5.4.1 The Calvin Cycle

Question 1

calvin cycle

Answer 1

• a light-independent series of reactions that involves the synthesis of carbohydrate from carbon dioxide
  (CO2).
• The first stage of the Calvin cycle involves carbon fixation. Carbon fixation is the incorporation of carbon (in the form of carbon dioxide) into a larger molecule.
• Carbon fixation takes place when CO2 is added to ribulose bisphosphate (RuBP), a five-carbon sugar, by the enzyme rubisco. A six-carbon molecule is formed, which then splits into two three-carbon molecules called 3-phosphoglycerate (3PG).
• In the second phase (the reduction phase) of the Calvin cycle, a phosphate group from ATP is transferred to each 3PG to form 1,3-bisphosphoglycerate. NADPH then reduces 1,3-bisphosphoglycerate and a phosphate group is removed to form glyceraldehyde 3-phosphate (G3P).
• Glyceraldehyde 3-phosphate is the first product of
  photosynthesis.

Question 2

note

Answer 2

• Review: A reaction cannot spontaneously proceed from a state of low energy to a state of high energy. An input of energy is needed. In the light-dependent reactions, energy from the sun is used to make ATP and NADPH.
• Remember: The goal is to make carbohydrates!
• The synthesis glucose from carbon dioxide requires enzymes and the input of energy. Carbon dioxide and water have a lower free energy than glucose; thus the reaction has a positive ∆G and won’t happen spontaneously.

Question 3

Which of these conversions in the Calvin cycle uses the NADPH and ATP from the light-dependent reactions?

Answer 3

• The conversion of 3-phosphoglycerate to glyceraldehyde 3-phosphate

Question 4

The Calvin cycle begins when carbon dioxide reacts with what five carbon molecule?

Answer 4

• ribulose bisphosphate

Question 5

The six-carbon molecule that results from carbon fixation in the Calvin cycle immediately breaks down into

Answer 5

• 3-phosphoglycerate

Question 6

Which of the following molecules are both produced by reactions in the thylakoids and consumed by reactions in the stroma?

Answer 6

• ATP and NADPH

Question 7

Which of the following statements is correct?

Answer 7

• The Calvin cycle is an example of light independent metabolism

Question 8

Which statement about the Calvin cycle is incorrect?

Answer 8

• ATP and NADPH form during the reduction phase