Biochemistry

Jeremy M. Berg, John L. Tymoczko, Gregory J. Gatto, Jr, Lubert Stryer

Chapter 20 The Calvin Cycle and the Pentose Phosphate Pathway - all with Video Answers

Educators

Chapter Questions

01:47

Problem 1

A vital cycle. Why is the Calvin cycle crucial to the functioning of all life forms?

Matthew Potter

Numerade Educator

01:44

Problem 2

Be nice to plants. Differentiate between autotrophs and heterotrophs.

Matthew Potter

Numerade Educator

01:16

Problem 3

Cabalistic reactions? Why are the reactions of the Calvin cycle sometimes referred to as the dark reactions? Do they take place only at night or are they grim, secret reactions?

Matthew Potter

Numerade Educator

03:14

Problem 4

Compare and contrast. Identify the similarities and differences between the Krebs cycle and the Calvin cycle.

Matthew Potter

Numerade Educator

00:58

Labeling experiments. When Melvin Calvin performed his initial experiments on carbon fixation, he exposed algae to radioactive carbon dioxide. After 5 seconds, only a single organic compound contained radioactivity but, after 60 seconds, many compounds had incorporated radioactivity. (a) What compound initially contained the radioactivity? (b) What compounds contained radioactivity after 60 seconds?

Dr. Seema Kelotra

Numerade Educator

01:58

Problem 6

Three-part harmony. The Calvin cycle can be thought of as occurring in three parts or stages. Describe the stages.

Matthew Potter

Numerade Educator

01:37

Problem 7

Not always to the swiftest. Suggest a reason why rubisco might be the most abundant enzyme in the world.

Matthew Potter

Numerade Educator

03:12

Problem 8

A requirement. In an atmosphere devoid of $\mathrm{CO}_{2}$ but rich in $\mathrm{O}_{2},$ the oxygenase activity of rubisco disappears. Why?

Matthew Potter

Numerade Educator

02:28

Problem 9

Reduce locally. Glyceraldehyde 3 -phosphate dehydrogenase in chloroplasts uses NADPH to participate in the synthesis of glucose. In gluconeogenesis in the cytoplasm, the isozyme of the dehydrogenase uses NADH. Why is it advantageous for the chloroplast enzyme to use NADPH?

Matthew Potter

Numerade Educator

03:07

Problem 10

Total eclipse. An illuminated suspension of the green alga Chlorella is actively carrying out photosynthesis. Suppose that the light is suddenly switched off. How would the levels of 3 -phosphoglycerate and ribulose 1,5 -bisphosphate change in the next minute?

Matthew Potter

Numerade Educator

02:58

Problem 11

$C O_{2}$ deprivation. An illuminated suspension of line Chlorella is actively carrying out photosynthesis in the presence of $1 \% \mathrm{CO}_{2}$. The concentration of $\mathrm{CO}_{2}$ is abruptly reduced to $0.003 \%$. What effect would this reduction have on the levels of 3 -phosphoglycerate and ribulose $1,5-$ bisphosphate in the next minute?

Matthew Potter

Numerade Educator

06:27

Problem 12

Salvage operation. Write a balanced equation for the transamination of glyoxylate to yield glycine.

Matthew Potter

Numerade Educator

00:47

Problem 13

Dog days of August. Before the days of pampered lawns, most homeowners practiced horticultural Darwinism. A result was that the lush lawns of early summer would often convert into robust cultures of crabgrass in the dog days of August. Provide a possible biochemical explanation for this transition.

Sisi Gao

Numerade Educator

03:24

Problem 14

Is it hot in here, or is it just me? Why is the C $_{4}$ pathway valuable for tropical plants?

Matthew Potter

Numerade Educator

02:52

Problem 15

No free lunch. Explain why maintaining a high concentration of $\mathrm{CO}_{2}$ in the bundle-sheath cells of $\mathrm{C}_{4}$ plants is an example of active transport. How much ATP is required per $\mathrm{CO}_{2}$ to maintain a high concentration of $\mathrm{CO}_{2}$ in the bundle-sheath cells of $\mathrm{C}_{4}$ plants?

Hafiza Rehmat

Numerade Educator

01:45

Problem 16

Breathing pictures? What is photorespiration, what is its cause, and why is it believed to be wasteful?

Matthew Potter

Numerade Educator

02:23

Problem 17

Global warming. $\mathrm{C}_{3}$ plants are most common in higher latitudes and become less common at latitudes near the equator. The reverse is true of $\mathrm{C}_{4}$ plants. How might global warming affect this distribution?

Matthew Potter

Numerade Educator

03:39

Problem 18

Communication. What are the light-dependent changes in the stroma that regulate the Calvin cycle?

Matthew Potter

Numerade Educator

06:41

Problem 19

Match 'em. Match each term with its description.
(a) Calvin cycle
(b) Rubisco
(c) Carbamate
(d) Starch
(e) Sucrose
(f) Amylose
(g) Amylopectin
(h) $\mathrm{C}_{3}$ plants
(i) $\quad \mathrm{C}_{4}$ plants
(j) Stomata
1. Catalyzes $\mathrm{CO}_{2}$ fixation
2. Storage form of carbohydrates
3. $\alpha-1,4$ linkages only
4. 3-Phosphoglycerate is formed after carbon fixation
5. The dark reactions
6. Includes $\alpha-1,6$ linkages
7. Required for rubisco activity
8. Carbon fixation results in oxaloacetate formation
9. Allow exchange of gases
10. Transport form of

Matthew Potter

Numerade Educator

04:07

Problem 20

Linked in. Describe how the pentose phosphate pathway and glycolysis are linked by transaldolase and transketolase.

Danielle Ashley

Numerade Educator

01:49

Problem 21

21. Biochemical taxonomy.
(a) Identify 6 -phosphoglucono- 8 -lactone.
(b) Which reactions produce NADPH?
(c) Identify ribulose 5 -phosphate.
(d) What reaction generates $\mathrm{CO}_{2} ?$
(e) Identify 6 -phosphogluconate.
(f) Which reaction is catalyzed by phosphopentose isomerase?
(g) Identify ribose 5 -phosphate
(h) Which reaction is catalyzed by lactonase?
(i) Identify glucose 6 -phosphate.
(j) Which reaction is catalyzed by 6 -phosphogluconate dehydrogenase?
(k) Which reaction is catalyzed by glucose 6 -phosphate dehydrogenase?
(FIGURE CANNOT COPY)

Joanna Quigley

Numerade Educator

02:55

Problem 22

Tracing glucose. Glucose labeled with $^{14} \mathrm{C}$ at $\mathrm{C}-6$ is added to a solution containing the enzymes and cofactors of the oxidative phase of the pentose phosphate pathway. What is the fate of the radioactive label?

Matthew Potter

Numerade Educator

02:34

Problem 23

Recurring decarboxylations. Which reaction in the citric acid cycle is most analogous to the oxidative decarboxylation of 6 -phosphogluconate to ribulose 5 -phosphate? What kind of enzyme-bound intermediate is formed in both reactions?

Sulav Pokhrel

Numerade Educator

01:08

Problem 24

Synthetic stoichiometries. What is the stoichiometry of the synthesis of (a) ribose 5 -phosphate from glucose 6 phosphate without the concomitant generation of NADPH?
(b) NADPH from glucose 6 -phosphate without the concomitant formation of pentose sugars?

Carlene Jimenez

Numerade Educator

01:23

Problem 25

Offal or awful? Liver and other organ meats contain large quantities of nucleic acids. In the course of digestion, RNA is hydrolyzed to ribose, among other chemicals. Explain how ribose can be used as a fuel.

Arun Bana

Numerade Educator

04:21

Problem 26

A required ATP. The metabolism of glucose 6-phosphate into ribose 5 -phosphate by the joint efforts of the pentose phosphate pathway and glycolysis can be summarized by the following equation.
5 Glucose 6 -phosphate $+$ ATP $\longrightarrow$ 6 ribose 5 -phosphate $+$ ADP Which reaction requires the ATP?

Danielle Ashley

Numerade Educator

02:18

Problem 27

No respiration. Glucose is normally completely oxidized to $\mathrm{CO}_{2}$ in the mitochondria. In what circumstance can glucose be completely oxidized to $\mathrm{CO}_{2}$ in the cytoplasm?

Matthew Potter

Numerade Educator

03:19

Problem 28

Watch your diet, doctor. The noted psychiatrist Hannibal Lecter once remarked to FBI Agent Clarice Starling that he enjoyed liver with some fava beans and a nice Chianti. Why might this diet be dangerous for some people?

Matthew Potter

Numerade Educator

03:59

Problem 29

No redundancy. Why do deficiencies in glucose 6-phosphate dehydrogenase frequently present as anemia?

Matthew Potter

Numerade Educator

02:18

Problem 30

Damage control. What is the role of glutathione in protection against damage by reactive peroxides? Why is the pentose phosphate pathway crucial to this protection?
(FIGURE CANNOT COPY)

Matthew Potter

Numerade Educator

07:32

Problem 31

Reductive power. What ratio of NADPH to NADP $^{+}$ is required to sustain $[\mathrm{GSH}]=10 \mathrm{mM}$ and $[\mathrm{GSSG}]=1 \mathrm{mM} ?$ Use the redox potentials given in Table 18.1

Niamat Khuda

Numerade Educator

02:03

Problem 32

An alternative approach. The mechanisms of some aldolases do not include Schiff-base intermediates. Instead, these enzymes require bound metal ions. Propose such a mechanism for the conversion of dihydroxyacetone phosphate and glyceraldehyde 3 -phosphate into fructose 1,6 -bisphosphate.

Mikayla Stephens

Numerade Educator

00:31

Problem 33

A recurring intermediate. Phosphopentose isomerase interconverts the aldose ribose 5 -phosphate and the ketose ribulose 5 -phosphate. Propose a mechanism.

Emily Himsel

Numerade Educator

05:21

Problem 34

Catching carbons. Radioactive-labeling experiments can yield estimates of how much glucose 6 -phosphate is metabolized by the pentose phosphate pathway and how much is metabolized by the combined action of glycolysis and the citric acid cycle. Suppose that you have samples of two different tissues as well as two radioactively labeled glucose samples, one with glucose labeled with $^{14} \mathrm{C}$ at $\mathrm{C}-1$ and the other with glucose labeled with $^{14} \mathrm{C}$ at $\mathrm{C}$ -6. Design an experiment that would enable you to determine the relative activity of the aerobic metabolism of glucose compared with metabolism by the pentose phosphate pathway.

Susan Hallstrom

Numerade Educator

03:06

Problem 35

You do what you can do. Red blood cells lack mitochondria. These cells process glucose to lactate, but they also generate $\mathrm{CO}_{2}$. What is the purpose of producing lactate? How can red blood cells generate $\mathrm{CO}_{2}$ if they lack mitochondria?

Matthew Potter

Numerade Educator

03:29

Problem 36

Better to focus on one. Rubisco catalyzes both a carboxylation reaction and a wasteful oxygenase reaction. Below are the kinetic parameters for the two reactions.
(EQUATIONS CANNOT COPY)
(a) Determine the values of $k_{\mathrm{cat}} \mathrm{CO}_{2} / K_{\mathrm{M}} \mathrm{CO}_{2}$ and $k_{\mathrm{cat}} \mathrm{O}_{2} /$ $K_{\mathrm{M}}^{\mathrm{O}_{2}}$ as $\mathrm{s}^{-1} \mathrm{M}^{-1}$
(b) In light of the $k_{\text {cat }} / K_{\mathrm{M}}$ values for the two reactions, why does the oxygenation reaction occur?

Niamat Khuda

Numerade Educator

01:35

Problem 37

Photosynthetic efficiency. Use the following information to estimate the efficiency of photosynthesis. The $\Delta G^{o \prime}$ for the reduction of $\mathrm{CO}_{2}$ to the level of hexose is $+477 \mathrm{kJ} \mathrm{mol}^{-1}\left(+114 \mathrm{kcal} \mathrm{mol}^{-1}\right)$
A mole of 600 -nm photons has an energy content of $199 \mathrm{kJ}$ $(47.6 \mathrm{kcal})$
Assume that the proton gradient generated in producing the required NADPH is sufficient to drive the synthesis of the required ATP.

Niamat Khuda

Numerade Educator

01:17

Problem 38

A violation of the First Law? The complete combustion of glucose to $\mathrm{CO}_{2}$ and $\mathrm{H}_{2} \mathrm{O}$ yields $30 \mathrm{ATP},$ as shown in Table $18.4 .$ However, the synthesis of glucose requires only 18 ATP. How is it possible that glucose synthesis from $\mathrm{CO}_{2}$ and $\mathrm{H}_{2} \mathrm{O}$ requires only 18 ATP, but combustion to $\mathrm{CO}_{2}$ and $\mathrm{H}_{2} \mathrm{O}$ yields $30 \mathrm{ATP}$ ? Is it a violation of the First Law of Thermodynamics, or perhaps a miracle?

Matthew Potter

Numerade Educator

01:35

Problem 39

Deciding between 3 and $4 .$ Graph $\mathrm{A}$ shows the photosynthetic activity of two species of plant, one a $\mathrm{C}_{4}$ plant and the other a $\mathrm{C}_{3}$ plant, as a function of leaf temperature.
(TABLE CANNOT COPY)
(a) Which data were most likely generated by the $\mathrm{C}_{4}$ plant and which by the $\mathrm{C}_{3}$ plant? Explain.
(b) Suggest some possible explanations for why the photosynthetic activity falls at higher temperatures. Graph $\mathrm{B}$ illustrates how the photosynthetic activity of $\mathrm{C}_{3}$ and $\mathrm{C}_{4}$ plants varies with $\mathrm{CO}_{2}$ concentration when temperature $\left(30^{\circ} \mathrm{C}\right)$ and light intensity (high) are constant.
(TABLE CANNOT COPY)
(c) Why can $\mathrm{C}_{4}$ plants thrive at $\mathrm{CO}_{2}$ concentrations that do not support the growth of $\mathrm{C}_{3}$ plants?
(d) Suggest a plausible explanation why $\mathrm{C}_{3}$ plants continue to increase photosynthetic activity at higher $\mathrm{CO}_{2}$ concentrations, whereas $\mathrm{C}_{4}$ plants reach a plateau.

Joanna Quigley

Numerade Educator

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