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BICH 411 Final Exam new material

Terms in this set (137)

What is nitrogen fixation?
a. The reduction of NO3− to NH4+.
b. The formation of NH4+ from N2 gas.
c. The oxidation of NH4+ to N2.
d. The oxidation of NH4+ to NO3−.
e. The formation of NO2− from NO3−.
B
Animals are totally dependent on plants and microorganisms for nitrogen fixation and nitrate assimilation because animals:
a. do not have the reducing power (NADPH) to fix nitrogen.
b. lack the enzyme aminotransferase.
c. lack the enzymes to reduce N2 and NO3− to NH4+.
d. lack carbamoyl-phosphate synthetase I.
e. lack glutamate dehydrogenase.
C
Nitrifying bacteria obtain their chemical energy from:
a. the reduction of NO3− to NH4+.
b. the formation of NH4+ from N2 gas.
c. the oxidation of NH4+ to N2.
d. the oxidation of NH4+ to NO3−.
e. the formation of NO2− from NO3−.
D
Denitrifying bacteria are capable of all EXCEPT:
a. reducing NO3− to N2.
b. using NO3− as an electron acceptor in their energy-producing pathways.
c. oxidizing NH4+to NO3−.
d. reducing the combined-nitrogen levels.
e. being utilized in water treatment plants to reduce nitrogen entering lakes and streams.
C
Nitrate assimilation occurs in two steps: reduction of nitrate to ____ and further reduction to ____.
a. ammonia; nitrogen
b. nitrogen; ammonia
c. nitrite; nitrogen
d. nitrite; ammonia
e. none are correct
D
The correct sequence for electron-transport in nitrate reductase is:

A. NADH
B. −SH
C. FAD
D. Cyt b557
E. MoCo
F. NO3−

a. A, B, C, D, E, F
b. B, C, A, D, F, E
c. D, A, B, C, E, F
d. A, C, B, D, F, E
e. C, A, B, D, E, F
A
Nitrite reductase requires ____ electrons to reduce NO2− to NH4+ and the electrons are provided in higher plants through photosynthesis as reduced ____.
a. 2; plastoquinone
b. 3; plastoquinone
c. 4; heme
d. 5; heme
e. 6; ferredoxin
E
Nitrogen fixation involves the enzyme ____ catalyzing the reaction:
N2 + 10 ____ + ____ e− → 2 NH4+ + H2
a. nitrate reductase; H2O; 6
b. nitrogenase; H+; 8
c. nitrogenase; H+; 2
d. nitrogen reductase; H2O; 6
e. none are true
B
All N2-fixing systems are nearly identical and have all of the requirements EXCEPT:
a. ATP.
b. O2-free conditions.
c. the enzyme nitrogenase.
d. strong reductant such as ferredoxin.
e. all are true.
E
The involvement of ATP in the nitrogenase complex is because ATP is needed to:
a. provide electrons.
b. phosphorylate the enzyme.
c. break the N2 triple bond.
d. transfer electrons from ferredoxin.
e. all are true.
C
Control over nitrogenase activity is accomplished by which of the following?
a. ATP serves as an allosteric activator
b. AMP serves as an allosteric inhibitor
c. NH4+ prevents expression of the genes that encode nitrogenase
d. phosphorylation prevents activity
e. none of the above
C
N-acetylglutamate functions in ammonium incorporation into metabolic intermediates as:
a. a coenzyme for glutamine synthetase (GS).
b. a competitive inhibitor for glutamine synthetase (GS).
c. an allosteric activator for carbamoyl-phosphate synthetase I (CPS-I).
d. the energy source needed for the reductive amination of α-ketoglutarate (α-KG) to yield glutamate.
e. the substrate for the amination of the γ-glutamylphosphate.
C
What reaction does glutamate dehydrogenase (GDH) catalyze?
a. The reductive amination of α-ketoglutarate to yield glutamate.
b. Phosphorylation of carbamate to yield carbamoyl-phosphate.
c. The amidation of the γ-carboxyl group of glutamate to form glutamine.
d. The deadenylation of glutamine synthetase.
e. The adenylation of glutamine synthetase.
A
The reaction, glutamate + NAD(P)+ + H2O → NH4+ + α-ketoglutarate + NAD(P)H + H+, is catalyzed by:
a. Nitrogenase.
b. carbamoyl-phosphate synthetase (CPS-I).
c. glutamate dehydrogenase (GDH).
d. glutamine synthetase (GS).
e. none are true.
C
Glutamine synthetase is activated by which of the following molecules?
a. glycine
b. AMP
c. CTP
d. carbamoyl phosphate
e. none of the above
E
The reaction, 2 NH4+ + α-ketoglutarate + NADPH + ATP → glutamine + NADP+ + ADP + Pi + H2O, is the combined result of what two enzymes?
a. first, glutamate synthase, then glutamate dehydrogenase
b. first, glutamate dehydrogenase ,then glutamine synthetase
c. first, glutamine synthetase, then glutamate synthase
d. first, glutamine synthetase, then glutamate dehydrogenase
e. none of the above
B
Glutamate synthase catalyzes the reaction ____ + ____ + ____ → 2 glutamate + NADP+
a. α-ketoglutarate; NADPH; glutamine
b. glutamate; α-ketoglutarate; NADH
c. glutamyl-phosphate; glutamine; NADPH
d. N-acetylglutamate; α-ketoglutarate; NADH
e. none are true
A
Bacterial glutamine synthetase monomers are inactive because they must be:
a. phosphorylated for activity.
b. activated by binding glutamine.
c. stacked for interface active site development.
d. combined for allosteric regulation.
e. none are true.
C
All of the following act in feedback inhibition of glutamine synthetase in prokaryotes EXCEPT:
a. AMP.
b. glucosamine-6-phosphate.
c. histidine.
d. proline.
e. CTP.
D
All of the following are characteristic features of ATP:GS:adenylyl transferase (AT) EXCEPT:
a. It catalyzes the adenylation of glutamine synthetase.
b. It exists in two forms, PIIA and PIID. PIIA causes the deadenylation of glutamine synthetase and its activity increases with an increase in glutamine.
c. AT:PIIA is inhibited by α-ketoglutarate.
d. AT:PIIA needs ATP to complete the reaction.
e. It is an enzyme that causes the adenylation/deadenylation of a specific tyrosine residue.
B
What would be a result of a high [Gln]/[α-KG] ratio?
a. Increase in deadenylation of glutamine synthetase.
b. An increase in activity of glutamine synthetase.
c. An increase in the degree of adenylation of glutamine synthetase.
d. Inhibition of AT:PIIA and stimulation of AT:PIID.
e. A need for ammonium fixation by glutamine synthetase.
C
In plants and microorganisms, amino acid biosynthesis is a matter of synthesizing the appropriate ____ followed by transamination with ____.
a. acetyl-CoA derivatives; glutamine
b. α-ketoacid; glutamate
c. phospho-carbon skeleton; alanine
d. nitrogenous base; glutamate
e. none are true
B
In the process of amino acid biosynthesis, how are glutamic acid, glutamine, proline, and arginine all related?
a. They are all derived from α-KG.
b. They are all derivatives of acetyl CoA.
c. They are all derivatives of pyruvate.
d. They are all derived from aspartate.
e. They are all derivatives of 3-phosphoglycerate.
A
All of the following are true of transamination EXCEPT:
a. It is characterized by the transfer of an α-amino group from an amino acid to the α-keto position of an α-keto acid.
b. The amino donor becomes an α-keto acid.
c. The coenzyme needed is thiamin pyrophosphate (TPP).
d. Humans are capable of synthesizing the α-keto acid analog of nonessential amino acids and using transamination to form the amino acids, but are not able to construct carbon skeletons of the essential amino acids.
e. The α-keto acid acceptor becomes an α-amino acid.
C
Which of the following is both an essential amino acid (for humans) and also an exclusively ketogenic amino acid?
a. proline
b. valine
c. glutamine
d. leucine
e. phenylalanine
D
Which of the following is NOT a commonly used transamination pair?
a. Phe / phenylpyruvate
b. Asp / oxaloacetate
c. Glu / α-ketoglutarate
d. Ala / pyruvate
e. all are correct
A
____ is an intermediate in biosynthesis of ornithine and a regulator of carbamoyl-phosphate synthetase-I
a. γ-Glutamyl-phosphate
b. α-Ketoglutarate
c. N-Acetylglutamate
d. Glutamine
e. Glutamine-5-phosphate
C
All of the carbons and nitrogens of ornithine come biosynthetically from:
a. proline.
b. valine.
c. alanine.
d. glutamate.
e. glycine.
D
Ornithine serves three metabolically important roles, but is not found in proteins. What is one of the important roles of ornithine?
a. amine donor for many transamination reactions
b. an intermediate in the urea cycle
c. involved in the synthesis of serine, which serves as a precursor for glycine and cysteine
d. its reaction with methenyl tetrahydrofolate produces lysine
e. none of the above
B
All of the following are true of the urea cycle EXCEPT:
a. It helps in the excretion of excess nitrogen.
b. It is mainly confined to the liver.
c. It is linked to the citric acid cycle through fumarate.
d. Stimulation of carbamoyl-phosphate synthetase I (CPS-I) decreases the activity of the urea cycle.
e. It is completed by the regeneration of ornithine from arginine.
D
Which of the following directly serves as one of the nitrogen atoms of a urea molecule?
a. the amide N of Asn
b. the N of Asp
c. the R-group N of Lys
d. the N of glucosamine
e. none of the above
B
Aspartate is formed from transamination of:
a. asparagine.
b. aspartame.
c. oxaloacetate.
d. citrate.
e. α-ketoglutarate.
C
Homoserine and homocysteine are related to serine and cysteine by having:
a. an extra amino group.
b. an additional methylene group.
c. an additional carboxyl group.
d. an aldehyde group.
e. a phosphoryl group.
B
Amino acids biosynthesized from aspartate include all EXCEPT:
a. asparagine.
b. threonine.
c. methionine.
d. lysine.
e. glutamate.
E
Elevated levels of homocysteine in the blood is related to all EXCEPT:
a. homocysteinuria at very high levels.
b. folic acid deficiency.
c. folic acid-dependent conversion of homocysteine to methionine.
d. higher risk of heart attack and stroke.
e. all of the above are correct.
E
Transamination of pyruvate with glutamate as amino donor gives:
a. alanine.
b. serine.
c. cysteine.
d. aspartate.
e. valine.
A
All of the following are true statements regarding the 3-Phosphoglycerate (3-PG) family EXCEPT:
a. 3-PG is diverted from glycolysis by phosphoglycerate mutase.
b. Glycine can be derived from serine.
c. Serine, glycine and cysteine are all nonessential amino acids.
d. Production of glycine also produces N5, N10-methylene-THF which is important in the biosynthesis of purines.
e. Serine production is regulated by a direct feedback mechanism.
A
Chorismate biosynthesis occurs via the shikimate pathway and is an important precursor in the synthesis of all of the following EXCEPT:
a. vitamin K.
b. folic acid.
c. threonine.
d. tyrosine.
e. tryptophan.
C
Herbicides (e.g., "Roundup") that inhibit biosynthesis of "essential" amino acids are supposedly safe for animal exposure because animals do not have enzymes for:
a. synthesis of the members of the 3-phosphoglycerate family
b. the glyoxylate cycle.
c. the glutamine synthesis pathway.
d. Phe, Val, Leu, and Ile biosynthetic pathways.
e. none are correct.
D
All are convergent metabolic intermediates of α-amino acid carbon skeletons EXCEPT:
a. Citrate.
b. α-ketoglutarate.
c. Oxaloacetate.
d. succinyl-CoA.
e. Fumarate.
A
The term ketogenic amino acids refers to amino acids:
a. that are precursors for glucose synthesis.
b. degraded to yield acetyl CoA or acetoacetate.
c. that can not be converted to fatty acids or ketone bodies.
d. degraded to yield succinyl-CoA, pyruvate, α-ketoglutarate, fumarate and oxaloacetate.
e. none of the above.
B
The carbon skeletons of all of the amino acids below converge to pyruvate EXCEPT:
a. alanine.
b. serine.
c. cysteine.
d. glycine.
e. glutamate.
E
Degradation of valine, isoleucine and methionine leads to succinyl-CoA via the sequence of:

A. carboxylation using biotin and ATP
B. mutase
C. methylmalonyl-CoA
D. epimerase
E. Propionyl-CoA

a. E, B, A, C, D, C
b. E, A, C, D, C, B
c. A, C, D, C, E, B
d. C, A, D, B, C, E
e. D, A, C, B, C, E
B
All are characteristics of Maple Syrup Urine Disease EXCEPT:
a. hereditary enzyme defect.
b. elevated levels of val, leu, and ile and their corresponding α-keto acids in blood and urine.
c. restrictive intake of proteins with val, leu and ile is required.
d. fatal without detection and treatment.
e. elevated blood levels of acetoacetate and β-hydroxybutyrate.
E
All of the following are characteristics of phenylketonuria EXCEPT:
a. excretion of phenylpyruvate.
b. air oxidation causes urine to turn dark on standing.
c. treated by putting patient on a diet low in phenylalanine.
d. untreated patients suffer severe mental retardation.
e. deficiency or defect in phenylalanine hydroxylase.
B
All of the following are characteristics of alkaptonuria EXCEPT:
a. excretion of homogentisate
b. air oxidation causes urine to turn dark on standing
c. results in mental retardation due to accumulation of Phe metabolites
d. homogentisate accumulation in joints may cause arthritis
e. all are true
C
Glutamine synthetase plays an important role in the incorporation of ammonia (or ammonium ions) into glutamine. Which of the following mechanisms of covalent modification controls the activity of glutamine synthetase?
a. Phosphorylation/dephosphorylation
b. Adenylation/deadenylation
c. Acetylation/deacetylation
d. Methylation/demethylation
e. None of the above
B
Microorganisms that fix nitrogen have a symbiotic relationship with certain plants. What molecule is produced by plants to prevent oxygen poisoning of the nitrogenase enzyme?
a. α-ketoglutarate
b. leghemoglobin
c. glutamic acid
d. glucose
e. none of the above
B
Which of the following sequence of events best explains the mechanism of carbamoyl phosphate synthetase?
a. CO2 and ATP form a carbonic-phosphoric anhydride (CPA), then NH3 performs a nucleophilic attack on the CPA to form carbamate
b. Activated CO2 is transferred to biotin, then reacts with NH3 to produce carbamate
c. NH3 reacts with ATP, which then reacts with CO2 to produce carbamate
d. NH3 reacts with CO2 to produce carbamate followed by reaction with ATP
e. None of the above
A
Which of the following amino acids plays the most central role in nitrogen and amino acid metabolism?
a. Asn
b. Glu
c. Gly
d. Cys
e. none of the above
B
Glutamine synthetase is an important enzyme in the regulation of ammonia concentrations. Which of the following would be an activator of Gln synthetase?
a. α-ketoglutarate
b. glutamine
c. histidine
d. alanine
e. none of the above
A
All of the following statements about nucleotides are true EXCEPT:
a. They are produced by nearly all organisms.
b. The rate of proliferation of a cell can determine the amount of DNA and RNA synthesized per unit of time.
c. Uridine nucleotide derivatives of carbohydrates are common intermediates in cellular transformation of carbohydrates.
d. Many coenzymes are derivatives of nucleotides.
e. The nitrogenous bases serve as energy sources.
E
Many ____ and ____ are inhibitors of purine and pyrimidine biosynthesis.
a. eicosanoids; aspirin
b. NSAIDs; antibiotics
c. antibiotics; eicosanoids
d. anticancer drugs; antibiotics
e. anticancer drugs; eicosanoids
D
What is the limiting substance in the biosynthesis of purines?
a. ribose-5-phosphate
b. 5-phosphoribosyl-β amine
c. formylglycinamidine ribonucleotide
d. 5-phosphoribosyl-α-pyrophosphate (PRPP)
e. α-D-ribose-5-phosphate
D
Glutamine phosphoribosyl pyrophosphate amidotransferase catalyzes step 2 in the biosynthesis of purines. Which of the following is a true statement regarding the regulation of this enzyme?
a. It is accelerated by an input of ATP or GTP.
b. It is sensitive to activation by azaserine.
c. It is accelerated by an input of AMP or GMP.
d. The G series of nucleotides as well as the adenine nucleotides act as competitive inhibitors.
e. It is subject to feed-forward activation by ADP.
D
In purine biosynthesis when glycine adds to 5-phosphoribosyl-β-amine, the bond formed is a(n):
a. ester.
b. imine.
c. amine.
d. amide.
e. lactam.
D
The coenzyme for two single carbon additions in purine biosynthesis is:
a. THF.
b. biotin.
c. SAM.
d. TPP.
e. none are true.
A
Adenylosuccinase (adenylosuccinate lyase) catalyzes the reaction to remove ____ after ____ has formed an amide with a carbonyl group in purine biosynthesis.
a. succinate; glutamate
b. succinate; aspartate
c. fumarate; alanine
d. fumarate; aspartate
e. α-ketoglutarate; glutamate
D
All of the following are true concerning the regulation of the purine biosynthetic pathway EXCEPT:
a. ATP is the energy source for AMP synthesis.
b. ADP and GDP are feedback inhibitors of ribose-5-phosphate pyrophosphokinase.
c. "A" and "C" nucleotides allosterically inhibit glutamine phosphoribosyl pyrophosphate amidotransferase (Gln:PRPP amidotransferase).
d. The rate of IMP formation is dependent on the levels of the adenine and guanine nucleotides produced.
e. PRPP competitively inhibits the enzyme Gln:PRPP amidotransferase.
E
The fate of IMP is regulated by relative levels of ____ and ____; and energy to drive AMP synthesis is provided by ____, and energy for GMP synthesis by ____.
a. IMP; PRPP; ATP; GTP
b. PRPP; ATP; ATP; GTP
c. AMP; ATP; GTP; ATP
d. AMP; GMP; GTP; ATP
e. IMP; GMP; ATP; GTP
D
The reaction, base + PRPP → nucleoside-5-phosphate + PPi is catalyzed by the enzyme:
a. nucleotide diphosphate kinase.
b. phosphoribosyltransferase.
c. ribose-5-phosphate pyrophosphokinase.
d. adenylate kinase.
e. GMP synthetase.
B
Which of the following statements explains why methotrexate is effective as a cancer chemotherapeutic?
a. it serves as an analog of p-aminobenzoic acid and block bacterial synthesis of folate
b. acts as an inhibitor of dihydrofolate reductase, thus preventing production of tetrahydrofolate
c. it acts as a suicide substrates for the enzyme dihydropteroate synthetase
d. prevents the conversion of N5,N10-methenyl THF to N10-formyl THF which is required in 2 steps of the purine synthesis pathway
e. both b and d are correct
B
What is the function of phosphoribosyltransferases?
a. they are involved in the reversible reactions of purine salvage.
b. they mediate the degradation of AMP.
c. they are central to the re-synthesis of nucleotides from bases in salvage reactions.
d. they mediate the degradation of IMP.
e. they are competitive inhibitors employed in the salvage of purine nucleotides.
C
All are characteristics of Lesch-Nyham Syndrome EXCEPT:
a. gouty arthritis due to excessive uric acid accumulation
b. severe malfunctions of the nervous system
c. complete deficiency in HGPRT activity
d. congenital, recessive, sex-linked trait manifested only in males
e. all are true
E
About 30% of severe combined immunodeficiency syndrome (SCIDS) patients suffer from a deficiency in the activity of the enzyme ____ that is a ____-dependent enzyme and ____ deficiency can also lead to reduced immune function.
a. HGPRT; Ca2+; Ca2+
b. nucleosidase; Ca2+; Ca2+
c. nucleoside phosphorylase; Pi; Pi
d. adenosine deaminase; Zn2+; Zn2+
e. none are true
D
What is the common product of purine catabolism?
a. xanthine
b. uric acid
c. inosine
d. hypoxanthine
e. xanthosine
B
What is the importance of the purine nucleoside cycle?
a. It participates in the conversion of purines into pyrimidines.
b. It generates fumarate, which inhibits the formation of AMP from IMP.
c. It provides fumarate as an anaplerotic enhancement of the citric acid cycle.
d. It inhibits the citric acid cycle in skeletal muscles.
e. It is used in energy metabolism in the liver.
C
All are characteristics of xanthine oxidase EXCEPT:
a. present in large amounts in liver, intestinal mucosa and milk.
b. uses molecular oxygen and produces H2O2.
c. involved in production of urea.
d. possesses an electron-transport chain with FAD, Fe−S cluster and molybdenum cofactor.
e. all are true.
C
Allopurinol is an analog of ____ that tightly binds to ____ and prevents ____ formation.
a. hypoxanthine; xanthine oxidase; uric acid
b. guanine; guanine deaminase; xanthine
c. inosine; xanthine oxidase; xanthine
d. hypoxanthine; guanine deaminase; xanthine
e. none of the above
A
Which of the following statements explains why allopurinol is able to prevent gout?
a. it binds to uric acid thus preventing the formation of uric acid crystals
b. it acts as a diuretic to increase the elimination of uric acid
c. it inhibits the production of uric acid and allows for the more highly soluble xanthine and hypoxanthine to be excreted from the body
d. it stimulates the purine salvage pathway, thus eliminating the need for production of uric acid
e. none of the above
C
All are substrates of carbamoyl phosphate synthetase II (CPS-II) EXCEPT:
a. H2O.
b. NH4+.
c. HCO3−.
d. glutamine.
e. 2ATP.
B
In mammals CPS-II is the regulated step on pyrimidine biosynthesis; however, in bacteria ____ is the regulated step.
a. dihydroorotase
b. aspartate transcarbamoylase (ATCase)
c. OMP decarboxylase
d. dehydroorotate dehydrogenase
e. none are true
B
Which of the following serves as an activator of CPS-II in mammals?
a. thyrotropin
b. epidermal growth factor
c. cortisol
d. gonadotropin
e. none of the above
B
What type of reaction gives UMP from OMP?
a. reduction
b. decarboxylation
c. oxidation
d. condensation
e. hydrolysis
B
Which of the following is an advantage of metabolic channeling?
a. It allows the product of one reaction to be available for a reaction later in another pathway.
b. It allows the diffusion of substrates.
c. It allows the dilution of substrates.
d. It allows a more diverse interaction of substrates, intermediates, and enzymes.
e. It does not allow for substrate dilution into the milieu and for the accumulation of intermediates.
E
Which of the following is a true statement regarding pyrimidine biosynthesis in animals?
a. PRPP and ATP are allosteric inhibitors.
b. CTP is a feedback inhibitor.
c. It is allosterically regulated at aspartate transcarbomoylase.
d. UDP and UTP are feedback inhibitors of CPS-II.
e. ACTase catalyzes the committed step in pyrimidine synthesis.
D
Enzymatic ribonucleotide reduction is accomplished via a free radical mechanism. Which of the following statements is true regarding this process?
a. The substrate specificity site on the R1 homodimer determines if the enzyme is active or inactive.
b. R2 has a single active site containing two Fe atoms that generate the free radicals required for reduction.
c. R2, but not R1, function in the delivery of reducing equivalents.
d. R2 homodimer carries two regulatory sites.
e. A final decarboxylation forms the deoxyribonucleotide product.
B
The immediate reducing power of ribonucleotide reductase is provided by:
a. thioredoxin.
b. Ferredoxin.
c. NADH.
d. Fe−S complex.
e. Cyt P-450.
A
Which of the following statements regarding the activity of ribonucleotide reductase is correct?
a. the overall activity of the enzyme is inhibited by high levels of ATP
b. binding of ATP to the specificity site increases the use of GDP as a substrate
c. binding of dGTP to the specificity site increases the use of CDP as a substrate
d. binding of dTTP to the specificity site inhibits the use of UDP as a substrate
e. none of the above
D
Thymine nucleotides are not synthesized directly by cells but indirectly from other pyrimidine deoxyribonucleotides. All of the following statements regarding thymine nucleotide synthesis are true EXCEPT:
a. dUMP is the immediate precursor for dTMP.
b. The action of dUTPase allows dUTP to serve as a substrate in DNA synthesis.
c. Thymidylate synthase catalyzes the formation of dTMP from dUMP.
d. The methyl donor in the reaction of dTMP is N5, N10-methylene-THF.
e. THF is used as a cofactor.
B
Unlike hydrogen, which is often abstracted from substrates as H+, electronegative ____ cannot be readily eliminated as ____, thus enzyme inhibitors can be fashioned in which ____ replaces H at positions where catalysis involves H-removal as H+.
a. sodium; Na+; Na
b. potassium; K+; K
c. deuterium; D+; D
d. fluorine; F+; F
e. all are true
D
Thymidylate synthase synthesizes dTMP from ____ by ____ utilizing the coenzyme ____.
a. dCTP; carboxylation; biotin
b. dUMP; methylation; THF
c. dCMP; methylation; THF
d. dGMP; phosphorylation; ATP
e. dUMP; phosphorylation; ATP
B
Which of the following is the mechanism of action of 5-fluorouracil?
a. competitive inhibitor of dihydrofolate reductase
b. suicide substrate for thymidylate synthase
c. competitive inhibitor of ribonucleotide reductase
d. non-competitive inhibitor of thioredoxin reductase
e. none of the above
B
Which of the following is a source of 2 carbon atoms of the purine ring system?
a. aspartate
b. carbon dioxide
c. glycine
d. glutamine
e. glutamic acid
C
Which of the following serves as one of the nitrogen sources for the pyrimidine ring?
a. glutamate
b. carbamoyl phosphate
c. asparagine
d. glycine
e. none of the above
B
Which of the following would cause an increase in the conversion of IMP to GMP?
a. high levels of CMP
b. high levels of dTTP
c. high levels of UMP
d. high levels of AMP
e. none of the above
D
Which form of the folate coenzyme is directly involved in sythesis of the purine ring?
a. N5,N10-methenyl THF
b. N10-formyl THF
c. N5-formyl THF
d. tetrahydrofolate
e. dihydrofolate
B
Which of the following metabolic pathways is strictly anabolic?
a. glycolysis
b. gluconeogenesis
c. citric acid cycle
d. pentose phosphate cycle
e. β-oxidation of fatty acids
B
All are major components of anabolic pathways EXCEPT:
a. NADH.
b. glycolysis and citric acid cycle intermediates.
c. ATP, GTP, CTP, UTP.
d. NADPH.
e. all are true.
A
____ is the principal energy source for protein synthesis, ____ for phospholipid synthesis, and ____ for polysaccharide synthesis.
a. UTP; GTP; CTP
b. GTP; CTP; UTP
c. CTP; UTP; GTP
d. UTP; CTP; GTP
e. CTP; GTP; UTP
B
____ and ____ are unique in that they are the only compounds whose purpose is to couple the energy-yielding processes of ____ to the energy-consuming reactions of ____.
a. NADH; ATP; catabolism; anabolism
b. ATP; [FADH2]; catabolism; anabolism
c. [FADH2]; NADH; anabolism; catabolism
d. ATP; NADPH; catabolism; anabolism
e. ATP; NADPH; anabolism; catabolism
D
In photoautotrophs, ____ are fed into catabolism to generate the metabolic intermediates needed to supply ____.
a. lipids; photorespiration
b. proteins; photorespiration
c. carbohydrates; anabolism
d. carbohydrates; NADPH
e. proteins; NADPH
C
The overall thermodynamic efficiency of metabolism is determined through reaction-coupling with:
a. NADH oxidation.
b. CO2 release.
c. reduction of O2.
d. ATP hydrolysis and synthesis.
e. glucose oxidation.
D
Which of the following statements is true for ATP stoichiometry in metabolic pathways?
a. It is a consequence of evolution, only.
b. A singular number is not required, only.
c. It results from biological adaptation, only.
d. It cannot be predicted from any chemical considerations, only.
e. All are true
E
The two metabolic roles served by ATP are:
a. promoting increased reaction speed and dephosphorylation.
b. changing both Km and Vmax.
c. allosteric regulation and stoichiometric involvement.
d. preventing futile cycles and changing Km.
e. none of the above.
C
The reaction, ATP + AMP → 2ADP, is catalyzed by:
a. adenylate phosphorylase.
b. AMP-phosphotransferase.
c. ADP mutase.
d. adenylate kinase.
e. none are true.
D
All are true for the energy charge (EC) of a cell EXCEPT:
a. It is an index of adenylate phosphoric anhydrides.
b. EC has a range of 0 to 1.0.
c. It is a ratio of adenylate phosphoric anhydride bonds to total adenylate concentration.
d. It is 1.0 when all of the adenylate is ATP.
e. It is rapidly changed by adenylate kinase.
E
Regulatory enzymes, such as ____, in energy-producing pathways show greater activity at ____ energy charge.
a. fructose-1,6-bisphosphatase; low
b. acetyl-CoA carboxylase; low
c. pyruvate kinase; high
d. PFK-1; low
e. none of the above
D
An energy charge (EC) of 0.9 is roughly 80% ATP, 17% ADP and 3% AMP. At this EC, ____ enzyme activities are low and ____ enzyme activities higher.
a. ATP generating; ATP utilizing
b. ATP generating; NADH producing
c. ATP utilizing; ATP generating
d. ATP utilizing; NADH producing
e. NADH producing; ATP generating
A
The energy charge of healthy living cells is in the neighborhood of ____.
a. 0.55-0.60
b. 0.60-0.65
c. 0.65-0.75
d. 0.75-0.85
e. 0.85-0.88
E
Which of the following enzymes is activated upon phosphorylation by AMP activated protein kinase?
a. acetyl CoA carboxylase
b. phosphofructokinase-2
c. glycogen synthase
d. 3-hydroxy-3-methylglutaryl-CoA reductase
e. none of the above
B
A constant availability of fuels in the blood is called ____ and the order of preference for fuel usage is ____.
a. phosphorylation potential; glycogen> triacylglycerols> protein
b. fuel dynamics; triacylglycerols> glycogen> protein
c. metabolic regulation; triacylglycerols> glycogen> protein
d. caloric homeostasis; glycogen> triacylglycerols> protein
e. none are true
D
All of the following are paired with their preferred substrate EXCEPT:
a. brain: glucose
b. heart: fatty acids
c. resting skeletal muscle: glucose
d. anaerobic skeletal muscle: glucose
e. adipose tissue: fatty acids
C
All are characteristics of brain tissue EXCEPT:
a. 2% or so of body mass.
b. 20% of oxygen consumed by brain.
c. oxygen consumption is independent of mental activity.
d. has no significant fuel reserves.
e. all are true.
E
The brain prefers to use ____ as fuel, but under prolonged fasting or starvation it adapts to use ____.
a. fatty acids; glucose
b. glucose; β-hydroxybutyrate
c. glycogen; fatty acids
d. glucose; fatty acids
e. β-hydroxybutyrate; amino acids
B
During fasting or starvation, the brain:
a. converts endogenous fatty acids into β-hydroxybutyrate.
b. utilizes β-hydroxybutyrate from the blood stream.
c. utilizes amino acids for fuel from degradation of brain protein.
d. utilizes its glycogen stores as a first responding source of fuel.
e. all of the above.
B
Muscle contractions occur when a motor nerve impulse causes ____ release from specialized compartments, that bind to ____, a regulatory protein initiating events that result in sliding of ____ thick filaments along ____ thin filaments.
a. Fe++; myoglobin; actin; myosin
b. Na+; troponin C; IGG; actin
c. Ca++; troponin C; myosin; actin
d. Ca++; calmodulin; PKC; PLC
e. K+; Na+/K+ ATPase; subunit-α; subunit-β
C
All of the following are fuels for contracting muscles during strictly anaerobic metabolism EXCEPT:
a. ATP.
b. creatine phosphate.
c. glycogen.
d. glucose.
e. palmitic acid.
E
During strictly anaerobic exercise, muscle cells preferentially:
a. carboxylate pyruvate to oxaloacetate.
b. oxidize pyruvate to acetyl-CoA.
c. decarboxylate pyruvate to acetaldehyde.
d. reduce pyruvate to lactate.
e. none of the above.
D
Under strenuous aerobic exercise, which of the following would be true for skeletal muscle?
a. only glucose will serve as a fuel source
b. only fatty acids will serve as a fuel source
c. both glucose and fatty acids will be used as fuel with the use of glucose increasing with the intensity of the exercise
d. both glucose and fatty acids will be used as fuel with the use of fatty acids increasing with the intensity of the exercise
e. none of the above
C
Heart muscle differs from skeletal muscle in the following ways EXCEPT:
a. heart is completely aerobic.
b. heart prefers fatty acids as fuel.
c. heart has more phosphocreatine than skeletal muscle.
d. heart has limited quantities of glycogen.
e. all are true.
C
Energy metabolism in the heart is characterized by all of the following EXCEPT:
a. the preferred fuel is fatty acids.
b. it has minimal energy reserves.
c. it is unusually rich in mitochondria.
d. the heart consumes over 90% of the total oxygen supply during maximal physical exertion.
e. the range of activity is much less than that in muscle (200 fold).
D
Glucose is pivotal to adipocyte metabolism in all areas EXCEPT:
a. forms DHAP for reduction and esterification of fatty acids.
b. provides glucose-6-phosphate for generating NADPH from the pentose phosphate pathway.
c. synthesizes ketone bodies.
d. converts glucose to fatty acids for storage and export.
e. all are true.
C
Adipocytes lack the enzyme ____ and thus require DHAP for triacylglycerol synthesis.
a. DHAP reductase
b. glycerol kinase
c. acyldihydroxyacetonephosphate transferase
d. DHAP acyltransferase
e. carnitine acyl transferase
B
Fatty acids are released from adipocytes when:
a. insulin levels are high.
b. glycerol-3-phosphate levels are high.
c. adipose ATP levels are high.
d. blood glucose levels are low.
e. none are true.
D
All are characteristics associated with "brown fat" EXCEPT:
a. high levels of mitochondria rich in cytochromes.
b. presence of uncoupler protein-1, thermogenin, in the mitochondrial inner membrane.
c. energy from oxidation is converted to heat.
d. found in newborns and hibernating animals.
e. all are characteristics.
E
All are uses of glucose-6-phosphate in liver EXCEPT:
a. catabolized to acetyl-CoA for fatty acid biosynthesis.
b. generate NADPH and pentoses.
c. released as glucose to blood stream.
d. converted to glycogen.
e. all are true.
E
In addition to carbohydrate and lipid energy metabolism, the liver serves other purposes EXCEPT:
a. producing insulin to regulate metabolism.
b. converting amino acids into metabolic fuel.
c. ketone body production.
d. detoxification of poisons and drugs.
e. Gluconeogenesis.
A
All are characteristics of leptin EXCEPT:
a. it binds to hypothalamus, inhibits release of neuropeptide-Y and is thus an anorexic agent.
b. it is a signal molecule that limits food intake and increases energy expenditure.
c. it communicates the status of triacylglycerol levels in the adipocytes to the central nervous system.
d. if leptin levels are low, appetite is suppressed; and if leptin levels are high, appetite is increased.
e. it induces synthesis of β-oxidation enzymes and increases expression of uncoupler protein-2 (UCP-2) to increase thermogenesis.
D
Which of the following hormones that governs eating behavior is INCORRECTLY defined?
a. insulin: stimulation of adipocyte leptin production
b. leptin: appetite suppression when levels are high
c. ghrelin: released from stomach in response to food to further stimulate appetite
d. cholecystokinin: released from the intestines during eating to signal satiety
e. all are correct
C
Ethanol metabolism in liver is characterized by all of the following EXCEPT:
a. decreased pH levels due to lactic acidosis.
b. two oxidation steps to convert ethanol to acetate, both reactions produce NADH.
c. decreased gluconeogenesis activity resulting in hypoglycemia.
d. decreased NADH/NAD+ ratio in the cell.
e. increased acetaldehyde-protein adducts impairing protein function.
D
Which of the following comments regarding resveratrol is INCORRECT?
a. produced in plants, particularly in grape skins, in response to stress
b. activates SIRT1 NAD+-dependent deacetylase activity
c. inhibits AMPK in the brain
d. has many of the same effects as caloric restriction
e. all of the above are correct
C
Of the following, which tissue is correctly described?
a. brain: use of glucose and fatty acids as fuel
b. pancreas: production of insulin and glucagon
c. adipose tissue: storage of carbohydrates and triacylglycerols
d. liver: overall control of metabolism through hormone production
e. none of the above are correct
B
During the fasting phase, which of the following events occurs?
a. release of hormones such as gastrin and cholecystokinin
b. release of insulin by the pancreatic β-cells
c. activation of lipolysis
d. production of glycogen
e. none of the above
C
During the feeding phase, which of the following pathways would be inhibited in the liver?
a. glycogen synthesis
b. fatty acid synthesis
c. pentose phosphate pathway
d. gluconeogenesis
e. none of the above
D
During prolonged fasting (more than 48 hours), which of the following would show a dramatically increased concentration in the blood?
a. glucose
b. fatty acids
c. ketone bodies
d. lipoproteins
e. none of the above
C
Energy balance in the cell (ATP/ADP/AMP levels) is an important factor in the metabolic pathways we have studied. How does this regulation take place?
a. ATP, ADP and/or AMP bind to DNA to modulate transcription of genes for enzymes involved in metabolism
b. ATP, ADP and/or AMP bind to enzymes involved in metabolism, allosterically changing the enzyme activity
c. High levels of ATP result in nonenzymatic phosphorylation of the enzymes involved in metabolism, changing their activity
d. High levels of ATP result in excessive production of cyclic AMP, causing activation of pathways such as glycogenolysis and gluconeogenesis
e. None of the above
B
Under conditions where glucose levels are high and acetyl CoA is needed for fatty acid synthesis, which of the following pathways would NOT be active in adipose tissue?
a. Pentose phosphate pathway
b. Glycogen synthesis
c. Glycolysis
d. Glycerol synthesis from DHAP
e. All of the above would be active
B
Leptin is an important hormone that indicates a generally satisfactory amount of metabolites available in the body. Which of the following is true regarding leptin?
a. Leptin is produced in adipose tissue in response to the presence of large amounts of triacylglycerols
b. One of the results of leptin production is the increase in thermogenesis in adipose tissue brought about through an increase in the expression of thermogenin
c. The primary site of leptin's action is upon the hypothalamus where it ultimately results in the release of norepinephrine
d. All of the above are correct
e. A and C are correct
D
5- flurorouracil does what
thymidylate synthase and DNA synthesis
Dihydrofolate reductase
blocks DNA synthesis first
first step of nitrification
ammonia is converted to hydroxyalamine
Anammox
dinitrogen from nitrite and ammonia???
denitrification
the process by which a nitrate becomes molecular nitrogen
methyl cycle requires what
vitamin B12
lysine synthesized from
2-ketogluturate
there is no salvage pathways for:
dNTPs
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