Sugar interconversion Flashcards
What transporter is required for movement of all sugars across membrane?
GLUT 2
What transporter is required for fructose movement across membrane?
GLUT 5
What happens to fructose in order to be part of glycolysis?
Phosphorylated via hexokinase to Fructose 6-phosphate
Fructose to Fructose 6-phosphate is common/uncommon? Why?
Uncommon because hexokinase is usually saturated with glucose
Fructose is primarily made into?
Fructose 1-phosphate by Fructokinase (requires ATP)
Fructose 1-phosphate is…
Catalyzed by aldolase B and made into glyceraldehyde and dihydroxyacetone phosphate which are then metabolized
What are the two products of fructose metabolism?
By aldolase B to glyceraldehyde and dihydroxyacetone phosphate
Excessive ingestion of fructose leads to?
Sequestering of phosphate by fructokinase and inefficient recycling by metabolism of downstream metabolites
Where is fructokinase located?
Liver
What is essential fructosuria?
Mutation in fructokinase, usually very benign leading to fructose in urine
What is hereditary fructose intolerance?
Aldolase B is mutated and this is severe cqausing liver damage, hypoglycemia, and kidney damage. Happens because intermediates of fructose metabolism F1P sequester phosphorus…too little ATP
What is a potential for glucose in elevated circumstances if it does not go through glycolysis/glycogen synthesis?
Aldose reductase takes it to sorbitol
How is sorbitol formed?
Excess glucose is taken to sorbitol by aldose reductase and NADPH
How is sorbitol potentially broken down?
Via sorbitol dehydrogenase to generate fructose and NADH
T or F: Sorbitol is highly osmotic
T
Excess sorbitol in tissues leads to?
Cataracts, peripheral neuropathy, and kidney problems (think diabetes)
What is galactosemia?
Inability to digest glactose
Excess levels of galactose in blood lead to formation of?
Galacticol via an aldose reductase that causes cataracts
Describe healthy galactose metabolism
Galactose taken to galactose 1 P via galactokinase and ATP, galactose 1 P taken to glucose 1P via UDP-glucose UDP-galactose 1 P uridylyltransferase
What is classical galactosemia?
Break in galactose 1 6 uridylyltransferase leading to severe phosphorus sequestering
What is non-classical galactosemia?
Mutation in galactokinase meaning that galactose is not able to be digested
What is UDP glucose epimerized to?
UDP galactose via an epimerase enzyme
What are glycoaminoglycans?
Repeated dimer of an acidic sugar and a N-acetylated amino sugar
What is the precursor for glycoaminoglycans?
UDP glucose
What are the general properties of glycoaminoglycans?
Mucopolysaccharides and proteoglycans (think of cartilage in the knee)
Chondroitin sulfate is an example of?
Gylcoaminoglycans
Heparin is a?
Glycosaminoglycan (anti-clotting)
Hunter’s syndrome and Sanfilippo’s syndrome are examples of diseases in?
Glycosaminoglycans
What is a glycoprotein?
Protein with a sugar attached either at a N or O of AA
What is characteristic of glycoprotein structure?
Core pentasaccarhide of galactose (acetylated) and Mannose (often attached to asparagine or others)
What are some functions of glycoproteins?
Cell cell recognition = immune system
Cataracts are caused by what two build-ups talked about?
Sorbitol and galactinol
