Review Problems #3 Calvin Cycle, Pentose Phosphate Pathway
1) Rubisco contains an essential active site magnesium. Draw the relevant substrate
contacts, as well as any special groups from the enzyme that make direct contact.
1a) Describe the chemical role of magnesium in promoting catalysis.
2) Draw the reaction and a notional mechanism for the transformation catalyzed by
rubisco.
3) Draw the unwanted competing side reaction (and a mechanism) catalyzed by rubisco.
3a) What is the ultimate fate of the molecules produced in this unwanted process?
3b) Why is this process referred to as photorespiration?
4) What are the three stages of the Calvin cycle?
5) Draw the molecules that start and end the first stage of the cycle.
6) Draw the molecules that start and end the second stage of the cycle.
7) What are the three enzymes of the Calvin cycle that are responsible for forming
carbon-carbon bonds?
8) Name the essential cofactor and draw the chemically active portion this molecule used
in two carbon transfer processes in the Calvin cycle and pentose phosphate pathway.
8a) Draw the mechanism of the reaction catalyzed in question eight
.
9) The Calvin cycle contains two transformations that generate five carbon sugars. Draw
these two reactions. Draw the reaction that generates a seven carbon sugar.
10) Draw the mechanism for the enzyme that catalyzes addition of DHAP to an aldose.
Make sure to show the structure and role of the covalent enzyme-substrate adduct.
11) What are the energetic requirements of a full turn through the cycle? (Don’t forget
reductants)
12) What two major storage forms of sugar are found in plants?
13) What molecules regulate the Calvin cycle? Explain the logic of how these molecules
relate to photosynthesis.
14) Draw the mechanism for the transketolase reaction.
15) What are the basic differences between the regeneration portion of the Calvin cycle
and the nonoxidative portion of the PPP?
16) Why do these differences exist?
17) What is the basic difference between aldolase and transaldolase?
18) Was is meant by an enzymopathy? What is the major enzymopathy associated with
the PPP? What are the consequences?
19) What are the sources of NADPH in mammalian systems?