Pentose, Galactose and Fructose
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What are the 2 parts of the Pentose pathway?
- Oxidative Phase: Get NADPH
- Non-Oxidative Phase: Reshuffling
What is Ribose-5-P used for?
What reactions/enzymes form NAPDH?
- G6P --> 6-Phosphoglucanolactone (G6P DH)
- 6-Phophogluconate --> Rubulose-5-Phosphate (6-phosphogluconate DH)
What occurs due to a deficiency in G6P DH?
- Low NAPDH concentration
- Manifested in RBC
- Hemolytic anemia
What is NAPDH directly used for in RBCs?
To reduce glutathione and allow the breakdown of H2O2 to H2O
Where do the molecules of the pentose pathway re-enter glycolysis?
What enzyme's activity is measured in order to determine thiamine deficiency?
If only NADPH is needed, how does the pentose pathway proceed?
- Oxidative reactions to make NADPH
- Nonoxidative reactions to make F6P and GAP
- THEN, these are remade into G6P to redo again
If NADPH and ribose-5-P are needed, how does the pentose pathway proceed?
- Oxidative reactions make NADPH and ribulose-5-P
- Ribulose 5-P is converted to ribose-5-P
If only ribose-5-P is needed, how does the pentose pathway proceed?
Nonoxidative reactions only - in reverse
What inhibits G-6-P dehydrogenase?
If NADPH and pyruvate are needed, how does the pentose pathway proceed?
- Normally through oxidative and non-oxidative
- Then continues through glycolysis upon formation of F6P and GAP
What is the structure of sucrose?
Glucose (alpha 1,2) Frucose
What is the structure of lactose?
Galactose (beta 1,4) Glucose
What enzyme function is seen in frucose, galactose and glucose metabolism?
An initial kinase that sequesters the molecule in the cell
Where do the products of frucose matabolism enter glycolysis?
What transporter is used to transport fructose into the liver?
- Deficiency: Fructokinase
- Benign, asymptomatic
- 90% is eventually metabolized
Describe fructose intolerance:
- Deficiency: Aldolase B
- Build up of F-1-P
- Inhibits gluconeogenesis and glycogenolysis
- Causes: Hypoglycemia and lactic acidosis
What is lactose made of in the mammary gland and using what enzyme?
- Glucose + UDP-Galactose
- Enzyme: Lactose synthase
What are the final products of galactose metabolism and where do they go?
- Glucose-6-P --> glycolysis
- Glucose --> other tissues
How is glucose formed from glucose-6-P in the metabolism of galactose?
Describe non classical galactosemia
- Deficiency: Galactokinase
- Causes: Build up of galactose
- Result: Formation of cataracs due to build up of galactitol
Describe classical galactosemia:
- Deficiency: Galactose-1-P Uridylyltransferase
- Causes: Accumulation of galactose-1-P
- Result: Severe neurological effects and liver damage
What 2 enzymes do the reshuffling during nonoxidative phase of the pentose pathway?
What cofactor is used during the non-oxidative phase and by who?
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