BIOC Exam 1
In the five steps used by photosynthetic organisms to convert solar energy into chemical energy, which molecules store the solar energy before sugar synthesis? A. ATP and NADPH B. none of these answers are correct. C. Chlorophylls D. H2O and O2 E. NADH and FADH2
A. ATP and NADPH
What energy conversion process is used by both heterotrophs and autotrophs? ____________ ___________________?
Aerobic Respiration
Which of the following is an example of a disaccharide? Choose one: A. Glucose B. Galactose C. Raffinose D. Lactose
D. Lactose
What is the role of most chlorophyll molecules in a photosynthetic membrane? Choose one: A. to directly convert NADP+ to NADPH B. to participate in fluorescence reactions C. to photooxidize electron carrier proteins D. to serve as light-harvesting antennae
D. to serve as light-harvesting antennae
Which disaccharide can be found in fermented beverages such as beer? maltose none of these answers are correct. glucose sucrose lactose
maltose
The photosynthetic Z scheme describes the production of O2. reduction of NADPH. none of these answers are correct. movement of electrons driven by the reflection of light energy. synthesis of glucose from CO2
none of these answers are correct.
What group in photosystem II (PSII) directly reacts with H2O during its light-driven oxidation? tyrosine P680 pheophytin none of these answers are correct. oxygen evolving center
oxygen evolving center
Where do electrons come from to re-reduce the oxidized P700+ state in PSI? NADPH plastocyanin H2O O2 plastoquinol plastoquinone
plastocyanin
What is the energy requirement in kJ/mol to transport 1 H+ across the thylakoid membrane in chloroplasts at 25ºC, given that the pH differential across this membrane is 3.5 pH units, and the membrane potential is essentially 0 V due to counter ion transport. +20.0 kJ/mol -3.1 kJ/mol -20 kJ/mol +200 kJ/mol +1.67 kJ/mol kJ/mol +66.1 kJ/mol +3.1 kJ/mol -1.67 kJ/mol kJ/mol
+20.0 kJ/mol
2-phosphoglycerate(2PG) is converted to phosphoenolpyruvate (PEP) by the enzyme enolase. The standard free energy change(deltaGo') for this reaction is +1.7 kJ/mol. If the cellular concentrations are 2PG = 0.5 mM and PEP = 0.1 mM, what is the free energy change at 37 oC for the reaction 2PG ↔ PEP? +2.4 kJ/mol +4146.4 kJ/mol -2.4 kJ/mol The correct answer is not given. -5.8 kJ/mol -4146.4 kJ/mol 5.8 kJ/mol
-2.4 kJ/mol
Which of the following is FALSE concerning cyclic photophosphorylation? Choose one: A. No O2 is produced. B. No NADP+ is produced. C. Ferredoxin is involved in the reduction of PQB. D. This process helps control the ATP-to-NADPH ratios.
B. No NADP+ is produced.
How do light harvesting chlorophylls transfer energy? A. Peltier energy transfer B. Resonance energy transfer C. Thermal energy transfer D. Fluorescence energy transfer
B. Resonance energy transfer
Plants (autotrophs) can convert sunlight energy into chemical energy, but animals (heterotrophs) cannot. Plants and animals can both convert redox energy into chemical energy. 2a. What metabolic pathway do plants have that animals do not have? 2b. What metabolic pathway do both plants and animals use at night? 2c. What organelle do both plants and animals have for NADH oxidation? 2d. What are living organism trying to put off as long as possible? 1. Photosynthesis 2. Enthalpic equality 3. Anaerobic respiration 4. Photoremediation 5. Nucleus 6. Equilibrium 7. Aerobic respiration 8. Chloroplast 9. Thermodynamics 10. Autofluorescence 11. Mitochondria 12. Lactose tolerance
1, 3, 11 ,6
Put the following steps in photosynthesis in the correct order to generate 2 NADPH and 3 ATP following absorption of 8 photons and return of 12 H+ from the thylakoid space to the stroma. • ___ The sun comes up. • ___ PSII absorbs 4 photons leading to photooxidation of 4 chlorophyll molecules and oxidation of 2 H2O to replace the 4 e- in chlorophyll and release 4 H+ into the thylakoid lumen. • ___ Oxidation of pheophytin initiates a series of redox reactions culminating in the reduction of 4 plastocyanin and translocation of 8 H+ across the thylakoid membrane. • ___ PSI absorbs 4 photons leading to the photooxidation of 4 plastocyanin and initiation of a series of redox reactions culminating in the reduction of 2 NADP+ to yield 2 NADPH. • ___ A total of 12 H+ enter the chloroplast ATP synthase to generate 3 ATP when they return to the stroma and induce conformational changes in the head piece of the complex.
1,2,3,4,5
Put the following steps in photosynthesis in the correct order to generate 2 NADPH and 3 ATP following the absorption of 8 photons and return of 12 H+ from the thylakoid space to the stroma. PSI absorbs 4 photons leading to the photooxidation of 4 plastocyanin and initiation of a series of redox reactions culminating in the reduction of 2 NADP+ to yield 2 NADPH. A total of 12 H+ enter the chloroplast ATP synthase to generate 3 ATP when they return to the stroma and induce conformational changes in the head piece of the complex. Oxidation of pheophytin initiates a series of redox reactions culminating in the reduction of 4 plastocyanin and translocation of 8 H+ across the thylakoid membrane. PSII absorbs 4 photons leading to photooxidation of 4 chlorophyll molecules and oxidation of 2 H2O to replace the 4 e- in chlorophyll and release 4 H+ into the thylakoid lumen. The sun comes up.
4,5,3,2,1
What happens when the e- returns to the ground state without transferring energy? (Multiple Answers) A. Energy is lost as heat B. The e- is absorbed by H2O C. The e- is transferred to Pheo D. Energy is lost as fluorescence
A. Energy is lost as heat D. Energy is lost as fluorescence
Which of the following is false? A. Mesophyll cells open and close to allow gas exchange and processing B. Guard cells prevent/allow gas exchange when necessary C. Mesophyll cells form malate in chloroplasts from OAA which was made from fixated gases D. Bundle sheath cells generate pyruvate from the fixated carbon molecules
A. Mesophyll cells open and close to allow gas exchange and processing
The net change in stage 3 of the Calvin cycle can be represented as which of the following? Choose one: A. C3 + C4 + C6 + C7 → 4 C5 B. 5 C3 → 3 C5 C. 3 C5 → 5 C3
B. 5 C3 → 3 C5
The oxygenase activity of the enzyme rubisco produces one mole of 2-phosphoglycolate and one mole of 3- phosphoglycerate per mole of ribulose-1,5 bisphosphate metabolized. Why is this wasteful? A. In the process of converting 2-phosphoglycolate to 3- phosphoglycolate, NAD+ is consumed. B. CO2 is lost without production of energy--rich compounds needed for nighttime respiration. C. The rubisco reaction requires ATP, which is wasted if 2- phosphoglycerate is produced. D. During the process of converting 2—phosphoglycerate into 4- phosphoglycerate, 2 ATP are used up
B. CO2 is lost without production of energy--rich compounds needed for nighttime respiration.
Choose the true statement(s) referring to the following coupled reactions: Rxn1 A↔B 𝚫G°' = -2 kJ/mol Rxn2 B↔C 𝚫G°' = +7 kJ/mol Rxn3 C↔D 𝚫G°' = -8 kJ/mol Net Rxn A↔D 𝚫G°' = -3 kJ/mol A. The net reaction of A→D is unfavorable because the 𝚫G°' value is less than 0. B. Rxn2 (B↔C) is unfavorable in the forward direction on its own, but if coupled to Rxn3 (C↔D), the overall conversion of B to D will occur. C. For Rxn2, if the 𝚫G°' value changes to +9 kJ/mol, the rate of the overall reaction A↔D will decrease. D. Rxn1 is a favorable reaction and will proceed in cells even if cellular concentrations of reactants and products change..
B. Rxn2 (B↔C) is unfavorable in the forward direction on its own, but if coupled to Rxn3 (C↔D), the overall conversion of B to D will occur.
If rubisco retains molecular oxygen in its active site, what are the consequences? (Multiple Answers) A. 2 molecules of 3-phosphoglycolate are formed B. Three organelles (chloroplasts, peroxisomes, and mitochondria) are needed to form the correct products C. Requires energy to convert glycerate to 3-phosphoglycerate D. Does not cause any issues for C4 and CAM plants
B. Three organelles (chloroplasts, peroxisomes, and mitochondria) are needed to form the correct products C. Requires energy to convert glycerate to 3-phosphoglycerate
Photons first enter the Z scheme via which molecule? Choose one: A. Plastocyanin B. Chlorophyll P700 C. Chlorophyll P680 D. Plastoquinone
C. Chlorophyll P680
What are the three main stages of the Calvin cycle? (Multiple Answers) A. Oxidation B. Duplication C. Regeneration D. Fixation E. Resonance Energy Transfer F. Light reaction G. Reduction
C. Regeneration D. Fixation G. Reduction
What must be the chemical property of the electron acceptor molecule that is reduced by electron transfer when chlorophyll loses an electron as a result of photooxidation? Choose the TWO best answers. A. The ring structures of the acceptor molecule and chlorophyll cannot both contain nitrogen B. The metal ion in both the acceptor molecule and chlorophyll must both contain manganese. C. The acceptor molecule must have a higher reduction potential than chlorophyll (more positive). D. The acceptor molecule must be in close proximity and be oriented correctly to facilitate the electron transfer reaction. E. The acceptor molecule must have a lower reduction potential than chlorophyll (more positive). F. The acceptor molecule must have a higher reduction potential than chlorophyll (less positive). G. There are not two correct answers.
C. The acceptor molecule must have a higher reduction potential than chlorophyll (more positive). DThe acceptor molecule must be in close proximity and be oriented
Identify the inputs and outputs of the Calvin cycle.
Calvin Cycle Inputs CO2 ATP NADPH Calvin Cycle Outputs NADP+ ADP + Pi Triose phosphates
Answer true or false for each of the following statements. T / F: ATP synthesis by ATP synthase requires a substrate level phosphorylation reaction. T / F: The tight, loose, and open conformations in the binding change mechanism refer to the contacts made between the central gamma subunit and the beta subunit where ATP synthesis occurs. T / F: Protons move through the ATP synthase by entering a half channel in one protein subunit associating with the c ring, then exiting through a different half channel. T / F: Hydrolysis of ATP by the ATP synthase will drive rotation of the gamma subunit in the opposite direction that it rotates when ATP is being synthesized.
F,F,T,T
How can an unfavorable reaction (mc007-1.jpg > 0) still occur in a metabolic pathway? None of these questions are correct. Link it to a favorable reaction. Link it to another unfavorable reaction. Increase the temperature of the reaction.
Link it to a favorable reaction.
CAM Plants
Malate stored in vacuoles Use temporal separation of CO2 fixation and rubisco activity to decrease photorespiration rates Saguaro cactus is an example. Stomata open only at night.
Paraquat is an effective herbicide the kills plants by disrupting the photosynthetic electron transport system. Why then was the spraying of marijuana fields with paraquat discontinued in the 1980s? Choose the ONE best answer. It was discovered that aerial spraying of paraquat is very dangerous to livestock and should never be used for crop management because it inhibits PSI in cows. It was stopped because the governments of the countries involved could not decide who should pay for it. It was known at the time that marijuana was resistant to paraquat so it was a waste of money. None of these statements are correct. It was not discontinued, in fact paraquat is still used today to destroy marijuana crops in Colorado.
None of these statements are correct.
Considering that the PSI complex alone does not translocate protons across the thylakoid membrane, why is photon absorption by PSI required to sustain proton translocation by the cytochrome b6f complex in the presence of light?
Plastocyanin is oxidized by PSI in response to light. If electron flow through cytochrome b6f is inhibited because no oxidized plastocyanin is available, then proton translocation is also inhibited.
Which is a way that light controls the Calvin cycle activity? High levels of ATP and NADPH from the light reactions inhibit the Calvin cycle enzymes. None of these answers are correct. Reduced ferredoxin from the light reactions keeps thioredoxin reduced, which keeps Calvin cycle enzymes in an active form. Calvin cycle or dark reaction enzyme activators are present at higher levels in the dark. Calvin cycle enzymes are inhibited by the lower H+, which is pumped out of the stroma by light reactions.
Reduced ferredoxin from the light reactions keeps thioredoxin reduced, which keeps Calvin cycle enzymes in an active form.
What must be the chemical property of the electron acceptor molecule that is reduced by electron transfer when chlorophyll loses an electron as a result of photooxidation? Choose the TWO best answers. The acceptor molecule must have a lower reduction potential than chlorophyll (more positive). The acceptor molecule must be in close proximity and be oriented correctly to facilitate the electron transfer reaction. The acceptor molecule must have a higher reduction potential than chlorophyll (more positive). The metal ion in both the acceptor molecule and chlorophyll must both contain manganese. The ring structures of the acceptor molecule and chlorophyll cannot both contain nitrogen. The acceptor molecule must have a higher reduction potential than chlorophyll (less positive). There are not two correct answers.
The acceptor molecule must be in close proximity and be oriented correctly to facilitate the electron transfer reaction. The acceptor molecule must have a higher reduction potential than chlorophyll (more positive).
Why are 8 photons required for the net reaction of the photosynthetic electron transport system? (2 H20 + 8 photons +2 NADP+ + 3 ADP + 3Pi O2 + 2 NADPH +3 ATP)
The oxidation of 2 H20 generates 4 electrons; however, 4 photons are required at each of the PSII and PSI reactions centers to move the electron through the photosynthetic electron transport system. *Remember the Z-scheme*
Choose the one statement below that most accurately describes the biochemical basis for the emergence of MRSA infections. None of these statements are correct Staph aureus exports methicillin faster than it can inhibit the transpeptidase Staph aureus express high levels of beta-lactamase The transpeptidase enzyme in Staph aureus does not bind methicillin Penicillin and methicillin are structurally similar, which causes antibiotic resistance.
The transpeptidase enzyme in Staph aureus does not bind methicillin
Paper is made from cellulose fibers. Explain why paper loses its shape and planar strength when it is soaked in water but not when it is soaked in oil.
Water disrupts intrafiber H-bonds that hold the cellulose together, whereas oil has no effect on these bonds
Which of the following statements about photosystem I in chloroplasts are correct? (Multiple Answers) a) Photosystem I is activated by light independently from Photosystem II. b) Plastocyanin reduces photo-oxidised P700 in PSI. c) Plastocyanin reduces photo-oxidised P680 in PSI. d) Electrons ejected from P700 in photosystem I are replaced with electrons from water. e) The Calvin Cycle occurs only in light.
a) Photosystem I is activated by light independently from Photosystem II. b) Plastocyanin reduces photo-oxidised P700 in PSI. d) Electrons ejected from P700 in photosystem I are replaced with electrons from water.
Some Calvin Cycle enzymes contain disulfide bonds that must be reduced through a mechanism involving thioredoxin in order for the enzyme to be active in sunlight. What is the name of the key regulatory protein that inactivates these same Calvin Cycle enzymes by oxidation when the sun goes down? a) There is no regulatory protein that oxidizes these Calvin Cycle enzymes; oxidation is spontaneous b) Thioredoxin has multiple light-sensing properties and when the sun goes down it turns into a strong oxidant c) Ferredoxin-thioredoxin reductase. d) RuBP Carboxylase Activase e) None of the above
a) There is no regulatory protein that oxidizes these Calvin Cycle enzymes; oxidation is spontaneous
Which glycan contains both mc025-1.jpg-1,4 glycosidic bonds and mc025-2.jpg-1,6 glycosidic bonds? cellulose amylose chitin ribose amylopectin
amylopectin
Choose the one best statement below that accurately describes O-linked glycoproteins. an oligosaccharide forms an O-glycosidic bond with an Asn residue of the protein an oligosaccharide forms an O-glycosidic bond involving the anomeric carbon of the oligosaccharide and a Ser or Thr residue on the protein an oligosaccharide forms an O-glycosidic bond with the α-carbon on a residue of the protein None of these statements are correct. an oligosaccharide forms an O-glycosidic bond between a residue on the protein and an -OH group on the oligosaccharide
an oligosaccharide forms an O-glycosidic bond involving the anomeric carbon of the oligosaccharide and a Ser or Thr residue on the protein
What explains the observation that crabgrass, which uses the C4 pathway of carbon fixation, has a growth advantage over turfgrass when temperatures are high? a) Crabgrass always grows faster than turfgrass. b) High temperatures cause more O2 to dissolve than CO2, leading to increased photorespiration in turfgrass, but less so in crabgrass. c) High temperatures cause more O2 to dissolve than CO2, leading to increased photorespiration in crabgrass, producing more ATP. d) High temperatures cause more CO2 to dissolve than O2, leading to decreased photorespiration in crabgrass, but less so in turfgrass.
b) High temperatures cause more O2 to dissolve than CO2, leading to increased photorespiration in turfgrass, but less so in crabgrass.
C4 plants are thought to be more efficient than C3 plants because they none of these answers are correct. can concentrate the CO2 in chloroplasts and therefore minimize side reactions with O2. make larger sugar molecules from CO2. can produce sugar molecules at night in addition to during the day. can live in dry climates.
can concentrate the CO2 in chloroplasts and therefore minimize side reactions with O2.
The primary difference between ATP synthesis during the photosynthetic light reactions and ATP synthesis in the mitochondrial electron transport chain is the enzyme catalyzing the ATP synthesis. number of NADPH required to produce ATP. number of ATP produced per 360mc036-1.jpg rotation of the F1 subunit of ATP synthase. cellular location of the proton motive force.
cellular location of the proton motive force.
The enzyme in the photosynthetic Z scheme that catalyzes the PQ cycle, which is analogous to Complex III and the Q cycle in the mitochondrial electron transport chain, is photosystem I cytochrome b6f plastocyanin photosystem II
cytochrome b6f
Which of the following statements about the mechanism of the light-dependent reactions of photosynthesis is correct? a) Electrons from photosystem I reduce NADPH. b) Electrons from photosystem I reduce pheophytin. c) Electrons from NADPH revert photosystem II back to the ground state. d) Ferredoxin-NADP reductase reduces NADP+ to NADPH.
d) Ferredoxin-NADP reductase reduces NADP+ to NADPH.
Which plant is most likely to use the CAM pathway to keep photorespiration to a minimum during the day? a) Sugarcane b) Juniper c) Oak tree d) Saguaro e) Pine tree
d) Saguaro
Paraquat is an effective herbicide the kills plants by disrupting the photosynthetic electron transport system. Why then was the spraying of marijuana fields with paraquat discontinued in the 1980s? Choose the ONE best answer. It was discovered that aerial spraying of paraquat is very dangerous to livestock and should never be used for crop management because it inhibits PSI in cows. None of these statements are correct. It was not discontinued, in fact paraquat is still used today to destroy marijuana crops in Colorado. It was stopped because the governments of the countries involved could not decide who should pay for it. It was known at the time that marijuana was resistant to paraquat so it was a waste of money.
None of these statements are correct.
Question 1 1 / 1 point The hormone insulin activates phosphofructokinase 2 (2PFK2). This leads to a(n) __________ in concentration of fructose 2,6 bisphosphate, which favors the __________ pathway. decrease; gluconeogenesis increase; gluconeogenesis decrease; glycolysis increase; glycolysis
increase; glycolysis
Under what condition(s) do the wasteful side reaction of O2 with rubisco become significant? increased rubisco concentrations higher levels of CO2 than O2 increased temperature and intense light at night none of these answers are correct.
increased temperature and intense light
Under what conditions does cyclic photophosphorylation take place? with high levels of ATP in an acidic stroma with an inactivated photosystem I none of these answers are correct. with high levels of NADH
none of these answers are correct.
Energy conversion in living systems is required for what three types of work? osmotic work, chemical work, potential work osmotic work, photosynthetic work, mechanical work kinetic work, chemical work, mechanical work osmotic work, chemical work, mechanical work none of these questions are correct.
osmotic work, chemical work, mechanical work
What enzyme class in the nonoxidative phase of the pentose phosphate pathway allows for the reaction of ribose-5-phosphate and xylulose-5-phosphate to produce glyceraldehyde-3-phosphate and seduheptulose-7-phosphate? oxidoreductase kinase transferase hydrolase isomerase
transferase
Which enzyme in the pentose phosphate pathway is regulated to control flux through the pathway? transaldolase ribulose-5-phosphate epimerase none of these answers are correct. 6-phosphogluconate dehydrogenase glucose-6-phosphate dehydrogenase
glucose-6-phosphate dehydrogenase
Gluconeogenesis would most likely be allosterically activated simultaneously along with which other metabolic process? glycolysis citrate cycle glycogen synthesis pentose phosphate pathway calvin cycle
glycogen synthesis
Approximately how many ATP are synthesized per O2 molecule generated in photosynthesis light reactions? 8 3 12 4 the correct answer is not given.
3
The first two reactions of gluconeogenesis are required to reverse reaction 10 (or the last reaction) of glycolysis. How many ATP equivalents are used by these first two reactions of gluconeogenesis? 4 2 6 3 1
2
For every four reduced plastoquinol molecules (PQBH2) that are oxidized in the PQ cycle, how many protons are translocated into the thylakoid lumen?
8
Based on the overall reactions for photosynthetic electron transport and the Calvin cycle reactions, how many photons of light are required to generate enough ATP to produce glyceraldehyde-3-phosphate? Choose one: A. 24 B. 36 C. 16 D. 8
A. 24
R is the highly active form of an allosteric enzyme and T is the less active form of enzyme. What would happen to [T]/[R] if substrate concentration is decreased? A. Increase B. Remain the same C. Decrease
A. Increase
Which chromophore appears orange and absorbs in the blue range of the visible spectrum? Choose one: A. β-carotene B. Phycocyanobilin C. Phycoerythrobilin D. Chlorophyll
A. β-carotene
Among the Calvin cycle inputs, which ones are generated by the light reactions of photosynthesis? Choose one: A. CO2 and ATP B. ATP and NADPH C. CO2 and NADP+ D. ADP and NADP+
B. ATP and NADPH
14. (5 pts.) Explain why AB type individuals can accept packed red blood cells (RBCs) from any donor. A. Because AB plasma contains A and B type antibodies that do not react with donor RBCs from anyone. B. Because AB plasma does not contain A or B type antibodies so RBCs from any donor are compatible. C. Because AB type individuals contain RBCs without antigens so their plasma is free of O type antibodies. D. Because A, B, AB, O type individuals have RBCs that are not recognized as non-self to AB antibodies. E. Because plasma from A, B, AB, O type individuals contains antibodies that recognize A but not B RBCs.
B. Because AB plasma does not contain A or B type antibodies so RBCs from any donor are compatible.
Which of the following is an example of a polysaccharide? Choose one: A. Galactose B. Glycogen C. Maltose D. Raffinose
B. Glycogen
Which of the following is an example of a monosaccharide? Choose one: A. Maltose B. Mannose C. Sucrose D. Raffinose
B. Mannose
Which electron carrier in chloroplasts brings electrons to initiate a cycle similar to the Q cycle in mitochondria? Choose one: A. Plastocyanin B. Pheophytin C. Plastoquinone D. Cytochrome b6f
C. Plastoquinone
11. (5 pts.) The cytochrome b6f complex of the photosynthetic electron transport system is responsible for translocating 8 H+ into the thylakoid space from the stroma. However, a total of 12 H+ accumulate inside the thylakoid space as a result of photon absorption by PSII and PSI. What is the origin of the other 4 H+? A.ThereductionofO2 toform+4H+ +4e-+H2O B. The phosphate transporter delivers 4 H+ for each 4 ATP C.Theoxidationof2H2OtoformO2 +4H+ +4e- D. The PQ cycle runs twice and delivers 2 H+ per each cycle E. The PSI and PSII reaction centers each contribute another 2 H+
C.Theoxidationof2H2OtoformO2 +4H+ +4e-
16. (5 pts) Which TWO statements below accurately describe the difference between the oxidative phase and the nonoxidative phase of the Pentose Phosphate Pathway? 1. The oxidative phase generates 6 NADPH per glucose-6P converted to ribulose-5P, whereas the nonoxidative phase generates 6 glucose-6P for every 5 ribulose-5P. 2. The nonoxidative phase interconverts C3, C4, C5, C6, and C7 sugars with no change in carbons, whereas the oxidative phase generates 6 CO2 from 6 glucose-6P to produce 6 ribulose-5P. 3. The oxidative phase is responsible for regenerating fructose-6P, whereas the nonoxidative phase is responsible for generating NADPH. 4. The nonoxidative phase produces ribose-5P for nucleotide synthesis and the oxidative phase generates NADPH for biosynthetic reactions in the cell. 5. The nonoxidative phase is responsible for regenerating ribulose-5P, whereas the oxidative phase is responsible for generating FADH2. A. 1and3 B. 2and5 C. 2and3 D. 4and5 E. 2and4
E. 2and4
10. (5 pts.) Light activation of PSI leads to the reduction of ferredoxin, which then reduces not only NADP+ but also thioredoxin, which uses the electrons to reduce disulfide bridges in several Calvin cycle enzymes, leading to their activation. What turns off these Calvin cycle enzymes when the Sun goes down? A. Magnesium levels increase in the stroma when the Sun goes down and inhibits the enzymes. B. The pH inside the thylakoid lumen equilibrates with the pH in the stroma, both of which are pH5 at night. C. The enzymes spontaneously reduce in the presence of air when the Sun goes down and are inactivated. D. Malate is transported to the stomata, which increases the size of grana and results in enzyme inhibition. E. None of these statements are correct.
E. None of these statements are correct.
R is the highly active form of an allosteric enzyme and T is the less active form of enzyme. What would happen to [T]/[R] if substrate concentration is decreased? Decrease Remain the same Increase
Increase
Which THREE of the following statements about autotrophs and heterotrophs on Earth are TRUE? Heterotrophs depend on autotrophs for conversion of light energy to chemical energy. Heterotrophs that do not eat autotrophs every day will die in a short time. There are no metabolic differences between autotrophs and heterotrophs. Heterotrophs evolved on Earth before autotrophs. The majority of autotrophs on Earth require aerobic respiration in order to survive. Autotrophs depend on heterotrophs to oxidize sugar and release CO2 into the atmosphere. Heterotrophs are dependent on autotrophs to generate O2 from H2O in order to support aerobic respiration. The majority of heterotrophs on Earth do not use aerobic respiration as a form of energy conversion.
Heterotrophs are dependent on autotrophs to generate O2 from H2O in order to support aerobic respiration. The majority of autotrophs on Earth require aerobic respiration in order to survive. Heterotrophs depend on autotrophs for conversion of light energy to chemical energy.
The Biosphere 2 project, in Tucson, Arizona, was an experiment involving a large sealed terrarium with humans and photosynthetic plants living in balance. Why did the project have to be interrupted after only a few months? Levels of CO2 rose to dangerous levels. The rate of photosynthesis was too high. The humans ran out of food. The plants stopped producing oxygen.
Levels of CO2 rose to dangerous levels.
C4 Plants
Malate transferred to bundle sheath cells Use spatial separation of CO2 fixation and rubisco activity to decrease photorespiration rates Stomata open during the day. Sugarcane is an example.
A middle-Eastern family presents for evaluation because their infant son died in the nursery with severe hemolysis and jaundice. The couple had two prior female infants who are alive and well, and the wife relates that she lost a brother in infancy with severe hemolysis induced after a viral infection. Red blood cells from the patient have very low concentrations of reduced glutathione. Defective synthesis of which of the following pairs of compounds would likely be found in this patient? Ribose and NADPH Fructose-6-phosphate and ATP Glucose and NADH Lactate and NADPH Deoxyribose and NADP+ Glucose-6-phosphate and NADH
Ribose and NADPH
Why is referring to the Calvin cycle reactions as the dark reactions a misnomer? They occur primarily at night. They do not absolutely require sunlight energy for a short period of time (seconds). They absorb, and do not reflect, the sunlight energy. They do not absorb sunlight energy. They require an active photosynthetic system in the light, so are not the "dark reactions" in everyday biochemistry.
They require an active photosynthetic system in the light, so are not the "dark reactions" in everyday biochemistry.
If one heterozygous parent expresses the GTA glycosyltransferase and the other heterozygous parent expresses the GTB glycosyltransferase, what is the probability of a child with a blood type of O? 0% 75% 100% 25%
25%
7. (5 pts) 7. (5 pts) Put the following steps in the photosynthetic electron transport system in the correct order beginning with a photon absorption event. a. A total of 12 H+ enter the chloroplast ATP synthase to generate 3 ATP when they return to the stroma and induce conformational changes in the head piece of the complex. b. PSII absorbs 4 photons leading to photooxidation of 4 chlorophyll molecules and oxidation of 2 H2O to replace the 4 e- in chlorophyll and release 4 H+ into the thylakoid lumen. c. Oxidation of pheophytin initiates a series of redox reactions culminating in the reduction of 4 plastocyanin and translocation of 8 H+ across the thylakoid membrane. d. The sun goes down. e. PSI absorbs 4 photons leading to the photooxidation of 4 plastocyanin and initiation of a series of redox reactions culminating in the reduction of 2 NADP+ to yield 2 NADPH. A. 4,2,1,5,3 B.3,1,2,5,4 C.4,1,2,5,3 D)4,3,2,5,1 E)3,2,1,5,4
4,1,2,5,4
Cyclic photophosphorylation produces __________, but does not produce __________. Choose one: A. ATP ; O2 or NADPH B. NADPH ; ATP or O2 C. ATP ; a proton gradient D. O2 ; ATP or NADPH
A. ATP ; O2 or NADPH
Which of the following steps used to convert solar energy to chemical energy does NOT involve the movement of electrons? Choose one: A. ATP synthesis by the chloroplast ATP synthase complex B. Absorption of photons by photosystem I C. Absorption of photons by chlorophyll molecules in photosystem II D. The transport system involving carrier molecules PQ and PC
A. ATP synthesis by the chloroplast ATP synthase complex
The __________ pathway is used by plants that thrive in high temperate conditions, such as sugarcane. Choose one: A. C4 B. C2 C. C3 D. CAM
A. C4
What is a major difference between the mechanisms used by C4 and CAM plants to minimize photorespiration and maximize fixation of CO2 by rubisco? Choose one: A. CAM plants allow CO2 to enter the mesophyll cells only at night. The CO2 is stored as malate and then malate is decarboxylated during the day. The CO2 then enters the Calvin cycle. C4 plants capture CO2 in mesophyll cells, convert the CO2 to malate, and transfer the malate to neighboring bundle sheath cells, where the Calvin cycle operates on the CO2 derived from decarboxylated malate. B. C4 plants allow CO2 to enter the mesophyll cells only at night. The CO2 is stored as malate and then malate is decarboxylated during the day. The CO2 then enters the Calvin cycle. CAM plants capture CO2 in mesophyll cells, convert the CO2 to malate, and transfer the malate to neighboring bundle sheath cells, where the Calvin cycle operates on the CO2 derived from decarboxylated malate. C. The chloroplasts in C4 mesophyll cells lack photosystem II reaction centers. This prevents the formation of O2, and thus virtually eliminates oxygenase activity of rubisco. In CAM plants, the mesophyll cells have chloroplasts with fully functional photosystems. D. The chloroplasts in CAM mesophyll cells lack photosystem II reaction centers. This prevents the formation of O2, and thus virtually eliminates oxygenase activity of rubisco. In C4 plants, the mesophyll cells have chloroplasts with fully functional photosystems.
A. CAM plants allow CO2 to enter the mesophyll cells only at night. The CO2 is stored as malate and then malate is decarboxylated during the day. The CO2 then enters the Calvin cycle. C4 plants capture CO2 in mesophyll cells, convert the CO2 to malate, and transfer the malate to neighboring bundle sheath cells, where the Calvin cycle operates on the CO2 derived from decarboxylated malate.
20. (5 pts) The Cori Cycle has a net metabolic cost of 4 ATP in the conversion of glucose lactate glucose after intense exercise. What accounts for this net cost of 4 ATP when running the Cori Cycle? A. Glucose metabolism yields 2 ATP, whereas glucose synthesis requires 6 ATP net cost is 4 ATP. B. Glucose synthesis costs 8 ATP, whereas glucose metabolism yields 4 ATP net cost is 4 ATP. C. Glucose metabolism yields 1 ATP, whereas glucose synthesis requires 5 ATP net cost is 4 ATP. D. Glucose and lactate are stereoisomers that use a total of 4 ATP to generate one phosphoenolpyruvate. E. None of these statements are correct.
A. Glucose metabolism yields 2 ATP, whereas glucose synthesis requires 6 ATP net cost is 4 ATP.
13. (5 pts.) What causes flatulence in humans (and pigs) who consume vegetables such as broccoli? A. Intestinal bacteria contain glycosidases that metabolize raffinose oligosaccharides to produce methane. B. Broccoli, cabbage, and soybeans contain an alpha-1,6-glycosidase enzyme that produces gas. C. Humans and pigs contain an intestinal alpha-1,6-glycosidase enzyme that produces gas. D. Flatulence is a normal process in humans and pigs that results from eating plants with chlorophyll. E. None of these statements are correct.
A. Intestinal bacteria contain glycosidases that metabolize raffinose oligosaccharides to produce methane.
9. (5 pts) (9a) What molecule reduces the oxidized chlorophyll in PSII after the chlorophyll transfers an electron to an acceptor following photooxidation? (9b) What molecule reduces the oxidized PSI chlorophyll after it transfers an electron? Your first answer corresponds to (9a) and your second answer to (9b).
A. Water, plastocyanin B. Magnesium, pheophytin C. Plastocyanin, pheophytin D. Cytb6f, plastocyanin E. LHCI, plastoquinone
1. (5 pts.) Eduard Buchner is considered the forefather of biochemistry because he was the first to prove that ________ are sufficient for alcoholic fermentation in the absence of live yeast as long as _________ is provided A. enzymes, glucose B. sugars, glycine C. lipids, raffinose D. nucleic acids, DNA
A. enzymes, glucose
Phosphoglycerate kinase transfers a phosphate group between ATP and 3-phosphoglycerate. In which of the following three pathways does the phosphoglycerate kinase reaction generate ATP? Choose one: A. glycolysis B. Calvin cycle C. gluconeogenesis
A. glycolysis
In the five steps used by photosynthetic organisms to convert solar energy into chemical energy, which molecules store the solar energy before sugar synthesis? ATP and NADPH chlorophylls NADH and FADH2 none of these answers are correct.
ATP and NADPH
Which of the following cellular structures is NOT involved in the glyoxylate cycle? Choose one: A. Mitochondria B. Chloroplasts C. Lipid stores D. Glyoxysome
B. Chloroplasts
Which of the following is responsible for transporting protons across the thylakoid membrane? Choose one: A. Photosystem II B. Cytochrome b6f C. Photosystem I D. Plastoquinone
B. Cytochrome b6f
Select the TWO true statements from the list below that most accurately describe enzyme structure and function. A. Enzymes decrease the equilibrium constant of biochemical reactions and increase the rates of reactions from years to minutes. B. Enzymes increase the rates of biochemical reactions without changing the equilibrium constant. C. Phosphorylation of serine residues, and conformational changes in enzyme subunits, always inhibit enzyme activity. D. All proteins are not enzymes but all enzymes are proteins. E. The substrate can be predicted by simply knowing the structure of the unoccupied enzyme active site, similar to a key fitting a lock. F. Enzymes function only in their cellular environment. G. Enzyme cofactors can increase the chemical functionality of enzymes, which are otherwise limited by the R groups of amino acids. H. Hydrogen bonding networks are all that is required for enzymes to catalyze biochemical reactions.
B. Enzymes increase the rates of biochemical reactions without changing the equilibrium constant. G. Enzyme cofactors can increase the chemical functionality of enzymes, which are otherwise limited by the R groups of amino acids.
5. (5 pts.) R is the highly active form of an allosteric enzyme and T is the less active form. What would happen to the ratio of [T] / [R] if the concentration of a positive allosteric regulator were to increase? A. The ratio is increased B. The ratio is decreased C. Unchanged ratio D. Ratio = 1.0 E. Ratio = 0
B. The ratio is decreased
R is the highly active form of an allosteric enzyme and T is the less active form. What would happen to the ratio of [T] / [R] if the concentration of a positive allosteric regulator were to increase? A. The ratio is increased B. The ratio is decreased C. Unchanged ratio D. Ratio = 1.0 E. Ratio = 0
B. The ratio is decreased
Which of the following is not a common feature of glycoconjugates? Choose one: A. are covalently attached to lipids and proteins B. are always branched structures C. contain both modified and unmodified monosaccharides D. frequently contain the hexosamine N-acetylgalactosamine
B. are always branched structures
What is the name of the pathway that seedlings use in the first few days after germination to make carbohydrates that are transported to the developing stem and leaves? Choose one: A. C4 pathway B. glyoxylate cycle C. glycolate cycle D. glycolysis pathway
B. glyoxylate cycle
In a chloroplast, ATP synthase releases newly synthesized ATP into which of the following? Choose one: A. thylakoid lumen B. stroma C. space between the inner and outer chloroplast membranes D. grana
B. stroma
18. (5 pts.) Fructose-2,6-bisphosphate (F-2,6-BP) is an allosteric regulator that controls flux through the glycolytic and gluconeogenic pathways. Levels of F-2,6-BP increase in the cell in response to insulin and decrease in response to glucagon. Choose the number corresponding to the correct underlined answer. Insulin signaling in liver cells leads to the phosphorylation (1) / dephosphorylation (2) of PFK-2/FBPase-2, which activates the PFK-2 activity of the enzyme and phosphorylation of fructose-6P (3) / fructose-1P (4). The net result of increased F-2,6-BP levels in liver cells is to stimulate (5) / inhibit (6) flux through the glycolytic pathway by allosterically-activating the enzyme aldolase (7) / phosphofructokinase-1 (8). In contrast, glucagon inhibits (9) / stimulates (10) protein kinase A (PKA) signaling in liver cells leading to the activation of the FBPase-2 domain of the dual function enzyme PFK-2/FBPase-2 which results in increased (11) / decreased (12) levels of F-2,6-BP. A.1,4,5,7,10,11 B.2,3,5,8,10,12 C.1,3,6,8,9,12 D.2,3,6,8,10,11 E.2,4,5,7,9,12
B.2,3,5,8,10,12
Eduard Buchner is credited with discovering reaction conditions required for in vitro fermentation using protein extracts prepared from yeast. Louis Pasteur, at the urging of the local wineries in France, had also tried to reproduce fermentation in vitro using yeast cell extracts, but to no avail. Describe three things that Buchner did differently from Pasteur that are thought to have contributed to his success.
Buchner (1) used a different strain of yeast than Pasteur used, (2) prepared the yeast extract using quartz mixed with diatomaceous earth rather than glass, and (3) his extract buffer contained glucose, the carbon source for fermentation.
17. (5 pts) A continual supply of reduced glutathione is required to protect red blood cells against the toxic effects of primaquine, a malarial prophylactic. Why would individuals with a defect in the enzyme glucose 6- phosphate dehydrogenase (G6PDH) be susceptible to primaquine-induced hemolytic anemia? A. They are susceptible because they cannot release glucose from liver cells in response to glucagon. B. The enzyme G6PDH is responsible for reducing reactive oxygen species, so too many ROIs in cell. C. A G6PDH deficiency leads to insufficient NADPH to protect against primaquine-induced anemia. D. Individuals with a G6PDH deficiency detoxify primaquine in the kidneys instead of the liver. E. Primaquine-induced hemolytic anemia is caused by the malarial parasite, so less G6PDH is good.
C. A G6PDH deficiency leads to insufficient NADPH to protect against primaquine-induced anemia.
Which of the following statements is correct about the flow of electrons in photosystem I? Choose one: A. The electron carriers that interact with PSI are moving electrons in both directions across the thylakoid membrane. That is, electrons flow from the lumen through PSI to the stroma and from the stroma through PSI to the lumen. B. All electron carriers that interact with PSI and all electron carriers within PSI are embedded in the thylakoid membrane. C. Electrons enter PSI from electron carriers in the thylakoid lumen and exit PSI via electron carriers in the stroma. All electron carriers in PSI are embedded in the thylakoid membrane. D. Electrons enter PSI from electron carriers in the stroma and exit PSI via electron carriers in the thylakoid lumen. All electron carriers in PSI are embedded in the thylakoid membrane.
C. Electrons enter PSI from electron carriers in the thylakoid lumen and exit PSI via electron carriers in the stroma. All electron carriers in PSI are embedded in the thylakoid membrane.
12. (5 pts.) Paper is made from cellulose fibers. Explain why paper loses its shape and planar strength when it is soaked in water but not when it is soaked in oil. Structure of cellulose A. Paper floats on water, which makes it wrinkle, oil is hydrophobic so paper sinks. B. Oil contains contaminants that interfere with glycosidase enzymes so they are inactive. C. Paper is held together by water soluble glue and the glue dissolved in water not oil. D. Water disrupts the intrafiber hydrogen bonds whereas oil does not affect hydrogen bonds. E. None of these statements are correct.
D. Water disrupts the intrafiber hydrogen bonds whereas oil does not affect hydrogen bonds. E. None of these statements are correct.
Having PSII and PSI complexes unevenly distributed in the thylakoid membrane offers several advantages for the light reactions of photosynthesis. Among the reasons below, which is not correct? Choose one: A. Keeping PSII and PSI complexes separated reduces nonproductive energy transfer from PSII to PSI, instead ensuring the photooxidation of PSII, which is essential for ATP production. B. The phosphorylation state of LHC II is regulated by a feedback loop involving the redox state of plastoquinones. This, in turn, controls the light absorption by PSII and PSI. C. It ensures that plastocyanin and ferredoxin, soluble electron carriers associated with PSII and PSI, respectively, are able to come into close contact and transfer electrons with each other during cyclic photophosphorylation. D. PSI localization to the lamellae increases its accessibility to NADP+ molecules in the stroma.
C. It ensures that plastocyanin and ferredoxin, soluble electron carriers associated with PSII and PSI, respectively, are able to come into close contact and transfer electrons with each other during cyclic photophosphorylation.
8. (5 pts) What is the biochemical advantage of CO2 fixation in C4/CAM plants compared to C3 plants? A. There is a higher percentage of O2 fixation in C4/CAM plants, which gives them energy at night. B. The C4/CAM plants increase cyclic photophosphorylation, which provides more ATP in warm climates. C. The C4/CAM plants limit photorespiration, which gives them a growth advantage in warm climates. D. The C4/CAM plants store malate in daylight and release the CO2 at night when Calvin Cycle is active. E. None of these statements are correct.
C. The C4/CAM plants limit photorespiration, which gives them a growth advantage in warm climates.
Enzymes of the Calvin cycle are controlled by light in three different ways. Which of the following is not one of those mechanisms? Choose one: A. Calvin cycle enzyme inhibitors, such as CA1P, are present at greater levels in the dark than in the light. B. While the photoactivated electron transport system is operating, thioredoxin is able to activate select Calvin cycle enzymes by maintaining their reduced disulfide bridges. C. The Calvin cycle enzyme transketolase, which transfers a C2 group from a ketose to an aldose, requires a light-activated thiamine pyrophosphate coenzyme for its function. D. Calvin cycle enzymes are activated by a decrease in proton concentration and an increase in Mg2+ levels in the stroma, which are both products of an active photosynthetic electron transport system.
C. The Calvin cycle enzyme transketolase, which transfers a C2 group from a ketose to an aldose, requires a light-activated thiamine pyrophosphate coenzyme for its function.
15. (5 pts.) Heparin has one of the highest negative charge densities ever found in a biomolecule and is used commercially to prevent blood clotting. Heparin binds to and activates antithrombin, thereby inhibiting the blood clotting cascade. An accidental heparin overdose can be fatal. How does infusion with protamine sulfate, a cationic protein, counteract the effects of a heparin overdose? The molecular structure of heparin is shown here. A. Protamine binds to and inhibits antithrombin and thereby indirectly counteracts heparin overdose. B. Protamine stimulates antithrombin degradation by the proteasome and thereby counteracts heparin C. The positively charged protamine sulfate binds to the negatively charged heparin and inactivates it. D. The negatively charged heparin molecule is degraded by protamine sulfate through ionic interactions. E. None of these statements are correct.
C. The positively charged protamine sulfate binds to the negatively charged heparin and inactivates it.
3. (5 pts.) DNA encodes the genetic information of cells. Based on your understanding of the Central Dogma of Biochemistry, choose the most correct underlined words below and record your answers. Genetic inheritance requires that DNA be copied by a process called replication / translation. Gene segments of RNA / DNA are functional units defined by the nucleic acid products they produce. RNA molecules that encode proteins are called ribosomal / messenger RNA and are used as templates for transcription / translation. Proteins are the workhorses of living cells and function as metabolic enzymes / cofactors, as well as signaling molecules such as receptors. A. replication, RNA, messenger, transcription, enzymes B. translation, DNA, ribosomal, transcription, cofactors C. replication, DNA, messenger, translation, enzymes D. replication, DNA, messenger, transcription, cofactors E. replication, RNA, ribosomal, translation, enzymes
C. replication, DNA, messenger, translation, enzymes
4. (5 pts). 1A) (8 points) Calculate the G value at 25 °C for the reaction converting fumarate to malate, given the standard change in free energy of this reaction is -3.8 kJ/mol, the concentration of fumarate is 0.010 M, and concentration of malate is 0.02 mM. A. -2.1 kJ/mol B. +1.3 kJ/mol C. +11.5 kJ/mol D. -19.2 kJ/mol E. -5.5 kJ/mol
D. -19.2 kJ/mol
Calculate the 𝚫G value at 25 °C for the reaction converting fumarate to malate, given the standard change in free energy of this reaction is -3.8 kJ/mol, the concentration of fumarate is 0.010 M, and concentration of malate is 0.02 mM. A. -2.1 kJ/mol B. +1.3 kJ/mol C. +11.5 kJ/mol D. -19.2 kJ/mol E. -5.5 kJ/mol
D. -19.2 kJ/mol
2. (5 pts) Plants (autotrophs) can convert sunlight energy into chemical energy, but animals (heterotrophs) cannot. Plants and animals can both convert redox energy into chemical energy. A. enzymes, glucose B. sugars, glycine C. lipids, raffinose D. nucleic acids, DNA E. proteins, citric acid 2a. What metabolic pathway do plants have that animals do not have? (pick a number) 2b. What metabolic pathway do both plants and animals use at night? (pick a number) 2c. What organelle do both plants and animals have for NADH oxidation? (pick a number) 2d. What are living organism trying to put off as long as possible? (pick a number) 1. Photosynthesis 2. Enthalpic equality 3. Anaerobic respiration 4. Photoremediation 5. Nucleus 6. Equilibrium 7. Aerobic respiration 8. Chloroplast 9. Thermodynamics 10. Autofluorescence 11. Mitochondria 12. Lactose tolerance The BEST answers for questions 1a through 1d - using the numbered choices to the right - would be: A. 3,4,5,2 B. 4,10,4,6 C. 10,3,8,6 D. 1,7,11,6 E. 1,3,5,12
D. 1,7,11,6
19. (5 pts) The glycolytic enzyme enolase catalyzes: 2-phosphoglycerate phosphoenolpyruvate The free energy change for this reaction is close to zero. What gluconeogenic enzyme catalyzes the reverse reaction? A. Fructose 1,6-bisphosphatase B. Pyruvate carboxylase C. Glyceraldehyde 3-phosphate dehydrogenase D. Enolase E. Glucokinase
D. Enolase
Which of the following equations represents the initial enzyme-catalyzed reaction in the Hatch-Slack pathway? Choose one: A. CO2 + H2O → HCO3- + Pi B. CO2 + phosphoenolpyruvate → malate + Pi C. CO2 + oxaloacetate → malate D. HCO3- + phosphoenolpyruvate → oxaloacetate + Pi
D. HCO3- + phosphoenolpyruvate → oxaloacetate + Pi
Which of the following is NOT a stage of the Calvin cycle? Choose one: A. Reduction B. Regeneration C. Fixation D. Oxidation
D. Oxidation
Which molecular complexes are involved in the formation of the proton gradient across the thylakoid membrane? Choose one: A. PSII and ATP synthase B. PSI and cytochrome b6f C. PSII and PSI D. PSII and cytochrome b6f
D. PSII and cytochrome b6f
Where does the CO2 come from that is used in the Calvin cycle? Choose one: A. from the soil B. from the light reactions C. from the H2O D. from the air
D. from the air
Where do the reactions of the Calvin cycle occur? Choose one: A. in the lumen of the thylakoids B. in the lamellae within a chloroplast C. in the grana within a chloroplast D. in the stroma of a chloroplast
D. in the stroma of a chloroplast
The reduction stage (stage 2) of the Calvin cycle is similar to a portion of glycolysis and gluconeogenesis. In stage 2 of the Calvin cycle, phosphoglycerate kinase, triose phosphate isomerase, and glyceraldehyde-3-phosphate dehydrogenase convert 3-phosphoglycerate to dihydroxyacetone phosphate. Which of the three enzymes catalyze reversible reactions? Choose one: A. phosphoglycerate kinase and glyceraldehyde-3-phosphate dehydrogenase only B. phosphoglycerate kinase and triose phosphate isomerase only C. triose phosphate isomerase and glyceraldehyde-3-phosphate dehydrogenase only D. phosphoglycerate kinase, triose phosphate isomerase, and glyceraldehyde-3-phosphate dehydrogenase
D. phosphoglycerate kinase, triose phosphate isomerase, and glyceraldehyde-3-phosphate dehydrogenase
Select the TWO true statements from the list below that most accurately describe enzyme structure and function. Enzyme cofactors can increase the chemical functionality of enzymes, which are otherwise limited by the R groups of amino acids. Hydrogen bonding networks are all that is required for enzymes to catalyze biochemical reactions. Enzymes function only in their cellular environment. Enzymes increase the rates of biochemical reactions without changing the equilibrium constant. Phosphorylation of serine residues, and conformational changes in enzyme subunits, always inhibit enzyme activity. All proteins are not enzymes but all enzymes are proteins. Enzymes decrease the equilibrium constant of biochemical reactions and increase the rates of reactions from years to minutes. The substrate can be predicted by simply knowing the structure of the unoccupied enzyme active site, similar to a key fitting a lock.
Enzymes increase the rates of biochemical reactions without changing the equilibrium constant. Enzyme cofactors can increase the chemical functionality of enzymes, which are otherwise limited by the R groups of amino acids.
Choose the true statement(s) referring to the following coupled reactions: Rxn1 A↔B DG°' = -2 kJ/mol Rxn2 B↔C DG°' = +7 kJ/mol Rxn3 C↔D DG°' = -8 kJ/mol Net Rxn A↔D DG°' = -3 kJ/mol The net reaction of A→D is unfavorable because the DG°' value is less than 0. Rxn1 is a favorable reaction and will proceed in cells even if cellular concentrations of reactants and products change. For Rxn2, if the DG°' value changes to +9 kJ/mol, the rate of the overall reaction A↔D will decrease. Rxn2 (B↔C) is unfavorable in the forward direction on its own, but if coupled to Rxn3 (C↔D), the overall conversion of B to D will occur.
Rxn2 (B↔C) is unfavorable in the forward direction on its own, but if coupled to Rxn3 (C↔D), the overall conversion of B to D will occur.
Select the THREE statements below that accurately describe the difference between the oxidative phase and nonoxidative phase of the Pentose Phosphate Pathway. The nonoxidative phase interconverts C3, C4, C5, C6, and C7 sugars with no change in total carbons, whereas in the oxidative phase the conversion of glucose-6P to ribulose-5P leads to a loss of a carbon as carbon dioxide. The oxidative phase occurs in the mitochondria where oxygen is available and the nonoxidative phase occurs in the muscle, which uses anaerobic metabolism and generates lactic acid. The nonoxidative phase is responsible for regenerating ribulose-5P, whereas the oxidative phase is responsible for generating NADPH. The oxidative phase is responsible for regenerating glucose-6P, whereas the nonoxidative phase is responsible for generating NADPH. The nonoxidative phase produces ribulose-5P for nucleotide synthesis and the oxidative phase generates NADPH for biosynthetic reactions in the cell. The oxidative phase requires the enzyme glucose-6P dehydrogenase and the nonoxidative phase requires the enzyme transketolase. The oxidative phase generates 2 NADPH for each glucose-6P that is converted to ribulose-5P, whereas the nonoxidative phase generates 5 glucose-6P for every 6 ribulose-5P that are metabolized in the oxidative phase. The nonoxidative phase is dependent on glutathione reductase, however the oxidative phase is dependent on glucose-6P dehydrogenase.
The oxidative phase generates 2 NADPH for each glucose-6P that is converted to ribulose-5P, whereas the nonoxidative phase generates 5 glucose-6P for every 6 ribulose-5P that are metabolized in the oxidative phase. The oxidative phase requires the enzyme glucose-6P dehydrogenase and the nonoxidative phase requires the enzyme transketolase. The nonoxidative phase interconverts C3, C4, C5, C6, and C7 sugars with no change in total carbons, whereas in the oxidative phase the conversion of glucose-6P to ribulose-5P leads to a loss of a carbon as carbon dioxide.
Some Calvin Cycle enzymes contain disulfide bonds that must be reduced through a mechanism involving thioredoxin in order for the enzyme to be active in sunlight. What is the name of the key regulatory protein that inactivates these same Calvin Cycle enzymes by oxidation when the sun goes down? Choose the ONE best answer. None of these answers are correct. Sunlight is a reducing energy and moonlight is an oxidizing energy, so when the moon comes out at night, the Calvin Cycle enzymes are oxidized spontaneously. Thioredoxin has multiple light-sensing properties and when the sun goes down it turns into a strong oxidant. The protein is called ferredoxin-thioredoxin reductase. There is no regulatory protein that oxidizes these Calvin Cycle enzymes; oxidation is spontaneous. Thioredoxin requires sunlight for proper folding into its functional three dimensional structure, so in the absence of light, it is unfolded and cannot reduce these enzymes.
There is no regulatory protein that oxidizes these Calvin Cycle enzymes; oxidation is spontaneous.
Which statement regarding CAM plants is true? None of these answers are correct. They store CO2 in 3-phosphoglycerate before releasing it to the Calvin cycle. They absorb CO2 during the day and release it to the Calvin cycle at night. They use one cell type to absorb and store CO2 before utilizing it in the Calvin cycle in another cell type. They are more efficient than C4 plants.
They absorb CO2 during the day and release it to the Calvin cycle at night.
How would individuals with decreased levels of the pentose phosphate enzyme glucose-6-phosphate dehydrogenase respond to oxidative stress? None of these answers are correct. They would not have the ability to regenerate reduced glutathione as rapidly. They would compensate with higher than normal levels of pentose phosphate pathway activity. Higher than normal levels of NADPH would accumulate. They would rapidly neutralize cellular levels of H2O2 and other reactive oxygen species.
They would not have the ability to regenerate reduced glutathione as rapidly.
Which of the following best defines the first law of thermodynamics? Entropy is a measure of disorder. There is no entropy at zero Kelvin. Total amount of energy in the universe is a constant. All spontaneous processes in the universe tend toward dispersal of energy. None of these answers are correct.
Total amount of energy in the universe is a constant.
