Final Flashcards
1
Q
Both adenylation and uridylation play uncharacteristic roles in the formation of Gln from Glu. What are those roles?
Transfer of phosphoryl groups, forming a key reactive intermediate.
Production of additional energy from inorganic pyrophosphate acting on PPi
Regulation of Glu and Gln transport across the mitochondrial membrane
Regulation of glutamine synthetase activity
Transfer of the required second nitrogen-containing group
A
Regulation of glutamine synthetase activity
2
Q
Which of the following statements is true about gout?
Gout is caused by excessive breakdown of pyrimidine nucleotides
Gout can be treated by administration of fluorouracil.
Gout is particularly prevalent in patients lacking xanthine oxidase
Gout leads to deposition of sodium urate crystals in the joints
Eating more liver is an effective way to treat the symptoms of gout.
A
Gout leads to deposition of sodium urate crystals in the joints
3
Q
CMP, UMP, and TMP all have ___________ as a common precursor.
adenosine aspartate glutamine inosine S-adenosyl methionine
A
aspartate
4
Q
The ribosyl phosphate moiety needed for the synthesis of orotidylate, inosinate, and guanylate is provided most directly by:
5-phosphoribosyl 1-pyrophosphate adenosine 5’-phosphate guanosine 5’-phosphate ribose 5-phosphate ribulose 5-phosphate
A
5-phosphoribosyl 1-pyrophosphate
5
Q
Orotic aciduria is an inherited metabolic disease in which orotic acid (orotate) accumulates in the tissues, blood and urine. The metabolic pathway in which the enzyme defect occurs is:
epinephrine synthesis purine breakdown purine synthesis pyrimidine breakdown pyrimidine synthesis
A
pyrimidine synthesis
6
Q
De novo purine biosynthesis is distinguished from de novo pyrimidine biosynthesis by:
condensation of the completed purine ring with ribose phosphate
incorporation of CO2
inhibition by azaserine (a glutamine analog)
participation of aspartate
participation of PRPP (phosphoribosyl pyrophosphate)
A
incorporation of CO2
7
Q
Which of the following is not a chemotherapeutic drug?
azaserine allopurinol fluorouracil methotrexate acivicin
A
allopurinol
8
Q
An intermediate of purine degradation in humans is:
glutamate NH4+ Succinate Urea Uric acid
A
Uric acid
9
Q
A cell that is unable to synthesize or obtain tetrahydrofolic acid (H4 folate) would probably be deficient in the biosynthesis of:
CMP GMP Orotate Thymidylate (TMP) UMP
A
Thymidylate (TMP)
10
Q
Which one of the following statements correctly describes the biosynthetic pathway for purine nucleotides?
Purine deoxynucleotides are made by the same path as ribonucleotides, followed by reduction of the ribose moiety
The first enzyme in the pathway is aspartate transcarbamoylase (ATCase)
The nitrogen in the purine base that is bonded to ribose in the nucleotide is derived originally from glycine
The pathway occurs only in plants and bacteria, not in animals
The purine rings are first synthesized, then condensed with ribose phosphate
A
Purine deoxynucleotides are made by the same path as ribonucleotides, followed by reduction of the ribose moiety
11
Q
The most direct precursors of the nitrogens of UMP are: aspartate and carbamoyl phosphate glutamate and asparate glutamate and carbamoyl phosphate glutamine and aspartate glutamine and carbamoyl phosphate
A
aspartate and carbamoyl phosphate
12
Q
Which of the following is not true about the anammox reaction?
A. Anammox converts ammonia to nitrogen.
B. Anammox is performed by symbiotic bacteria of leguminous plants.
C. Anammox generates the highly reactive molecule hydrazine that is a component of rocket fuel.
D. Anammox occurs anaerobically.
E. The ultimate electron acceptor in anammox is nitrite.
A
B. Anammox is performed by symbiotic bacteria of leguminous plants.
13
Q
Glutamine synthetase converts ____ to ___, whereas glutamate synthase converts _____ to ____.
A. formate; glutamine; ammonia; glutamate
B. asparagine; glutamine; alpha‐ketoglutarate; glutamate
C. alpha ketoglutarate; glutamine; oxaloacetic acid; glutamate
D. alpha‐ketoglutarate; glutamine; alpha‐ketoglutarate; glutamate
E. glutamate; glutamine; alpha‐ketoglutarate; glutamate
A
glutamate; glutamine; alpha‐ketoglutarate; glutamate
14
Q
An amino acid that does not derive its carbon skeleton, at least in part, from alpha‐ ketoglutarate is: A. arginine. B. glutamate. C. glutamine. D. proline. E. threonine.
A
threonine
15
Q
If a cell were unable to synthesize or obtain tetrahydrofolic acid (H4 folate), it would probably be deficient in the biosynthesis of: A. isoleucine. B. leucine. C. lysine. D. methionine. E. serine.
A
methionine
16
Q
An important intermediate in the biosynthetic pathway to aromatic amino acids is: A. benzoic acid. B. lactate. C. orotate. D. shikimate. E. alpha‐ketoglutarate
A
An important intermediate in the biosynthetic pathway to aromatic amino acids is: A. benzoic acid. B. lactate. C. orotate. D. shikimate. E. alpha‐ketoglutarate
17
Q
Bile pigments are: A. formed in the degradation of heme. B. generated by oxidation of sterols. C. responsible for light reception in the vertebrate eye. D. secreted from the pancreas E. the products of purine degradation
A
A. formed in the degradation of heme.
18
Q
Glutathione is a(n):
A. enzyme essential in the synthesis of glutamate.
B. isomer of oxidized glutamic acid.
C. methyl‐group donor in many biosynthetic pathways.
D. product of glutamate and methionine.
E. tripeptide of glycine, glutamate, and cysteine.
A
tripeptide of glycine, glutamate, and cysteine.
19
Q
Porphyrias is the disease associated with A. Heme degradation pathway B. Heme biosynthesis pathway C. Tyrosine biosynthesis D. Bromatic amino acid biosynthesis E. Bilirubin accumulation
A
B. Heme biosynthesis pathway
20
Q
Which of these is not a protease that acts in the small intestine? A. Chymotrypsin B. Elastase C. Enteropeptidase D. Secretin E. Trypsin
A
D. Secretin
21
Q
In amino acid catabolism, the first reaction for many amino acids is a(n):
A. decarboxylation requiring thiamine pyrophosphate (TPP).
B. hydroxylation requiring NADPH and O2.
C. oxidative deamination requiring NAD+.
D. reduction requiring pyridoxal phosphate (PLP).
E. transamination requiring pyridoxal phosphate (PLP).
A
transamination requiring pyridoxal phosphate (PLP).
22
Q
Which of these amino acids are both ketogenic and glucogenic? 1. Isoleucine 2. Valine 3. Histidine 4. Arginine 5. Tyrosine
A. 1 and 5 B. 1, 3, and 5 C. 2 and 4 D. 2, 3, and 4 E. 2, 4, and 5
A
A. 1 and 5
23
Q
Purine nucleotide and Histidine synthesis both use which pair of molecules early in the pathways?
A. Phosphoribosyl pyrophosphate and ATP B. Ribose 5‐phosphate and ATP C. GTP and Ribulose 5‐phosphate D. Pyridoxal phosphate and ATP E. NAD(P)H and ATP
A
A. Phosphoribosyl pyrophosphate and ATP
24
Q
5‐Phosphoribosyl‐alpha‐pyrophosphate (PRPP) is a synthe
A
arginine
25
The synthesis of purine and pyrimidine nucleo
purine biosynthesis starts with the formation of PRPP, whereas pyrimidines incorporate the PRPP near the end of the pathway.
26
Precursors for the biosynthesis of the pyrimidine ring system include:
A. carbamoyl phosphate and aspartate.
B. glutamate, NH3, and CO2.
C. glycine and succinyl‐CoA.
D. glycine, glutamine, CO2, and aspartate.
E. inosine and aspartate
A. carbamoyl phosphate and aspartate.
27
```
Orotic aciduria is an inherited metabolic disease in which orotic acid (orotate) accumulates in the tissues, blood, and urine. The metabolic pathway in which the enzyme defect occurs is:
A. epinephrine synthesis.
B. purine breakdown.
C. purine synthesis.
D. pyrimidine breakdown.
E. pyrimidine synthesis.
```
E. pyrimidine synthesis.
28
An enzyme used in both glycolysis and gluconeogenesis is:
```
A. 3‐phosphoglycerate kinase.
B. glucose 6‐phosphatase.
C. hexokinase.
D. phosphofructokinase‐1.
E. pyruvate kinase.
```
A. 3‐phosphoglycerate kinase.
29
Which one of the following statements about gluconeogenesis is false?
A. For starting materials, it can use carbon skeletons derived from certain amino acids.
B. It consists entirely of the reactions of glycolysis, operating in the reverse direction.
C. It employs the enzyme glucose 6‐phosphatase.
D. It is one of the ways that mammals maintain normal blood glucose levels between meals.
E. It requires metabolic energy (ATP or GTP).
It consists entirely of the reactions of glycolysis, operating in the reverse direction.
30
In humans, gluconeogenesis:
A. can result in the conversion of protein into blood glucose.
B. helps to reduce blood glucose a_er a carbohydrate-rich meal.
C. is activated by the hormone insulin
D. is essential in the conversion of fatty acids to glucose.
E. requires the enzyme hexokinase.
Which of the following substrates cannot contribute to net gluconeogenesis in the mammalian liver?
can result in the conversion of protein into blood glucose.
31
Which of the following substrates cannot contribute to net gluconeogenesis in mammalian liver?
```
A. Alanine
B. Glutamate
C. Palmitate
D. Pyruvate
E. a‐ketoglutarate
```
Palmitate
32
The coenzyme required for all transaminations is derived from:
```
A niacin.
B. pyridoxine (vitamin B6).
C. riboflavin.
D. thiamin.
E. vitamin B12
```
B. pyridoxine (vitamin B6).
33
Which of the following reactions involving an amino acid cannot be catalyzed via a PLP‐dependent mechanism?
```
A. Hydrolysis
B. Decarboxylation
C. Racemization
D. Transamination
E. Transimination
```
Hydrolysis
34
Glutamate is metabolically converted to a‐ketoglutarate and NH4+ by a process described as:
```
A. deamination.
B. hydrolysis.
C. oxidative deamination.
D. reductive deamination.
E. transamination
```
oxidative deamination.
35
The conversion of glutamate to an a‐ketoacid and NH4 :
A. does not require any cofactors.
B. is a reductive deamination.
C. is accompanied by ATP hydrolysis catalyzed by the same enzyme.
D. is catalyzed by glutamate dehydrogenase.
E. requires ATP.
is catalyzed by glutamate dehydrogenase.
36
Conversion of ornithine to citrulline is a step in the synthesis of:
```
A. aspartate.
B. carnitine.
C. pyruvate.
D. tyrosine.
E. urea.
```
urea
37
Which of the following amino acids are essential for humans?
```
A. Alanine
B. Aspartic acid
C. Asparagine
D. Serine
E. Threonine
```
Threonine
38
Which of these amino acids can be directly converted into a citric acid cycle intermediate by transamination?
```
A. Glutamic acid
B. Serine
C. Threonine
D. Tyrosine
E. Proline
```
A. Glutamic acid
39
Serine or cysteine may enter the citric acid cycle as acetyl‐CoA after conversion to:
```
A. oxaloacetate.
B. propionate.
C. pyruvate.
D. succinate.
E. succinyl‐CoA
```
pyruvate
40
The human genetic disease phenylketonuria (PKU) can result from:
A. deficiency of protein in the diet.
B. inability to catabolize ketone bodies.
C. inability to convert phenylalanine to tyrosine.
D. inability to synthesize phenylalanine.
E. production of enzymes containing no phenylalanine.
inability to convert phenylalanine to tyrosine.
41
Which of the following enzymes is not involved in the assimilation of inorganic nitrogen into an organic molecule?
```
A. Dinitrogenase reductase
B. Nitrate reductase
C. Nitrite reductase
D. Nitrile reductase
E. Dinitrogenase
```
Nitrile reductase
42
Which of the following enzymes is not involved in the assimilation of inorganic nitrogen into an organic molecule?
```
A. Arginase
B. Glutamate dehydrogenase
C. Glutamate synthase
D. Glutamine synthetase
E. Dinitrogenase
```
Arginase
43
Glutamine, arginine, and proline:
A. do not have a common precursor.
B. may all be derived from a citric acid cycle intermediate.
C. may all be derived from a Cori cycle intermediate.
D. may all be derived from a glycolytic intermediate.
E. may all be derived from a urea cycle intermediate.
B. may all be derived from a citric acid cycle intermediate.
44
An amino acid that does not derive its carbon skeleton, at least in part, from oxaloacetate is:
```
A. aspartate.
B. lysine.
C. methionine.
D. proline.
E. threonine.
```
proline
45
Erythrose 4‐phosphate is a precursor of:
```
A. aspartate.
B. cysteine.
C. phenylalanine.
D. serine.
E. threonine.
```
C. phenylalanine.
46
L‐Dopa is an intermediate in the conversion of:
```
A. phenylalanine to homogentisic acid.
B. phenylalanine to tyrosine.
C. tyrosine to epinephrine.
D. tyrosine to phenylalanine.
E. tyrosine to phenylpyruvate
```
C. tyrosine to epinephrine.
47
The amino acid that gives rise to the biological messenger NO is:
```
A. glutamine.
B. arginine.
C. proline.
D. lysine.
E. histidine.
```
B. arginine.
48
One amino acid directly involved in the purine biosynthetic pathway is:
```
A. alanine.
B. aspartate.
C. glutamate.
D. leucine.
E. tryptophan
```
aspartate.
49
5‐Phosphoribosyl‐a‐pyrophosphate (PRPP) is a synthetic precursor for all of the following except:
```
A. AMP.
B. arginine.
C. histidine.
D. tryptophan.
E. UMP.
```
arginine.
50
Glutamine is a nitrogen donor in the synthesis of:
```
A. CTP.
B. dTTP.
C. inosinic acid (IMP).
D. orotate.
E. UMP.
```
C. inosinic acid (IMP).
51
All enzyme-catalyzed aminotransferase reactions remove amino groups from amino acids, producing what byproduct that is important during metabolic stress?
```
A. Pyruvate
B A hydride and a H+
C. One of the ketone body molecules
D. Fumarate
E. An alpha-ketoacid
```
E. An alpha-ketoacid
52
The acidic and alkaline environments of the upper gastrointestinal tract promote what type of enzymes needed to activate pro-enzymes that are required for protein metabolism?
```
A. Aminotransferases
B Mixed-function oxidases
C. Peptidases
D. Dehydrogenases
E. Hydratases
```
C. Peptidases
53
Amino acids are not stored in appreciable concentrations. However, what amino acid would be found in significant concentration in blood of basketball players after a long and intense workout in a gym?
```
A. Histadine
B Alanine
C. Glutamine
D. Cysteine
E. Proline
```
Alanine
54
Two nitrogen-containing groups are used to make urea in liver cells. What two molecules of the Urea Cycle contribute to those two groups ?
```
A. Carbamoyl phosphate and Asp
B Ala and Glu
C. Glu and Gln
D. Carbamoyl phosphate and Glu
E. Arg and Asp
```
A. Carbamoyl phosphate and Asp
55
The Urea Cycle itself requires two different cellular compartments. What other pathway also requires two cellular compartments?
```
A. Glycolysis
B Pentose phosphate, oxidative phase
C. Beta-oxidation
D. Gluconeogenesis
E. Glyoxylate
```
D. Gluconeogenesis
56
What molecule that is produced in the cytosol by the Urea Cycle can be used by the Citric Acid Cycle, but cannot pass the inner mitochondrial membrane?
```
A. Malate
B Arginosuccinate
C. Ornithine
D. NAD+
E. Fumarate
```
Fumarate
57
Amino acid oxidation requires cofactors that can serve as a one-carbon source for amino acid and nucleotide synthesis. Which molecule below does not function as a one-carbon transfer molecule?
```
A. Pyridoxal phosphate
B Biotin
C. S-adenosylmethionine
D. Tetrahydrofolate
E. All of the above are involved in one-carbon transfers.
```
A. Pyridoxal phosphate
58
Which molecule below is produced by oxidation of most amino acids, leading to potential carbon loss by organisms that cannot fix carbon?
```
A. Methane
B Acetate
C. Glycine
D. Bicarbonate
E. Carbon dioxide
```
E. Carbon dioxide
59
What molecule is produced from oxidation of a number of amino acids, and which can be used to produce ATP efficiently via oxidative phosphorylation?
```
A. NADPH
B Acetate
C. NADH
D. Ammonia
E. FADH2
```
NADH
60
What is the metabolic use of Ketogenic amino acids?
A. All are used to produce alpha-ketoglutarate for Kreb’s Cycle.
B All are used to produce ketone bodies.
C. All are used to produce the keto-forms of carbohydrates that substitute for glycolytic intermediates.
D. All are used as one-carbon donors for the formation of alpha-ketoacids.
E. All are used in Ketogenesis, the formation of ketone-containing amino acids
B All are used to produce ketone bodies.
61
Bacteria deep in a corn field fix nitrogen early in the spring. Once the farmer begins plowing the soil, which process would contine while the others slow or stop?
```
Nitrifcation
Denitrification
Fermentation
Nitrogen fixation
All of the above would slow or stop
```
Nitrifcation
62
Nitrogen fixation by the Dinitrogenase Complex produces what gas?
```
oxygen
carbon dioxide
hydrogen
nitrogen
carbon monoxide
```
hydrogen
63
Some of the pathways for amino acid and nucleotide synthesis require which molecule as an intermediate, not a cofactor or prosthetic group?
```
pyrixoxal phosphate
phosphoribosyl pyrophosphate
cyanocobalamine
lipoate
nicotinamide
```
pyrixoxal phosphate
64
The conversion of inosinate to adenylate requires Asp, a nucleoside triphosphate, and it produces fumarate. What other pathway has this same strategy?
```
A. Cys synthesis
B. Glu synthesis from Gln
C. Pentose Phosphate, non-oxidative
D. Urea Cycle
E. Calvin Cycle, Third Stage
```
D. Urea Cycle
65
Ribonucleotide reductase was altered by site-directed mutagenesis such that Met was added in place of Cys. What effect would this have on the activity of the enzyme?
A. The active site would remove the correct hydroxyl group from ribose.
B. The active site would be non-functional.
C. The substrate specificity site would not function.
D. There would be no effect on the activity of the enzyme.
E. The enzyme would produce incorrect deoxyribonucleotides due to a lack of regulation.
B. The active site would be non-functional.
66
Which of the following compounds cannot serve as the starting material for the synthesis of glucose via gluconeogenesis?
```
acetate
glycerol
lactate
oxaloacetate
a-ketoglutarate
```
acetate
67
All of the following enzymes involved in the flow of carbon from glucose to lactate (glycolysis) are also involved in the reversal of this flow (gluconeogenesis) except:
```
3-phosphoglycerate kinase.
aldolase.
enolase.
phosphofructokinase-1.
phosphoglucoisomerase.
```
phosphofructokinase-1.
68
Gluconeogenesis must use “bypass reactions” to circumvent three reactions in the glycolytic pathway that are highly exergonic and essentially irreversible. Reactions carried out by which three of the enzymes listed must be bypassed in the gluconeogenic pathway?
```
A- Hexokinase
B-Phosphoglycerate kinase
C-Phosphofructokinase-1
D-Pyruvate kinase
E-Triosephosphate isomerase
```
```
A 1, 2, 3
B 1, 2, 4
C 1, 4, 5
D 1, 3, 4
E 2, 3, 4
```
D
69
In the digestion of protein that occurs in the small intestine, which enzyme is critical in the activation of zymogens?
```
Enteropeptidase
Hexokinase
Papain
Pepsin
Secretin
```
Enteropeptidase
70
Which of the following is a zymogen that can be converted to an endopeptidase that hydrolyzes peptide bonds adjacent to Lys and Arg residues?
```
Chymotrypsinogen
Pepsin
Pepsinogen
Trypsin
Trypsinogen
```
Trypsinogen
71
In amino acid catabolism, the first reaction for many amino acids is a(n):
decarboxylation requiring thiamine pyrophosphate (TPP).
hydroxylation requiring NADPH and O2.
oxidative deamination requiring NAD+.
reduction requiring pyridoxal phosphate (PLP).
transamination requiring pyridoxal phosphate (PLP).
transamination requiring pyridoxal phosphate (PLP).
72
Transamination from alanine to α-ketoglutarate requires the coenzyme:
biotin.
NADH.
No coenzyme is involved.
pyridoxal phosphate (PLP).
pyridoxal phosphate (PLP).
73
Pyridoxal phosphate is a cofactor in this class of reactions:
acetylation.
desulfuration.
methylation.
reduction.
transamination.
transamination
74
Which of the following is not true of the reaction catalyzed by glutamate dehydrogenase?
It is similar to transamination in that it involves the coenzyme pyridoxal phosphate (PLP).
NH4+ is produced.
The enzyme can use either NAD+ or NADP+ as a cofactor.
The enzyme is glutamate-specific, but the reaction is involved in oxidizing other amino acids.
α-Ketoglutarate is produced from an amino acid.
It is similar to transamination in that it involves the coenzyme pyridoxal phosphate (PLP).
75
Glutamate is metabolically converted to α-ketoglutarate and NH4+ by a process described as:
deamination.
hydrolysis.
oxidative deamination.
reductive deamination.
transamination.
oxidative deamination.
76
The conversion of glutamate to an α-ketoacid and NH4+:
does not require any cofactors.
is a reductive deamination.
is accompanied by ATP hydrolysis catalyzed by the same enzyme.
is catalyzed by glutamate dehydrogenase.
requires ATP.
is catalyzed by glutamate dehydrogenase.
77
Which of the following conversions require more than one step?
1. Alanine → pyruvate
2. Aspartate → oxaloacetate
3. Glutamate → α−ketoglutarate
4. Phenylalanine → hydroxyphenylpyruvate
5. Proline → glutamate
```
1 and 4
1, 2, and 4
1, 3, and 5
2, 4, and 5
4 and 5
```
4 and 5
78
Urea synthesis in mammals takes place primarily in tissues of the:
brain.
kidney.
liver.
skeletal muscle.
small intestine.
liver
79
Which substance is not involved in the production of urea from NH4+ via the urea cycle?
```
Aspartate
ATP
Carbamoyl phosphate
Malate
Ornithine
```
Malate
80
Which of these directly donates a nitrogen atom for the formation of urea during the urea cycle?
```
Adenine
Aspartate
Creatine
Glutamate
Ornithine
```
Aspartate
81
In the urea cycle, ornithine transcarbamoylase catalyzes:
cleavage of urea to ammonia.
formation of citrulline from ornithine and another reactant.
formation of ornithine from citrulline and another reactant.
formation of urea from arginine.
transamination of arginine.
formation of citrulline from ornithine and another reactant.
82
Which of the following statements is false in reference to the mammalian synthesis of urea?
Krebs was a major contributor to the elucidation of the pathway involved.
The amino acid arginine is the immediate precursor to urea.
The carbon atom of urea is derived from mitochondrial HCO3–.
The precursor to one of the nitrogens of urea is aspartate.
The process of urea production is an energy-yielding series of reaction
The process of urea production is an energy-yielding series of reaction
83
Which of the following amino acids are essential for humans?
```
alanine
aspartic acid
asparagine
serine
threonine
```
threonine
84
If a person's urine contains unusually high concentrations of urea, which one of the following diets has he or she probably been eating recently?
High carbohydrate, very low protein
Very high carbohydrate, no protein, no fat
Very very high fat, high carbohydrate, no protein
Very high fat, very low protein
Very low carbohydrate, very high protein
Very low carbohydrate, very high protein
85
Which of these amino acids can be directly converted into a citric acid cycle intermediate by transamination?
```
glutamic acid
serine
threonine
tyrosine
proline
```
glutamic acid
86
Which of these amino acids are both ketogenic and glucogenic?
1. Isoleucine
2. Valine
3. Histidine
4. Arginine
5. Tyrosine
```
1 and 5
1, 3, and 5
2 and 4
2, 3, and 4
2, 4, and 5
```
1 and 5
87
Tetrahydrofolate (THF) and its derivatives shuttle between different substrates.
```
electrons
H+
acyl groups
one carbon units
NH2 groups
```
one carbon units
88
The amino acids serine, alanine, and cysteine can be catabolized to yield:
fumarate.
pyruvate.
succinate.
α-ketoglutarate.
none of the above
pyruvate.
89
Serine or cysteine may enter the citric acid cycle as acetyl-CoA after conversion to:
oxaloacetate.
propionate.
pyruvate.
succinate.
succinyl-CoA.
pyruvate
90
The human genetic disease phenylketonuria (PKU) can result from:
deficiency of protein in the diet.
inability to catabolize ketone bodies.
inability to convert phenylalanine to tyrosine.
inability to synthesize phenylalanine.
production of enzymes containing no phenylalanine.
inability to convert phenylalanine to tyrosine.
91
In the human genetic disease maple syrup urine disease, the metabolic defect involves:
a deficiency of the vitamin niacin.
oxidative decarboxylation.
synthesis of branched chain amino acids.
transamination of an amino acid.
uptake of branched chain amino acids into liver.
oxidative decarboxylation.
92
ccumulates in the tissues, blood, and urine. The metabolic pathway in which the enzyme defect occurs is:
```
epinephrine synthesis.
purine breakdown.
purine synthesis.
pyrimidine breakdown.
pyrimidine synthesis.
```
pyrimidine synthesis.
93
Precursors for the biosynthesis of the pyrimidine ring system include:
```
carbamoyl phosphate and aspartate.
glutamate, NH3, and CO2.
glycine and succinyl-CoA.
glycine, glutamine, CO2, and aspartate.
inosine and aspartate.
```
carbamoyl phosphate and aspartate.
94
CMP, UMP, and TMP all have ________________ as a common precursor.
```
adenosine
aspartate
glutamine
inosine
S-adenosyl methionine
```
aspartate
95
Which of the following is not true of the reaction catalyzed by ribonucleotide reductase?
Glutathione is part of the path of electron transfer.
It acts on nucleoside diphosphates.
Its mechanism involves formation of a free radical.
There is a separate enzyme for each nucleotide (ADP, CDP, GDP, UDP).
Thioredoxin acts as an essential electron carrier.
There is a separate enzyme for each nucleotide (ADP, CDP, GDP, UDP).
96
Which one of the following statements correctly describes the biosynthetic pathway for purine nucleotides?
Purine deoxynucleotides are made by the same path as ribonucleotides, followed by reduction of the ribose moiety.
The first enzyme in the path is aspartate transcarbamoylase (ATCase).
The nitrogen in the purine base that is bonded to ribose in the nucleotide is derived originally from glycine.
The pathway occurs only in plants and bacteria, not in animals.
The purine rings are first synthesized, then condensed with ribose phosphate.
Purine deoxynucleotides are made by the same path as ribonucleotides, followed by reduction of the ribose moiety.
97
Which of the following statements about the fixation of atmospheric nitrogen (N2) into NH3 by living cells is false?
It involves the transfer of 8 electrons per mol of N2.
It occurs in certain microorganisms, but not in humans.
It requires a source of electrons, normally ferredoxin.
It requires one ATP per mol of N2 fixed.
It requires two key protein components, each containing iron.
It requires one ATP per mol of N2 fixed.
98
Which of the following enzymes is not involved in the assimilation of inorganic nitrogen into an organic molecule?
```
Arginase
Glutamate dehydrogenase
Glutamate synthase
Glutamine synthetase
Nitrogenase
```
Arginase
99
The enzymatic machinery to fix atmospheric N2 into NH4+ is:
a means of producing ATP when excess N2 is available.
composed of two key proteins, each containing iron.
relatively stable when exposed to O2.
specific to plant cells.
unaffected by the supply of electrons.
composed of two key proteins, each containing iron.
100
Erythrose 4-phosphate is a precursor of:
aspartate.
cysteine.
phenylalanine.
serine.
threonine.
phenylalanine.
101
Nonessential amino acids:
are amino acids other than those required for protein synthesis.
are not utilized in mammalian proteins.
are synthesized by plants and bacteria, but not by humans.
can be synthesized in humans as well as in bacteria.
may be substituted with other amino acids in proteins.
can be synthesized in humans as well as in bacteria.
102
An amino acid that does not derive its carbon skeleton, at least in part, from α-ketoglutarate is:
arginine.
glutamate.
glutamine.
proline.
threonine.
threonine
103
Glutamine, arginine, and proline:
do not have a common precursor.
may all be derived from a citric acid cycle intermediate.
may all be derived from a Cori cycle intermediate.
may all be derived from a glycolytic intermediate.
may all be derived from a urea cycle intermediate.
may all be derived from a citric acid cycle intermediate.
104
In which group are all the amino acids closely interrelated metabolically?
Arginine, hydroxyproline, and histidine
Arginine, tyrosine, and glutamate
Glycine, valine, glutamine, and aspartate
Ornithine, alanine, glycine, and valine
Ornithine, alanine, glycine, and valine
105
An amino acid that does not derive its carbon skeleton, at least in part, from oxaloacetate is:
aspartate.
lysine.
methionine.
proline.
threonine.
threonine.
106
Homoserine is:
```
a precursor of both methionine and threonine.
a precursor of serine.
derived from homocysteine.
derived from serine.
derived from threonine.
```
a precursor of both methionine and threonine.
107
The nitrogen atom in the side chain of lysine is derived from which amino acid?
```
aspartic acid.
glutamic acid.
glutamine.
asparagine.
arginine
```
glutamic acid.
108
δ-Aminolevulinic acid is formed from succinyl-CoA and __________ and is an intermediate in the biosynthesis of _________.
```
acetyl-CoA; long chain fatty acids
glycine; heme
serine; heme
serine; sphingosine
α-ketoglutarate; glutamate and proline
```
glycine; heme
109
The hormones epinephrine and norepinephrine are derived biosynthetically from:
arginine.
histidine.
isoleucine.
tryptophan.
tyrosine.
tryptophan
110
In skeletal muscle, phosphocreatine functions as:
a reservoir of Pi for mitochondria.
reservoir of high-energy of phosphate to replenish ATP.
reservoir of amino acids for protein synthesis.
an electron acceptor under anaerobic conditions.
none of the above.
reservoir of high-energy of phosphate to replenish ATP.
111
One distinction between peptide and steroid hormones is that peptide hormones:
act through nonspecific receptors, whereas steroid hormones act through specific receptors.
are generally water-insoluble, whereas steroid hormones are water soluble.
are more stable than steroid hormones.
bind to cell surface receptors, whereas steroid hormones bind to nuclear receptors.
bind to their receptors with high affinity, whereas steroid hormones bind with low affinity.
bind to cell surface receptors, whereas steroid hormones bind to nuclear receptors.
112
Insulin is an example of a(n) ____________ hormone.
```
catecholamine
eicosanoid
paracrine
peptide
steroid
```
peptide
113
Epinephrine is an example of a(n) ____________ hormone.
```
catecholamine
eicosanoid
paracrine
peptide
steroid
```
catecholamine
114
An example of an eicosanoid hormone is:
```
epinephrine.
retinoic acid.
testosterone.
thromboxane.
thyroxine.
```
thromboxane
115
An example of a steroid hormone is:
```
epinephrine.
retinoic acid.
testosterone.
thromboxane.
thyroxine.
```
testosterone.
116
Some hormones are derived from amino acids; for example, catecholamines are derived from while NO is derived from.
```
tyrosine; arginine
tryptophan; lysine
tyrosine; histidine
tryptophan; arginine
histidine; lysine
```
tyrosine; arginine
117
The tropic hormones (such as thyrotropin, somatotropin, and luteinizing hormone) are produced and released by the:
```
anterior pituitary.
hypothalamus.
ovaries.
pancreas.
posterior pituitary.
```
anterior pituitary.
118
The normal sequence of action of these components of the hormonal hierarchy is:
adrenal cortex → hypothalamus → anterior pituitary
anterior pituitary → adrenal cortex → hypothalamus
anterior pituitary → hypothalamus → adrenal cortex
hypothalamus → adrenal cortex → anterior pituitary
hypothalamus → anterior pituitary → adrenal cortex
hypothalamus → anterior pituitary → adrenal cortex
119
In its role in the hormonal hierarchy, the hypothalamus produces and releases:
epinephrine.
insulin.
progesterone.
releasing factors.
thyroxine.
releasing factors.
120
When blood glucose is abnormally high, the pancreas releases:
epinephrine.
glucagon.
glucose.
insulin.
trypsin.
insulin
121
When blood glucose is abnormally low, the pancreas releases:
epinephrine.
glucagon.
glucose.
insulin.
trypsin
glucagon.
122
An elevated insulin level in the blood:
inhibits glucose uptake by the liver.
inhibits glycogen synthesis in the liver and muscle.
results from a below-normal blood glucose level.
stimulates glycogen breakdown in liver.
stimulates synthesis of fatty acids and triacylglycerols in the liver.
stimulates synthesis of fatty acids and triacylglycerols in the liver.
123
An elevated insulin level in the blood:
inhibits glucose uptake by the liver.
inhibits glycogen synthesis in the liver and muscle.
results from a below-normal blood glucose level.
stimulates glycogen breakdown in liver.
stimulates synthesis of fatty acids and triacylglycerols in the liver.
stimulates synthesis of fatty acids and triacylglycerols in the liver.
124
The radioimmunossay (RIA) is based on competition of unlabeled and radiolabeled:
antibodies for binding to a hormone.
antibodies for binding to a receptor.
hormone for binding to a receptor.
hormone for binding to an antibody.
receptor for binding to a hormone.
hormone for binding to an antibody.
125
One distinction between peptide and steroid hormones is that peptide hormones:
act through nonspecific receptors, whereas steroid hormones act through specific receptors.
are generally water-insoluble, whereas steroid hormones are water soluble.
are more stable than steroid hormones.
bind to cell surface receptors, whereas steroid hormones bind to nuclear receptors.
bind to their receptors with high affinity, whereas steroid hormones bind with low affinity.
are more stable than steroid hormones.
| bind to cell surface receptors, whereas steroid hormones bind to nuclear receptors.
126
Insulin is an example of a(n) ____________ hormone.
```
catecholamine
eicosanoid
paracrine
peptide
steroid
```
peptide
127
The maturation of insulin from its precursor (preproinsulin) involves:
acetylation.
oxidation.
phosphorylation.
proteolysis.
reduction.
proteolysis.
128
Epinephrine is an example of a(n) ____________ hormone.
```
catecholamine
eicosanoid
paracrine
peptide
steroid
```
catecholamine
129
An example of an eicosanoid hormone is:
```
epinephrine.
retinoic acid.
testosterone.
thromboxane.
thyroxine.
```
thromboxane.
130
An example of a steroid hormone is:
```
epinephrine.
retinoic acid.
testosterone.
thromboxane.
thyroxine.
```
testosterone.
131
Some hormones are derived from amino acids; for example, catecholamines are derived from while NO is derived from .
```
tyrosine; arginine
tryptophan; lysine
tyrosine; histidine
tryptophan; arginine
histidine; lysine
```
tryptophan; arginine
132
The tropic hormones (such as thyrotropin, somatotropin, and luteinizing hormone) are produced and released by the:
```
anterior pituitary.
hypothalamus.
ovaries.
pancreas.
posterior pituitary.
```
anterior pituitary.
133
The normal sequence of action of these components of the hormonal hierarchy is:
adrenal cortex → hypothalamus → anterior pituitary
anterior pituitary → adrenal cortex → hypothalamus
anterior pituitary
→ hypothalamus → adrenal cortex
hypothalamus → adrenal cortex → anterior pituitary
hypothalamus → anterior pituitary → adrenal cortex
hypothalamus → anterior pituitary → adrenal cortex
134
In its role in the hormonal hierarchy, the hypothalamus produces and releases:
epinephrine.
insulin.
progesterone.
releasing factors.
thyroxine.
releasing factors.
135
Which of the following statements about metabolism in the mammalian liver is false?
Most plasma lipoproteins are synthesized in the liver.
The enzymatic complement of liver tissue changes in response to changes in the diet.
The liver synthesizes most of the urea produced in the body.
The presence of glucose 6-phosphatase makes liver uniquely able to release glucose into the bloodstream.
Under certain conditions, most of the functions of the liver can be performed by other organs.
Under certain conditions, most of the functions of the liver can be performed by other organs.
136
Glucokinase:
acts in the conversion of liver glycogen to glucose 1-phosphate.
converts fructose-6-phosphate to glucose-6-phosphate
converts glucose 6-phosphate to fructose 6-phosphate.
is a hexokinase isozyme found in liver hepatocytes.
is found in all mammalian tissues
is a hexokinase isozyme found in liver hepatocytes
137
In skeletal muscle:
amino acids are an essential fuel.
at rest, fatty acids are the preferred fuel.
large quantities of triacylglycerol are stored as fuel.
phosphocreatine can substitute for ATP as the direct source of energy for muscle contraction.
stored muscle glycogen can be converted to glucose and released to replenish blood glucose.
at rest, fatty acids are the preferred fuel.
138
In skeletal muscle, phosphocreatine functions as:
a reservoir of Pi for mitochondria.
reservoir of high-energy of phosphate to replenish ATP.
reservoir of amino acids for protein synthesis.
an electron acceptor under anaerobic conditions.
none of the above.
reservoir of high-energy of phosphate to replenish ATP.
139
The Cori cycle is:
the conversion of lactate to pyruvate in skeletal muscle to drive glycogen synthesis.
the interconversion between glycogen and glucose l-phosphate.
the production of lactate from glucose in peripheral tissues with the resynthesis of glucose from lactate in liver.
the synthesis of alanine from pyruvate in skeletal muscle and the synthesis of pyruvate from alanine in liver.
the synthesis of urea in liver and degradation of urea to carbon dioxide and ammonia by bacteria in the gut.
he production of lactate from glucose in peripheral tissues with the resynthesis of glucose from lactate in liver.
140
Which one of the following statements is true?
The brain prefers glucose as an energy source, but can use ketone bodies.
Muscle cannot use fatty acids as an energy source.
In a well-fed human, about equal amounts of energy are stored as glycogen and as triacylglycerol.
Fatty acids cannot be used as an energy source in humans because humans lack the enzymes of the glyoxylate cycle.
Amino acids are a preferable energy source over fatty acids.
The brain prefers glucose as an energy source, but can use ketone bodies.
141
When blood glucose is abnormally high, the pancreas releases:
epinephrine.
glucagon.
glucose.
insulin.
trypsin.
insulin
142
The largest energy store in a well-nourished human is:
ATP in all tissues.
blood glucose.
liver glycogen.
muscle glycogen.
triacylglycerols in adipose tissue.
triacylglycerols in adipose tissue.
143
levated epinephrine levels do not normally stimulate:
```
fatty acid mobilization in adipose tissue.
gluconeogenesis in liver.
glycogen breakdown in muscle.
glycogen synthesis in liver.
glycolysis in muscle.
```
glycogen synthesis in liver.
144
Epinephrine triggers an increased rate of glycolysis in muscle by:
activation of hexokinase.
activation of phosphofructokinase-1.
conversion of glycogen
phosphorylase a to glycogen
phosphorylase b.
inhibition of the Cori Cycle
the Pasteur effect.
activation of phosphofructokinase-1.
145
Long-term maintenance of body weight is regulated by the hormone:
adiposin.
hypothalmin.
leptin.
obesin.
testosterone
leptin
146
Among its numerous metabolic effects, the protein leptin:
decreases the production of glucocorticoids.
inactivates the enzyme 5’-AMP-activated protein kinase (AMPK).
increases the production of sex hormones.
makes muscle and liver cells more sensitive to insulin.
raises the production of thyroid hormone.
makes muscle and liver cells more sensitive to insulin.
147
The hormone leptin appetite; insulin appetite.
increases; increases
increases; decreases
decreases; increases
decreases; decreases
no effect; no effect
decreases; decreases
148
The peptide hormone adiponectin, produced in adipose tissue, circulates in the blood and:
enhances fatty acid synthesis in liver cells.
increases the rate of β-oxidation of fatty acids in muscle cells.
inhibits glucose uptake and catabolism in muscle and liver cells.
reduces the transport of fatty acids into muscle cells.
stimulates gluconeogenesis in liver cells.
increases the rate of β-oxidation of fatty acids in muscle cells.
