Lecture 3 - Pentose Phosphate Pathway

Question 1

What are the functions of the pentose phosphate pathway?

Answer 1

1) Produce NADPH that is needed for reductive biosynthesis or to counter damaging effects of oxygen radicals
2) Make pentoses

Question 2

What are the 2 phases of the pentose phosphate pathway and what are their functions?

Answer 2

1) Oxidative phase - production of energy and pentoses

2) Non-oxidative phase - rearrangement of pentoses back to hexoses

Question 3

Where are pentoses made and what are they used for?

Answer 3

• Made in bone marrow/skin and intestinal mucosa

- Used for RNA/DNA and coenzymes

Question 4

What is the first step of the oxidative phase of the pentose phosphate pathway?

Answer 4

Glucose-6-phosphate is converted to gluconolactone-6-phosphate

Question 5

Enzyme of step 1 of oxidative phase

Answer 5

Glucose-6-phosphate dehydrogenase

Question 6

Cofactors of step 1 of oxidative phase

Answer 6

NADP+ -> NADPH + H+

Question 7

Delta G of step 1 of oxidative phase

Answer 7

-0.4 kJ/mol

Question 8

What happens in the second step of the oxidative phase of the pentose phosphate pathway?

Answer 8

Gluconolactone-6-phosphate is converted to gluconate 6-phosphate

Question 9

Enzyme of step 2 of oxidative phase

Answer 9

Lactonase

Question 10

Cofactor of step 2 of oxidative phase

Answer 10

H2O in

Question 11

Delta G of step 2 of oxidative phase

Answer 11

-20.5 kJ/mol

Question 12

What happens in the third step of the oxidative phase of the pentose phosphate pathway?

Answer 12

Gluconate 6-phosphate is converted to ribulose 5-phosphate

Question 13

What happens in the fourth step of the oxidative phase of the pentose phosphate pathway?

Answer 13

Ribulose 5-phosphate is converted to ribose 5-phosphate

Question 14

Enzyme of step 3 of oxidative phase

Answer 14

Gluconate 6-phosphate dehydrogenase

Question 15

Enzyme of step 4 of oxidative phase

Answer 15

Ribose-phosphate isomerase

Question 16

Cofactors of step 3 of oxidative phase

Answer 16

• NADP+ -> NADPH + H+

- CO2 out

Question 17

What happens in the first step of the non-oxidative phase of the pentose phosphate pathway?

Answer 17

Xylulose 5-P is converted to ribulose 5-P, which is converted to ribose 5-P

Question 18

What happens in the second step of the non-oxidative phase of the pentose phosphate pathway?

Answer 18

Xylulose 5-P and ribose 5-P are converted to Glyceraldehyde 3-P and sedoheptulose 7-P

Question 19

Enzyme of step 1 of non-oxidative phase

Answer 19

Ribose 5-P epimerase and then ribose-P isomerase

Question 20

Enzyme of step 2 of non-oxidative phase

Answer 20

Transketolase

Question 21

Cofactor of step 2 of non-oxidative phase

Answer 21

TPP

Question 22

Transketolase has a similar reaction mechanism to _____ because _____

Answer 22

• Pyruvate dehydrogenase

- It contains TPP

Question 23

What happens in the third step of the non-oxidative phase of the pentose phosphate pathway?

Answer 23

Sedoheptuloase 7-P and glyceraldehyde 3-P are converted to fructose 6-P and erythrose 4-P

Question 24

Enzyme of step 3 of non-oxidative phase

Answer 24

Transaldolase

Question 25

What happens in the fourth step of the non-oxidative phase of the pentose phosphate pathway?

Answer 25

Erythrose 4-P and xylulose 5-P are converted to fructose 6-P and glyceraldehyde 3-P

Question 26

Enzyme of step 4 of non-oxidative phase

Answer 26

Transketolase

Question 27

What happens in the fifth step of the non-oxidative phase of the pentose phosphate pathway?

Answer 27

Glyceraldehyde 3-P is converted to fructose 6-P (all the same steps of glycolysis except reversed)

Question 28

What happens in the sixth step of the non-oxidative phase of the pentose phosphate pathway?

Answer 28

Fructose 6-P is converted to Glc 6-P and the cycle continues

Question 29

Enzyme of step 6 of non-oxidative phase

Answer 29

Phosphogluco isomerase