5D- PPP, Fructose and Galactose Flashcards
How does dietary frustose enter the epithelial cells?
Fructose enter epithelial cells and other types of cell by facilitated diffusion on the GLUT V transporter
What are the 2 mechanisms by which fructose can enter the glycolosis pathway?
Why is fructose considered to be more unregulated in metabolism compared to glucose?
Since it gives the products DHAP and G3P and can enter glycolysis, they skip over the rate limiting step of PFK-1 in glycolysis.
What would accumulate in the liver and kidney if a pt had an aldolase B deficeincy?
fructose 1-phosphate
What would be depleted in the liver and kidney if a pt had a deficiency in aldolase B?
free phosphate stores. theyre all being used for the accumulating F1P
How would the [glucose] in the blood be for a pt with an aldolase B deficiency?
Hypoglycemia results from inhibition of glycogenolysis and gluconeogenesis this result in lactic acidosis
What is the presentation of patients with a deficiency of fructokinase?
Fructose will accumulate in the urine and is detected as a reducing sugar that gives the indication of falsely high glucose reading
This condition is benign because no toxic metabolites of fructose accumulated in the liver and patient remains nearly asymptomatic.
What is the overall reaction of the pylol pathway?
glucose + NADPH –> sorbitol (pylol) + NADP + NAD+ –> fructose + NADH
Why is the conversion of glucose to sorbitol bad clinically?
Aldose reductase can lead to major problems in the lens of the eye, where it is responsible for the production of sorbitol from glucose and galactitol from galactose.
In diabetes when glucose and galactose is high, this reaction is pushed forward in the eye. The conversation to fructose is slow and the increased concentration of sorbitol and galactose alcohols are synthesized in the lens more rapidly than they are removed, leading to increased intraocular pressure and the glycosylaton of the lens protein which will cause an opaque cloudiness of the lens known as cataract.
What is “classical” galactosemia?
It is caused by a deficiency of galactose 1-phosphate uridylyltransferase.
Increased amount of galactose 1-P & UDP glucose
Galactose 1 P + UDP glucose→ UDP galactose + Glucose 1-P
Galactose 1-phosphate accumulated in tissues and galactose is elevated in the blood and urine
One serious problem is irreversible mental retardation
What is “nonclassical” galactosemia?
More rare
Deficiency of galactokinase
Galactose + ATP →Galactose 1-p +ADP via galactokinase
Increase amount of galactose since galactokinase isn’t working
Galactosemia and galactosuria occur but galactose 1 phosphate is not formed
In the oxidative phase of the PPP, what is produced?
Pentose Phosphate pathway is a bypass route around the first stage of glycolysis that generate NADPH and ribulose 5-phosphate & non oxidative pathway will generate two fructose 6-P and one glyceraldehyde-3-P to go into glycolysis
What are the products of the nonoxidative phase of the PPP?
Ribose 5-phosphate & xylulose 5-phosphate undergo reactions, catalyzed by transketolase & transaldolase that transfer carbon units, ultimately forming two fructose 6-phosphate(transaldolse) and one glyceraldehyde 3-phosphate (transketolase)
What is the overall reaction of the PPP?
Three glucose-6-P + 6 NADP+ → three ribulose-5-p + 3 CO2+6 NADPH
Three ribulose 5-p → 2xylulose 5-P + ribose 5-P
Two xylulose-5-p + ribose 5-P→ two fructose 6-P + glyceraldehyde-3-P (goes into glycolysis)
What is the relationship between tiamine and transketolase?
Transketolase requires thiamine.
Transketolase activity of RBC is used to measure thiamine nutritional status and diagnose the present of thiamine deficiency
Both are reversible reaction.
Give a general schema of the G6PDH and glutathione pathway
