Lecture 17: Pentose Phosphate Pathway

What can glucose be used for?

1. Synthesis of structural polymers (ECM and cell wall plysaccharides)

2. Storage (Glycogen, starch, sucrose)

3. Oxidation via PPP (Ribose 5-phosphate)

4. Oxidation vis glycolysis (pyruvate)

What is Pentose?

Sugar with 5 carbons

Can be linear or cyclic

What is DNA?

Where genetic information is encoded.

Template for identical DNA molecules

What is a Nitrogenous base/nucleobase?

Adenine, Thymine, Guanine, Cytosine

What is a Nucleosid?

Ribose sugar AND Nitrogenous base

What is a Nucleotide?

Phosphate AND Sugar AND Nitrogenous base

What is this Nucleobase?

Adenine

What is this?

Guanine

What is this?

Cytosine

What is this?

Thymine

What is this?

Uracil

What is the purpose of the PPP?

Alternative pathway for glucose oxidation

What does the PPP yield?

2 NADH/glucose

Pentoses to synthesize nucleotides

Reduced cofactors to synthesize amino acids, fatty acids, sterols, etc

What is an important intermediate for the PPP?

Glucose 6-phosphate

What cells/tissues use the PPP?

Rapidly dividing cells (need more DNA)

Tissues that carry out fatty acid synthesis

Tissues that synthesize cholesterol and steroid hormones (liver, adrenal glands, gonads)

What reactions make up the PPP?

Oxidative and non-oxidative

What steps are irreversible?

1st and 3rd oxidative reactions

What steps are reversible?

nonoxidative reactions

What is Oxidative Step 1?

Glucose 6-phosphate to 6-phosphoglucono-delta-lactone.

Glucose 6-phosphate dehydrogenase (G6PD) Oxidizes and uses NADP+ as electron acceptor

What is Oxidative step 2?

6-phospho-glucono-delta-lactone to 6-phosphogluconate

LACTONASE does this

What is Oxidative step 3?

6-phosphogluconate forms ribulose 5-phosphate and NADPH

6-phosphogluconate dehydrogenase oxidizes and decarboxylates

What is Oxidative step 4?

Ribulose 5-phosphate to ribose 5-phosphate

Phosphopentose isomerase converts

What does nonoxidative phase of the PPP do?

Recycles pentose phosphates to glucose 6-phosphate

What is this?

Nonoxidative PPP reactions

What is the overall equation of the PPP?

What does the Reductive Pentose Phosphate pathway do?

Converts hexose phosphates to pentose phosphates

Reversal of the nonoxidative reactions of the pentose phosphate pathway

How is the PPP inhibited?

NADPH inhibits the PPP

Why does NADPH inhibit the PPP?

Concentrations of NADP+ and NADPH determine whether glucose 6-phosphate enters glycolysis or the PPP

If there is too much NADPH, glucose 6-phosphate can continue through Glycolysis