Lecture 20 - Pentose Phosphate Pathway and NADPH Flashcards
Where is the Pentose Phosphate Pathway?
Occurs in cytosol of cells Major tissue where PPP is active include: - adipose tissue - mammary gland - liver - adrenal cortex - RBC - testes PPP has little activity in skeletal muscle
Role of Pentose Phosphate Pathway
Provide a way to interconvert 5-C and 6-C sugars
Produces NADPH
Produce 5-C suars for nucleotide synthesis
- e.g. ATP, RNA, DNA
Metabolise dietary 5-C sugars
Important for producing cellular reducing equivalents
What are the two pathways of the Pentose Phosphate Pathway?
Oxidative
- oxidises glucose-6-phosphate to ribose-5-phosphate
- generates NADPH
Non-oxidative
- series of C transfer reactions producing glycolytic intermediates
- converts 5-C sugar phosphates to hexose phosphate sugars and vice versa
- net result is the synthesis of 2 hexoses and 1 triose from 3 pentoses
Control of the Pentose Phosphate Pathway
Oxidative
- level of NADP+
- glucose-6-phosphate dehydrogenase is rate limiting step
- if more NADP+ than NADPH then G6P dehydrogenase activity elevated and vice versa
Non-oxidative
- availability of substrates
For both pathways, flow of PPP depends on need for NADPH, ribose-5-phosphate and ATP
Reactive Oxygen Species
Free radical that accumulates in cells
Reacts with DNA, lipids in membranes and proteins to cause damage
What happens when the cell needs more ribose-5-phosphate than NADPH in the PPP?
Needed for rapidly dividing cells
Once ribose-5-phosphate being synthesised, cell shuts down rest of non-oxidative pathway in order to limit R5P consumption
R5P then used for nucleic acid synthesis
What happens when the cell requires more reducing power in the form of NADPH?
Needed for fatty acid/steroid synthesis
Stimulates non-oxidative pathway to produce fructose-6-phosphate
This is then converted back to glucose-6-phosphate via enzyme
This starts the oxidative pathway over and more NADPH produced
