stu chap 15 glycolysis 2013

Fundamentals of Biochemistry

Fourth Edition

Chapter 15Glucose Catabolism

Glycolysis

Copyright © 2013 by John Wiley & Sons, Inc. All rights reserved.

Donald Voet • Judith G. Voet • Charlotte W. Pratt

Glycolysis –Central to carbohydrate metabolism but works in conjunction with other pathways

Glycolysis

A. 1st step in glucose metabolism

B. Ultimate goal is to make ATP from glucose

C. Overall:

glucose + 2 ADP + 2 NAD+ + 2 Pi 2 pyruvate + 2 ATP + 2 NADH + 2 H2O + 2 H+

Glycolysis

Key Points

1. Energya.

glucose G-6-PF-6-P F-1,6-bisP

b. 1,3-bisphosphoglycerate 3-phosphoglycerate (x 2)PEP pyruvate (x 2)

c. glyceraldehyde 3-P 1,3-bisphosphoglycerate (x 2)

Glycolysis

Key Points

2. Carbon Compounds

Glycolysis

Key Points

3. Control PointsEnzyme Activator Inhibitor

 a. glucose G-6-P hexokinase ------- G-6-P

b. F-6-P F-1,6-bisP phosphofructokinase-1 F-2,6-bisP citrateAMP,ADP ATP

c. PEP pyruvate pyruvate kinase F-1,6-bisP ATP acetylCoAfatty acids

phosphorylation

 Know these enzymes

Glycolysis

Key Points

4. Glycolysis occurs in cell cytosol

5. Phosphorylation of glycolytic intermediates is importanta. helps keep compounds in cellb. ATP formation coupled to breakdown of some

phospho compoundsc. Phosphoryl group important for enzyme binding.

The two phases of glycolysis

2

2

2

2

2

The two phases of glycolysis

The two phases of glycolysis

Glycolysis

Let’s look at the reactions of glycolysis

Look for steps where

-- energy compounds are consumed or made

-- regulation occurs

-- other notes as we discuss them

Step 1

Phosphorylation of Glucose

Hexokinase

Step 2

Phosphoglucose Isomerase Mechanism

Phosphoglucose Isomerase Mechanism

Phosphoglucose Isomerase Mechanism

Phosphoglucose Isomerase Mechanism

Phosphoglucose Isomerase Mechanism

Phosphoglucose Isomerase Mechanism

Phosphoglucose Isomerase Mechanism

Step 3

The committed step

Actually Phosphofructokinase-1

Step 4

Step 5

Step 6

The glyceraldehyde 3-phosphate dehydrogenase reaction

Step 7

Substrate level phosphorylation

Arsenate can act as an uncoupler.

AsO43- similar to…..

Step 6Arsenate reacts like in this reaction

Step 7

Substrate level phosphorylation

Step 8

Step 9

Step 10

Pyruvate Kinase Reaction

Pyruvate Kinase Reaction

Pyruvate Kinase Reaction

Glycolysis

2

2

2

2

2

What is the fate of pyruvate?

Aerobic conditions:

Anaerobic conditions:

Possible Fates of Pyruvate

Anaerobic conditions

Anaerobic conditions -- yeast

Anaerobic conditions: 2 ATP/glucose

Aerobic conditions: many more ATP (~30-32 ATP/glucose)

The 2,3 bisphosphoglycerate Story

How does glycolysis affect O2 binding to Hb?

Regulation

General Aspects

Reactions at equilibrium are essentially substrate-limited (increase [S] increases vo).

Regulation occurs at reactions far from equilibrium.

Reactions far from equilibrium are enzyme-limited.– Rate of reaction depends on enzyme activity.

Regulation

Enzyme Limited Reactions

Rate of a sequence of reactions depends on activity of enzymes at “rate limiting steps”.

These reactions are largely irreversible steps.

These steps are often targets for regulation

a) Allosteric regulation

b) Can be hormonal regulation

c) Reversible covalent modification

Regulated enzymes often at “committed steps” of pathways

Regulation of Glycolysis

Hexokinase

1) 1st step

2) Inhibited by Glucose-6-phosphate.

Regulation of Glycolysis

Pyruvate Kinase

1) Last step

2) Feedforward activation by Fructose-1,6-bisphosphate

3) Inhibited by ATP, long chain fatty acids, acetyl CoA (Ala)

4) Phosphorylation by ATP (liver enzyme)

Feedforward Activation

2

2

2

2

2

Regulation of Glycolysis

Phosphofructokinase-1

1) 3rd step -- Committed step

2) Most highly regulated enzyme

3) Inhibited by citrate and ATP

4) Stimulated by ADP and AMP

5) Stimulated by Fructose-2,6-bisphosphate

(in liver– the main glucose control organ in body)

Regulation

Substrate Cycling

Substrate cycling can influence net flux.

phosphatase)

Energetics

Energetics

What about other sugars?

We get glucose from starches and sucrose.

We also ingest other sugars

How do other sugars fit in with glycolysis?

Fructose metabolism is simple in muscle, more complex in liver

What Happens after Glycolysis?

One Application of Your Glycolysis Knowledge

Positron Emission Tomography(PET Scans)

Used to study tissue metabolism

Especially for identifying cells with abnormal metabolism, i.e., cancers and epileptic regions.

2-deoxy-2-(18F)fluoro-D-glucose

– 18F half-life is 110 minutes.

p. 555

Figure 1. “The Case of the Forgetful Professor”Brain scans from a patient with transient epileptic amnesia. (A) Fluid-attenuated inversion-recovery MRI scanning during a prolonged amnestic episode reveals hyperintensity in the left hippocampus. (B) 2-Fluoro-2-[18F]-deoxy-d-glucose PET

scanning during the same episode shows hypermetabolism localized to the left anterior hippocampus. (C) Metabolism in the left anterior hippocampus returned to normal 1 month later. Abbreviation: L = left.

PET Scans and2-deoxy-2-(18F)fluoro-D-glucose

Behaves very similarly to glucose.

Absorbed by cells and phosphorylated by hexokinase.

Distribution “the same” as glucose in tissues.

But what about step 2 of glycolysis????

Fig. 18-8, p. 541

Isomerization of Glucose-6-P to Fructose-6-P

PET Scans and2-deoxy-2-(18F)fluoro-D-glucose

So 18FDG, taken up by cells, phosphorylated and .

What happens to this radioactive glucose analog?

PET Scans and2-deoxy-2-(18F)fluoro-D-glucose

18F decays by losing a positron.(a positive antimatter particle from a

proton.)

Converts a nuclear proton into a neutron resulting in….

PET Scans and2-deoxy-2-(18F)fluoro-D-glucose

18O- picks up a proton from surrounding aqueous environment forming glucose (with “heavy” but non-radioactive oxygen).

Differences between Slow-twitch muscle and Fast-twitch muscle