Deck 20: Carbohydrate Biosynthesis in Plants and Bacteria

Question 1

Which of the following is not true of the P_i-triose phosphate antiporter?

A)The antiporter can move phosphate in or out of the chloroplast.
B)When P_i is moved into the chloroplast,it supports synthesis of ATP.
C)When triose phosphates are moved out of the chloroplast,they become incorporated into sucrose.
D)ATP and reducing equivalents are moved into the chloroplast by the antiporter.
E)The antiporter is found in the inner membrane of chloroplasts.

Answer 1

ATP and reducing equivalents are moved into the chloroplast by the antiporter.

Question 2

In the carbon assimilation ("dark")reactions of photosynthesis,the biosynthesis of 1 mol of hexose from 6 mol of carbon dioxide requires:

A)12 mol of NADPH and 12 mol of ATP.
B)12 mol of NADPH and 18 mol of ATP.
C)18 mol of NADPH and 12 mol of ATP.
D)18 mol of NADPH and 18 mol of ATP.
E)no NADPH and 12 mol of ATP.

Answer 2

12 mol of NADPH and 18 mol of ATP.

Question 3

The compound that condenses with CO₂ in the first reaction of carbon dioxide assimilation is:

A)3-phosphoglycerate.
B)ribose 1,5-bisphosphate.
C)ribulose 1,5-bisphosphate.
D)ribulose 5-phosphate.
E)rubisco.

Answer 3

ribulose 1,5-bisphosphate.

Question 4

In "C₄" plants of tropical origin,the first intermediate into which ¹⁴CO₂ is fixed is:

A)aspartate.
B)phosphoenolpyruvate.
C)oxaloacetate.
D)malate.
E)3-phosphoglycerate.

Question 5

Which of the following is not required to activate rubisco?

A)ATP hydrolysis
B)Carbamoylation of the active site lysine by rubisco activase
C)Release of ribulose 1,5-bisphosphate from the active site
D)Release of 2-carboxyarabinitol from the active site
E)Binding of Mg²⁺

Question 6

Transketolase requires the coenzyme:

A)cobalamin (vitamin B₁₂).
B)lipoic acid
C)pyridoxal phosphate.
D)tetrahydrofolic acid.
E)thiamine pyrophosphate.

Question 7

When transketolase acts on fructose 6-phosphate and glyceraldehyde 3-phosphate,the products are:

A)3-phosphoglycerate and glyceraldehyde 3-phosphate.
B)3-phosphoglycerate and two molecules of glyceraldehyde 3-phosphate.
C)dihydroxyacetone phosphate and glucose 6-phosphate.
D)xylulose 5-phosphate and erythrose 4-phosphate.
E)xylulose 5-phosphate and ribose 5-phosphate.

Question 8

The synthesis of starch and sucrose in plants uses _________ as the substrate,rather than _________,which is used in the synthesis of glycogen in animal cells.

A)ADP-fructose;UDP-glucose
B)ADP-glucose;UDP-glucose
C)fructose 1-phosphate;glucose 1-phosphate
D)glucose 1-phosphate;glucose 6-phosphate
E)UDP-glucose;ADP-glucose

Question 9

Which of these enzymes is not part of the Calvin cycle?

A)Aldolase
B)Glyceraldehyde 3-phosphate dehydrogenase
C)Phosphofructokinase-1
D)Ribulose-5-phosphate kinase
E)Transketolase

Question 10

The known mechanisms of activation of rubisco or of other enzymes of the Calvin cycle during illumination include all of the following except:

A)increased stromal pH.
B)light-driven entry of Mg²⁺ into the stroma.
C)phosphorylation by cAMP-dependent protein kinase.
D)phosphorylation of phosphoenolpyruvate carboxylase.
E)reduction of a disulfide bridge by thioredoxin.

Question 11

Which of these chloroplast enzymes is not regulated by light?

A)Fructose 1,6-bisphosphatase
B)Glyceraldehyde-phosphate dehydrogenase
C)Ribulose 5-phosphate kinase
D)Sedoheptulose 1,7-bisphosphatase
E)All of the above

Question 12

The final product that is formed by the enzyme rubisco is:

A)3-phosphoglycerate.
B)ATP.
C)ribulose 1,5-bisphosphate.
D)glyceraldehyde-3-phosphate.
E)CO₂.

Question 13

The synthesis of glycogen,starch,and sucrose all:

A)involve addition of a sugar residue at the reducing end of the growing polymer.
B)take place in liver and muscle of mammals.
C)use a sugar nucleotide as substrate.
D)use glucose 1-phosphate as the only substrate.
E)use glucose-6-phosphate as substrate.

Question 14

The assimilation of CO₂ into organic compounds (triose phosphates)in green plants:

A)involves condensation of the two-carbon compound acetate with CO₂ to form 3-phosphoglycerate.
B)requires NADPH.
C)results in the production of ATP.
D)takes place at equal rates in light and darkness.
E)takes place in the cytosol.

Question 15

Which of the following is not true about plastids?

A)Most of the proteins in a plastid are encoded in nuclear genes.
B)Plastids are encoded by a double membrane.
C)Plastids are self-replicating.
D)Plastids contain a small circular genome.
E)The inner membrane of plastids is permeable to polar and charged molecules.

Question 16

All are true of photorespiration except:

A)It is driven by light.
B)It oxidizes substrates to CO₂.
C)It produces O₂.
D)It results from a lack of specificity of the enzyme rubisco.
E)It results in no fixation of carbon.

Question 17

Which of these compounds is not directly involved in the Calvin cycle?

A)Erythrose 4-phosphate
B)Glyceraldehyde 3-phosphate
C)Mannose 6-phosphate
D)Ribulose 5-phosphate
E)Sedoheptulose 7-phosphate

Question 18

The carbon assimilation ("dark")reactions of photosynthetic plants:

A)are driven ultimately by the energy of sunlight.
B)are important to plants,but ultimately of little significance for bacteria and animals.
C)cannot occur in the light.
D)yield (reduced)NADH.
E)yield ATP,which is required for the light reactions.

Question 19

The glycine decarboxylase complex in the leaves of pea or spinach plants is localized mainly in the:

A)chloroplast.
B)endoplasmic reticulum.
C)mitochondrion.
D)cell membrane.
E)peroxisome.

Question 20

The three subcellular organelles involved in the phosphoglycolate salvage pathway are:

A)endoplasmic reticulum,chloroplast,and mitochondrion.
B)nucleus,endoplasmic reticulum,and chloroplast.
C)golgi apparatus,chloroplast,and mitochondrion.
D)mitochondrion,peroxisome,and chloroplast.
E)peroxisome,endoplasmic reticulum,and chloroplast.

Question 21

Draw the structure of 3-phosphoglycerate.Circle the atom(s)that would be labeled first in plants grown in CO₂ labeled with radioactive carbon.

Question 22

A precursor in the synthesis of the peptidoglycan of bacterial cell walls is UDP-:

A)galactose.
B)glucose.
C)glucuronic acid.
D)N-acetylglucosamine.
E)penicillin.

Question 23

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.

Question 24

The major regulator of sucrose biosynthesis in plants is:

A)fructose 2,6-bisphosphate.
B)fructose 1,6-bisphosphate.
C)sucrose.
D)glucose and fructose.
E)glucose 6-phosphate.

Question 25

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.

Question 26

Which one of the following sugar phosphates is not part of the pool of readily interconvertible metabolites used by the plant cell?

A)Dihydroxyacetone phosphate
B)Fructose 2,6-bisphosphate
C)Glucose 1-phosphate
D)6-phosphogluconate
E)Xylulose 5-phosphate

Question 27

Show the reaction catalyzed by ribulose 1,5-bisphosphate carboxylase/oxygenase (rubisco).

Question 28

When glycerol is converted to glucose via gluconeogenesis in germinating seeds,the first glycolytic intermediate formed is:

A)1,3-bisphosphoglycerate.
B)dihydroxyacetone phosphate.
C)glycerol 1,3-bisphosphate.
D)glycerol 3-phosphate.
E)ribulose 1,5-bisphosphate.

Question 29

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

Question 30

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.

Question 31

Which of the following is not true about the biosynthesis of cellulose?

A)UDP-glucose is used as a substrate.
B)Glucose is transported across the membrane via a lipid-linked oligosaccharide intermediate.
C)The extracellular form of cellulose synthase adds up to 15,000 glucose units to one chain.
D)Cellulose polymers line up in an anti-parallel fashion.
E)The reaction catalyzed by cellulose synthase proceeds via inversion of configuration.

Question 32

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.

Question 33

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

Question 34

The precursors for sucrose biosynthesis are:

A)glucose and fructose.
B)UDP-glucose and fructose 6-phosphate.
C)UDP-fructose and glucose 6-phosphate.
D)UDP-glucose and fructose.
E)UDP-glucose and UDP-fructose.

Question 35

Explain why photorespiration occurs in plant cells carrying out photosynthesis.

Question 36

Which one of the following cellular organelles is not unique to plant cells?

A)Amyloplasts
B)Chloroplasts
C)Glyoxysomes
D)Mitochondria
E)Vacuoles

Question 37

Penicillin inhibits the synthesis of peptidoglycan:

A)branches.
B)chains.
C)crosslinks.
D)precursors.
E)All of the above

Question 38

Which one of the following reactions,cycles,or pathways is not found in plant systems?

A)The Calvin cycle
B)The gluconeogenesis pathway
C)The glyoxalate cycle
D)The rubisco reaction
E)The urea cycle

Question 39

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.

Question 40

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

Question 41

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

Question 42

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

Question 43

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

Question 44

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

Question 45

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

Question 46

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

Question 47

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