8.2 The Calvin Cycle

Question 1

the Calvin cycle consists of:

Answer 1

15 reactions that synthesize carbohydrates from CO2 (can be grouped into three main steps)

Question 2

what is the first step in the Calvin cycle?

Answer 2

CARBOXYLATION-carbon dioxide absorbed from the air is added to a 5-carbon molecule (RuBP), catalyzed by the enzyme rubisco

Question 3

what is the second step in the Calvin cycle?

Answer 3

REDUCTION-energy and electrons are transferred to the compounds formed from carboxylation, NADP transfers two electrons and one proton; inorganic phosphate and NADP+ is released

Question 4

what is the third step in the Calvin cycle?

Answer 4

REGENERATION-of the 5-carbon molecule needed for carboxylation, 3-carbon compounds are reorganized and combined to produce RuBP

Question 5

ribulose 1,5-bisphosphate (RuBP)

Answer 5

the 5-carbon sugar to which carbon dioxide is added by the enzyme rubisco

Question 6

ribulose bisphosphate carboxylase oxygenase (rubisco)

Answer 6

the enzyme that catalyzes the carboxylation reaction in the Calvin cycle

Question 7

what do you call an enzyme that adds carbon dioxide to another molecule?

Answer 7

carboxylase

Question 8

3-phosphogylcerate (3-PGA)

Answer 8

a 3-carbon molecule; two molecules of 3-PGA are the first stable products of the Calvin cycle

Question 9

what is the reducing agent of the Calvin cycle?

Answer 9

NADPH (a cofactor/coenzyme)-it transfers the electrons that allow carbohydrates to be synthesized from CO2

Question 10

NADPH can move freely within the stroma of the chloroplast buy only transfers energy/electrons under:

Answer 10

catalysis of a specific enzyme

Question 11

the reduction of 3-PGA involves two steps:

Answer 11

1) ATP donates a phosphate group to 3-PGA

2) NADPH transfers two electrons plus one proton to the phosphorylated compound which releases one phosphate groups

Question 12

one molecule of carbon dioxide-3 molecules of 3-PGA which requires:

Answer 12

2 ATP and two NADPH for each molecule of carbon dioxide incorporated by rubisco

Question 13

ATP plays an essential role in preparing:

Answer 13

3-PGA for the addition of energy and electrons from NADPH

Question 14

what provides most of the energy incorporated in the bonds of the carbohydrate molecules?

Answer 14

NADPH

Question 15

triose phosphate

Answer 15

a 3-carbon carbohydrate molecule, produced by the Calvin cycle and exported from the chloroplast, starting point for synthesis of larger sugars ex. glucose and sucrose

Question 16

most triose phosphate molecules are used to:

Answer 16

regenerate RuBP

Question 17

for every six triose phosphate molecules produced, how many can be withdrawn from the Calvin cycle?

Answer 17

only one

Question 18

twelve reactions of the Calvin cycle occur in which step?

Answer 18

the last step: regeneration of RuBP

Question 19

what is required for the regeneration of RuBP?

Answer 19

ATP

Question 20

what is the total energy requirements of the Calvin cycle for each molecule of carbon dioxide incorporated by rubisco?

Answer 20

2 NADPH and 3 ATP

Question 21

during regeneration, five 3-carbon triose phosphate molecules turns into:

Answer 21

three 5-carbon RuBP molecules

Question 22

the Calvin cycle does not use:

Answer 22

sunlight directly - referred to the light independent or dark reactions of photosynthesis

Question 23

in a photosynthetic cell, the Calvin cycle occurs only in the light because:

Answer 23

NADPH and ATP are supplied by the photosynthetic electron transport chain and several cofactors are activated by the transport chain too

Question 24

how were the steps of the Calvin cycle determined?

Answer 24

through the use of radioactive carbon dioxide

Question 25

the Calvin cycle is capable of producing more carbohydrates than the cells need which is dangers because:

Answer 25

if carbohydrates accumulate in the cell, they cause water to enter the cell by osmosis, which might damage the cell

Question 26

excess carbohydrates are converted to:

Answer 26

starch