Chapter 8.6: Carbon Fixation: The Calvin Cycle

Question 2

What happens during reduction?

Answer 2

o PGA is reduced by G3P

Question 3

Define Calvin Cycle

Answer 3

the dark reactions of C₃ photosynthesis

Question 4

What is the main cycle of the dark reaction, in which CO₂ binds to ribulose 1,5-biphosphate (RuBP) to form two 3-carbon phosphoglycerate (PGA) molecules?

Answer 4

C₃ photosynthesis

Question 5

Define C₃ photosynthesis

Answer 5

the main cycle of the dark reaction, in which CO₂ binds to ribulose 1,5-biphosphate (RuBP) to form two 3-carbon phosphoglycerate (PGA) molecules

Question 6

How are carbohydrates built?

Answer 6

• To build carbohydrates, cells use energy and a source of electrons produced by the light-dependent reactions of the thylakoids o Energy  ATP (provided by cyclic and noncyclic photophosphorylation) drives the endergonic reactions o Reduction Potential  NADPH (provided by photosystem I) provides a source of protons and the energetic electrons needed to bind them to carbon atoms

Question 7

the four-subunit enzyme in the chloroplast that catalyzes the carbon fixation reaction joining CO₂ to RuBP

Answer 7

• Ribulose Biphosphate Carboxylase/Oxygenase (rubisco)

Question 8

After o CO₂ reacts with RuBP to form a 6-carbon intermediate that immediately splits into two molecules of the 3-carbon 3-phosphoglycerate (PGA), what is the last step of the Calvin cycle?

Answer 8

o Carbon is Transferred Through Cycle Intermediates, Eventually Producing Glucose  6 molecules of CO₂ are bound to six RuBP by rubisco to produce 12 molecules of PGA (containing 36 carbon atoms in all)  The 36 carbon atoms then undergo a cycle of reactions that regenerates the six molecules of RuBP used in the initial step (containing 30 carbon atoms) • This leaves two molecules of glyceraldehyde 3-phosphate (G3P) (each with three carbon atoms) as the net gain  These two molecules of G3P can then be used to make one molecule of glucose

Question 9

What is the net equation of the Calvin cycle?

Answer 9

• 6CO₂ + 18 ATP + 12 NADPH + water  2 glyceraldehyde 3-phosphate + 16 P_i + 18 ADP + 12 NADP⁺

Question 10

What is in the Calvin cycle, the 5-carbon sugar to which CO₂ is attached, accomplishing carbon fixation?

Answer 10

 Ribulose 1,5-Biphosphate (RuBP)

Question 11

What are the 3 phases of the Carbon cycle?

Answer 11

1. Carbon Fixation 2. Reduction 3. Regeneration of RuBP

Question 12

Define  Ribulose 1,5-Biphosphate (RuBP)

Answer 12

in the Calvin cycle, the 5-carbon sugar to which CO₂ is attached, accomplishing carbon fixation

Question 13

What is the first step of the Calvin cycle?

Answer 13

o Photosynthetic cells produce ribulose 1,5-biphosphate (RuBP) by reassembling the bonds of fructose 6-phosphate and glyceraldehyde 3-phosphate (G3P)

Question 14

What is the dark reactions of C₃ photosynthesis?

Answer 14

calvin cycle

Question 15

What happens during carbon fixation?

Answer 15

o Generates two molecules of the 3-carbon acid PGA

Question 16

After o Photosynthetic cells produce ribulose 1,5-biphosphate (RuBP) by reassembling the bonds of fructose 6-phosphate and glyceraldehyde 3-phosphate (G3P), what is the next step of the Calvin cycle?

Answer 16

o CO₂ reacts with RuBP to form a 6-carbon intermediate that immediately splits into two molecules of the 3-carbon 3-phosphoglycerate (PGA)  Called carbon fixation reaction because inorganic carbon (CO₂) has been incorporated into an organic form: the acid PGA  Carried out by the enzyme rubisco

Question 17

What happens during regenration of RuBP?

Answer 17

o PGA is used to regenerate RuBP

Question 18

Define • Ribulose Biphosphate Carboxylase/Oxygenase (rubisco)

Answer 18

the four-subunit enzyme in the chloroplast that catalyzes the carbon fixation reaction joining CO₂ to RuBP