Pentose Phosphate Pathway

Question 1

pentose phosphate pathway aka

Answer 1

hexose monophosphoate shunt

Question 2

PPP is available to glucose in the…

Answer 2

cytosol

Question 3

2 products of PPP

Answer 3

1. pentose phosphates
2. NADPH

Question 4

pentose phosphates are needed for

Answer 4

synthesis of nucleic acids found in DNA and RNA and other nucleotides

Question 5

NADPH is needed for

Answer 5

important metabolic functions
1. biosynthesis of fatty acids
2. maintenance of reducing substrates in red blood cells necessary to ensure functional integrity of the cells
3. drug metabolism in liver

Question 6

what cells have high demand for NADPH?

Answer 6

cells active in fatty acid synthesis
EX: mammary gland, adipose tissue, adrenal cortex, liver
these tissues engage PPP by recycling pentose phosphates back to G6P to repeat cycle and have more NADPH

Question 7

oxidative reactions of PPP

Answer 7

dehydrogenase rxns
form NADPH from NADP+

Question 8

PPP also synthesizes

Answer 8

3, 4, 5, 6, and 7-carbon sugars

Question 9

PPP step 1

Answer 9

oxidizing G6P: 2 dehydrogenase rxns catalyzed by G6P dehydrogenase (G6PD) and 6-phosphogluconate dehydrogenase (6-PGD)

require NADP+ to NADPH

Question 10

G6P dehydrogenase reaction regulation

Answer 10

highly regulated
irreversible
strongly inhibited by
NADPH and fatty acid CoAs

Question 11

how is pentose phosphate formed?

Answer 11

decarboxylation of 6-phosphogluconate to form the pentose phosphate (ribulose 5-phosphate)
ribulose 5-phosphate is isomerized to ribose 5-phosphate

Question 12

pentose phosphate recycling

Answer 12

pentose phosphates recycled back to hexose phosphates through transketolase and transaldolase rxns

Question 13

why would we want to recycle pentose phosphates?

Answer 13

ensures production of NADPH as cycle repeats

Question 14

nonoxidative rxns of PPP

Answer 14

re-formation of G6P from pentose phosphates through transketolase, transaldolase, and hexose phosphate isomerase

Question 15

enzymes that catalyze complex reactions in which 3, 4, 5, 6, and 7-carbon phosphate sugars are interconverted

Answer 15

transketolase and transaldolase

Question 16

are transketolase and transaldolase rxns reversible?

Answer 16

YES!

Question 17

why is it important that transketolase and transaldolase rxns are reversible?

Answer 17

allows hexose phosphates to be converted directly into pentose phosphates
bypass the oxidative rxns!

used by cells that replicate rapidly and need pentose phosphates more use this option

Question 18

PPP activity in skeletal muscle

Answer 18

low activity
bc of limited demand for NADPH (fatty acid synthesis)
AND
bc muscles rely on glucose and fatty acids for energy metabolism

Question 19

G6P can enter which two pathways?

Answer 19

glycolysis OR PPP

Question 20

how do we decide where G6P goes?

Answer 20

1. cell’s need for energy (assess ATP/ADP ratio)
2. cell’s need for biosynthesis (assess NADP+/NADPH ratio)
   NADPH is usually higher