Deck 17: Amino Acid Metabolism

Question 1

Microorganisms capable of fixing nitrogen into a form usable by animals obtain the energy for this process from .

A) lightning
B) oxidation and reduction respiration)
C) photosynthesis of host plants
D) soil nutrients

Answer 1

photosynthesis of host plants

Question 2

Which of the following is/are true concerning transanimation reactions?

A) They can convert a-keto acids to a-amino acids.
B) All require the coenzyme pyridoxal phosphate.
C) The catalyzed reactions are near-equilibrium.
D) All of the above

Answer 2

All of the above

Question 3

Which is not part of the synthesis reactions for histidine?

A) phosphoribosyl pyrophosphate PRPP)
B) glutamine
C) imidazole glycerol phosphate
D) indole glycerol phosphate
E) None of the above

Answer 3

indole glycerol phosphate

Question 4

Ammonia is incorporated into amino acids via which of the following?

A) glutamate
B) glutamine
C) carbamoyl phosphate
D) All of the above

Question 5

An amino acid formed by transamination of a citric acid cycle intermediate is .

A) aspartate
B) cysteine
C) serine
D) alanine

Question 6

A key precursor in the synthesis of aromatic amino acids tryptophan, tyrosine and phenylalanine) is .

A) prephenate
B) chorismate
C) 4-hydroxyphenylpyruvate
D) indole

Question 7

At neutral pH, the main ionic form of ammonia is .

A) N₂
B) NH₄⁺
C) NH₃
D) NH₂^-
E) None of the above

Question 8

Which of the following is an amide-containing amino acid?

A) alanine
B) arginine
C) aspartate
D) asparagine

Question 9

What would be the product of the transamination of the structure shown below? The unionized forms are shown.)

A) I
B) II
C) III
D) IV

Question 10

Nitrogen fixation may occur via all of the following bacteria, except

A) Azobacter.
B) Klebsiella.
C) cyanobacteria.
D) E. coli.

Question 11

Aspartate is the precursor for which of the following amino acids?

A) lysine
B) threonine
C) methionine
D) All of the above

Question 12

Which of the following is/are true statements) about glutamine?

A) It is a nitrogen donor in many biosynthetic reactions.
B) It is a nitrogen source for glutamate synthase.
C) It carries nitrogen and carbon between tissues, thus avoiding high toxic levels of NH₄⁺ in blood.
D) All of the above

Question 13

Glutamate dehydrogenase has different roles in different organisms. Which of these listed is mismatched?

A) E. coli bacterium) - generates NH₄⁺ + glutamate
B) N. crassa fungus) - aminates a-ketoglutarate
C) mammals - degradation of amino acids and release of NH₄⁺
D) mammals - formation of glutamate

Question 14

Which of the following amino acids is/are derived from 3-phosphoglycerate?

A) serine
B) glycine
C) cysteine
D) All of the above

Question 15

Because they lack aspartate kinase and aspartate semialdehyde dehydrogenase, cannot synthesize lysine, methionine or threonine.

A) bacteria
B) fungi
C) tobacco plants
D) mammals

Question 16

Nitrogenases

A) are protected from oxygen to prevent inactivation.
B) consist of two protein components.
C) contain an electron transport system.
D) A and B only
E) All of the above

Question 17

Physiological roles for glutamate dehydrogenase include all of the following, except

A) the generation of glutamate when NH₄⁺ is present at high concentrations in E. coli.
B) the conversion of glutamate to glutamine in most organisms.
C) the use of an NADPH-dependent enzyme for reductive amination in Neurospora crassa.
D) the degradation of amino acids and generation of NH₄⁺ in mammals.

Question 18

Transamination reactions require which coenzyme?

A) PLP
B) TPP
C) ATP
D) FMN

Question 19

a-ketoglutarate is a precursor for each of the following, except

A) glutamine.
B) arginine.
C) proline.
D) glycine.

Question 20

Industrially, nitrogen for use in fertilizers is converted to ammonia by .

A) a simple, energy efficient reaction of N₂ with water
B) a cryogenic very low temperature) process between N₂ and H₂
C) special catalysts which drive the reduction of N₂ by H₂
D) a reaction between nitric acid and hydrogen gas

Question 21

Phenylalanine hydroxylase requires molecular and tetrahydrobiopterin.

A) hydrogen
B) nitrogen
C) water
D) oxygen

Question 22

Nitric oxide is formed from arginine. It is a messenger molecule with several functions that include all below except

A) macrophage activation.
B) reacting with superoxide anions to form more toxic substances.
C) constricting red blood cells.
D) neurotransmitter in the brain.

Question 23

Which amino acids are purely ketogenic?

A) arginine and lysine
B) valine and isoleucine
C) tryptophan only
D) lysine and leucine
E) all essential amino acids

Question 24

The proteases responsible for cell death are called . They cleave on the carboxyl side of residues.

A) caspases; aspartate
B) typsins; lysine and arginine
C) carnitines; cysteine
D) ureases; uridine

Question 25

The degradation of arginine, histidine and proline all lead to the product .

A) pyruvate
B) acetyl CoA
C) acetoacetate
D) glutamate

Question 26

If an amino acid is glucogenic, it will not be degraded to .

A) pyruvate
B) glutamate
C) fumarate
D) acetoacetate

Question 27

The changes that occur in cells that lead to its death are called .

A) cellular necroptosis
B) programmed lysis
C) apoptosis
D) morpholytic degradation

Question 28

Defects in which of the following may result in elevated levels of phenylalanine?

A) deficiencies in dihydropteridine reductase
B) deficiencies in 4a-carbinolamine dehydratase
C) defects in the biosynthesis of tetrahydrobiopterin
D) All of the above

Question 29

Which disease is caused by a defect in ornithine transaminase activity?

A) alcaptonuria
B) gyrate atrophy
C) cystinuria
D) maple syrup urine disease
E) nonketotic hyperglycinemia

Question 30

In amino acid catabolism the α-amino groups are initially released as .

A) nitrous oxide
B) ammonium ion
C) nitrate ion
D) glutamine

Question 31

Which statement is false about protein turnover?

A) The turnover rate is directly proportional to the stability of the proteinʹs tertiary structure.
B) Rapid turnover ensures that some regulatory proteins are degraded so that the cell can respond to changing conditions.
C) The half-life of a given protein is similar in different organs and species.
D) Turnover rates vary to give half-lives from a few minutes to several weeks.

Question 32

What type of reaction is shown below? ^{Amino acid} + ^α-^{Ketoglutarate}⇋ ^α-^{Keto acid} + ^Glutamate

A) reductive amination
B) oxidation
C) transamination
D) hydrolysis

Question 33

Which type of organisms can eliminate excess nitrogen by the direct excretion of ammonia?

A) mammals
B) birds
C) fish
D) reptiles

Question 34

Glycine is a precursor for all of the following except

A) cytidine.
B) creatine phosphate.
C) porphobilinogen.
D) bile salts.
E) glyoxylate.

Question 35

Nitric oxide is produced from which reaction?

A) arginine to citrulline
B) glutamate to α-ketoglutarate
C) bicarbonate to carbamoyl phosphate
D) tryptophan to acetyl CoA

Question 36

Phenylketonuria PKU) is a disease caused by a defect in formation.

A) phenylalanine
B) a-ketoglutarate
C) tyrosine
D) urea

Question 37

The structure shown below is .

A) urea
B) uridine
C) uric acid
D) carbodiamine

Question 38

The degradation of which amino acid requires the coenzyme tetrahydrofolate?

A) histidine
B) serine
C) leucine
D) alanine

Question 39

Which type of protein might have a very short half-life and be specifically targeted for degradation?

A) transport protein
B) mutated abnormal protein)
C) ribosomal protein
D) hormone protein

Question 40

Which is not produced from the degradation of branched-chain amino acids?

A) succinyl CoA
B) acetyl CoA
C) malonyl CoA
D) propionyl CoA

Question 41

In animals glutamate synthase is essential for the production of glutamate.

Question 42

A patient is experiencing uncontrolled diabetes mellitus with an overproduction of β-hydroxybutyric acid. Which statement is false?

A) The patient will exhale extra amounts of carbon dioxide.
B) Glutamine will be catabolized to reform lost bicarbonate ion.
C) The basic amino acids, lysine and arginine, neutralize the β-hydroxybutyric acid in the blood.
D) The anion of β-hydroxybutyric acid will be excreted in the urine.

Question 43

The enzyme is one of the most abundant in liver mitochondria and catalyzes the synthesis of the molecule shown below.

A) arginase
B) carbamoyl phosphate synthetase I
C) 4a-carbinolamine dehydratase
D) transaminase

Question 44

Which statements) apply to urea?

A) highly soluble in water
B) produced in the liver
C) major solute in urine of mammals
D) compound used as a means of removing excess nitrogen
E) All of the above

Question 45

In the urea cycle which molecule is transported from the mitochondrial matrix to the cytosol as ornithine is transported in the opposite direction?

A) arginine
B) citrulline
C) glutamate
D) carnitine

Question 46

In mammals, ureogenesis occurs almost exclusively in the .

A) liver
B) kidney
C) pancreas
D) lining of the small intestine

Question 47

The essential amino acids are those that mammals cannot synthesize, but must obtain from the diet.

Question 48

Oxaloacetate is the amino-group acceptor in the synthesis of aspartate.

Question 49

How many ATP are consumed in the conversion of bicarbonate to carbamoyl phosphate?

A) one
B) two
C) three
D) none

Question 50

At the subcellular level where does the urea cycle occur?

A) mitochondrial matrix only
B) mitochondrial matrix and the mitochondrial inner membrane
C) mitochondrial matrix and the cytosol
D) cytosol only

Question 51

The glucose-alanine cycle provides .

A) an alternate site for production of urea in the kidney
B) transport of important enzymes for gluconeogenesis
C) an indirect means for muscle to eliminate nitrogen and replenish its energy supply
D) a cycle for the direct synthesis of carbohydrates in muscle

Question 52

The carbon in urea originates from .

A) aspartate
B) ornithine
C) bicarbonate
D) ATP

Question 53

In the urea cycle the nitrogen atoms originate from .

A) α-ketoglutarate
B) ornithine
C) lysine
D) aspartate

Question 54

Most green plants contain both nitrate reductase and nitrite reductase to reduce nitrogen oxides to ammonia.

Question 55

In mammals, most amino acids undergo deamination in the .

A) liver
B) kidney
C) pancreas
D) mitochondria of all cell types

Question 56

is hydrolytically cleaved to directly yield urea in the urea cycle.

A) Ornithine
B) Glutamate
C) Arginine
D) Carbamoyl phosphate

Question 57

A large percentage of nitrogen, undergoing metabolism, comes from nitrogen fixation.

Question 58

Nitrogenase catalyzes the reduction of N₂ to nitrate.

Question 59

Virtually all of the nitrogen used in metabolism comes directly from nitrogen fixation.

Question 60

Carbamoyl phosphate synthetase

A) is an essential precursor in pyrimidine biosynthesis.
B) catalyzes the synthesis of carbamoyl phosphate from bicarbonate and glutamine.
C) is one of the most abundant enzymes in liver mitochondria.
D) A and B only
E) All of the above

Question 61

Protein turnover of regulatory proteins helps cells to quickly respond to changing conditions.

Question 62

Periportal cells of the liver are nearest to the inflow of blood and have a higher capacity for urea synthesis than the perivenous cells that are near the outflow.

Question 63

Nitric oxide is a very reactive compound. In vivo it reacts with oxygen and water to form nitrates and nitrites within seconds.

Question 64

Chorismate is a key branch-point intermediate in aromatic amino acid synthesis.

Question 65

During the catabolism of amino acids, the carbon skeleton is first degraded, followed by the removal of the amino group.

Question 66

Tryptophan synthaseʹs a subunit catalyzes the cleavage of indole glycerol phosphate to glyceralde 3-phosphate and indole.

Question 67

The amino acids tyrosine and tryptophan are both ketogenic and glucogenic.

Question 68

The disease alcaptonuria is caused by a defect in the kidney transport of cysteine.

Question 69

Only growing and reproducing cells require a continuous supply of amino acids for the synthesis of new protein molecules.

Question 70

Most animals and plants can tolerate moderately high cellular concentrations of ammonia; however, unusable excess is generally eliminated via the urea cycle.

Question 71

Amino acids that are degraded to pyruvate or citric acid cycle intermediates are called ketogenic.

Question 72

All 20 common amino acids are metabolized through the citric acid cycle by first being converted to either pyruvate or acetyl CoA.

Question 73

Nitric oxide functions as a neurotransmitter in the brain.