The PPP

Question 1

What is a reduced cofactor in the pentose phosphate pathway?

Answer 1

NADPH

Question 2

Where does the PPP occur ?

Answer 2

The cytoplasm

Question 3

What are the two important uses of the produced NADPH?

Answer 3

Used for the reductive biosynthesis of lipids

As an antioxidant, fuels the reduction of glutathione which oxidation fuels the conversion of H2O2 to H2O (reducing oxidative stress)

Question 4

What compound protects Hb in RBC against oxidative damage?

Answer 4

Glutathione

Question 5

What is a consequence of deficiency of glucose 6 phosphate dehydrogenase?

Answer 5

Haemolytic anaemia (No NADPH to act as an antioxidant, RBC damaged)

Question 6

What is the first, determining step of the PPP?

Answer 6

G6P to
6-phosphogluconolactone.

Catalysed by glucose-6-phosphate dehydrogenase

Question 7

What 5C sugar is produced as a result?

Answer 7

Ribose-5-phosphate

Question 8

What does the PPP produce overall?

Answer 8

Converts 6C sugar to 5C sugar

2xNADPH

CO2

Question 9

What happens to ribulose 5 phosphate?

Answer 9

Undergoes reversible non-oxidative interconversions to produce sugars of differing lengths.

Question 10

What enzymes catalyse the interconversions of sugar?

Answer 10

Transketolases move 2C between molecules

Transaldolases move 3C between molecules

Question 11

What are 3C and 5C sugars used for?

Answer 11

3C - substrate of glycolysis

5C - synthesis of nucleotides

Question 12

What stimulates and inhibits G-6-P dehydrogenase?

Answer 12

NADP+ stimulates and NADPH inhibits

Question 13

Which enzyme regulates the oxidative PPP?

Answer 13

G-6-P dehydrogenase

Question 14

What regulates the non-oxidative phases of the PPP?

Answer 14

Freely reversible and so flux through them is controlled by the levels of their substrates and products. (i.e. the need and availability of different sugars).

Question 15

What occurs if many ribose sugars are required?

Answer 15

G-6-P will proceed down glycolysis to make fructose-6-phosphate and glyceraldehyde-3-phosphate.

Transketolase and transaldolase can then rearrange these sugars to make ribose-5-phosphate.

Question 16

What occurs if there is an equal need for NADPH and ribose sugars?

Answer 16

G-6-P will proceed through the oxidative reactions of the PPP generating NADPH and ribose-5-phosphate.

Question 17

What occurs if there is a need for high NADPH?

Answer 17

Glucose-6-phosphate will proceed through the oxidative reactions of the PPP to generate NADPH and R-5-P.

R-5-P will then go through the non-oxidative reactions to generate F-6-P and G-3-P.

These sugars return through the gluconeogenic pathway to make more G-6-P for the synthesis of more NADPH (starvation).