Topic 7: Hexose Monophosphate Shunt (HMPS)/Pentose Phosphate Pathway/Phosphogluconate Pathway Flashcards
What are all the names of this thing?
Hexose Monophosphate Shunt
Pentose Phosphate Pathway
Phosphogluconate Pathway
What are the two stages of HMPS?
Oxidative: Two step process that yields 2 NADPH and Pentose (5 C) from Glucose/Hexose (6 C)
Non-oxidative: Multi-step clusterfuck that takes 6 Pentoses and turns them into 5 Hexoses
What happens in Step 1 of Oxidative HMPS?
Glucose-6-Phosphate (product of Step 1 of glycolysis) via Glucose-6-Phosphate Dehydrogenase becomes 6-Phosphogluconate.
The aldehyde on glucose is oxidized. H20 is used.
Yields NADPH
What happens in Step 2 of Oxidative HMPS?
6-PG via 6-PGDH becomes Ribulose-5-Phosphate.
Yields NADPH, and CO2 (irreversible reaction).
Requires Mg++ as cofactor.
How the hell does the Non-oxidative HMPS work?
3 molecules Ribulose-5-phosphate is acted upon by two different enzymes, epimerase and isomerase, twice (for a total of 6 Pentoses used) to make two different molecules: Ribose-5-P and Xylulose-5-P.
By action of TRANSKETOLASE these enzymes swap carbons to eventually produce Fructose-6-Phosphate and Glyceraldehyde-3-Phosphate. (Products of Step 2 and Step 4 of glycolysis, respectively) These are converted BACK to Glucose for cycle to continue OR These can continue on with Glycolysis normally now.
NO ATP USED.
Why do HMPS?
NADPH (several fates) and Ribose (nucleotide synthesis)
What is NADPH used for?
Fat synthesis: adipose and lactating mammary glands
Steroid synthesis: gonads and adrenal cortex (corticosteroids)
Brain: Nitric Oxide/NO (neurotransmitter) synthesis
RBCs: VERY important for Antioxidant Defense System (GSH/GSSH)
Where are all the enzymes of HMPS located?
Cytosol
What tissues DON’T do HMPS very much?
Striated Muscle (cardiac and skeletal)
What Vitamin is essential for HMPS to work?
THIAMINE/B1 for Transketolase function
How many glycolytic intermediates does HMPS yield?
Each Cycle yields 2 Fructose-6-Phosphate and 1 Glyceraldehyde-3-Phosphate. There are TWO cycles so net yield is:
4 Fructose-6-Phosphate
2 GA-3-P
These can regenerate 5 Glucose-6-Phosphates or go on through glycolysis.
Why does Dr. Eng say HMPS takes 6 pentoses to make 5 hexoses?
Because the F-6-P + GA3-P which HMPS yields can be converted back to Glucose-6-phosphate but with a lot of other goodies as well.
6 Glucose-6-Phosphate + 12 NADP+ + 7H20 –> 5 Glucose-6-Phosphate + 6 CO2 + 12 NADPH + 12 H+ + Pi
Suck on that for a minute!
How many CO2 are made form each glucose molecule in HMPS?
1 CO2 per Glucose as opposed to 6 CO2 per glucose in glycolysis
