Lecture 3 - Pentose Phosphate Pathway Flashcards
What are the functions of the pentose phosphate pathway?
1) Produce NADPH that is needed for reductive biosynthesis or to counter damaging effects of oxygen radicals
2) Make pentoses
What are the 2 phases of the pentose phosphate pathway and what are their functions?
1) Oxidative phase - production of energy and pentoses
2) Non-oxidative phase - rearrangement of pentoses back to hexoses
Where are pentoses made and what are they used for?
- Made in bone marrow/skin and intestinal mucosa
- Used for RNA/DNA and coenzymes
What is the first step of the oxidative phase of the pentose phosphate pathway?
Glucose-6-phosphate is converted to gluconolactone-6-phosphate
Enzyme of step 1 of oxidative phase
Glucose-6-phosphate dehydrogenase
Cofactors of step 1 of oxidative phase
NADP+ -> NADPH + H+
Delta G of step 1 of oxidative phase
-0.4 kJ/mol
What happens in the second step of the oxidative phase of the pentose phosphate pathway?
Gluconolactone-6-phosphate is converted to gluconate 6-phosphate
Enzyme of step 2 of oxidative phase
Lactonase
Cofactor of step 2 of oxidative phase
H2O in
Delta G of step 2 of oxidative phase
-20.5 kJ/mol
What happens in the third step of the oxidative phase of the pentose phosphate pathway?
Gluconate 6-phosphate is converted to ribulose 5-phosphate
What happens in the fourth step of the oxidative phase of the pentose phosphate pathway?
Ribulose 5-phosphate is converted to ribose 5-phosphate
Enzyme of step 3 of oxidative phase
Gluconate 6-phosphate dehydrogenase
Enzyme of step 4 of oxidative phase
Ribose-phosphate isomerase
Cofactors of step 3 of oxidative phase
- NADP+ -> NADPH + H+
- CO2 out
What happens in the first step of the non-oxidative phase of the pentose phosphate pathway?
Xylulose 5-P is converted to ribulose 5-P, which is converted to ribose 5-P
What happens in the second step of the non-oxidative phase of the pentose phosphate pathway?
Xylulose 5-P and ribose 5-P are converted to Glyceraldehyde 3-P and sedoheptulose 7-P
Enzyme of step 1 of non-oxidative phase
Ribose 5-P epimerase and then ribose-P isomerase
Enzyme of step 2 of non-oxidative phase
Transketolase
Cofactor of step 2 of non-oxidative phase
TPP
Transketolase has a similar reaction mechanism to _____ because _____
- Pyruvate dehydrogenase
- It contains TPP
What happens in the third step of the non-oxidative phase of the pentose phosphate pathway?
Sedoheptuloase 7-P and glyceraldehyde 3-P are converted to fructose 6-P and erythrose 4-P
Enzyme of step 3 of non-oxidative phase
Transaldolase
What happens in the fourth step of the non-oxidative phase of the pentose phosphate pathway?
Erythrose 4-P and xylulose 5-P are converted to fructose 6-P and glyceraldehyde 3-P
Enzyme of step 4 of non-oxidative phase
Transketolase
What happens in the fifth step of the non-oxidative phase of the pentose phosphate pathway?
Glyceraldehyde 3-P is converted to fructose 6-P (all the same steps of glycolysis except reversed)
What happens in the sixth step of the non-oxidative phase of the pentose phosphate pathway?
Fructose 6-P is converted to Glc 6-P and the cycle continues
Enzyme of step 6 of non-oxidative phase
Phosphogluco isomerase
