EXERCISE AND NUTRITIONAL SCIENCES 632

PHYSIOLOGICAL CHEMISTRY OF EXERCISE

Michael J. Buono, Ph.D.

Fred W. Kolkhorst, Ph.D.

San Diego State University

http://www-rohan.sdsu.edu/~ens632/

BIOENERGETICS-how the body acquires, converts, stores, and utilizes energyFirst Law of Thermodynamics (conservation of energy)

energy cannot be created or destroyed, only converted from one form (chemical, thermal, mechanical, light, etc) to another; thus, the total energy in the universe remains constant. (examples: photosynthesis = light to chemical, exercise = chemical to mechanical)

Second Law of Thermodynamicswhenever energy is exchanged between forms the exchange is imperfect and some energy is lost as heat (randomness increases) (humans are 25% efficient, 75% heat). Specific heat of the human body is .83 kcal/kg/oC, thus a 60 kg person needs to retain 50 kcal of heat (.83 x 60) to increase the core body temperature 1 oC. Thus, running a mile (100 kcal) theoretically should increase the core body temperature 2 oC if no heat was lost.

• Exercise

Photosynthesis

Internal combustion engine

Space heater

BIOENERGETICS (cont.)

• Exergonic Rx– a reaction that gives up (releases) energy (burning of a tree, hydrolysis of ATP, oxidation of carbohydrate,

etc.)

• Endergonic Rx– a reaction that absorbs (takes in) energy (growth of a tree, resynthesis of ATP, formation of carbohydrate via

photosynthesis)

• Exergonic Rx ATP Endergonic Rx

Oxidation of food ATP Muscular contraction, ion gradients (CHO, Fat)

Coupled Reactions in Animals

ATP (adenosine triphosphate)

• ATP need in rapidly contracting skeletal muscle is over 100x greater than ATP need at rest.

ATP is needed for:1.) myosin ATPase (50%)2.) sarcoplasmic reticulum Ca++ ATPase (SERCA) (40%)3.) Na+ /K+ ATPase (10%)

Sodium-Potassium ATPase

Humans have ECF [ Na+] of 140 mM and ICF [Na+] of 10 mM

Humans have ECF [ K+] of 4 mM and ICF [K+] of 150 mM

Excitation-Contraction Coupling

Ca++ cycling

Dihydropyridine (DHP) receptor Ryanodine receptor

Sarcoplasmic Reticulum ATPase (SERCA)

Cross-bridge cycle - Myosin ATPase

ATP Structure

Electrostatic repulsion

~ = phospho-anhydride

bond

ATP (cont.)

ATP + H20 ADP + Pi + H+ + free energy

Free Energy (-G) of ATP = -7.3 kcal/mole exergonic reaction: thus (–) in value

(products have less free energy than reactants)

kcal = energy needed to raise 1L of water 1 C

mole = atomic wt. of substance in grams (6.02 x 1023 molecules)

Free energy(-G)

of various

biological compounds

G and ATP

Early Studies on ATP

• Fletcher (1920s) believed lactic acid caused muscular contraction

• Embden (1920s) rapid freezing of isolated muscle showed contraction without HLA formation

• Cain (1940s) poisoned CPK with DNFB and showed ATP decreased with each contraction thus showing that hydrolysis of ATP provided the energy needed for muscular contraction.

Substrate Level Phosphorylation

• PC + ADP + H + ATP + Cr

(-10.1 kcal/mole) G (-7.3 kcal/mole) G

CPK

ATP Use During Exercise

CP and ATP Use During Exercise

Myokinase reaction 2 ADP ATP + AMP

Changes in ATP,ADP and AMP

Amount of ATP needed to run a Marathon