Name the stage of the Calvin cycle for each of these…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Name the stage of the Calvin cycle for each of these. (a) RuBP is joined to carbon dioxide. (b) 3-PGA is changed to triose phosphate. (c) RuBP is made again. (d) Which stages spend ATP, and which stage spends NADPH? (e) In which part of the chloroplast does the cycle run?
Need a reminder? The key ideaShow
Calvin cycle (C3 pathway, in the stroma): carboxylation (RuBP, 5C, plus carbon dioxide, by RuBisCO, gives two 3-PGA, 3C), reduction (2 ATP and 2 NADPH for each carbon dioxide, gives triose phosphate), regeneration (1 ATP for each carbon dioxide). Each carbon dioxide: 3 ATP and 2 NADPH. One glucose: 6 turns, 18 ATP, 12 NADPH. Six turns: 6 RuBP (30 C) and 6 CO2 (6 C) give 12 triose phosphate (36 C); 2 leave as glucose (6 C) and 10 (30 C) rebuild 6 RuBP.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. (a) Joining carbon dioxide to RuBP is carboxylation, with the enzyme RuBisCO.
Step 2. (b) PGA to triose phosphate is reduction.
Step 3. (c) Making RuBP again is regeneration.
Step 4. (d) Reduction spends ATP and NADPH. Regeneration spends ATP. Only reduction spends NADPH.
Step 5. (e) The cycle runs in the stroma.
Answer: (a) carboxylation; (b) reduction; (c) regeneration; (d) ATP in reduction and regeneration, NADPH in reduction only; (e) the stroma.
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