Biochemistry of Sports (TC 20103)

Lecture 8Exercise Metabolism,

Carbohydrate and LipidsBo Eng, Cheong

Exercise Metabolism Principles of Exercise Metabolism Five Means of Metabolic Control in Exercise Four Classes of Energy Sources in Exercise Carbohydrates Monosaccharides Oligosaccharides Polysaccharides Lipids Fatty Acids Triacylglycerol Phospholipids Steroids Cell Membranes

Guidelines for Lecture 8

Exercise Metabolism

What is “metabolism” ?

What is “catabolism” ?

What is “anabolism” ?

Metabolism the sum of the chemical reactions occurring in a living

organism. E.g. ?

Anabolismthe set of metabolic pathways that construct molecules

from smaller units. These reactions require energy. E.g. ?

Catabolismthe set of metabolic pathways that break down

molecules into smaller units and release energy. E.g. ?

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.

Exercise Metabolism

What is “exercise metabolism” ? (hint: definition of metabolism)

As a student of Sport Science, why do youthink it is important to know about “exercise metabolism” ?

1. Exercise metabolism obeys the need for increased energy supply to the contracting muscles. Anabolism or catabolism?

2. Most kinds of exercise cause increased break-down of carbohydrate and lipids.

3. Exercise changes metabolism not only in the exercising muscles but also in other organs and tissues (liver, adipose tissue).

Principles of Exercise Metabolism

4. Metabolism does not return to the resting state immediately after the end of exercise. Many changes persist for hours or days, while others are manifest during recovery rather than exercise.

5. Training – can change metabolism to an extent great enough to make the metabolic profile of a trained individual different from an untrained individual.

Principles of Exercise Metabolism

• Mammals have developed a multitude of mechanisms to modify their metabolism during exercise. The mechanisms are:

1. Allosteric Regulation Metabolic reactions are catalyzed by enzymes. The binding of a

compound whose concentration increases with exercise to a site on an enzyme distinct from the active site may modify the enzyme’s activity.

If the activity increases, the compound is called an activator. If decreases, the compound is called an inhibitor (feedback inhibition of a metabolic pathway).

Five Means of Metabolic Control in Exercise

Five Means of Metabolic Control in Exercise

2. Covalent Modification The activity of certain enzymes is controlled by the

reversible addition of chemical groups to their molecules. This covalent modification can take places within seconds.

The addition and subsequent removal of chemical groups are catalyzed by specific enzymes, which can be activated or inhibited by biochemical factors affected by exercise.

E.g. the control of glycogen synthesis and breakdown by phosphorylation of the responsible enzyme (coming soon).

Five Means of Metabolic Control in Exercise

3. Changing Substrate ConcentrationThe increase or decrease in the concentration

of a reaction’s substrate during exercise may cause a similar change in reaction rate.

E.g. the increase in the amount of glucose entering the exercising muscles from the blood speeds up its use for energy supply.

Five Means of Metabolic Control in Exercise

4. Changing Enzyme ConcentrationDifferent kinds of exercise create biochemical stimuli

that modify the concentrations of various enzymes.Cells often achieve this by altering the transcription

rates of the genes encoding these enzymes.Changing enzyme concentration is the slowest

means of regulation – requires hours.Covered in lecture 6? The effect of exercise on gene

expression.

Five Means of Metabolic Control in Exercise

5. Nervous and Hormonal ControlFocus on hormone.Hormones are compounds that coordinate the

functioning of different cells in multi-cellular organisms.They are synthesized in endocrine glands and secreted

in the blood, which disseminates them to the rest of the body.

They alter specifically the function of tissues, organs, or cells called target tissues, target organs, or target cells.

Five Means of Metabolic Control in Exercise

The 1st principle of exercise metabolism – Exercise metabolism obeys the need for increased

energy supply to contracting muscles. Four classes of biological substances serve this need:

1. Compounds of high phosphoryl transfer potential2. Carbohydrates3. Lipids4. Proteins

Four Classes of Energy Sources in Exercise

The most important energy source!

Compounds of the molecular formula CnH2nOn or are derived from such compounds.

If one takes “n” as a common factor, the formula becomes (CH2O)n, hence the name carbo-hydrate.

Carbohydrate

Serve a multitude of needs in living organisms:Sources of energyOffer cells external protection. Cellulose is the

support of the entire plant kingdomPart of building block of nucleic acids (as

ribose or deoxyribose)Divided into monosaccharides,

oligosaccharides, and polysaccharides

Carbohydrate

The simplest forms of carbohydrates.Has 3 to 7 carbon atoms and is called specifically triose

(3C), tetrose (4C), pentose (5C), hexose (6C) or heptose (7C).

For sugars with more than one chiral center, the D or L designation refers to the asymmetric carbon farthest from the aldehyde or keto group.

Most naturally occurring sugars are D isomers. D & L sugars are mirror images of one another. They have

the same name. For example, D-glucose and L-glucose.

Monosaccharides

The smallest monosaccharides, glyceraldehyde and dihydroxyacetone.

Monosaccharides – Triose (3C)

Ribose – the component of ribonucleotides (DNA, RNA)

Can be either open chain or cyclic

Monosaccharides – Pentose (5C)

Glucose and fructose, which occur in fruits and account for their sweetness

Both have the molecular formula C6H12O6

Appear in open-chain and cyclic form (predominates in biological systems)

Cyclic glucose is called glucopyranose

Monosaccharides – Hexose (6C)

When 2 to 10 monosaccharides are linked covalently, oligosaccharides result.

The linkages between monosaccharide units in an oligosaccharide are called glycosidic linkage

Maltose and sucrose

Oligosaccharides

Cellulose – dietary fiber, main component of your books, clothes, and cotton

Starch – stored energy form in plants

Glycogen – stored energy form in animals

Glycogen - one of our focuses in Lecture 9

Polysaccharides

Lipids present a great variety of structures and functions.

Encompasses the main constituent of a large tissue (adipose tissue), membrane components, hormones, vitamins and etc.

Low solubility in water.Four categories: fatty acids, triacylglycerols,

phospholipids, and steroids.

Lipids

Organic acids containing large numbers of carbon atoms (usually 12-26)

Consist of a long carbon chain with hydrogens all around (aliphatic chain) and a carboxyl group at one end

Fatty Acids

The carboxyl group (with negative charge) is hydrophilic, whereas the aliphatic chain is hydrophobic, produce an amphipathic compound (poorly soluble in water).

Fatty acids are different in the number of double bonds. If the carbons of a fatty acid are linked by single bonds only, the fatty acid is called saturated because there is no room to add anymore hydrogens.

Conversely, if there are double bonds between some of the carbons, the fatty acids is called unsaturated (could be cis- or trans- configuration).

Fatty Acids

Fatty Acids

Triacylglycerols, or triglycerides, are the most abundant lipid category.

Serve mainly as energy depots.

Consist of a glycerol unit and three fatty acid units.

Triacylglycerols

• Glycerol is a compound of three carbons and three hydroxyl groups. Each hydroxyl group is linked to the carboxyl group of a fatty acid through an ester linkage.

Triacylglycerols

Presenting a remarkable structural variety.

A major component of all cell membranes as they can form lipid bilayers.

Phospholipids

Complex lipid category, encompassing hormones.

All are derivatives of cholesterol. E.g. testosterone, progesterone, estrogen and etc.

Steroids

The anabolic steroid testosterone, the principal male sex hormone.

Progesterone, a steroid hormone involved in the female menstrual cycle, pregnancy and embryogenesis.

Thank You