Question 1

Explain why both ATP and NADPH are required for the operation of the Calvin cycle, and why these two reactants are required in different amounts.

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Question 2

Explain why photorespiration occurs in plant cells carrying out photosynthesis.

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Question 3

What is an action spectrum, and what do peaks in an action spectrum signify? Show a typical action spectrum plot for photosynthesis.

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Question 4

Give five general classes of electron carriers that function in both mitochondrial electron transfer to O₂ and photosynthetic electron transfer.

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Question 5

Diagram the reaction catalyzed by transketolase when fructose 6-phosphate and glyceraldehyde 3-phosphate are the substrates.

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Question 6

Describe the interconversions between the triose-, pentose- and hexose-phosphate pools in the plant cell.

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Question 7

How does glyceraldehyde 3-phosphate formed in the chloroplast stroma by the Calvin cycle reactions enter the cytosol?

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Question 8

Describe the oxygenase activity of ribulose 1,5-bisphosphate carboxylase/oxygenase (rubisco) and explain why this reaction is undesirable from the point of view of a plant.

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Question 9

Explain the utility to plants in using sucrose as the transport form of carbon.

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Question 10

Describe how thioredoxin participates in the regulation of several chloroplast enzymes by light.

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Question 11

Diagram the pathway by which sucrose is synthesized from glucose 6-phosphate; indicate how any required cofactors are involved.

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Question 12

Describe the reaction sequence by which 2-phosphoglycolate (produced when O₂ replaces CO₂ as substrate for rubisco) is converted to serine. Name each enzyme and any cofactors required and indicate the subcellular compartment in which the reaction takes place.

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Question 13

The processes of oxidative phosphorylation coupled with electron transfer (in mitochondria) and photophosphorylation (in chloroplasts) resemble each other in certain respects. Describe five ways in which the two processes are similar, and describe three significant differences between the two processes.

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Question 14

Describe what happens at photosystem I from the point where an antenna chlorophyll molecule absorbs a photon of light to the passage of an electron to NADP⁺.

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Question 15

CAM plants, such as cactus and pineapple, are native to very hot and dry environments. Briefly describe the biochemical events that allow CAM plants to minimize water loss by closing their stroma during daylight hours.

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Question 16

Name one similarity and one difference between the biosynthesis of glycogen and the biosynthesis of cellulose.

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Question 17

Describe briefly how the allosteric effector fructose 2,6-bisphosphate (F2,6BP) regulates starch and sucrose synthesis.

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Question 18

Describe the role of fructose 2,6-bisphosphate in the regulation of sucrose biosynthesis in plant cells.

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Question 19

Describe how plants and some microorganisms can, unlike animals, convert acetyl-CoA derived from fatty acids into glucose or sucrose.

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Question 20

Show the reaction in which 3-phosphoglycerate is converted into glyceraldehyde 3-phosphate. Show all required cofactors, and circle the carbon atom(s) in glyceraldehyde 3-phosphate that is/are derived from CO₂ during the photosynthetic fixation of CO₂.

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Quiz 20: Carbohydrate Biosynthesis in Plants and Bacteria