  3. True · With no tag, no docking happens and the chain finishes at home.
  4. The protein follows the new tag · Presence and type of tag predict destination.
  5. Proteins for export or membranes · Docked ribosomes feed export and membrane cargo into the ER.
  6. It pauses at the signal, then ends on the ER · Targeting interrupts translation mid stream to dock the ribosome.
  7. False · Without docking they stay in the home market.
  8. False · The new tag docks its ribosome on the ER.
Worksheet · LightMySky