Question 1

Which enzyme catalyzes the initial fixation of CO$$_2 in $$the Calvin cycle, and what is the immediate product of this reaction?

Accepted Answer

Rubisco; two molecules of 3-phosphoglycerate

Question 2

During the Calvin cycle, which molecule acts as the direct precursor for the synthesis of the storage polysaccharide amylose?

Accepted Answer

Glucose-1-phosphate

Question 3

How many molecules of glyceraldehyde 3-phosphate (GAP) are produced from six molecules of CO$$_2$$ entering the Calvin cycle, and how many of these are used for hexose synthesis?

Accepted Answer

12 GAP produced; 2 used for hexose synthesis

Question 4

Which of the following best describes the role of ATP and NADPH in the Calvin cycle?

Accepted Answer

ATP is used for phosphorylation, and NADPH is used for reduction reactions

Question 5

Which reaction in the Calvin cycle is analogous to a step in gluconeogenesis, and what enzyme catalyzes this reaction?

Accepted Answer

Dephosphorylation of fructose 1,6-bisphosphate by fructose 1,6-bisphosphatase

Question 6

In the regeneration phase of the Calvin cycle, how are the six molecules of RuBP (ribulose-1,5-bisphosphate) reformed from the products of the previous steps?

Accepted Answer

By combining two hexoses and six trioses

Question 7

What is the overall stoichiometry for the Calvin cycle in terms of CO$$_2$$ fixation and GAP production per glucose molecule synthesized?

Accepted Answer

$$6\ \mathrm{CO}_2 \rightarrow 12\ \mathrm{GAP}$$

Question 8

A plant is exposed to a chemical that inhibits phosphoglycerate kinase. Which Calvin cycle intermediate would you expect to accumulate as a result?

Accepted Answer

3-phosphoglycerate

Question 9

Which step in the Calvin cycle directly consumes ATP?

Accepted Answer

Phosphorylation of 3-phosphoglycerate to 1,3-bisphosphoglycerate

Question 10

If a mutation rendered ribulose-5-phosphate kinase nonfunctional, what would be the immediate consequence for the Calvin cycle?

Accepted Answer

Accumulation of ribulose-5-phosphate and inability to regenerate RuBP

Question 11

Which of the following best explains why only two out of twelve GAP molecules produced per six CO$$_2$$ fixed are used for hexose synthesis?

Accepted Answer

The remaining GAP molecules are used to regenerate RuBP

Question 12

Which enzyme catalyzes the combination of GAP and DHAP to form fructose 1,6-bisphosphate in the Calvin cycle?

Accepted Answer

Fructose bisphosphate aldolase

Question 13

A plant is genetically engineered to overexpress fructose 1,6-bisphosphatase in the chloroplast. What is the most likely metabolic consequence?

Accepted Answer

Increased conversion of fructose 1,6-bisphosphate to fructose 6-phosphate

Question 14

Which of the following equations best represents the net reaction of the light and dark reactions of photosynthesis?

Accepted Answer

$$6\ \mathrm{CO}_2 + 6\ \mathrm{H}_2O + 48\ 	ext{photons} ightarrow C_6H_{12}O_6$ + 6\ O_2$

Question 15

Which Calvin cycle intermediate is directly isomerized to glucose-6-phosphate before being converted to glucose-1-phosphate?

Accepted Answer

Fructose-6-phosphate

Question 16

A plant is exposed to a herbicide that blocks the reduction of 1,3-bisphosphoglycerate. Which molecule would you expect to accumulate?

Accepted Answer

1,3-bisphosphoglycerate

Question 17

Which of the following best describes the fate of dihydroxyacetone phosphate (DHAP) in the Calvin cycle?

Accepted Answer

It is combined with GAP to form fructose 1,6-bisphosphate

Question 18

Which step in the Calvin cycle is most directly responsible for the regeneration of the CO$$_2$$ acceptor molecule?

Accepted Answer

Phosphorylation of ribulose-5-phosphate by ribulose-5-phosphate kinase

Question 19

Which of the following statements about the Calvin cycle is FALSE?

Accepted Answer

The Calvin cycle operates independently of the light reactions

The Calvin Cycle: Carbon Reactions in Photosynthesis

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