Glycolysis pathway Flashcards
glucose
glucose-6-phosphate
SGLUT1
Expressed in intestinal mucosa, kidney tubules
Co-transport: 1 molecule of glucose or galactose with 2Na
GLUT2
Expressed in: liver, pancreatic beta cells, small intestine, kidney.
Transports: glucose, galactose and fructose.
Low affinity-High capacity
Is the glucose ‘sensor’ in pancreatic beta cells.
GLUT4
Expressed in: Skeletal and cardiac muscles, adipocytes
Insulin-responsive
Transports glucose
high affinity
Hexokinase
Glucose+ATP –> Glucose-6-phosphate + ADP
∆G=-27KJ/mol
irreversible
Hexokinase I: km=0.03mM, most tissues, inhibited by G6P
Hexokinase II: km=0.3mM. In muscle, adipose tissue. Inhibited by G6P
In muscle: Fructose + ATP –> Fructose-6-phosphate + ADP –≥ glycolysis
Glucokinase
Glucose+ATP–> ADP+ glucose-6phosphate
km=5mM (blood conc.). In liver and pancreas. Not inhibited by G6P!
Glucokinase regulatory protein: bound to glucokinase in the cell nucleus. It is released into the cytoplasm when high blood glucose to catalyze the reaction.
Phosphofructokinase
fructose-6-phosphate + ATP (Mg++)–> fructose-1,6-bisphosphate+ ADP
∆G=-26 KJ/mol
commiting step to glucose metabolization
Inhibitors: ATP, citrate,phosphoenolyruvate
Activators (deinhibitor of ATP): ADP, AMP, cAMP, FBP, F2,6P, F6P, NH4+, Pi
Adenylate kinase
2ADP ATP + AMP
Fructokinase
Fructose + ATP –> Fructose-1-phosphate + ADP Fructose-1-phosphate (open chain)
- 1st reaction in fructose liver metabolism.
Fructose-1-phosphate aldolase
Fructose-1-phosphate –> glyceraldehyde
- 2nd reaction in fructose liver metabolism
- type b in liver: uses F-1-P
Glyceraldehyde kinase
Glyceraldehyde + ATP –> Glyceraldehyde-3phosphate + ADP –> Glycolysis
-3rd step in fructose liver metabolism
Alcohol dehydrogenase
Glyceraldehyde + NADH –> Glycerol + NAD+
-4th step in fructose liver metabolism
glycerol kinase
glycerol + ATP –> glycerol-3-phosphate + ADP
-5th step in fructose liver metabolism
glycerol phosphate dehydrogenase
Glycerol-3-phosphate+ NAD –> dihydroxyacetone + NADH
-6th step in fructose liver metabolism
triose phosphate isomerase
Dihydroxyacetone phosphate –> Glyceraldehyde-3-phosphate –> glycolysis.
7th and last step in fructose liver metabolism.
Fructose intolerance
genetic
Lack of F-1-P aldolase
-Symptoms: liver damage (jaundice), diarrhea, vomiting
-Buildup of F-1-P –> results in reduced ATP + Pi (in order to make ATP)
-treatment: don’t eat fructose
Galactokinase
Galactose + ATP –> Galactose-1-phosphate + ADP (irreversible)
1st step in galactose metabolism
Galactose-1-phosphate uridylyl transferase
Galactose-1-phosphate + UDP-glucose –> UDP-galactose + Glucose-1-phosphate
2nd step in galactose metabolism
UDP-galactose-4-epimerase
UDP-galactose –> UDP-glucose
-3rd step in galactose metabolism
phosphoglucomutase
Glucose-1-phosphate glucose-6-phosphate –≥ glycolysis.
Galactosemia, type 1
Uridylyl transferase deficiency
- Most common
- Symptoms: mental retardation, liver damage, cataract
- Treatment: removal of galactose and lactose from diet
- Worst type because of ATP + pi depletion
Galactosemia, type 2
galactokinase deficiency
Galactosemia, type 3
epimerase deficiency
Galactose making
G1P + UtP –> UDP glucose + PPi
PPi (inorganic pyrophosphatase) –>2Pi coupled with UDP-glucose (UDP-galactose-4-epimerase) –> UDP galactose
-UDP-galactose + Glucose (lactose synthase) –> Lactose
