Pentose Phosphate Pathway

Question 1

What is the key thing to remember about the Pentose Phosphate Pathway?

Answer 1

It produces NADPH

Question 2

What is another name for the Pentose Phosphate Pathway?

Answer 2

Hexose Monophosphate Pathway

Question 3

True or false: NAD+ is interchangeable with NADP+ and NADH is interchangeable with NADPH.

Answer 3

False

Question 4

What sorts of pathways tend to require NADPH and ATP?

Answer 4

Endergonic pathways like fatty acid biosynthesis and cholesterol synthesis

Question 5

Which is an ATP producer (synthesizes ATP), NADH or NADPH?

Answer 5

NADH

Question 6

Which is an ATP utilizer (uses ATP), NADH or NADPH?

Answer 6

NADPH

Question 7

What is the ratio of [NAD+] to [NADH] maintained in cells? What does this favor, reduction or oxidation?

Answer 7

1000:1 ; favors metabolic oxidation and the synthesis of ATP

Question 8

What is the ratio of [NADP+] to [NADPH] in cells?

Answer 8

1:100 ; favors metabolic reduction

Question 9

What pathway maintains the ratio of NADP+ to NADPH in cells?

Answer 9

Pentose Phosphate (or Hexose Monophosphate) Pathway

Question 10

Which tissues are rich in Pentose Phosphate Pathway enzymes?

Answer 10

Lipid biosynthesis tissues such as liver, adipose tissue, mammary glands, and adrenal cortex.

Question 11

What percentage of liver glucose oxidation occurs via the Pentose Phosphate Pathway (rather than glycolysis)?

Answer 11

30%

Question 12

What are the products of the Pentose Phosphate Pathway?

Answer 12

1) 6 NADPH
2) 6 H+
3) 3 CO2
4) 2 F6P
5) GAP

Question 13

What are the reactants in the net reaction for Pentose Phosphate Pathway?

Answer 13

1) 3 G6P
2) 6 NADP+
3) H20

Question 14

Which final products of the Pentose Phosphate Pathway are produced in the first stage of the pathway?

Answer 14

6 NADPH + 6H+ + 3 CO2

Question 15

What is the product of the first stage of the pathway that is converted to either ribose-5-phosphate or Xu5P?

Answer 15

Ribulose-5-Phosphate

Question 16

What are the ribose-5-phosphate and Xu5P or the second stage of the pathway converted to in the third stage?

Answer 16

2 F6P and 1 GAP

Question 17

Which stages of the Pentose Phosphate Pathway are freely reversible? What controls these pathways?

Answer 17

Stages 2 and 3; the needs of the cell (concentrations)

Question 18

Which stage of the Pentose Phosphate Pathway is not reversible?

Answer 18

Stage 1

Question 19

What controls almost all of stage 1 of the Pentose Phosphate Pathway? How does it work?

Answer 19

The enzyme G6PD (G-6-P Dehydrogenase); it is specific for NADP+ and inhibited by NADPH.

Question 20

True or false: G-6-D Dehydrogenase is inhibited by NADP+.

Answer 20

False; it is specific for NADP+ and inhibited by NADPH

Question 21

What are the two main products of the Pentose Phosphate Pathway?

Answer 21

ribose-5-phosphate (R5P) and NADPH

Question 22

What happens when NADPH need is greater than R5P need in nucleotide biosynthesis?

Answer 22

R5P is converted to glycolysis intermediates GAP and F6P, which are consumed in glycolysis or recycled in gluconeogenesis to form G6P, which can be used in the Pentose Phosphate Pathway to form NADPH.

Question 23

What is ribose-5-phosphate used in?

Answer 23

Any kind of tissue repair, clotting, and any production of genetic material (DNA).

Question 24

True or false: Glucose-6-phosphate dehydrogenase is strongly inhibited by NADP+.

Answer 24

False; it is strongly inhibited by NADPH

Question 25

What is the key enzyme in the control of the PPP?

Answer 25

Glucose-6-phosphate dehydrogenase (G6PD)

Question 26

What is the key regulator of G6PD (and, therefore, of the PPP?

Answer 26

Availability of [NADP+] (regulated by substrate availability)

Question 27

What happens when R5P need is greater than NADPH need?

Answer 27

F6P and GAP are diverted from glycolysis for R5P synthesis.