Metabolism of Other Mono- and Disachharides

Question 1

____ and _____ occur in significant amounts in the diet

Answer 1

Fructose, galactose

Question 2

Fructose and galactose are primarily in

Answer 2

disaccharides

Question 3

Fructose and galactose make important contributions to

Answer 3

energy metabolism

Question 4

___ is an important component of structural carbohydrates

Answer 4

Galactose

Question 5

This contributes to a significant source of calories in a Western diet.

Answer 5

Fructose

Question 6

Where do we obtain fructose?

Answer 6

Sucrose
High Fructose Corn Syrup
Honey
Fruits

Question 7

The entry of fructose into cells is

Answer 7

NOT insulin-dependent

Question 8

_____ does not promote insulin secretion

Answer 8

Fructose

Question 9

Why is fructose metabolized more rapidly than glucose?

Answer 9

Because it bypasses the PFK-1 step

Question 10

Name the steps of Fructose Metabolism.

Answer 10

1. Phosphorylation of fructose

2. Cleavage of fructose 1-phosphate

Question 11

What enzymes are responsible for the phosphorylation of fructose?

Answer 11

Fructokinase and/or Hexokinase

Question 12

Where does fructokinase metabolize fructose?

Answer 12

In the liver, kidney and small intestinal mucosal cells

Question 13

Where is most of fructose metabolized?

Answer 13

Within the liver

Question 14

Which enzyme requires ATP, therefore making it an irreversible step? Which step is this enzyme present?

Answer 14

Fructokinase in Step 1: Phosphorylation of fructose

Question 15

Hexokinase can phosphorylate fructose producing

Answer 15

fructose 6-phosphate

Question 16

Which enzyme has a high Km (low affinity) for fructose?

Answer 16

Hexokinase

Since it has a high Km (low affinity)–it does not contribute significantly

Question 17

Hexokinase can act in

Answer 17

all other tissues

Question 18

The enzyme responsible for Step 2: Cleavage of fructose 1-phosphate is

Answer 18

Aldolase B

Question 19

All of the aldolase isoenzymes have the ability to cleave ____

Answer 19

Fructose 1-6 BP

Question 20

Only _____ can cleave fructose 1-P

Answer 20

aldolase B

Question 21

_____ can directly enter glycolysis or gluconeogenesis

Answer 21

DHAP

Question 22

_____ can be phosphorylated to glyceraldehyde 3-phosphate via ____ and enter glycolysis (or gluconeogenesis)

Answer 22

Glyceraldehyde; triose kinase

Question 23

_____ can also be converted to glyercol to enter other pathways

Answer 23

Glyceraldehyde

Question 24

The enzymes responsible for converting glucose to fructose via sorbitol:

Answer 24

Aldose reductase and sorbitol dehydrogenase

Question 25

This enzyme is found in many tissues including lens, retina, Schwann cells of peripheral nerves, liver, kidney, cells of ovaries and seminal vesicles.

Answer 25

Aldose reductase

Question 26

Tissues that express only ________, which can make sorbitol but not further metabolize it, will be damaged by long-term elevation of blood glucose

Answer 26

aldose reductase

Question 27

Sorbitol accumulation results in osmotic uptake in water, leading to _______, ________, _____ and _____ ___, which are typically seen in diabetic patients.

Answer 27

cataracts, retinopathy, nephropathy, and peripheral neuropathy

Question 28

Production of _____ ties up much of available cellular phosphate, making liver and kidney cells compromised. This leads to hepatomegaly, jaundice, hypoglycemia and renal dysfunction.

Answer 28

fructose 1-P

Question 29

The large amount of AMP building up due to lack of ATP production results in AMP being degraded and resulting in ________

Answer 29

hyperuricemia

Question 30

Galactose is a ( _____ epimer) of glucose

Answer 30

C-4

Question 31

______ may come from lysosomal degradation of complex carbs

Answer 31

Galactose

Question 32

The transport of galactose into cells IS/IS NOT insulin dependent.

Answer 32

Is NOT

Question 33

Name the steps of Galactose Metabolism

Answer 33

1) Phosphorylation of Galactose | 2) Formation of UDP-galactose

Question 34

________ is only present in mammary glands

Answer 34

alpha-Lactalbumin

Question 35

Lactose is synthesized in the _____

Answer 35

Golgi Apparatus

Question 36

_____ is a milk sugar produced by lactating mammary glands

Answer 36

Lactose

Question 37

Elevated ____ can cause cataracts

Answer 37

galactitol

Question 38

_______ can be converted into UDP-glucose and enter glucose metabolic pathways

Answer 38

UDP-Galactose

Question 39

What is the enzyme responsible for Step 1) Phosphorylation of galactose?

Answer 39

Galactokinase

Question 40

What is the enzyme responsible for Step 2) Formation of UDP-galactose?

Answer 40

GALT

Question 41

What happens in Hereditary Fructose Intolerance ("Fructose Poisoning")?

Answer 41

Fructose is phosphorylated and trapped within the cell results in a build up (since it cannot be metabolized)

Question 42

``` In ____________, there's a: -lack of fructokinase -autosomal recessive (1:130,000) -Benign condition -Fructose accumulates in the urine ```

Answer 42

Essential Fructosuria

Question 43

Mannose 6-phosphate is a substrate for ___________ that converts it to fructose-6 phosphate

Answer 43

Phosphomannoseisomerase