L16- Glycolysis II and Other Sugars Flashcards
What reaction does the enzyme fructokinase catalyze?
Fructose + ATP -> fructose-1-phosphate + ADP.
What are the substrates for the enzyme aldolase B?
Aldolase B can cleave both fructose-1-phosphate and fructose-1,6-bisphosphate.
The enzyme aldolase B cleaves fructose-1-phosphate into which two products?
Dihydroxyacetone-phosphate, which can enter glycolysis, and glyceraldehyde, which must be phosphorylated before it can enter glycolysis.
Deficiency of which enzyme results in dietary fructose intolerance that is accompanied by accumulation of fructose-1-phosphate?
Aldolase B.
Deficiency of fructokinase results in which condition?
Hereditary fructosuria.
How does aldolase B deficiency affect the blood concentration of glucose, free phosphorous and uric acid?
The concentration of glucose falls because fructose-1-phosphate inhibits glycogen breakdown. The concentration of free phosphorous falls because the cellular supply of phosphorous becomes trapped in fructose-1-phosphate. The concentration of uric acid rises because of an increase in the metabolism of purine nucleotides.
Which enzyme catalyzes the phosphorylation of mannose to mannose-6-phosphate?
Hexokinase.
How does mannose enter the glycolytic pathway?
Mannose is phosphorylated to mannose-6-phosphate by hexokinase. Mannose-6-phosphate is then isomerized to fructose-6-phosphate by phosphomannose isomerase.
What is the main source of dietary galactose?
Lactose (found in dairy products).
Which enzyme catalyzes the phosphorylation of galactose to galactose-1-phosphate?
Galactokinase.
Which enzyme catalyzes the reversible isomerization of glucose-6-phosphate to glucose-1-phosphate?
Phosphoglucomutase.
Galactose-1-phosphate is toxic to cells when present in excess. Which enzyme prevents the accumulation of galactose-1-phosphate by catalyzing its conversion to UDP-galactose?
Galactose-1-phosphate uridyltransferase.
What coenzyme is required for the interconversion of UDP-galactose with UDP-glucose by the enzyme UDP-galactose-4-epimerase?
NAD+.
Which enzyme permits the glycosylation of proteins and lipids with galactose even in the absence of dietary galactose?
UDP-galactose-4-epimerase. This enzyme can isomerize UDP-glucose to UDP-galactose, and can therefore produce UDP-galactose even when galactose is absent in the diet.
Name three enzymes of galactose metabolism that, when deficient, can lead to galactosemia (accumulation of galactose in the blood).
Galactokinase, galactose-1-phosphate uridyltransferase, and UDP-galactose-4-epimerase.
Accumulation of which metabolite in the lens of the eye can lead to the development of cataracts in individuals with galactokinase deficiency?
Galactitol.
Lack of growth in newborns, accumulation of galactose-1-phosphate and accumulation of galactitol-1-phosphate are all associated with the deficiency of what enzyme?
Galactose-1-phosphate uridyltransferase.
Which organ metabolizes the majority of the alcohol absorbed into the bloodstream following ingestion?
The liver.
Name the primary enzyme that catalyzes the conversion of alcohol into acetaldehyde.
Alcohol dehydrogenase (ADH).
What is the microsomal ethanol oxidizing system (MEOS) and in which cellular compartment is it found?
MEOS is found in the smooth endoplasmic reticulum. Its activity increases during chronic alcohol consumption, thereby accounting for increased alcohol tolerance in heavy drinkers.
The build up of which alcohol metabolite makes people ill when consuming too much alcohol?
Acetaldehyde.
What is the chemical equation for the reaction catalyzed by aldehyde dehydrogenase?
Acetaldehyde + NAD+ -> acetate + NADH + H+.
What are two ways in which alcohol consumption can lead to acidosis?
- Acetate, an alcohol metabolite, may appear in the blood and lead to acidosis 2. Metabolism of alcohol depletes cellular stores of NAD+. To restore NAD+, there will be an increased conversion of pyruvate to lactate by lactate dehydrogenase, which can lead to lactic acidosis.
Wernicke-Korsakoff syndrome can arise from deficiency of which vitamin?
Vitamin B1 (thiamine).
Which enzyme catalyzes the phosphorylation of fructose to fructose-6-phosphate?
Hexokinase.
What is the reaction catalyzed by fructokinase?
Fructose -> fructose-1-phosphate.
What is the reaction catalyzed by galactokinase?
Galactose -> galactose-1-phosphate.
