Fructose and Galactose Flashcards
What is taken up by SGLT1?
- Galactose and glucose (Na+ dependent transporter)
What is fructose taken up by?
What kind of diffusion is involved?
GLUT-5
- Facilitated diffusion
What is the chemical formula for glucose and its isomers (galactose, fructose)?
C6 H12 O6
What transporter transports Glucose, galactose and fructose from the cell to the interstitium?
GLUT2
What is the major source of fructose from?
Sucrose
What breaks down Fructose to Fructose-1-Phosphate?
Fructokinase (found in liver)
- Requires ATP
What enzyme splits the 5 Carbon F1P into 2 3 carbon molecules; Glyceraldehyde and Dihydroxyacetone Phosphate?
Aldolase B
What enzyme converts Glyceraldehyde to Glyceraldehyde-3-phosphate?
Triokinase
What 2 molecules can fructose-6-phosphate be converted into which enters them into the glycolysis pathway?
- Glyceraldehyde-3-phosphate (via Glyceraldehyde, triokinase)
- Dihydroxyacetone Phosphate
Enzyme: Aldolase B
Why is the metabolism of fructose faster than that of glucose?
Fructose bypasses the rate limiting step of glycolysis (Phosphofructokinase 1)
What can hexokinase covert Fructose into?
F6P (only a small amount)
- Only really relevent if deficient in other enzymes
What is essential fructosuria due to a deficiency in?
Fructokinase
(Fructose cannot be converted to
What is hereditary Fructose Intolerance due to a deficiency in?
Aldolase B
What does hereditary Fructose Intolerance (aldolase B deficiency) result in?
- Build-up of F1P
- Depletion of ATP
- Decrease of Gluconeogenesis and glycogen breadown
- Hypoglycemia/vomitting
- Hepatomegaly (glycogen not broken down) -> Liver Failure
How may hereditary Fructose Intolerance (aldolase B deficiency) present?
Presents just after weaning from breast milk (no fructose in the milk)
- Failure to thrive
- Hypoglycemia (seizures)
- Enlarged liver -> failure
- Part of newborn screening panel
How is Hereditary Fructose Intolerance (aldolase B deficiency) treated?
- Avoid fructose, sucrose, sorbitol
Describe the Polyol pathway?
Glucose -> Sorbitol (NADPH-> NADP+)
Sorbitol -> Fructose (NAD+ -> NADH)
What enzyme converts Glucose to Sorbitol?
Aldose Reductase (Polyol pathway) - NADPH -> NAP+ also
What enzyme converts Sorbitol to Fructose?
Sorbitol dehydrogenase
- NAD+ -> NADH
Part of polyol pathway
Why is sorbitol to be avoided in those with Hereditary Fructose Intolerance?
It can be converted to fructose via sorbitol dehydrogenase (polyol pathway)
What is galactose converted into in order to be involved in glycolysis/gluconeogenesis or glycogen synthesis?
- Galactose 1-Phosphate
- > Glucose 1-Phosphate -> Glycogen
- Glucose 1 Phosphate Glucose 6-phosphate (ccan be used for glycolysis or glucose)
What enzyme converts galactose into galactose 1-Phosphate?
Galactokinase (ATP required)
What enzyme convers Galactose 1-Phosphate to glucose 1-Phosphate?
Galactose 1-Phosphate Uridyltransferase (GALT)
- Also requires UDP-Glucose
What does GALT require in order to convert Galactose 1-Phosphate to Glucose 1-Phosphate?
UDP-Glucose
