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17 Cards in this Set

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first thing that happens to fructose

and the enzyme that does it
gets phosphorylated to Fructose 1-phosphate

by Fructokinase
metabolism of Fructose 1-P
Aldolase B converts Fructose 1-P to


dihydroxyacetone phosphate (DHAP)

and

glyceraldehyde
what happens to the glyceraldehyde and DHAP evolved in the metabolism of Fructose
the DHAP launches into the glycolytic cycle

the glyceraldehyde is phosphorylated by Triose kinase

and follows on
why is fructose metabolized faster than glucose
its products enter the glycolytic cycle after PFK1, the major regulatory step
hereditary fructose intolerance is a defect in the gene
Aldolase B


no symptoms unless fructose is ingested

hypoglycemia
essential fructosuria

a deficiency in the enzyme __________
fructokinase

fructosuria

usu. benign- fructose in urine
many tissues can create fructose from glucose via the intermediate __________
sorbitol

thats where the sorbitol in cataracts comes from

they call it the Polyol pathway
in Hereditary Fructose Intolerance

how can eating fructose cause a hypoglycemic event?
defect in Aldolase B causes an accumulation of Fructose 1-phosphate

Fructose 1-P stimulates glycolysis via a feed-forward effect on pyruvate kinase

while simultaneously inhibiting glycogen phosphorylase

and tying up all the phosphate so there's not enough to drive gluconeogenesis
what is the main source of galactose in the diet
from lactose
first step in the metabolism of galactose, and the enzyme
phosphorylation to galactose 1-phosphate

by the enzyme galactokinase
in galactose metabolism, what does Galactose 1-P react with

and what is the product of the reaction
UDP-glucose

via the enzyme galactose 1-phosphate uridyl transferase


the product of the reaction is Glucose 1-phosphate, which can be converted to Glc 6-P by phosphoglucomutase
in galactose metabolism

what becomes of the UDP-galactose formed in the transformation of Galactose 1-P to Glucose 1-P
the UDP-galactose is converted to UDP-glucose again by an enzyme called

4-epimerase
what can result from Galactokinase deficiency
galactosemia

galactosuria

galacticol, the sugar alcohol, can accumulate in the lens of they eye, causing cataracts
classical galactosemia is a deficiency of what enzyme
galactose 1-phosphate uridyl transferase
deficiency of galactose 1-phosphate uridyl transferase can lead to
galactosemia, galactosuria and cataracts

AND liver damage and mental retardation as Gal 1-P accumulates and ties up all the organic phosphate
in lactose synthesis, what form is the galactose used
UDP-galactose
lactose synthase has two subunits

one is galactosyl transferase

one of them isn't even an enzyme but a modifier protein. What is its name and why is it interesting
alpha-lactalbumin

it is synthesized after childbirth in response to prolactin

alpha-lactalbumin combines with galactosyl transferase and lowers its Km for glucose from 1200 mM to 1 mM