What causes essential pentosuria?
Click to see answer
Deficiency of the enzyme that converts xylulose to xylitol.
Click to see question
What causes essential pentosuria?
Deficiency of the enzyme that converts xylulose to xylitol.
Which enzyme catalyzes the oxidation of D-glucuronic acid?
L-gulonic dehydrogenase.
What condition results from the absence of xylitol dehydrogenase?
Essential pentosuria.
What pigment is formed from heme via heme oxygenase?
Biliverdin.
What is the first step in the uronic acid pathway?
Conversion of glucose 6-phosphate to glucose 1-phosphate via phosphoglucomutase.
What happens to UDP Glucose in the Uronic Acid Pathway?
It is oxidized at C6 by NAD+-dependent UDP glucose dehydrogenase to form UDP-glucuronic acid.
What does ascorbic acid donate to organic radicals?
A hydrogen atom (H+).
What are the consequences of Vitamin C deficiency on collagen?
It leads to impaired collagen functions, resulting in poor wound healing, osteoporosis, capillary fragility, and anemia.
What metabolic pathway does D-xylulose 5-phosphate enter?
The HMP Shunt.
What happens to hemoglobin in RBCs after 120 days?
It is phagocytosed by macrophages into heme and globin.
What is the uronic acid pathway primarily involved in?
Oxidative pathway for glucose metabolism into glucuronic acid, ascorbic acid, and pentoses.
What enzyme reduces L-xylulose to xylitol?
Xylitol dehydrogenase (xylulose reductase).
What is released as a byproduct during the decarboxylation of 3-keto-L-gulonic acid?
CO2.
What is the role of D-glucuronic acid in the liver?
It is conjugated to non-polar acceptor molecules for easier excretion via bile.
What is produced during the oxidation of L-gulonic acid?
3-keto-L-gulonic acid and NADH.
What is the first step in the Uronic Acid Pathway?
Conversion of Glucose 6-phosphate to Glucose 1-phosphate via phosphoglucomutase.
What is the product of the decarboxylation of β-L-gulonate?
L-xylulose.
What process converts 3-keto-L-gulonic acid to L-xylulose?
Decarboxylation.
What are the primary functions of the uronic acid pathway in humans?
It synthesizes sugar acids for glucuronide synthesis and provides metabolic intermediates.
What condition is caused by a lack of vitamin C in the diet?
Scurvy.
Which glycolytic intermediate serves as a branch point for the uronic acid pathway?
Glucose 1-phosphate.
What enzyme catalyzes the reoxidation of xylitol to D-xylulose?
D-xylulose dehydrogenase.
What is the primary function of the Uronic Acid Pathway?
It serves as an alternate oxidative pathway for glucose metabolism into glucuronic acid, ascorbic acid, and pentoses without ATP generation.
What is the final step involving xylitol?
Reoxidation of xylitol to D-xylulose.
What are some clinical implications of deficiencies in the Uronic Acid Pathway?
Deficiencies can lead to clinical disorders arising from deficient enzymes involved in the pathway.
What is D-glucuronic acid oxidized to?
L-gulonic acid.
What is the significance of glucuronic acid in the body?
Glucuronic acid is used in conjugation reactions and is a precursor for ascorbic acid in humans.
How is L-xylulose converted to xylitol?
By reduction via xylitol dehydrogenase or xylulose reductase.
What are the components of hyaluronic acid and chondroitin 4-sulfate?
β-glucuronic acid.
What intermediate of the uronic acid pathway is utilized in most conjugation reactions in the body?
UDP glucuronate.
What is essential pentosuria?
It is a condition characterized by high quantities of xylulose in urine due to a lack of xylulose reductase.
What is the first step in the synthesis of ascorbic acid?
Formation of L-gulonolactone from L-gulonic acid by lactonase.
What role does ascorbic acid (Vitamin C) play in biological systems?
It acts as a chain-breaking antioxidant.
Which enzyme's absence prevents humans from synthesizing ascorbic acid?
L-gulonolactone oxidase.
How does Vitamin C contribute to carnitine synthesis?
Vitamin C serves as a cofactor in the synthesis of carnitine from lysine, which is essential for transporting fatty acids to mitochondria.
What is the next step after xylitol in the pathway?
Reoxidation of xylitol to D-xylulose via D-xylulose dehydrogenase.
How is UDP Glucose formed in the Uronic Acid Pathway?
Glucose 1-phosphate is activated by UTP via UDP glucose pyrophosphorylase.
What is the role of Vitamin C in catecholamine synthesis?
Vitamin C acts as a cofactor for dopamine ß-hydroxylase in the conversion of dopamine to norepinephrine.
What is D-xylulose phosphorylated to?
D-xylulose 5-phosphate.
What is the role of L-gulonolactone oxidase in ascorbic acid synthesis?
It oxidizes L-gulonolactone at carbon 2 to form 3-keto-L-gulonolactone.
What is UDP glucose converted to in the uronic acid pathway?
UDP glucuronic acid.
What is formed when UDP glucuronic acid is hydrolyzed?
UDP and D-glucuronic acid.
What is formed when D-xylulose is phosphorylated at carbon 5?
D-xylulose 5-phosphate.
What metabolic pathway does glucose 6-phosphate enter to synthesize uronic acids?
It enters the hexose monophosphate (HMP) pathway.
How is bilirubin made more water-soluble?
By conjugation with D-glucuronate to form diglucuronide.
What is the unreactive radical formed from Vitamin C?
Dehydroascorbyl radical (As*).
What is the role of ascorbate in collagen synthesis?
Ascorbate acts as a cofactor to maintain iron in the reduced state (Fe +2) during the hydroxylation of proline and lysine in procollagen.
What condition is caused by a deficiency of xylitol dehydrogenase?
Essential pentosuria.
What is a common misdiagnosis for essential pentosuria?
Diabetes mellitus.
Why do humans need to obtain Vitamin C from their diet?
Humans lack L-gulonolactone oxidase, preventing them from synthesizing ascorbic acid.
What is the role of Vitamin C in hydroxylation reactions?
It is oxidized to dehydroascorbate during the decarboxylation of α-ketoglutarate.
What is the significance of UDP-glucuronic acid?
It serves as a source of glucuronate for reactions involving incorporation into proteoglycans or conjugation with substrates for excretion.
What is the fate of D-glucuronic acid in the body?
It is used for the synthesis of proteoglycans and for detoxification.
What is the role of glucuronic acid in the body?
It is involved in the synthesis of proteoglycans and conjugation reactions for excretion of substances like steroid hormones and drugs.
