Transamination, Ammonia and the Urea Cycle · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Passing nitrogen safely to urea

Science · Biochemistry & Molecular Biology · ages 21-22
Name ______________________   Date ____________

  1. Where does the urea cycle run?

    • In the stomach
    • In red blood cells
    • In the liver

  2. What is the first move an amino group makes toward disposal?

    • Direct release as free ammonia into blood
    • Transamination onto alpha ketoglutarate to form glutamate
    • Packaging into uric acid crystals

  3. Ammonia is poisonous even at low levels, so animals convert it into safer carriers.

    Circle one:   True   False

  4. After its amino group leaves, an amino acid remnant becomes pyruvate. What can the body do with it?

    • Excrete it unchanged as urea
    • Burn it for fuel or rebuild it
    • Store it as a gas

  5. Why does the cell move amino groups between carriers instead of releasing ammonia at once?

    • Bound nitrogen stays safe until locked into urea
    • Carriers are slower and waste time
    • Ammonia cannot dissolve in water

  6. Why do birds and reptiles pay extra energy for uric acid instead of using urea?

    • To fly faster
    • To avoid making ATP
    • To save water

  7. True or false: the urea cycle frees nitrogen gas into the air.

    Circle one:   True   False

  8. A student claims muscle frees ammonia into blood and the kidney finishes the job alone. What is wrong?

    • Nitrogen travels bound to the liver, where the cycle acts
    • Ammonia is harmless, so no job exists
    • The kidney makes all amino acids itself
LightMySky · lightmysky.comW1-mt_MFu5uQKyFL-s1

Answer key

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

Passing nitrogen safely to urea W1-mt_MFu5uQKyFL-s1

  1. In the liver · The liver frees ammonia from glutamate and captures it into urea there.
  2. Transamination onto alpha ketoglutarate to form glutamate · Transamination passes the group to a carrier instead of freeing it.
  3. True · Toxicity forces packaging: urea for mammals, uric acid for birds and reptiles.
  4. Burn it for fuel or rebuild it · Carbon skeletons rejoin metabolism as fuel or building material.
  5. Bound nitrogen stays safe until locked into urea · Each handoff keeps poison bound, releasing it only where the cycle can catch it.
  6. To save water · Uric acid needs little water for excretion, which suits their tighter water budgets.
  7. False · It shuttles nitrogen into urea, keeping it managed.
  8. Nitrogen travels bound to the liver, where the cycle acts · Free release never happens, and the liver, not the kidney, runs the capture cycle.
Worksheet · LightMySky