Metabolism of Other Mono- and Disachharides Flashcards
____ and _____ occur in significant amounts in the diet
Fructose, galactose
Fructose and galactose are primarily in
disaccharides
Fructose and galactose make important contributions to
energy metabolism
___ is an important component of structural carbohydrates
Galactose
This contributes to a significant source of calories in a Western diet.
Fructose
Where do we obtain fructose?
Sucrose
High Fructose Corn Syrup
Honey
Fruits
The entry of fructose into cells is
NOT insulin-dependent
_____ does not promote insulin secretion
Fructose
Why is fructose metabolized more rapidly than glucose?
Because it bypasses the PFK-1 step
Name the steps of Fructose Metabolism.
- Phosphorylation of fructose
2. Cleavage of fructose 1-phosphate
What enzymes are responsible for the phosphorylation of fructose?
Fructokinase and/or Hexokinase
Where does fructokinase metabolize fructose?
In the liver, kidney and small intestinal mucosal cells
Where is most of fructose metabolized?
Within the liver
Which enzyme requires ATP, therefore making it an irreversible step? Which step is this enzyme present?
Fructokinase in Step 1: Phosphorylation of fructose
Hexokinase can phosphorylate fructose producing
fructose 6-phosphate
Which enzyme has a high Km (low affinity) for fructose?
Hexokinase
Since it has a high Km (low affinity)–it does not contribute significantly
Hexokinase can act in
all other tissues
The enzyme responsible for Step 2: Cleavage of fructose 1-phosphate is
Aldolase B
All of the aldolase isoenzymes have the ability to cleave ____
Fructose 1-6 BP
Only _____ can cleave fructose 1-P
aldolase B
_____ can directly enter glycolysis or gluconeogenesis
DHAP
_____ can be phosphorylated to glyceraldehyde 3-phosphate via ____ and enter glycolysis (or gluconeogenesis)
Glyceraldehyde; triose kinase
_____ can also be converted to glyercol to enter other pathways
Glyceraldehyde
The enzymes responsible for converting glucose to fructose via sorbitol:
Aldose reductase and sorbitol dehydrogenase
This enzyme is found in many tissues including lens, retina, Schwann cells of peripheral nerves, liver, kidney, cells of ovaries and seminal vesicles.
Aldose reductase
Tissues that express only ________, which can make sorbitol but not further metabolize it, will be damaged by long-term elevation of blood glucose
aldose reductase
Sorbitol accumulation results in osmotic uptake in water, leading to _______, ________, _____ and _____ ___, which are typically seen in diabetic patients.
cataracts, retinopathy, nephropathy, and peripheral neuropathy
Production of _____ ties up much of available cellular phosphate, making liver and kidney cells compromised.
This leads to hepatomegaly, jaundice, hypoglycemia and renal dysfunction.
fructose 1-P
The large amount of AMP building up due to lack of ATP production results in AMP being degraded and resulting in ________
hyperuricemia
Galactose is a ( _____ epimer) of glucose
C-4
______ may come from lysosomal degradation of complex carbs
Galactose
The transport of galactose into cells IS/IS NOT insulin dependent.
Is NOT
Name the steps of Galactose Metabolism
1) Phosphorylation of Galactose
2) Formation of UDP-galactose
________ is only present in mammary glands
alpha-Lactalbumin
Lactose is synthesized in the _____
Golgi Apparatus
_____ is a milk sugar produced by lactating mammary glands
Lactose
Elevated ____ can cause cataracts
galactitol
_______ can be converted into UDP-glucose and enter glucose metabolic pathways
UDP-Galactose
What is the enzyme responsible for Step 1) Phosphorylation of galactose?
Galactokinase
What is the enzyme responsible for Step 2) Formation of UDP-galactose?
GALT
What happens in Hereditary Fructose Intolerance (“Fructose Poisoning”)?
Fructose is phosphorylated and trapped within the cell results in a build up (since it cannot be metabolized)
In \_\_\_\_\_\_\_\_\_\_\_\_, there's a: -lack of fructokinase -autosomal recessive (1:130,000) -Benign condition -Fructose accumulates in the urine
Essential Fructosuria
Mannose 6-phosphate is a substrate for ___________ that converts it to fructose-6 phosphate
Phosphomannoseisomerase
