Glucose and Fructose Metabolism Flashcards
Why is glucose used as fuel?
Yields a good amount of energy
Efficiently stored in polymeric form
Some tissues meet their energy needs on glucose only
What three organs/cells use glucose a sole energy source?
Brain
Red blood cells
Sperm
One molecule of glucose in the glycolytic pathway produces…?
2 ATP
2 NADH
2 Pyruvate
How is glucose transported into the cell?
Facilitate transport mediated by 5 glucose transporters
What is the role of insulin?
Increases number and activity of glucose transporters
GLUT1-5
Insulin is not required for glucose transport into what organ?
Liver
What is the function of hexokinase?
First step of glycolysis, Phosphorylates glucose
Present in most tissues
Inhibited by Glucose-6-phosphate
What is glucokinase?
Enzyme that catalyzes first reaction of glycolysis
Present only in the liver, and is only active after a meal
Not inhibited by G6P (unlike hexokinase)
What is the function of phosphofructokinase-1?
Catalyzes third glycolytic reaction, Fructose-6-phosphate –> Fructose 1,6-bisphosphate
Regulated step
What things increase the activity of PFK-1?
AMP
ADP
Fructose-2,6-bisphosphate
What decreases the activity of PFK-1?
ATP
Citrate
H+
What is the function of pyruvate kinase?
Catalyzes the last reaction of glycolysis
Phosphoenolpyruvate –> Pyruvate
Key regulatory enzyme for glycolysis
What activates and inhibits pyruvate kinase?
Activators: F-1,6BP, Dephosphorylation
Inhibitors: ATP, phosphorylation, alanine
What is the Warburg effect?
Cancer cells carry out glycolysis at much higher rate than normal cells, even when oxygen is available
Principle behind PET scans
What are the fates of pyruvate under anaerobic conditions?
Ethanol - fermentation (plants)
Lactic Acid - humans
What is the fate of pyruvate under aerobic conditions?
Acetyl CoA in mitochondria
How is galactose produced and what is it metabolized to?
Product of lactose digestion
Metabolized to glucose-1-phosphate
What is the cause of galactosemia?
Defect in galactose-1-phosphate uridyltransferase
What problems are associated with galactosemia?
Galactose-1-Phosphate build up, toxic to liver
Galactitol build up, cataracts and CNS damage
How is galactosemia treated?
Removal of lactose and galactose from diet
Describe fructose metabolism.
More rapidly metabolized than glucose
Phosphorylated than cleaved to DHP and glyceraldehyde by aldolase B
What causes the accumulation of F-1-P in fructose metabolism?
The activity of fructokinase exceeds aldolase B.
More F1P is produced than can be broken down
What does accumulation of F-1-P cause?
Inhibits ox-phos in the liver and causes damage
Inhibiting ox-phos in the liver due to fructose metabolism causes build up of ADP and AMP, what will this result in?
Catabolism of ADP and AMP will result in high concentrations of uric acid which can cause gout
How does fructose metabolism affect PFK-1?
Bypasses the enzyme, which controls glycolysis
Leads to high levels of lactic acid and lipogenesis
What does Aldolase B deficiency cause?
Fructose intolerance
What does fructokinase deficiency cause?
Essential fructosuria
What reactions in glycolysis use ATP?
Hexokinase
Phosphofructokinase-1
What reactions in glycolysis produce ATP?
Phosphoglycerate kinase
Pyruvate kinase
What reaction in glycolysis produces NADH?
Glyceraldehyde-3-phosphate dehydrogenase
