The Pentose Phosphate Pathway

Question 1

what is the pentose phosphate pathway

Answer 1

It runs in parallel to glycolysis
* Takes place in the cytosol
* Largely anabolic – formation of important molecules
* Divided into oxidative and non-oxidative stages

Question 2

What are the end products of PPP

Answer 2

1. Nicotinamide adenine dinucleotide phosphate (N ADPH)
2. Ribose 5-phosphate C5H10O5

Question 3

What is the end product Nicotinamide adenine dinucleotide phosphate (N ADPH)

Answer 3

1.Coenzyme for reductive reactions e.g. synthesis of fatty acids, cholesterol, hormones
2.First line defence against oxidative stress

Question 4

What is the end product Ribose 5-Phosphate

Answer 4

1.Biosynthesis of nucleotides e.g. RNA, DNA
2.Biosynthesis of other amino acids

Question 5

what makes PPP unique

Answer 5

1. At no stage is ATP used or produced!
2. It is active in tissues where fatty acid synthesis occurs –
   adipose, mammary gland, adrenal cortex
3. One of the body’s main ways of producing molecules with reducing power (NADPH)
4. The 5 carbon sugar created, ribose, is used as the backbone of RNA and DNA

Question 6

what are the 2 main stages in the PPP

Answer 6

oxidative (irreversible) and non-oxidative stage (reversible)

Question 7

what is the first step in the oxidative stage

Answer 7

1. OIL RIG – Oxidation is loss!, Reduction is gain!
   * first stage oxidizes a 6 carbon sugar molecule, removing 1 carbon
   * Loss of electrons
   * This molecule (G6P) subsequently now has 5 carbons
   * 5 carbon sugars are known as a Pentose e.g. ribose and xylose

Question 8

what is the equation for the oxidative stage

Answer 8

Glucose 6-phosphate + 2NADP+ + H2O —–> Ribulose 5-phosphate + 2 NADPH + CO2 + 2H+

Question 9

what do you have after the oxidative stage

Answer 9

-1H2O
* +2 NADPH
* +1CO2

Glucose 6-phosphate dehydrogenase is the rate-limiting enzyme, controlled by the ratio of NADPH:NADP+

Question 10

what is NADPH

Answer 10

1. it is a co-enzyme/ co-factor
2. NADH is produced via glycolysis and the TCA cycle and Glucose 6-phosphate + 2H+
3. used to generate ATP via the ETC.
4. Functions primarily in catabolic reactions.
5. NADPH is produced via the PPP and used in anabolic reactions

Question 11

what is NADPH used as

Answer 11

1. Fight oxidative stress or used as a cofactor, via the
   donation of electrons and hydrogens for some enzymes
2. NADPH is required to synthesize larger molecules in anabolic pathways, i.e Cholesterol & fatty acids.

Question 12

what is the equation for the non-oxidative stage

Answer 12

Ribulose 5-phosphate —-> xylulose-5-phosphate + ribose-5-phosphate

Question 13

what is converted in the non-oxidative stage

Answer 13

xylulose 5-P and Ribose 5-P is converted into glyceraldehyde-3-P and fructose 6-P

Question 14

what is Ribose-5-Phosphate used in the formation of

Answer 14

nucleic acids, the building block of RNA & DNA

Question 15

what are the 2 ned products of PPP

Answer 15

NADPH (produced in oxidative stage) and ribose-5-phosphate (non-oxidative stage).

Question 16

what is the pathway in the PPP

Answer 16

Biosynthetic pathway to generate precursors for biosynthesis

Question 17

What is the starting molecule in the PPP

Answer 17

Glucose-6-phosphate

Question 18

what is the end product in the PPP

Answer 18

NADPH no ATP produced

Question 19

what Sugar intermediates generated in PPP

Answer 19

Pentose sugars (ribose, xylulose, ribulose)

Question 20

what does the end product enter into

Answer 20

enter into glycolysis