Pentose Phosphate Pathway - General Flashcards
What are the 2 main biological objectives of the PPP?
- Generate 5-carbon sugars.
- Can be used to create nucleic acids.
- Generate reducing agents in the form of NADPH.
Where does the PPP occur in the cell?
In the cytosol.
What are the two phases of the PPP?
The oxidative phase and the non-oxidative phase.
The oxidative phase starts with this sugar:
Glucose-6-P.
For every glucose-6-P that enters the pathway, how many NADPH are produced?
2.
What are the 2 major products of the PPP that are produced in phase 1 and 2?
- Oxidative: NADPH
- Non-oxidative: ribose-5-P
What is the first enzyme in the oxidative part of the PPP?
Glucose-6-P dehydrogenase.
What primarily regulates the PPP?
Levels of NADP+
Which sugar can be metabolized by both glycolysis and the PPP? Why?
Glucose-6-P. It can enter either pathway because both are located in the cytosol.
Other than NADP+, the cell’s need for what other two things decide whether G-6-P will enter the PPP or glycolysis?
- Ribose-5-P
- ATP
Mode 1: the need for ribose-5-P is greater than the need for NADPH. What will happen to the glucose-6-P? When is this a situaton that could happen?
Most of the glucose-6-P will be metabolized through glycolysis to fructose-6-P and glyceraldehyde-3-P. These can then enter the non-oxidative portion of the PPP. This could occur in cells that are rapidly dividing and need to synthesize a lot of DNA.
Mode 2: the need for NADPH and ribose-5-P are about the same. What will happen to the glucose-6-P?
Glucose-6-P will be metabolized through the oxidative portion of the PPP, producing NADPH. The ribulose-5-P that is produced will then be converted to ribose-5-P in the non-oxidative portion.
Mode 3: the need for NADPH is greater than that for ribose-5-P. Where does this occur? What will happen to the glucose-6-P? Where can the metabolites of this mode be funneled and using what sugar?
This occurs in the liver. Glucose-6-P is converted to ribulose-5-P by the oxidative portion of the PPP which will result in NADPH production. The ribulose-5-P produced can then be easily converted to ribose-5-P, which can then be converted to fructose-6-P and glyceraldehyde-3-P by the non-oxidative reactions of the PPP. The last two metabolites can then be used in gluconeogenesis to produce glucose-6-P.
Mode 4: both NADPH and ATP are required. What will happen to the glucose-6-P? What pathway will the metabolites of these reactions funnel into and how?
Glucose-6-P will be oxidized through the PPP to obtain NADPH and ribulose-5-P. The ribulose-5-P will be converted to fructose-6-P and glyceraldehyde-3-P by the non-oxidative portion of the PPP. These metabolites can then enter glycolysis and be metabolized to pyruvate producing ATP.
