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
What is classic galactosemia due to a deficiency in?
Galactose 1-Phosphate Uridyltransferase (GALT)
What molecules builds up in classic galactosemia ?
Galactose 1-phosphate accumulates in cells and liver -> damage
- Galactitol accumulates in cells (polyol pathway, galactose broken down to it via aldose reductase)
How is classic galactosemia inherited?
Aut Recessive
What substance leads to cataracts in classic galactosemia?
Galactitol
When does classic galctosemia present, how does it?
- First few days of life, after milk consumption
Liver accumulates galactose/galacitol
- LF, jaundice, hepatomegaly
- Failure to thrive
Cataracts (due to galactitol)
How is classic galactosemia diagnosed?
Screening
- GALT enzyme activity assay
How is classic galactosemia treated?
Avoid galactose, no milk
What is galactokinase deficiency?
What does it lead to?
- Milder form of galactosemia
- Galactose not taken up by cells
- Accumulates in blood and urine
- Cataracts as a child/young adult (vision problems)
What does galactokinase break down?
Galactose into Galactose 1-Phosphate
requires ATP
Why are there not liver problems in galactokinase deficiency but there are with classic galactosemia?
- Liver is not depleted of phosphate in glactokinase deficiency