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Flashcards in 2.1 Fructose metabolism Deck (44)
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Key sources of fructose in diet

Fructose
High Fructose Corn Syrup
Sucrose

1

What are the two monosaccharides that make up Sucrose

Glucose and Fructose

2

What is the key difference between High Fructose Corn Syrup and Sucrose

Sucrose is a disaccharide of Glucose and Fructose
HFCS is a mixture of monosaccharides of Glucose and Fructose

3

Fructose absorption into the intestinal cells occurs how and through what type of transport?

Through GLUT 5
Facilitated Transport

4

Fructose absorption into the bloodstream from the intestinal cells occurs how and through what type of transport?

GLUT 5 or GLUT 2 (mainly GLUT 2)
Facilitated Transport

5

In the muscle, how in what structure does fructose enter glycolysis

Fructose --> Fructose 6-phosphate

6

What enzyme catalyzes the reaction of Fructose to Fructose 6-phosphate in the muscle?

Hexokinase

7

How does Fructose enter glycolysis in the liver

Fructose --> Fructose 1-phosphate --> Glyceraldehyde and Dihydroxyacetone phosphate --> Glyceraldehyde 3-phosphate

8

What enzyme catalyzes reaction of fructose to fructose 1-phosphate in the liver

Fructokinase

9

What enzyme catalyzes Fructose 1-phosphate to Glyceraldehyde and Dihydroxyacetone phosphate

Aldolase B (Fructose 1-phosphate aldolase)

10

What crucial step of normal glycolysis does Fructose skip as it enters glycolysis in the liver?

It bypasses PFK1

11

What is the result of Fructose bypassing PFK1 in the liver?

Increased lipogenesis and Increased appetite

12

Excessive dietary intake of fructose may lead to decrease in what?

available phosphate which means that it is insufficient to meet demands of ATP regeneration

13

What are the two major genetic disorders of fructose metabolism

Enzyme deficiency with Fructokinase
Enzyme deficiency with Aldolase B

14

Which genetic disorder of fructose metabolism is severe

Enzyme deficiency with Aldolase B or Hereditary fructose intolerance

15

What happens when there is an enzyme deficiency with fructokinase in the liver?

Fructose cannot be phosphorylated to fructose 1-phosphate and cannot be trapped in the cell. This could lead to Essential Fructosuria

16

What is the purpose of converting glucose to sorbitol?

To trap glucose in the cell without expending ATP.

17

What enzyme catalyzes the reaction of Glucose to Sorbitol?

Aldose Reductase

18

What coenzyme is used in the reaction of Glucose to Sorbitol?

NADPH

19

When is there a buildup of Sorbitol?

During hyperglycemia

20

In what cells does Sorbitol build up and why?

Lens, Kidney and Nerve
Sorbitol cannot be converted to Fructose in these cells

21

Sorbitol is converted to Fructose by what enzyme in the Liver?

Sorbitol Dehydrogenase

22

How does Mannose enter glycolysis?

By being converted to Fructose 6-phosphate

23

Reaction of Mannose to Mannose 6-phosphate is catalyzed by what enzyme?

Hexokinase

24

Mannose 6-phosphate to Fructose 6-phosphate reaction is catalyzed by what enzyme?

Phosphomannose isomerase

25

How does Galactose enter glycolysis?

Glucose 6-phosphate

26

Briefly outline the pathway of Galactose being converted to Glucose 6-phosphate

*Galactose --> Galactose 1-phosphate
*Galactose 1-phosphate + UDP-Glucose --> UDP-Gal + Glu 1-Phosphate
*Glucose 1-phosphate --> Glucose 6-phosphate
**UDP-galactose --> UDP-glucose (to be used to produce glu-1-P)

27

What enzyme catalyzes the reaction of Galactose --> Galactose 1-phosphate

Galactokinase

28

What enzyme catalyzes the placement of uridine phosphate on Galactose 1-phosphate and the production of Glucose-1-phosphate

Galactose 1-phosphate uridylyl transferase

29

What enzyme catalyzes reaction of UDP-galactose to UDP-glucose?

UDP-Galactose-4-epimerase