Deck 20: The Calvin Cycle and the Pentose Phosphate Pathway

Question 1

What is another name for ribulose 1,5-bisphosphate carboxylase/oxygenase?

A) rubisco
B) ribulooxidase
C) ribulocarboxidase
D) ribulose bisphosphatase
E) None of the answers is correct.

Answer 1

A

Question 2

When NADPH is abundant, the nonoxidative phase of the pentose phosphate pathway may still be used to produce _______________.

Answer 2

ribose 5-phosphate

Question 3

In C₄ plants, carbon dioxide is added to ____________________ to form oxaloacetate, which is reduced to malate, which carries CO₂ to the bundle-sheath cells.

Answer 3

phosphoenolpyruvate

Question 4

The binding site of Mg²⁺ to rubisco requires the formation of a ________________ group between lysine 201 and CO₂.

Question 5

Hemolytic anemia is caused by a deficiency of the enzyme ______________________.

Question 6

A _______________ intermediate is formed between the carbonyl group of the ketose substrate and the ε-amino group of a lysine residue of transaldolase.

Question 7

Which of the following types of organisms can synthesize glucose from carbon dioxide and water?

A) heterotrophs
B) autotrophs
C) chemotrophs
D) phototrophs
E) autotrophs and phototrophs

Question 8

What prosthetic group is tightly bound to the enzyme transketolase?

A) biotin
B) tetrahydrofolate
C) FAD
D) pyridoxal phosphate
E) thiamine pyrophosphate

Question 9

What pathway ensures that sufficient amounts of CO₂ are available to minimize wasteful photorespiration by transporting CO₂ from the mesophyll cells to the bundle sheath cells?

A) crassulacean acid metabolism
B) gluconeogenesis
C) C₄ pathway
D) sucrose synthesis
E) cellulose synthesis

Question 10

The enzymes that catalyze the dark reactions of photosynthesis are located in the ___________ of the chloroplasts.

Question 11

The first step of the Calvin cycle involves the addition of CO₂ to _______________________ to produce two molecules of 3-phosphoglycerate.

Question 12

The enzyme transketolase transfers a ________-carbon fragment from a ketose to an aldose.

Question 13

Which of the following enzymes is involved in both the Calvin cycle and the pentose phosphate pathway?

A) glucose-6-phosphate dehydrogenase
B) fructose-1,6-bisphosphatase
C) 3-phosphoglycerate kinase
D) transaldolase
E) triose phosphate isomerase

Question 14

What metabolic adaptation is employed by plants living in hot dry climates to prevent water loss and decrease photorespiration?

A) crassulacean acid metabolism
B) cellulose synthesis at night
C) C₄ pathway
D) increased fructose-2,6-bisphosphatase activity
E) inhibition of glycolate salvage

Question 15

Which of the following is a readily mobilized sugar that is commonly used to transport carbohydrates through a plant?

A) glucose
B) fructose
C) sucrose
D) amylose
E) amylopectin

Question 16

What intermediate is formed in the oxygenase reaction catalyzed by rubisco?

A) glyoxylate
B) hydroxypyruvate
C) glycerate
D) phosphoglycolate
E) malate

Question 17

What thiol-containing molecule in its reduced state is critical to reducing reactive oxygen species?

A) NADPH
B) folate
C) vitamin E
D) vitamin C
E) glutathione

Question 18

The oxidative phase of the pentose phosphate pathway produces __________, which is required for lipid biosynthesis.

Question 19

In photorespiration, the oxidation of glycolate to glyoxylate occurs in the __________ .

Question 20

Which of the following types of organisms obtain their energy from chemical fuels produced by other organisms?

A) heterotrophs
B) autotrophs
C) chemotrophs
D) phototrophs
E) heterotrophs and chemotrophs

Question 21

What is the energy requirement for the formation of hexose from CO₂ in terms of ATP equivalents and NADPH?

Question 22

How many ATP are required by the C₄ pathway for each hexose that is produced?

A) 48
B) 30
C) 24
D) 18
E) 12

Question 23

The purpose of the pentose phosphate pathway is to

A) generate ATP.
D) A and B.
B) generate NADPH.
E) B and C.
C) metabolize 5-carbon sugars.

Question 24

Which coenzyme is required by glyceraldehyde-3-phosphate dehydrogenase in chloroplasts to convert 3-phosphoglycerate into glyceraldehyde 3-phosphate?

A) NADH
D) NADP⁺
B) NADPH
E) thiamine pyrophosphate
C) NAD⁺

Question 25

Which cofactor supplies the reducing power for reduction of glutathione by glutathione reductase?

A) FMN
B) TPP
C) FAD
D) NADPH
E) NADH

Question 26

What is the net reaction of the transketolase and transaldolase steps?

A) 3C₅ 2C₆ + C₃
D) 2C₅ 2C₄ + C₂
B) 2C₅ C₆ + C₄
E) None of the answers is correct.
C) 3C₅ C₆ + 3C₃

Question 27

Give the sequence of reactions involved in the synthesis of sucrose from two glucose
6-phosphate molecules.

Question 28

Which form of thioredoxin activates certain Calvin cycle enzymes?

A) reduced
B) oxidized
C) dimeric
D) phosphorylated
E) dephosphorylated

Question 29

Which of the following tissues have the least active pentose-phosphate pathway?

A) adrenal gland
B) liver
C) adipose tissue
D) ovary
E) skeletal muscle

Question 30

Which enzyme is cited as the most abundant enzyme in the biosphere? Why is this so?

Question 31

The C₄ pathway is necessary in tropical plants because

A) at high temperatures, the plants cannot maintain sufficient water levels within the cells.
B) tropical plants do not have proper day/light cycles to maintain the balance of CO₂ necessary for carbohydrate storage.
C) at high temperatures, the oxygenase activity of rubisco is high.
D) All of the answers are correct.
E) None of the answers is correct.

Question 32

What is photorespiration? Why is it wasteful?

Question 33

Which sugar(s) is (are) converted into ribulose 5-phosphate by a single enzymatic step?

A) ribose 5-phosphate
D) A and B
B) xylulose 5-phosphate
E) B and C
C) erythrose 4-phosphate

Question 34

Which of the following reactions is NOT part of the pentose phosphate pathway?

A)
B)
C)
D)
E) All of the answers are correct.

Question 35

In photosynthesis, light energy is transformed into ATP and biosynthetic reducing power in the form of _____.

A) NADPH
B) NADH
C) FADH₂
D) ADP
E) None of the answers is correct.

Question 36

In the overall equation for the Calvin cycle, three molecules of __________ and two molecules of ____________ are consumed in incorporating a single CO₂ molecule into a hexose.

A) NADPH; ATP
B) ATP; NADPH
C) NADPH; P_i
D) P_i; NADH
E) NADH; ATP

Question 37

What is the source of carbons for the Calvin cycle?

A) glucose
D) glyoxylate
B) carbon dioxide
E) None of the answers is correct.
C) glycogen

Question 38

In the Calvin cycle, 3-phosphoglycerate is ultimately converted into which hexose phosphate?

A) glucose 1-phosphate
D) All of the answers are correct.
B) glucose 6-phosphate
E) None of the answers is correct.
C) fructose 6-phosphate

Question 39

The K_M of glucose-6-phosphate dehydrogenase for NADP⁺ is _____________ the K_M for NAD⁺.

A) a thousand times greater than
D) ten times lower than
B) ten times greater than
E) a thousand times lower than
C) equivalent to

Question 40

Why is the chemistry of the "dark reactions" referred to as a cycle and not a pathway?

Question 41

How is the pentose phosphate pathway regulated?

Question 42

Several physiological modes are possible for the metabolic need for NADPH, ribose 5-phosphate, and ATP. In one scenario, such as found in adipose tissue, much more NADPH is required than ribose 5-phosphate. How is this maintained?

Question 43

Using structures draw out the reactions of the oxidative phase of the pentose phosphate pathway.

Question 44

How can a deficiency of glucose 6-phosphate confer a physiological advantage?

Question 45

Describe the role of thioredoxin in regulating the Calvin cycle.

Question 46

What is the hexose monophosphate pool?