Metabolic Engineering: Redirecting Flux Through a Production Host · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Steering carbon toward your product

Science · Microbiology · ages 23-24
Name ______________________   Date ____________

  1. What is a branch point leak?

    • A hole in the bioreactor wall
    • A native enzyme draining the shared intermediate into its own product
    • A mutation that deletes your whole pathway

  2. You move a new pathway into a host. What must it balance?

    • Carbon in and out, plus ATP and redox cofactors
    • Only the carbon atoms, nothing else
    • Only the culture temperature and pH

  3. A growth coupled or inducible design usually beats constant overexpression of the production pathway.

    Circle one:   True   False

  4. In a healthy cell, ATP runs high. What do the early energy enzymes do?

    • Throttle back through feedback
    • Work faster without limit
    • Switch to a different fuel permanently

  5. You found the branch point where a native enzyme steals your intermediate. How do you redirect flux?

    • Dial down the rival enzyme, or boost your own
    • Delete the feed stock from the medium
    • Raise the temperature until all enzymes slow equally

  6. Your strain has plenty of carbon feed but product flux stalls. Redox measurements show empty reserves. What caps the yield?

    • The carbon feed rate
    • The stirrer speed in the tank
    • Cofactor refill: each molecule spends redox and energy tokens

  7. In a growth coupled design the fastest growers are also the top producers. Why?

    • Fast cells eat the product of slow cells
    • The cell must make your product in order to grow
    • Growth medium always contains extra product

  8. An always on production strain loses output after many generations, and non producers take over. Why?

    • The product inhibits its own sale price
    • Constant burden invited mutants that dropped the pathway, and they outgrew the producers
    • Branch points seal themselves with age
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Answer key

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

Steering carbon toward your product W1-mt_fjz3EA-dDa-s1

  1. A native enzyme draining the shared intermediate into its own product · At the branch, the native rival siphons the intermediate you wanted.
  2. Carbon in and out, plus ATP and redox cofactors · Carbon, energy, and redox must all close, or the host starves while producing.
  3. True · Timed designs tax the cell only when production pays, instead of carrying the burden always.
  4. Throttle back through feedback · Feedback brakes keep carbon, energy, and redox in line without any engineer watching.
  5. Dial down the rival enzyme, or boost your own · Shifting the race at the branch sends more intermediate down your path.
  6. Cofactor refill: each molecule spends redox and energy tokens · Carbon alone cannot push flux when the redox and energy tokens run dry.
  7. The cell must make your product in order to grow · Coupling ties the two fates together, so selection for growth is selection for production.
  8. Constant burden invited mutants that dropped the pathway, and they outgrew the producers · Always on pathways tax the cell, so selection favors every mutant that sheds the load.
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