TOTAL

I. _________________/54

II. _________________/10

III. _________________/10

IV. _________________/26

_________________/100

EXAM IV

April 14, 2021Biochemistry IIBI/CH 422/622

I. MULTIPLE CHOICE. (54 points; 2 points each)Choose the BEST answer to the question by WRITING the appropriate letterin the BOX to the left of each question.

1. The use of Schiff-base formation is part of the enzyme mechanism for all of the following enzymes, except ___.

A. acetoacetate decarboxylaseB. transaldolaseC. transketolaseD. aldolaseE. aspartate transaminase

2. Which of the following statements about gluconeogenesis is true?

A. Gluconeogenesis uses the same glycolytic enzymes except for two in the beginning which are used to circumvent the exergonic pyruvate kinase reaction, and to synthesize PEP.

B. Regulation of gluconeogenesis uses the allosteric effector, Fru 1,6P2, whereas glycolysis is regulated by the effector, Fru 2,6P2.

C. Pyruvate carboxylase fixes CO2 in much the same way as rubisco.D. Since both glycolysis and gluconeogenesis involve enzymes only in the

cytosol, they must be coordinately regulated.E. The exergonic nature of the fructose bisphosphatase step is sufficient

to drive the whole gluconeogenesis pathway.

3. Which of these chloroplast enzymes is not regulated by light through the use of thioredoxin?

A. rubiscoB. fructose-1,6-bisphosphataseC. ribulose-5-phosphate kinaseD. glyceraldehyde-phosphate dehydrogenaseE. sedoheptulose-1,7-bisphosphatase

4. Absorption of a photon in the chloroplast of a photosynthetic organism is not associated with which one of the following?

A. release of most of the energy as fluorescenceB. antenna moleculesC. exciton transferD. eventual transfer of energy to a photochemical reaction centerE. transfer of energy from a chlorophyll molecule in a light-harvesting

complex to another chlorophyll or to a phycoerythrobilin molecule

Write your Course ID# in the box below.

NAME: For GradeScope, please write your FIRST and LAST name in CAPITAL letters WITHIN the box:

Page 2Which of the following statements about the pentose-phosphate pathway is true?

A. The pentose-phosphate pathway has two main roles, to make reducedNADH and ribose 5-phosphate for nucleotide biosynthesis.

B. After the oxidative phase of the pentose-phosphate pathway, theribulose 5-phosphate is isomerized to ribose 5-phosphate using anenediol mechanism much like the glycolytic enzymephosphoglucoisomerase that converts glucose 6-phosphate to fructose6-phosphate.

C. Ribose 5-phosphate is either recycled into glucose 6-phosphate orused to synthesize phosphoribosyl pyrophosphate (PRPP) using UTP.

D. The pentose-phosphate pathway enzyme transaldolase transfers a 2-carbon moiety from a ketose to an aldose.

E. The reducing capacity generated by the pentose-phosphate pathway isessential for regulation of the light-independent reactions in theCalvin cycle.

An enzyme used in both glycolysis and gluconeogenesis is:

A. hexokinase.B. glucose-6-phosphatase.C. 3-phosphoglycerate kinase.D. phosphofructokinase-1.E. pyruvate kinase.

The sequence of events in the response of hepatocytes to elevated epinephrine is:

The glycogen-branching enzyme catalyzes:

A. glycogen degradation in tree branches.B. formation of (a1Æ6) linkages during glycogen synthesis.C. formation of (a1Æ4) linkages in glycogen.D. removal of unneeded glucose residues at the ends of branches.E. the synthesis of the initial 6 glucose residues of glycogen

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

A. sedoheptulose-7-phosphateB. glyceraldehyde-3-phosphateC. erythrose-4-phosphateD. mannose-6-phosphateE. ribulose-5-phosphate

1. phosphorylated phosphorylase-a rapidly degrades glycogen2. adenylate cyclase is activated3. epinephrine binds to its receptor on the cell surface4. PKA phosphorylates phosphorylase kinase5. cAMP-dependent protein kinase (PKA) is activated

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

5.

9.

8.

7.

6.

Page 3

Glucagon (in liver) and epinephrine (in muscle):

A. activate glycogen phosphorylase and inactivate glycogen synthase.B. inhibit glycogen synthesis and activate glycogenolysis.C. act by raising the concentration of cyclic AMP (cAMP).D. act through a protein kinaseE. all of the above.

Glycogenin:

A. is the gene that encodes glycogen synthase.B. contains a Tyr on which new glycogen chains are initiated.C. is the enzyme responsible for forming branches in glycogen.D. regulates the synthesis of glycogen.E. catalyzes the conversion of starch into glycogen.

In Gluconeogenesis, which compound is not considered a precursor for making glucose via gluconeogenesis in humans?

A. acetyl‑CoAB. pyruvateC. glycerolD. succinyl‑CoAE. lactate

A person who cannot synthesize liver fructose-1,6-bisphosphatase would probablyexperience:

A. failure to synthesize fats when the diet contained excesscarbohydrate.

B. inability to metabolize fructose.C. inability to convert fructose-1,6-bisphosphate into triose

phosphates.D. inability to resynthesize glucose from lactate produced during

exercise.E. none of the above.

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

A. carbamylation of a Lys residue by CO2.B. relief of the inhibition by the "nocturnal inhibitor," 2-

carboxyarabinitol-1-phosphate.C. light-driven entry of Mg2+ into the stroma.D. phosphorylation by cAMP-dependent protein kinase.E. reduction of a disulfide bridge by thioredoxin.

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

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

In the light-independent ("dark") reactions of photosynthesis, the biosynthesisof 1 mole of hexose from 6 moles of carbon dioxide requires:

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

10.

11.

12.

13.

14.

15.

16.

Page 4The Cori cycle is:

A. the interconversion between glycogen and glucose-l-phosphate.B. the synthesis of alanine from pyruvate in skeletal muscle and the

synthesis of pyruvate from alanine in liver.C. the synthesis of urea in liver and degradation of urea to carbon

dioxide and ammonia by bacteria in the gut.D. the production of lactate from glucose in peripheral tissues with

the resynthesis of glucose from lactate in liver.E. none of the above.

Which of the following statements about the light reactions in photosyntheticplants is false ?

A. There are two distinct photosystems, linked together by an electrontransfer chain.

B. A membrane-bound ATPase couples ATP synthesis to electron transfer.C. The ultimate source of electrons for the process is H2O.D. The ultimate electron acceptor is O2.E. No CO2 is fixed during the light reactions.

The fixation of CO2 into organic compounds (triose phosphates) in green plants:A. takes place in the cytosol.B. results in the production of ATP.C. involves condensation of the two-carbon compound acetate with CO2

to form 3-phosphoglycerate.D. requires NADPH.E. takes place at equal rates in light and darkness.

Which of the following is true of glycogen synthase?

A. It catalyzes addition of glucose residues to the nonreducing end of a glycogen chain through (a1Æ4) bonds.

B. The conversion of an active to an inactive form of the enzyme is controlled by the concentration of cAMP.

C. Activation of the enzyme involves a phosphorylation.D. The enzyme has measurable activity only in liver.

Transketolase requires the coenzyme:

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

Glucokinase, an isozyme of hexokinase, is _____________

17.

18.

19.

20.

21.

22.

A. more active when blood glucose concentrations are high.B. has a lower Km value for glucose than the other hexokinase

isozymes.C. is found in muscle and is important for partitioning glucose

between glycolysis and gluconeogenesis.D. is inhibited by glucose 6‑phosphate.E. is sequestered in the mitochondria and released when Fru 1-P

binds to the complex, allowing its migration to the cytosol.

Page 5

Photosynthetic phosphorylation and oxidative phosphorylation appear to begenerally similar processes, both consisting of ATP synthesis coupled to thetransfer of electrons along an electron-carrier chain. Which of the followingis not true of both processes?

A. Both make use of oxygen as a terminal electron acceptor.B. Both contain cytochromes and flavins in their electron carrier chains.C. Both processes are associated with membranous elements of the cell.D. Each represents the major route of ATP synthesis in those cells in

which it is found.E. Both contain a membrane complex with a "Q-cycle" that helps create the

proton-motive force.

The process of photophosphorylation in chloroplasts use all of the following reactions except _______.

A. a membrane-bound complex containing cytochromes f and b6 and binding sites for plastoquinone and plastocyanin, which leads to establishment of a proton gradient.

B. multiple light-absorbing molecules in the appropriate distances for efficient energy transfer

C. a photosystem that creates reduced ferrodoxin with a reduction potential sufficient for subsequent reduction of NADPH or plastiquinone.

D. a photosystem that uses H2O2 as a source of electrons.E. a photosystem with a special pair of chlorophyll molecules that don't

perform energy transfer, but perform electron transfer.

André Jagendorf showed _______.A. that the pH gradient across the mitochondrial membrane is sufficient to

drive ATP synthase.B. that the pH gradient across the plasma membrane is sufficient to drive

ATP synthase.C. that the pH gradient across the lysosomal membrane is sufficient to

drive ATP synthase.D. that the pH gradient across the thylakoid membrane is insufficient to

drive ATP synthase and requires a membrane potential.E. that the pH gradient across the thylakoid membrane is sufficient to

drive ATP synthase.

Which of the following is true about xanthine oxidase?

Gout is caused by excess production of uric acid, which forms rather insoluble salts and gets depsited in the joints. Blocking the production of uric acid would involve the inhibition of ______________, one of the enzymes in purine degradation, by the well known drug called __________.

A. AMP deaminase; coformycinB. Xanthine oxidase; coformycinC. AMP deaminase; allopurinolD. Xanthine oxidase; allopurinolE. purine nucleoside phophorylase; ribitol

A. contains a molybdenum ion complex involved in redox reactions withoxygen

B. oxidizes both xanthine and adenineC. is inhibited by coformycinD. is inhibited by allantoinE. oxidizes both purines and pyrimidines

23.

24.

25.

26.

27.

Page 6II. True/False. (10 points)TYPE/WRITE EITHER "T" or "F" in the BOX to the left of each question.

III. MATCHING. (10 points)WRITE the best choice as a LETTER in the BOX(s) to the left of each number.

38. Pathways: For each pathway on the left, match it to an enzyme that operates inthat pathway. Items on the right column will be used only once or not at all.(10 pts)

A. water-splitting complex in PSIIB. phosphoenolpyruvate carboxykinaseC. ATP synthaseD. xanthine oxidaseE. glucose-6-phosphate dehydrogenaseF. 3-phosphoglycerate dehydrogenaseG. uricanaseH. glycine cleavage enzymeI. glycogen synthaseJ. rubiscoK. malate synthase

1. Nucleic acid degradation

2. Photosynthesis (light rxns)

3. Glycolate Cycle

4. ATP synthesis

5. Glyoxylate/Kornberg Cycle

6. Calvin Cycle

7. Gluconeogenesis

8. Glycogen synthesis

9. Pentose phosphate pathway

Glutathione is important in combating the ROS generated in metabolism.

The degradation of CMP contributes to the urea cycle.

Pyrimidine degradation produces a dead-end product that does not contribute to the citric acid cycle and energy production, and is rather excreted as an oxidized pyrimidine ring; uridine.

Hyperuricemia can be caused by energy depletion.

Urate oxidase is missing in humans, whereas most animals possess this enzyme. This enzyme is mis-named and is more properly called urate dioxygenase.

Plastocyanin is different from ferrodoxin in that it contains an essential copper ion.

While the 1.8 V of energy in a photon is sufficient to drive the synthesis of at least 5 ATP molecules from ADP + Pi, it is not sufficient for both driving ATP synthesis and creating the chemical species with reduction potentials for redox reactions to both create an electron acceptor capable of splitting water (ca. +1.4V) and an electron donor capable of reducing NADPH (ca. –1.4V). Hence the need to evolve two photosystems.

NADPH reductase has a TPP cofactor for transferring electrons one at a time to NADPH.

Many diabetics do not respond to insulin because of a deficiency of insulin receptors on their cells. This lack of insulin response lowers the rate of glycogen synthesis in muscle by the inability to activate PP-1, which normally converts glycogen synthase to its active form.

Many diabetics do not respond to insulin because of a deficiency of insulin receptors on their cells. This lack of insulin response lowers the rate of glycolysis in muscle by the inability to activate PP-1, which normally converts PFK-2/FBPase-2 to its active kinase form, which would have provided sufficient Fru2,6P2 to allosterically activate PFK-1.

28.

29.

30.

31.

32.

33.

34.

35.

36.

37.

Page 7

Cause of charge separation Energy created per einstein

41. Four possible immediate products are produced from glucose-6-phosphate in the liver. Each is indicated with the end product, pathway, or location listed near each box. Name the intermediate and the enzyme that catalyzes its production in the boxes. Put acheck mark in the small box if the enzyme is regulated in its activity. (10 pts)

Glucose 6-phosphate

IV. SHORT ANSWER/FILL IN. (26 points)Give a brief answer or fill in the blanks as directed to each problem or questionbelow. Put your answers WITHIN the boxes provided.

39. H218O is added to a suspension of chloroplasts capable of photosynthesis.

40.

PS-II PS-I

SP SP

Cofactor accepting electron

Receives electron from PS-II

Receives electron from PS-I

Cofactor accepting electron

Fills electron hole in PS-I

Fills electron hole in PS-II

Glycogen

Pyruvate

Blood

Rib 5-P

Where does the 18O label appear when the suspension is exposed to light? Explain. (2 pts)

During photophosphorylation, charge separation occurs at special pairs (SP) of chlorophyll molecules in the photosystems. This initiates electron flow through a series of carriers in the chloroplast. Identify the donors of electrons to fill the holes created the enter each photosystem, and the acceptor of the electrons created that leave each photosystem. Also, name the cofactor in each photosystem that immediately attains these excited electrons. Lastly, indicate what causes this charge separation and how much energy is created? (8 pts)

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

Indicate with an arrow the atom(s) that would end up on the C-l of Ribulose1,5-bisphosphate after completion of the Calvin cycle starting from 3-phosphoglycerate. (4 pts)

43. Draw the R-group of Lys-210 as it is in active Rubisco. Recall thismodified Lys becomes negatively charged and complexes with the magnesiumcofactor. It initiates the carboxylation reaction by acting as a base. (2 pts)

Page 8

Answer Key for Exam 4 04/14/21 Page 1No. onTest Correct Answer

1 C2 E3 A4 A5 B6 C7 C8 B9 D10 E11 B12 A13 D14 D15 B16 C17 D18 D19 D20 A21 B22 A23 A24 D25 E26 D27 A

28

D, G

A

H

C

K

J

B

I

E

293031323334353637

38

TTFTTTTFTT

1.

2.

3.

4.

5.

6.

7.

8.

9.

Page 2No. onTest Correct Answer

36

The label appears as 18O: oxygenH2

18O + CO2 + light -----> (CH2O) + 18O2

Plastoquinone(PQ)

H2O

Ferrodoxin(Fd)

photon absorption (Light) 1.5 V

Answer Key for Exam 4 04/14/21

39.

40.

41.

Pheophytin

Plastocyanin (PC)

A0

Glucose

6-phospho gluconolactone

Fru 6-P

Glc 1-P

phosphohexosisomerase

Phosphoglucomutase

Glc-6-Pase

Glc-6-P dehydrogenaseX

X

42.

43.

Carbamate