L16- Glycolysis II and Other Sugars

Question 1

What reaction does the enzyme fructokinase catalyze?

Answer 1

Fructose + ATP -> fructose-1-phosphate + ADP.

Question 2

What are the substrates for the enzyme aldolase B?

Answer 2

Aldolase B can cleave both fructose-1-phosphate and fructose-1,6-bisphosphate.

Question 3

The enzyme aldolase B cleaves fructose-1-phosphate into which two products?

Answer 3

Dihydroxyacetone-phosphate, which can enter glycolysis, and glyceraldehyde, which must be phosphorylated before it can enter glycolysis.

Question 4

Deficiency of which enzyme results in dietary fructose intolerance that is accompanied by accumulation of fructose-1-phosphate?

Answer 4

Aldolase B.

Question 5

Deficiency of fructokinase results in which condition?

Answer 5

Hereditary fructosuria.

Question 6

How does aldolase B deficiency affect the blood concentration of glucose, free phosphorous and uric acid?

Answer 6

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.

Question 7

Which enzyme catalyzes the phosphorylation of mannose to mannose-6-phosphate?

Answer 7

Hexokinase.

Question 8

How does mannose enter the glycolytic pathway?

Answer 8

Mannose is phosphorylated to mannose-6-phosphate by hexokinase. Mannose-6-phosphate is then isomerized to fructose-6-phosphate by phosphomannose isomerase.

Question 9

What is the main source of dietary galactose?

Answer 9

Lactose (found in dairy products).

Question 10

Which enzyme catalyzes the phosphorylation of galactose to galactose-1-phosphate?

Answer 10

Galactokinase.

Question 11

Which enzyme catalyzes the reversible isomerization of glucose-6-phosphate to glucose-1-phosphate?

Answer 11

Phosphoglucomutase.

Question 12

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?

Answer 12

Galactose-1-phosphate uridyltransferase.

Question 13

What coenzyme is required for the interconversion of UDP-galactose with UDP-glucose by the enzyme UDP-galactose-4-epimerase?

Answer 13

NAD+.

Question 14

Which enzyme permits the glycosylation of proteins and lipids with galactose even in the absence of dietary galactose?

Answer 14

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.

Question 15

Name three enzymes of galactose metabolism that, when deficient, can lead to galactosemia (accumulation of galactose in the blood).

Answer 15

Galactokinase, galactose-1-phosphate uridyltransferase, and UDP-galactose-4-epimerase.

Question 16

Accumulation of which metabolite in the lens of the eye can lead to the development of cataracts in individuals with galactokinase deficiency?

Answer 16

Galactitol.

Question 17

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?

Answer 17

Galactose-1-phosphate uridyltransferase.

Question 18

Which organ metabolizes the majority of the alcohol absorbed into the bloodstream following ingestion?

Answer 18

The liver.

Question 19

Name the primary enzyme that catalyzes the conversion of alcohol into acetaldehyde.

Answer 19

Alcohol dehydrogenase (ADH).

Question 20

What is the microsomal ethanol oxidizing system (MEOS) and in which cellular compartment is it found?

Answer 20

MEOS is found in the smooth endoplasmic reticulum. Its activity increases during chronic alcohol consumption, thereby accounting for increased alcohol tolerance in heavy drinkers.

Question 21

The build up of which alcohol metabolite makes people ill when consuming too much alcohol?

Answer 21

Acetaldehyde.

Question 22

What is the chemical equation for the reaction catalyzed by aldehyde dehydrogenase?

Answer 22

Acetaldehyde + NAD+ -> acetate + NADH + H+.

Question 23

What are two ways in which alcohol consumption can lead to acidosis?

Answer 23

1. 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.

Question 24

Wernicke-Korsakoff syndrome can arise from deficiency of which vitamin?

Answer 24

Vitamin B1 (thiamine).

Question 25

Which enzyme catalyzes the phosphorylation of fructose to fructose-6-phosphate?

Answer 25

Hexokinase.

Question 26

What is the reaction catalyzed by fructokinase?

Answer 26

Fructose -> fructose-1-phosphate.

Question 27

What is the reaction catalyzed by galactokinase?

Answer 27

Galactose -> galactose-1-phosphate.