Deck 20: Carbohydrate Biosynthesis in Plants and Bacteria

Question 1

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.

Answer 1

C

Question 2

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.

Answer 2

A

Question 3

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.

Answer 3

C

Question 4

Transketolase requires the coenzyme:

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

Question 5

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 6

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 7

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.

Question 8

Which enzyme 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 9

Which statement is NOT true of photorespiration?

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 10

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 11

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 12

Which statement 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 13

Which chloroplast enzyme 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) None of these enzymes is regulated by light.

Question 14

Which compound 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 15

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.

Question 16

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 17

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 18

The known mechanisms of activation of rubisco or of other enzymes of the Calvin cycle during illumination do NOT include:

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 19

Which factor 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 20

Which statement 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.

Question 21

Which sugar phosphate 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 22

Which statement is TRUE about reaction centers?

A) Cyanobacteria and plants have two reaction centers arranged in tandem.
B) Cyanobacteria contain a single reaction center of the Fe-S type.
C) Green sulfur bacteria have two reaction centers arranged in tandem.
D) Plant photosystems have a single reaction center of the pheophytin-quinone type.
E) Purple bacteria contain a single reaction center of the Fe-S type.

Question 23

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 24

In what order do the following five steps occur in the photochemical reaction centers? 1) excitation of the chlorophyll a molecule at the reaction center
2) replacement of the electron in the reaction center chlorophyll
3) light excitation of antenna chlorophyll molecule
4) passage of excited electron to electron-transfer chain
5) exiton transfer to neighboring chlorophyll

A) 1, 2, 3, 4, 5
B) 3, 2, 5, 4, 1
C) 3, 5, 1, 4, 2
D) 4, 2, 3, 5, 1
E) 5, 4, 3, 2, 1

Question 25

Photosynthetic phosphorylation and oxidative phosphorylation appear to be generally similar processes, both consisting of ATP synthesis coupled to the transfer of electrons along an electron carrier chain. Which statement is NOT true of both processes?

A) Both contain cytochromes and flavins in their electron carrier chains.
B) Both processes are associated with membranous elements of the cell.
C) Both use oxygen as a terminal electron acceptor.
D) Each represents the major route of ATP synthesis in those cells in which it is found.
E) Protons are pumped from the inside to the outside of both mitochondria and chloroplast membranes

Question 26

Which statement about the light reactions in photosynthetic plants is FALSE?

A) A membrane-bound ATPase couples ATP synthesis to electron transfer.
B) No CO₂ is fixed in the light reactions.
C) The ultimate electron acceptor is O₂.
D) The ultimate source of electrons for the process is H₂O.
E) There are two distinct photosystems, linked together by an electron transfer chain.

Question 27

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 28

Which reaction, cycle, or pathway 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 29

Which statement 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 30

The light reactions in photosynthetic higher plants:

A) do not require chlorophyll.
B) produce ATP and consume NADH.
C) require the action of a single reaction center.
D) result in the splitting of H₂O, yielding O₂.
E) serve to produce light so that plants can see underground.

Question 31

Which statement is NOT true about cyclic electron flow?

A) Cyclic electron flow produces more NADPH per photon than noncyclic electron flow.
B) Cyclic electron flow involves only PSI.
C) Plastocyanin is required for cyclic electron flow.
D) Cyclic electron flow leads to the build-up of a proton gradient.
E) Cyclic electron flow does not produce O₂.

Question 32

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 33

In photophosphorylation, absorption of light energy in chloroplast "light reactions" leads to:

A) absorption of CO₂ and release of O₂.
B) absorption of O₂ and release of CO₂.
C) hydrolysis of ATP and reduction of NADP⁺.
D) synthesis of ATP and oxidation of NADPH.
E) use of iron-sulfur proteins.

Question 34

In the photolytic cleavage of water by the oxygen-evolving complex [2H₂O $\rightarrow$ 4 H⁺ + 4e^- + O₂], how many photons of light at a wavelength of 680 nm are required?

A) one
B) two
C) four
D) six
E) eight

Question 35

Penicillin inhibits the synthesis of peptidoglycan:

A) branches.
B) chains.
C) crosslinks.
D) precursors.
E) All of the answers are correct.

Question 36

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 37

The experimental determination of the effectiveness of light of different colors in promoting photosynthesis is called the _____ spectrum.

A) absorption
B) action
C) difference
D) reflectance
E) refraction

Question 38

Oxidative phosphorylation and photophosphorylation do NOT share:

A) chlorophyll.
B) involvement of cytochromes.
C) participation of quinones.
D) proton pumping across a membrane to create electrochemical potential.
E) use of iron-sulfur proteins.

Question 39

Place the following electron-carriers into the CORRECT order as found in plant chloroplasts. 1) cytochrome b₆f complex
2) P680
3) P700
4) plastocyanin
5) NADPH

A) 2, 1, 3, 4, 5
B) 2, 4, 3, 1, 5
C) 3, 1, 4, 2, 5
D) 2, 1, 4, 3, 5
E) 3, 4, 2, 1, 5

Question 40

Which cellular organelle is NOT unique to plant cells?

A) amyloplasts
B) chloroplasts
C) glyoxysomes
D) mitochondria
E) vacuoles

Question 41

Cyclic electron flow in chloroplasts produces:

A) ATP and O₂, but not NADPH.
B) ATP, but not NADPH or O₂.
C) NADPH and ATP, but not O₂.
D) NADPH, but not ATP or O₂.
E) O₂, but not ATP or NADPH.

Question 42

How is the enzyme ADP-glucose pyrophosphorylase regulated in plants?

A) It is activated by both inorganic phosphate and 3-phosphoglycerate.
B) It is activated by inorganic phosphate and unaffected by 3-phosphoglycerate.
C) It is activated by inorganic phosphate and inhibited by 3-phosphoglycerate.
D) It is inhibited by both inorganic phosphate and 3-phosphoglycerate.
E) It is inhibited by inorganic phosphate and activated by 3-phosphoglycerate.

Question 43

Which of the reactions of the Calvin cycle is reversible?

A) the conversion of fructose-1,6-bisphosphate to fructose-6-phosphate
B) the conversion of ribulose-5-phosphate to ribulose-1,5-bisphosphate
C) the conversion of ribose-5-phosphate to ribulose-5-phosphate
D) the conversion of sedoheptulose-1,7-bisphosphate into sedoheptulose-7-phosphate
E) None of these reactions is reversible.

Question 44

Which pair of enzymes is activated in the absence of photosynthesis (i.e., in the dark) in plants?

A) fructose-1,6-bisphosphatase and fructose-2,6-bisphosphatase
B) fructose-1,6-bisphosphatase and PP_i-dependent phosphofructokinase
C) PP_i-dependent phosphofructokinase and fructose-2,6-bisphosphatase
D) phosphofructokinase-2 and fructose-2,6-bisphosphatase
E) phosphofructokinase-2 and PP_i-dependent phosphofructokinase

Question 45

Which cofactor in photosynthesis contain metal ions?

A) chlorophyll a
B) $\beta$ carotene
C) pheophytin a
D) lutein
E) both chlorophyll a and $\beta$ carotene

Question 46

Which enzyme is inhibited by fructose-2,6-bisphosphate in plants?

A) fructose-1,6-bisphosphatase
B) sucrose-6-phosphate synthase
C) sucrose-6-phosphate phosphatase
D) PPi-dependent phosphofructokinase
E) None of these enzymes is inhibited by fructose-2,6-bisphosphate.

Question 47

Which statement is FALSE concerning xylulose-5-phosphate and ribose-5-phosphate?

A) These molecules are isomers of each other.
B) These molecules are both ketopentoses.
C) These molecules can both be generated from ribulose 5-phosphate in a single reaction.
D) In the Calvin cycle, both of these are D enantiomers.
E) None of these statements is false.

Question 48

Which statement describes shared characteristics of both oxidative phosphorylation and photophosphorylation?

A) During electron transport, protons are exported across the outer membrane.
B) ATP synthesis occurs in conjunction with proton translocation.
C) Electron transport proceeds from compounds with lower reduction potentials than those with higher reduction potentials.
D) ATP synthesis occurs in conjunction with proton translocation, and electron transport proceeds from compounds with lower reduction potentials than those with higher reduction potentials.
E) None of these statements describes shared characteristics of both oxidative phosphorylation and photophosphorylation.

Question 49

Which compound is produced by sucrose synthase and used by cellulose synthase to make cellulose?

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

Question 50

Ferredoxin and plastocyanin are both:

A) integral membrane proteins.
B) found on the lumen side of thylakoid membranes.
C) proteins that interact with photosystem I.
D) All of the answers are correct.
E) None of the answers is correct.

Question 51

Reactions from which pathway are NOT specifically needed to synthesize carbohydrate from fatty acids in plants?

A) gluconeogenesis
B) glyoxylate pathway
C) citric acid cycle
D) glycolate pathway
E) All of these pathways are necessary to synthesize carbohydrates from fatty acids.

Question 52

Which statement about photophosphorylation is FALSE?

A) It can be uncoupled from electron flow by agents that dissipate the proton gradient.
B) The difference in pH between the luminal and stromal side of the thylakoid membrane is 3 pH units.
C) The luminal side of the thylakoid membrane has a higher pH than the stromal side.
D) The number of ATPs formed per oxygen molecule is about three.
E) The reaction centers, electron carriers, and ATP-forming enzymes are located in the thylakoid membrane.

Question 53

Quinone A (Q_A) and quinone B (Q_B) differ from each other in that:

A) only Q_A is an isoprenoid.
B) Q_A is a prosthetic group for photosystem II, while Q_B is a cosubstrate.
C) Q_A will only accept single electrons, while Q_B will accept two electrons.
D) only Q_A is an isoprenoid, and Q_A is a prosthetic group for photosystem II, while Q_B is a cosubstrate.
E) Q_A is a prosthetic group for photosystem II, while Q_B is a cosubstrate, and Q_A will only accept single electrons, while Q_B will accept two electrons.

Question 54

Cyclic electron flow in chloroplasts produces:

A) ATP and O₂, but not NADPH.
B) ATP, but not NADPH or O₂.
C) NADPH and ATP, but not O₂.
D) NADPH, but not ATP or O₂.
E) O₂, but not ATP or NADPH.

Question 55

Which statement is TRUE regarding ATP synthase in chloroplasts?

A) The CF₁ portion of the complex is located on the lumen side of thylakoid membranes.
B) This complex is homologous to the complex located in mitochondria.
C) This complex will act as an ATPase in membrane-free preparations.
D) The CF₁ portion of the complex is located on the lumen side of thylakoid membranes, and this complex is homologous to the complex located in mitochondria.
E) This complex is both homologous to the complex located in mitochondria and will act as an ATPase in membrane-free preparations.

Question 56

During carbon fixation in C₄ plants, which reaction type or process does NOT occur between the conversion of phosphoenolpyruvate to pyruvate?

A) movement of metabolites through plasmodesmata
B) oxidation of metabolites
C) ATP consumption
D) carboxylation
E) decarboxylation

Question 57

Which statement is FALSE regarding ribulose-1,5-bisphosphate?

A) This molecule is a phosphorylated ketopentose.
B) This molecule contains a phosphoester and an acyl-phosphate.
C) This molecule is one of the substrates of rubisco.
D) C2 in this molecule is the position where CO₂ is added during carbon fixation.
E) This molecule is an inhibitor of rubisco activation.

Question 58

Which process is NOT a mechanism of regulation for sucrose-6-phosphate synthase?

A) allosteric inhibition by phosphate
B) inhibition by phosphorylation
C) allosteric activation by fructose-6-phosphate
D) allosteric regulation by glucose-6-phosphate
E) inhibition of sucrose phosphate synthase kinase by glucose-6-phosphate

Question 59

Which process occurs in photosynthesis?

A) Carbon atoms in CO₂ become reduced.
B) Oxygen atoms in water become oxidized.
C) NADP is reduced to NADPH by electron transport processes.
D) All of the answers are correct.
E) None of the answers is correct.

Question 60

Which statement is TRUE regarding the conversion of malate to pyruvate by malic enzyme in C₄ plants?

A) This is an oxidative decarboxylation reaction.
B) The process generates NADH as a product.
C) This process requires ATP consumption.
D) This reaction increases rubisco-associated photorespiration.
E) This process occurs predominantly in plant mitochondria.

Question 61

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 62

Explain why photorespiration occurs in plant cells carrying out photosynthesis.

Question 63

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

Question 64

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

Question 65

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

Question 66

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

Question 67

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

Question 68

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 69

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

Question 70

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

Question 71

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

Question 72

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 73

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.

Question 74

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⁺.

Question 75

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 76

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

Question 77

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

Question 78

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

Question 79

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

Question 80

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.