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Chapter 15 Glucose Catabolism + 16.4 Gluconeogenesis

Detailed notes on full chapter and mechanisms (will help with final reviews)

Course

Biochemistry/Lab (CHEM 3650)

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Nova Southeastern University

Academic year: 2022/2023

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Glycolysis Overview

• Glycolysis occurs in 10 steps.

– Steps 1-5 = energy investment

– Steps 6-10 = energy payoff

• Glucose (a six-carbon molecule) is broken

down into two 3-carbon molecules.

• Electron carriers are reduced.

First 5 Steps of Glycolysis

10 Steps of

Glycolysis

Let’s look at

each step...

Step 1: Hexokinase Reaction

• Kinases are enzymes that phosphorylate

molecules.

• ATP is invested; ATP hydrolysis drives the reaction.

• Reaction is irreversible.

Step 2: Phosphoglucose Isomerase

Reaction

• Reaction is near equilibrium.

Step 3: Phosphofructokinase

Reaction

• Reaction is irreversible.

• Another ATP is invested; ATP hydrolysis drives the

reaction.

• Glycolysis is regulated at this step.

Step 4: Aldolase Reaction

• The aldolase reaction is the reverse of an aldol

condensation.

Step 5: Triose Phosphate Isomerase Reaction

• Converts DHAP to GAP (and vice versa)

• Result: 2 GAP’s proceed through remainder of glycolysis

• Even though ΔG>0, reaction proceeds forward because

GAP is quickly consumed.

Step 6: GAP Dehydrogenase Reaction

Notice: phosphate does not come from ATP. •

is reduced to NADH. + NAD •

Reaction is both a phosphorylation and an oxidation- •

reduction reaction.

42- , which competes with PO43- Reaction is inhibited by AsO •

for binding the enzyme.

Step 7: Phosphoglycerate Kinase Reaction

• ATP is formed.

• Since reaction occurs twice, 2 ATP have been

recouped from the energetic investment.

Enolase catalyzes a dehydration reaction.
H

2

O is produced.

Step 9: Enolase Reaction Forms 2

nd

“High-Energy” Intermediate

Step 10: Pyruvate Kinase Reaction

• Final step of glycolysis

• ATP formed: energetic payoff nets 2 ATP

• Glucose (a six-carbon molecule) has been broken down into

2 pyruvates (i., two three-carbon molecules)

Standard & Physiological Free Energy Changes of

Glycolytic Reactions

####### Identification of the rate-determining step(s) of the pathway by measuring the in vivo

####### free energy change for each reaction. Enzymes that operate far from equilibrium are

####### potential control points.

Only three reactions of glycolysis, those catalyzed by hexokinase, phosphofructokinase, and pyruvate

kinase, function with large negative free energy changes in heart muscle under physiological conditions.

These nonequilibrium reactions of glycolysis are candidates for flux-control points.

Regulation of Glycolysis

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