pack Flashcards
(14 cards)
What type of receptors does fructose use? Why does it use these specific receptors?
GLUT 5
(It uses these and not glut 4 because of the fact that it is not insulin inducing and not insulin dependent.)
What is the enzyme used in the liver and muscle cells to metabolize fructose? What is the product?
Liver:Fructokinase ===fructose-1-phosphate
Muscle: Hexokinase –> fructose-6-phosphate
What is the rate limting step in fructose metabolsim?
Aldose B
What is the main pathway for fructose metabolism?
Fructokinase bc it has higher affinity for fructose
(it makes sense since it happens in the liver)
What does aldose B do to fructose 1-phosphate?
It cleaves it to glyceraldhyde and dihydroxyacetone phosphate
What is the relation between fructose 6 phosphate and glucosamine 6-phosphate?
fructose 6-phosphate can be turned into glucosamine 6-phosphate which is the precursor of all the other amino sugars
What is the consquence of a high fructose diet?
Bc of the fact that Fructose 1-phosphate is a fast reaction but aldose B is slow, F1P accumulates in the body and slows ATP synthesis and causes sequestering phosphate (decrease Pi), which results in accumulation of ADP and AMP which lead to hyperurecemia (uric acid) and gout.
What is essential fructosuria?
Lack of fructose kinase
which causes fructose accumilation in the urine
What is hereditary fructose intolerance?
Lack of Aldose B which causes accmulation of F1P.
Accumulation of F1P inhibts other enzymes such as: Fructokinase, phosphorylase, 1,6-bisphosphate aldolase
Symptoms: Hypoglycemia, Hyperuricemia
How is glucose converted to sorbitol?
using aldose reductase
How is fructose produced from Sorbitol?
Sorbitol dehydrogenase
What is the effect of hyperglycemia on sorbitol metabolsim in the kidneys, retina, and nerves?
The kidneys, retina, and nerves don’t have the enzyme sorbitol dehydrogenase, so fructose won’t form.
This means that sorbitol will accumulate in the cells and will cause osmotic changes which cause problems such as catract.
What are the complications caused by defeceinies in: Galactose-1-phosphate-uridyltransferase
(most common)
Galactokinase (rare
UDP-galactose epimerase (rare)
How is milk synthesized in mammary glands?
From lactose synthase (galactosyltransferase)
Lactose synthase transfers Galactose from UDP-galactose to glucose, releasing UDP.
Protein A is a β-D-galactosyltransferase, and is found in a number of body tissues. Protein B is found only in lactating mammary glands. It is α-lactalbumin, and its synthesis is stimulated by the peptide hormone, prolactin.
