Deck 15: Nitrogen Metabolism II: Degradation

Question 1

In addition to urea, humans also excrete waste nitrogen as

A)Uric acid
B)Ammonia
C)Nitrous oxide
D)Guanidine
E)Elemental nitrogen

Answer 1

A

Question 2

Stress proteins

A) Are only produced when cells are exposed to high temperatures
B) Act solely as molecular chaperones
C) Are referred to as heat shock proteins
D) Both A and C are correct
E) None of the above is correct

Answer 2

C

Question 3

The ammonia that is incorporated into urea molecules is produced in reactions catalyzed by all of the following enzymes except

A) Urease activity possessed by intestinal bacteria
B) Serine dehydratase
C) Glutamate dehydrogenase
D) Serine hydroxymethyltransferase
E) L-Amino acid transferase

Answer 3

D

Question 4

N-Acetylglutamate is

A) Produced from glutamate and acetyl-CoA
B) Stimulates the activity of carbamoyl synthetase I
C) Inhibits the activity of carbamoyl synthetase I
D) Both A and B are true
E) Both A and C are true

Question 5

Amino acids whose degradation yields acetyl-CoA include all of the following except
________.

A) Threonine
B) Glycine
C) Glutamate
D) Alanine
E) Cysteine

Question 6

Homogentisate is an intermediate in the degradation of __________.

A) Threonine
B) Lysine
C) Arginine
D) Tryptophan
E) Tyrosine

Question 7

α-Ketoadipate is an intermediate in the degradation of ________.

A) Lysine
B) Valine
C) Proline
D) Leucine
E) Tyrosine

Question 8

In addition to phenylalanine-4-monooxygenase the conversion of phenylalanine to tyrosine requires ________.

A) Oxygen
B) BH₄
C) NADPH
D) Both A and C are correct
E) All of the above are correct

Question 9

Amino acids whose degradation yields -ketoglutarate include all of the following except _________.

A) Arginine
B) Glutamine
C) Leucine
D) Histidine
E) None of the above is correct

Question 10

Glutamate--semialdehyde is an intermediate in the degradation of _________.

A) Proline
B) Glutamate
C) Leucine
D) Histidine
E) Methionine

Question 11

Amino acids whose degradation yields succinyl-CoA includes all of the following except ________.

A) Methionine
B) Isoleucine
C) Valine
D) Histidine
E) None of the above is correct

Question 12

Alkaptonuria is caused by a deficiency of

A) Phenylalanine hydroxylase
B) Catechol-o-methyltransferase
C) Aldehyde dehydrogenase
D) Monoamine oxidase
E) Homogentisate oxidase

Question 13

Albinism is caused by the absence of

A) Phenylalanine hydroxylase
B) Tyrosinase
C) Branched chain-ketodehydrogenase
D) Cyanocobalamin
E) Monoamine oxidase

Question 14

The major route for protein degradation is

A) Cytoplasmic proteolytic enzymes
B) Lysosomes
C) UPS
D) Both A and B are correct
E) All of the above are correct

Question 15

Which of the following reactions require SAM?

A) Synthesis of dopamine
B) Synthesis of norepinephrine
C) Conversion of tryptophan to serotonin
D) Conversion of norepinephrine to epinephrine
E) None of the above is correct

Question 16

The production of antibodies

A) Occurs in B cells and is referred to as humoral immunity
B) Occurs in T cells and is referred to as cellular immunity
C) Occurs in B cells and is referred to as cellular immunity
D) Occurs in T cells and is referred to as humoral immunity
E) None of the above is correct

Question 17

Which of the following is not a characteristic N-terminal amino acid residue of long-lived proteins?

A)Sulfur containing amino acids
B)Bulky hydrophobic amino acids
C)Hydroxy containing amino acids
D)Non bulky hydrophobic amino acids
E)A and C

Question 18

Covalently bound chains with _________ or more ubiquitin monomers are required to transfer a protein to the proteosome.

A) 1
B) 2
C) 3
D) 4
E) 5

Question 19

Which of the following amino acids reacts with HOCl to form a nontoxic product during respiratory bursts?

A) Glycine
B) Phenylalanine
C) Taurine
D) Aspartate
E) Isoleucine

Question 20

The end product of uracil degradation is ________.

A) Urea
B) Ammonium ions
C) Allantoate
D) -Alanine
E) -Aminoisobutryate

Question 21

The end product of thymine degradation is _______.

A) Urea
B) Ammonium ions
C) Allantoate
D) -Alanine
E) -Aminoisobutryate

Question 22

Dihydropyrimidine dehydrogenase catalyzes the conversion of

A) Uridine to uracil
B) Uracil to dihydrouracil
C) Thymine to dihydrothymine
D) Both A and B are correct
E) Both B and C are correct

Question 23

Components of the transulfuration pathway include all of the following except ________.

A) SAM
B) Cysteine
C) Homocysteine
D) ATP
E) BH₄

Question 24

In adenosine deaminase deficiency large concentrations of dATP result in the inhibition of _____________.

A) Xanthine oxidase
B) Purine nucleoside phosphorylase
C) Aminohydrolase
D) 5'-nucleotidase
E) Ribonucleotide reductase

Question 25

Which of the following tissues can only replenish citric acid cycle intermediates by the purine nucleotide cycle?

A) Muscle
B) Brain
C) Heart
D) Liver
E) Kidney

Question 26

All of the following are directly involved in protein turnover except _______.

A) Hsp
B) Calpains
C) Cathepsin
D) Proteosome
E) None of the above is correct

Question 27

Propionyl-CoA and L-methylmalonyl-CoA are intermediates in the conversion of ________ to succinyl-CoA

A) Histidine
B) Isoleucine
C) Valine
D) Both A and B are correct
E) Both B and C are correct

Question 28

The end products of the transulfuration pathway are sulfate and _______.

A) ATP
B) Serine
C) Aspartate
D) Pyruvate
E) Oxaloacetate

Question 29

Methylmalonic acidemia results from a deficiency of

A) Branched chain -keto acid dehydrogenase
B) Methylmalonate dehydrogenase
C) Vitamin B₁₂
D) Vitamin B₆
E) None of the above is correct

Question 30

The main nitrogen storage molecule in animals is

A) Carbohydrates
B) Amino acids
C) Nucleic acids
D) Fats
E) None of the above

Question 31

Decomposers convert organic nitrogen to ________.

A) Ammonia
B) Nitrate
C) Nitrite
D) Dinitrogen
E) All of the above are correct

Question 32

In general, catabolism of amino acids begins with

A) Removal of the amino group
B) Decarboxylation
C) -Oxidation
D) Conversion to the CoA derivative
E) Conversion to pyruvate

Question 33

In muscle excess amino groups are transferred to _________ to produce glutamate

A) Pyruvate
B) Oxaloacetate
C) -Ketoglutarate
D) Glutamine
E) Oxalomalonate

Question 34

Ammonia is transferred to the liver as

A) Urea
B) Ammonia
C) Glutamine
D) Pyruvate
E) Aspartate

Question 35

Urea is synthesized in which organ?

A) Liver
B) Heart
C) Kidney
D) Muscle
E) All of the above

Question 36

In patients with alkaptonuria the urine is colored _________.

A) Yellow
B) Clear
C) Black
D) Blue
E) Both answers C and D are correct

Question 37

High phenylalanine blood levels from phenylketonuria results in damage to which organ?

A) Brain
B) Heart
C) Kidney
D) Live
E) Muscle

Question 38

Which of the following conditions result in a buildup of -ketoacids derived from branched chain amino acids?

A) Alkaptonuria
B) Albinism
C) Phenylketonuria
D) Maple syrup urine disease
E) Methyl-malonate acidemia

Question 39

A buildup of uric acid is characteristic of which of the following diseases?

A) Gout
B) Adenosine deaminase deficiency
C) Purine nucleoside phosphorylase deficiency
D) Albinism
E) Both A and C are correct

Question 40

Autophagy is

A) Used to degrade extracellular material
B) Another term for phagocytosis
C) Used to degrade worn out intracellular components
D) Used to degrade secreted intercellular components
E) Another term for endocytosis

Question 41

Phagocytosis is

A) Used to degrade extracellular material
B) Another term for autophagy
C) Involved in the degradation of intercellular material
D) Another term for exocytosis
E) None of the above

Question 42

Proteosomal digestion of what type of protein does not require ubiquination

A) Globular
B) Highly oxidized
C) Denatured
D) Structural
E) Intercellular

Question 43

Autophagy is triggered by

A) Hypoxia
B) Oxidative stress
C) Nutrient deprivation
D) High temperature
E) All of the above

Question 44

The ultimate products of autophagy include

A) Carbon dioxide
B) Fatty acids
C) Amino acids
D) Sugars
E) B, C, and D

Question 45

The major catabolic mechanism used by eukaryotic cells to maintain optimal function and respond to changing environmental conditions is

A) Microautophagy
B) Macroautophagy
C) Chaperone-mediated autophagy
D) Phagocytosis
E) Endocytosis

Question 46

What is maple syrup urine disease?

Question 47

What is phenylketonuria?

Question 48

What are T cells?

Question 49

What are  cells?

Question 50

What are the major nitrogenous waste products of metabolism in humans?

Question 51

What are three purposes served by protein turnover?

Question 52

What are the structural features of proteins that mark them for destruction?

Question 53

What are the seven metabolic products produced by the degradation of amino acids?

Question 54

In humans the purine ring cannot be degraded. How is it excreted?

Question 55

Describe how glutamate is degraded.

Question 56

Describe how the glucose-alanine cycle acts to transport ammonia to the liver.

Question 57

What are the metabolic intermediates in alanine degradation?

Question 58

Describe the Krebs bicycle. What compound links the citric acid and urea cycles?

Question 59

Describe how a protein is targeted for degradation by ubiquitination.

Question 60

Which of the following compounds yield uric acid when degraded: DNA, FAD, CTP, PRPP,-Alanine, urea, NAD⁺.

Question 61

Describe how tyrosine is degraded.

Question 62

Explain why the amino acid tryptophan is both ketogenic and glucogenic.

Question 63

Explain how tyrosinase deficiency causes albinism.

Question 64

Why can't humans degrade purine rings?

Question 65

The urea cycle occurs partially in the cytoplasm and partially in the mitochondrion. Discuss the urea cycle reactions with reference to these cellular locations.

Question 66

In individuals with PKU, is tyrosine an essential amino acid?

Question 67

Most amino acids are degraded in the liver. This is not true of the branch-chain amino acids, most of which degraded in extrahepatic tissues with high protein turnover. What is the primary tissue that uses branched chain amino acids?

Question 68

Explain why providing domestic cats with a vegetarian diet is a bad idea.

Question 69

Alkaptonuria, albinism, phenylketonuria are all examples of which kind of defiency?

Question 70

Why can't humans simply excrete waste nitrogen atoms as ammonia rather than utilize the energetically expensive process of urea synthesis?

Question 71

Phenylketonuria can be caused by deficiencies in phenylalanine hydroxylase and by enzymes catalyzing the formation and regeneration of 5,6,7,8,-tetrahydrobiopterin. How can this second deficit cause the symptoms of PKU?

Question 72

In their in vitro studies using liver slices, Krebs and Henseleit observed that urea formation was stimulated by the addition of ornithine, citrulline, and arginine. Other amino acids had no effect. Explain these observations.

Question 73

Caffeine, a methylated xanthine found in chocolate, coffee, and tea is excreted as uric acid. Use your knowledge of the metabolism of other purine compound to suggest how caffeine is metabolized.
Caffeine

Question 74

Discuss and compare the three forms of autophagy.

Question 75

Urea formation is energetically expensive, requiring the expenditure of 4 mol of ATP per mole of urea formed. However NADH is produced when fumarate is reconverted to aspartate. How many ATP molecules are produced by the mitochondrial oxidation of the NADH? What is the net ATP requirement for urea synthesis?