Metabolism Of Other Mono And Disaccharides Flashcards
An important component in structural carbohydrates
Galactose
Why is fructose metabolized more rapidly than glucose?
It bypasses the PFK1 step
Fructose metabolism steps
- Phosphorylation of fructose
2. Cleavage of fructose-1-phosphate
Enzymes of Phosphorylation of Fructose
Step 1 of Fructose Metabolism
Fructokinase:
- in liver, kidney, and small intestinal mucosal cells
- uses ATP (IRREVERSIBLE)
Hexokinase
- has a high Km/low affinity for fructose, therefore is does not contribute significantly
- acts in all other tissues
Aldolase B is the only aldolase enzyme that can..
Cleave fructose 1-P
All aldolase enzyme isoenzymes can cleave…
Fructose 1,6-BP
Products from Cleavage of Fructose 1-P
Glyceraldehyde (or glyceraldehyde 3-p) and DHAP (dihydroxyacetone phosphate)
After cleaved, glyceraldehyde can go onto what what process?
Glycolysis or gluconeogenesis
After it is phosphorylated by triose kinase to glyceraldehyde 3-P
Glyceraldehyde can also be converted to…. To enter other pathways?
Glycerol
What is sorbitol?
An intermediate between the conversion of glucose to fructose
Conversion of glucose to fructose via sorbitol
Aldose reductase
- converts glucose to sorbitol
- found in lens, retina, liver, kidney, cells of ovaries and seminal vesicles
Sorbitol dehydrogenase
- convert sorbitol to fructose
- only found in liver, ovaries, and seminal vesicles
Why do the seminal vesicles have sorbitol dehydrogenase?
The sperm uses fructose
How can tissues that express aldose reductase end up damaging the tissue itself?
By producing sorbitol from glucose, but not able to make fructose from sorbitol.
Will be damaged by long term elevation of blood glucose
Excess sorbitol can result in..
Osmotic uptake of water, which can cause cataracts, retinopathy, nephropathy, and peripheral neuropathy
Conversion of mannose to fructose 6-P
Important component of glycoproteins
Substrate for Hexokinase
- mannose -> mannose 6-P
Phosphomannoseisomerase
- mannose 6-P -> fructose 6-P
Essential Fructosuria
Fructokinase deficiency
Autosomal recessive
Fructose accumulates in the urine
Hereditary Fructose Intolerance
Aka Fructose Poisoning
Fructose is phosphorylated and trapped in the cell and builds up
The Fructose ties up most of the available phosphate, which means liver and kidney cells are compromised
Leads to hepatomegaly, jaundice, hypoglycemia, and renal dysfunction
(Hyperuricemia can occur too due to AMP buildup due to lack of ATP production)
What is the source of galactose?
Lactose, from milk and milk products
Some from lysosomal degradation of complex carbs
Galactose Metabolism steps
- Phosphorylation of galactose
Enzyme: galactokinase
Galactose -> galactose 1-P
2.Formation of UDP-galactose
Enzyme: GALT (galactose 1-P uridyltransferase)
Galactose 1-P can be converted into UDP-galactose or UDP-glucose
What are the possible products of Galactose Metabolism?
UDP-Galactose and UDP-Glucose
Elevated glucose can cause cataracts due to what disease?
Galactokinase Deficiency (galactose is not getting phosphorylated)
Accumulation of galactose 1-P can cause liver damage, retardation, and cataracts due to GALT deficiency is what disorder?
Classic Galactosemia
Elevated levels of galactitol in lens causing cataracts is cause by what enzyme disorder?
Aldose Reductase, converts galactitol to galactose
Where is Lactose synthesized?
Golgi apparatus
