Biochemistry of Sports (TC 20103)

Lecture 9Carbohydrate Metabolism

In Exercise IBo Eng, Cheong

Do you still remember?

Exercise metabolism obeys the need for increased energy supply to the contracting muscles.

Anabolism or catabolism?

Since you are studying the carbohydrate metabolism, what kind of metabolites you think will be involved?

The 1st principle of exercise metabolism?

Figure. Overview of metabolism. Shown here are the central metabolomic pathways and some key intermediates. Catabolic pathways (red) proceed downward and anabolic pathways (blue) proceed upward.

Based on the figure in left hand side, for carbohydrate metabolism, what kind of metabolic processes will be involved?

Glycogen MetabolismExercise Speeds Up Glycogenolysis in MuscleGlycolysisExercise Speeds Up Glycolysis in MusclePyruvate OxidationExercise Speeds Up Pyruvate Oxidation in

Muscle

Guidelines for Lecture 9

Stored mainly in the liver and muscles.

Glycogen is located in the cytosol in the form of granules.

In addition to glycogen, the granules contain the enzymes catalyzing the reactions of its synthesis and breakdown.

There is no glycogen in the blood.

Glycogen Metabolism

Where do hepatic glycogen and muscle glycogen come from?

Do you still remember the carbohydrate digestion until the synthesis of glycogen in liver?

Glycogen synthesis VS glycogenolysis

Glycogen Metabolism

Glycogen

Glucose

Glycogenolysis

Degradation of glycogen to produce glucose-1-phosphate

α1 4 glycosidic linkages of glycogen are broken down by Pi (inorganic phosphate) and phosphorylase according to the reaction

Glycogen Metabolism - Glycogenolysis

phosphorylase

The rate of glycogenolysis is low in a resting muscle but increases because of changes in the concentration of certain compounds as the muscle begins to contract.

The actions of these compounds fit into four of the five means of metabolic control in exercise discussed in Lecture 8: allosteric regulation, covalent modification, changing substrate concentration, and hormonal control.

Exercise Speeds Up Glycogenolysis in Muscle

1. Pi increase Result of the hydrolysis in the cytosol.

Activation of “phosphorylase” enzyme.

2. AMP and IMP increase; ATP decrease AMP and IMP are the activators for

phosphorylase enzyme while ATP is the inhibitor for the enzyme.

Exercise Speeds Up Glycogenolysis in Muscle

phosphorylase

3. Ca2+ increase Increase of cytosolic Ca2+ (release from the sarcoplasmic

reticulum during muscle contraction). Binds to phosphorylase kinase (activator of the enzyme).

4. Epinephrine increase Increase in the blood concentration of the hormone

epinephrine. Activates the cyclic-AMP cascade – control of

glycogenolysis.

Exercise Speeds Up Glycogenolysis in Muscle

Glycogenolysis produces glucose-1-phosphate from glycogen (liver/muscle).

Cells also contain glucose originating in the diet. Glucose-1-phosphate and glucose can yield energy

through glycolysis. Glycolysis is the breakdown of glucose to pyruvate

(most common metabolic pathway in cells). Anaerobic process. Consists of 10 reactions taking place in the cytosol

catalyzed by different enzymes.

Glycolysis

Glycolysis

Glycolysis

Glycolysis – 2 phases

Exercise can augment the glycolytic rate in a muscle by hundreds of times and by more than one mechanism.

1. Increased substrate Glycogenolysis , glucose-6-phosphate Enhanced blood (glucose inside) flow to the

muscle.

Exercise Speeds Up Glycolysis in Muscle

2. Phosphofructokinase activation (step 3)

AMP (mentioned in previous slide) increase, activate the enzyme (ATP inhibit the enzyme).

3. Pyruvate Kinase activation (step 10)

ADP increase, activate the enzyme.

Exercise Speeds Up Glycolysis in Muscle

Pyruvate can yield more ATP than is produced in glycolysis.

To do this, it has to pass from the cytosol to the mitochondria, where most of the biological oxidations and ATP resynthesis take place.

Pyruvate Oxidation

Upon entering the mitochondria matrix, pyruvate reacts with coenzyme A (CoA) to yield acetyl coenzyme A (acetyl CoA).

Acetyl CoA results from the attachment of an acetyl group to CoA.

The acetyl group is what remains from pyruvate after its carboxyl group is removed as carbon dioxide, a process called decarboxylation.

At the same time pyruvate is oxidized by NAD+, the whole reaction is irreversible.

Pyruvate dehydrogenase complex

Exercise Speeds Up Pyruvate Oxidation in Muscle

Thank You