(MD 1) Biochemistry > Uronic Acid Pathway > Flashcards

Uronic Acid Pathway Flashcards

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1
Q

The uronic acid pathway is:
A. The main ATP-generating pathway of glucose metabolism
B. An oxidative pathway producing sugar acids and precursors for conjugation reactions
C. Exclusively involved in glycogen degradation
D. Non-essential in humans

A

B. An oxidative pathway producing sugar acids and precursors for conjugation reactions

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2
Q

The first step in the uronic acid pathway involves the conversion of:
A. Glucose 6-phosphate to fructose 6-phosphate
B. Glucose 6-phosphate to glucose 1-phosphate
C. UDP-glucose to UDP-glucuronic acid
D. Glucose 1-phosphate to UDP-glucose

A

B. Glucose 6-phosphate to glucose 1-phosphate

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3
Q

The enzyme phosphoglucomutase catalyzes:
A. Oxidation of glucose 6-phosphate
B. Isomerization of glucose 6-phosphate to fructose 6-phosphate
C. Transfer of a phosphate group from carbon 6 to carbon 1 of glucose
D. Decarboxylation of UDP-glucuronic acid

A

C. Transfer of a phosphate group from carbon 6 to carbon 1 of glucose

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4
Q

UDP-glucose pyrophosphorylase activates glucose 1-phosphate by:
A. Direct oxidation to glucuronic acid
B. Attaching a UTP group to form UDP-glucose
C. Hydrolyzing glucose 1-phosphate
D. Reducing NADP+ to NADPH

A

B. Attaching a UTP group to form UDP-glucose

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5
Q

UDP-glucuronic acid acts as:
A. An inactive derivative with no physiological function
B. An activated glucuronate donor for conjugation with bilirubin and drugs
C. The final product excreted in urine
D. A signaling molecule in the immune system

A

B. An activated glucuronate donor for conjugation with bilirubin and drugs

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6
Q

Which enzyme catalyzes the oxidation of UDP-glucose to UDP-glucuronic acid?
A. UDP-glucose dehydrogenase
B. Phosphoglucomutase
C. Xylulose reductase
D. Beta-glucuronidase

A

A. UDP-glucose dehydrogenase

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7
Q

Uronic acid pathway intermediates such as UDP-glucuronic acid are essential for:
A. Glycogen synthesis only
B. Synthesis of proteoglycans like hyaluronic acid and chondroitin sulfate
C. DNA replication
D. RNA splicing

A

B. Synthesis of proteoglycans like hyaluronic acid and chondroitin sulfate

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8
Q

The process of glucuronidation in the liver enhances excretion of:
A. Water-soluble conjugates of steroids, bilirubin, and drugs
B. Fatty acids
C. Amino acids
D. Glucose derivatives not conjugated

A

A. Water-soluble conjugates of steroids, bilirubin, and drugs

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9
Q

D-glucuronic acid is hydrolyzed from UDP-glucuronic acid by:
A. Beta-glucuronidase
B. Glucoronidase
C. Phosphatase
D. Urease

A

B. Glucoronidase

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10
Q

The decarboxylation of 3-keto-L-gulonate produces which intermediate compound?
A. L-ascorbic acid
B. L-xylulose
C. Xylitol
D. Glucose 1-phosphate

A

B. L-xylulose

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11
Q

L-xylulose is reduced to xylitol by:
A. Xylitol dehydrogenase (or xylulose reductase)
B. Glucuronidase
C. UDP-glucose dehydrogenase
D. Lactate dehydrogenase

A

A. Xylitol dehydrogenase (or xylulose reductase)

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12
Q

Failure to properly reduce L-xylulose to xylitol results in:
A. Diabetes mellitus
B. Essential pentosuria
C. Alkaptonuria
D. Scurvy

A

B. Essential pentosuria—excessive L-xylulose in urine

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13
Q

The phosphorylation of D-xylulose produces:
A. D-xylulose 5-phosphate
B. Fructose 1,6-bisphosphate
C. Glucose 6-phosphate
D. Ribose 5-phosphate

A

A. D-xylulose 5-phosphate

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14
Q

D-xylulose 5-phosphate enters which biochemical pathway?
A. Glycolysis
B. Hexose Monophosphate (Pentose Phosphate) Pathway
C. Beta-oxidation
D. Urea cycle

A

B. Hexose Monophosphate (Pentose Phosphate) Pathway

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15
Q

Humans are unable to synthesize vitamin C due to the lack of:
A. L-gulonolactone oxidase
B. Xylulose reductase
C. UDP-glucose pyrophosphorylase
D. Phosphoglucomutase

A

A. L-gulonolactone oxidase

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16
Q

Lactonase catalyzes:
A. Hydrolysis of UDP-glucuronic acid
B. Formation of L-gulonolactone from L-gulonic acid
C. Decarboxylation of L-xylulose
D. Reduction of 3-keto-L-gulonate

A

B. Formation of L-gulonolactone from L-gulonic acid

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17
Q

Vitamin C deficiency results in:
A. Pernicious anemia
B. Scurvy
C. Essential pentosuria
D. Diabetes mellitus

A

B. Scurvy

This is characterized by defective collagen synthesis and poor wound healing

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18
Q

Vitamin C acts as a(n):
A. Enzyme inhibitor
B. Antioxidant
C. Protein structural element
D. Hormone

A

B. Antioxidant

It is a chain-breaking antioxidant neutralizing free radicals

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19
Q

In collagen synthesis, vitamin C is a cofactor for:
A. Hydroxylation of proline and lysine residues
B. Glycosylation of collagen
C. Cross-linking of elastin
D. ATP production

A

A. Hydroxylation of proline and lysine residues

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20
Q

Collagen with defective hydroxylation due to vitamin C deficiency causes:
A. Capillary fragility and easy bruising
B. Excess bone deposition
C. Increased muscle mass
D. Enhanced wound healing

A

A. Capillary fragility and easy bruising

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21
Q

Vitamin C is crucial for synthesis of:
A. Carnitine
B. Glucose only
C. Insulin
D. Hemoglobin

A

A. Carnitine

This transports fatty acids into mitochondria for β-oxidation

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22
Q

The catecholamines affected by vitamin C deficiency include:
A. Dopamine and serotonin exclusively
B. Norepinephrine via dopamine β-hydroxylase cofactor function
C. Adrenaline only
D. Acetylcholine

A

B. Norepinephrine via dopamine β-hydroxylase cofactor function

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23
Q

Ascorbic acid’s role in bile acid synthesis involves:
A. Oxidative reactions requiring vitamin C as a cofactor
B. Direct secretion of bile
C. Bile acid degradation
D. Transport of bile acids

A

A. Oxidative reactions requiring vitamin C as a cofactor

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24
Q

UDP-glucuronic acid formed in the uronic acid pathway acts in the liver to:
A. Facilitate conjugation of bilirubin, steroid hormones, and drugs for excretion
B. Store glucose as glycogen
C. Synthesize fatty acids
D. Cause oxidative stress

A

A. Facilitate conjugation of bilirubin, steroid hormones, and drugs for excretion

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25
The proteoglycans hyaluronic acid and chondroitin 4-sulfate are synthesized using: A. D-glucuronic acid as a key component B. Ascorbic acid as the main building block C. Ribose sugars D. Amino acids alone
A. D-glucuronic acid as a key component
26
In the liver, conjugation with glucuronic acid results in: A. More hydrophobic compounds B. More water-soluble conjugates for easier excretion C. Enhanced toxicity D. Increased drug half-life
B. More water-soluble conjugates for easier excretion
27
Bilirubin is converted into a more water-soluble form by: A. Oxidation via NADPH oxidase B. Conjugation with glucuronic acid mediated by UDP-glucuronyl transferase C. Reduction by xylulose reductase D. Phosphorylation by kinase
B. Conjugation with glucuronic acid mediated by UDP-glucuronyl transferase
28
A deficiency of UDP-glucuronyl transferase will most likely cause: A. Increased conjugation of bilirubin B. Jaundice due to accumulation of unconjugated bilirubin C. Defective collagen formation D. Essential pentosuria
B. Jaundice due to accumulation of unconjugated bilirubin
29
L-gulonic acid is converted biochemically into: A. Vitamin B6 B. 3-keto-L-gulonic acid C. Glucose 6-phosphate D. Amino acids
B. 3-keto-L-gulonic acid This is an intermediate in ascorbic acid synthesis
30
Essential pentosuria is caused by deficiency of: A. Xylulose reductase B. Glucuronidase C. Lactonase D. UDP-glucose pyrophosphorylase
A. Xylulose reductase / D.H.
31
The accumulation of L-xylulose in urine can cause false-positive diagnosis of: A. Diabetes mellitus B. Hemophilia C. Phenylketonuria D. Scurvy
A. Diabetes mellitus
32
Vitamin C deficiency impairs iron absorption and may lead to: A. Macrocytic anemia B. Iron deficiency anemia C. Megaloblastic anemia D. Polycythemia
B. Iron deficiency anemia
33
NADPH generated in the uronic acid pathway is primarily used for: A. ATP production in mitochondria B. Biosynthetic reactions and antioxidant defenses C. Protein synthesis D. DNA replication
B. Biosynthetic reactions and antioxidant defenses
34
The uronic acid pathway shares intermediates with: A. The urea cycle B. The hexose monophosphate (pentose phosphate) pathway C. The citric acid cycle only D. Fatty acid beta-oxidation
B. The hexose monophosphate (pentose phosphate) pathway
35
A common experimental method to detect essential pentosuria involves testing urine for: A. Glucose B. Reducing sugars C. Ketone bodies D. Protein
B. Reducing sugars
36
Which enzyme in the uronic acid pathway is NAD+-dependent? A. Xylitol dehydrogenase B. UDP-glucose dehydrogenase C. Phosphoglucomutase D. Gulonolactone oxidase
A. Xylitol dehydrogenase
37
Which species synthesizes vitamin C endogenously by converting glucose through the uronic acid pathway? A. Humans B. Primates C. Most mammals except some like guinea pigs D. None
C. Most mammals except some like guinea pigs
38
The uronic acid pathway has clinical significance due to its role in: A. Only glucose catabolism B. Conjugation and detoxification of bilirubin and drugs C. Hormone synthesis only D. Protein folding
B. Conjugation and detoxification of bilirubin and drugs
39
Which process ensures neurotransmitter precursors like glucuronic acid can be excreted in bile or urine? A. Glycogen synthesis B. Glucuronidation C. Metabolism by cytochrome P450 enzymes D. Passive diffusion
B. Glucuronidation
40
Glucuronic acid conjugation increases the: A. Lipid solubility of compounds B. Water solubility of compounds C. Molecular weight without effect on solubility D. Toxicity of compounds
B. Water solubility of compounds
41
Scurvy results from defective hydroxylation in collagen synthesis because vitamin C: A. Donates electrons to maintain the active site iron of prolyl and lysyl hydroxylases B. Acts as a structural crosslinker C. Is incorporated into collagen directly D. Inhibits degradation of collagen
A. Donates electrons to maintain the active site iron of prolyl and lysyl hydroxylases
42
Carnitine synthesis requires vitamin C as a cofactor for: A. Decarboxylation of amino acids B. Hydroxylation of lysine residues in the biosynthetic pathway C. Direct transport of fatty acids D. Synthesis of long chain fatty acids
B. Hydroxylation of lysine residues in the biosynthetic pathway
43
Dopamine β-hydroxylase, which converts dopamine to norepinephrine, requires vitamin C as a: A. Substrate B. Cofactor for hydroxylation C. Competitive inhibitor D. Transcription factor
B. Cofactor for hydroxylation
44
Which bile acid synthetic steps depend on vitamin C? A. Early cholesterol synthesis B. Hydroxylation reactions in bile acid formation C. Conjugation with taurine and glycine D. Bile acid secretion
B. Hydroxylation reactions in bile acid formation
45
A clinical feature of vitamin C deficiency NOT related to collagen is: A. Anemia due to impaired iron absorption B. Neurodegeneration from catecholamine shortage C. Hyperglycemia D. Increased bile secretion
A. Anemia due to impaired iron absorption
46
The hydrolysis of UDP-glucuronic acid to glucuronic acid and UDP occurs in which cellular organelle? A. Cytosol B. Mitochondria C. Lysosome D. Golgi apparatus
A. Cytosol
47
Individuals with essential pentosuria excrete excess L-xylulose primarily in: A. Sweat B. Saliva C. Urine D. Cerebrospinal fluid
C. Urine
48
Which pentose sugar is generated by decarboxylation and reduction steps of the uronic acid pathway? A. Ribose B. Xylulose C. Glucose D. Mannose
B. Xylulose
49
The activation of substrate molecules in the uronic acid pathway involves: A. Conversion to free acid forms B. Coupling with UDP C. Direct phosphorylation by ATP D. None of the above
B. Coupling with UDP (Uridine diphosphate)
50
Identify the enzyme that catalyzes the conversion of glucose 6-phosphate to glucose 1-phosphate.
Phosphoglucomutase
51
Identify the intermediate sugar acid that is conjugated to bilirubin in the liver
UDP-glucuronic acid
52
Which enzyme is missing in humans that prevents endogenous synthesis of vitamin C?
L-gulonolactone oxidase
53
Identify the vitamin C-dependent enzymes involved in collagen synthesis.
Prolyl and lysyl hydroxylase
54
Name the catecholamine synthesis enzyme requiring vitamin C as a cofactor.
Dopamine β-hydroxylase
55
TRUE OR FALSE: Humans synthesize vitamin C endogenously via the uronic acid pathway.
False
56
TRUE OR FALSE: Vitamin C deficiency leads to impaired hydroxylation of proline and lysine residues in collagen.
True
57
TRUE OR FALSE: Bilirubin conjugation with glucuronic acid increases its solubility and promotes excretion.
True
58
TRUE OR FALSE: Xylitol dehydrogenase deficiency results in the accumulation of xylitol in the blood and urine.
False
59
TRUE OR FALSE: D-xylulose 5-phosphate is a metabolite that connects the uronic acid pathway with the pentose phosphate pathway.
True
60
What is the only glucose derived vitamin
Ascorbic acid/ Vit. C However, human are NOT able to synthesize this in the body due to absence of L-gulonolactone oxidase
(MD 1) Biochemistry
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