Pentose phosphate pathway

The stoichiometry of NADPH to ribose 5-P in the pentose phosphate pathway is A. 1:2 B. 4:1 C. 3:1 D. 2:1 E. 1:1

2:1

One of the principal functions of the pentose phosphate pathway is to A. maintain the ratio of NADPH/NADP+ at a very high level in the cytosol B. produce fructose-6-phosphate C. metabolize galactose D. metabolize glucose completely to carbon dioxide E. maintain the ratio of NAD+/NADH at a very high level in the cytosol

A. maintain the ratio of NADPH/NADP+ at a very high level in the cytosol

Pentose phosphate pathway-

Also known as the pentose phosphate shunt produce NADPH (Key detoxification sugars

Products of the metabolism of glucose-6-phosphate include or are incorporated into: A. glycogen B. acetyl-CoA C. DNA and RNA D. All the above

D. All the above

Pentose Phosphate Pathway

Primary role is production precursor metabolites, NADPH Also known as the pentose phosphate shunt ● Utilizes glucose 6-phosphate ● One of the main functions of the pathway is to reduce NADP+ to produce NADPH ○ Phosphorylated form of NADH ○ Coenzyme that provides reductive power for many biosynthetic reactions (Key biosynthetic reducing power) ○ Needed in the synthesis of steroids, fatty acids, and for cellular detoxification ● Can be used to convert glucose into a variety of different sugars ○ Example ■ Pentose sugars that are used in synthesis of DNA and RNA

Which sugar produced by the pentose phosphate pathway is used in the synthesis of RNA and DNA? A. ribose 5-phosphate B. ribulose 5-phosphate C. fructose 6-phosphate D. xylulose 5-phosphate

a

When NADPH is in high demand by the cell, which two gluconeogenic intermediates produced by the pentose phosphate pathway can be used to resynthesize glucose 6-phosphate? A. fructose 6-phosphate and fructose 1,6-bisphosphate B. dihydroxyacetone phosphate and fructose 6-phosphate C. glyceraldehyde 3-phosphate and fructose 6-phosphate D. glyceraldehyde 3-phosphate and fructose 1,6-bisphosphate

c

Mode 2: NADPH and Ribose 5-Phosphate are both needed

○ Enters the pathway via the oxidative phase ○ NADPH is produced from the oxidative phase ○ The non-oxidative phase proceeds to obtain the Ribose 5-Phosphate

Mode 3: NADPH is greatly needed

○ Only occurs in times of high cellular energy ○ When the cell is going through heavy biosynthesis ○ Oxidative phase occurs to produce NADPH ○ Non-oxidative phase proceeds to obtain Fructose 6-Phosphate and Glyceraldehyde 3-Phosphate ○ These substrates can be funneled through the gluconeogenic pathway to produce more glucose 6-phosphate ○ These new glucose 6-phosphate can again be used to produce more NADPH

Mode 4: NADPH and ATP are needed

○ Oxidative phase occurs to produce NADPH ○ Non-oxidative phase proceeds to obtain Fructose 6-Phosphate and Glyceraldehyde 3-Phosphate ○ These substrates can be funneled through the glycolysis to produce ATP ○ Further proceeds to Krebs cycle and ETC

Mode 1: Ribose 5-Phosphate

○ Step 1: Production of Fructose 6-Phosphate and Glyceraldehyde 3-Phosphate via glycolysis ○ Step 2: Fructose 6-Phosphate and Glyceraldehyde 3-Phosphate come together to produce Ribose 5-Phosphate

Oxidative

● Glucose 6-Phosphate goes through two oxidation ● Decarboxylation of Glucose 6-Phosphate results in Ribulose 5-Phosphate ● 2 NADP+ are reduced to 2 NADPH ● CO2 is also released

Non-oxidative

● Ribulose 5-Phosphate can be converted into ○ Ribose 5-Phosphate ○ Xylulose 5-Phosphate ○ Sedoheptulose 7-Phosphate ○ Fructose 6-Phosphate ○ Erythrose 4-Phosphate ○ Glyceraldehyde 3-Phosphate