Physiology of Exercise Ch. 2

Bioenergetics and muscle metabolism

most important thing to remember

the main goal of producing energy via ATP to power cell function

breakdown of ATP - is what powers the cycling of the myosin head during cross-bridging aka muscle contraction

The Power of ATP: breakdown

ATP is stored in very small amounts until needed.

ATP + water + ATPase → ADP + Pi + energy

ADP: a lower-energy compound that is less useful

The power of ATP: synthesis

because of minimal storage, there is constant synthesis.

synthesis from ATP by-products

ADP + Pi + energy → ATP (via phosphorylation)

can occur in either absence or presence of O2

Three ATP synthesis pathways

ATP-PCr system (anaerobic metabolism)

Glycolytic System (glycolysis; anaerobic metabolism)

Oxidative System (oxidative phosphorylation; aerobic metabolism)

Substrates

fuel sources from which our bodies produce energy (carbs, fat, protein)

Bioenergetics

process by which chemical pathways in our cells convert substrates into energy

Metabolism

all of the chemical reactions in the body. Whe substrates are broken down, they typically produce heat and ATP

Calories

can be calculated from heat produced

1 calorie (cal) = heat energy required to raise 1g of water from 14.5 °C to 15.5 °C

1,000 cal = 1 kcal = 1 Calorie (dietary)

protein - 4 kcal/g

carbs - 4 kcal/g

fat - 9 kcal/g

Substrate: Carbs

carbs are broken down into glucose

glucose: used to produce ATP in muscles and brain, extra stored as glycogen in liver and muscles

glycogen: can be converted back to glucose to make more ATP, storage limited (2,500 kcal in body), dietary carb needed to replenish

primarily power short to medium bouts of intense exercise

Substrate: fat

efficient substrate, efficient storage

approximately 9 kcal/g, 70,000 + kcal stored in body

energy substrate for prolonged, less intense exercise

yields high net ATP but slow ATP production, must be broken down into free fatty acids (FFA’s) and glycerol

• FFA’s (not glycerol) is then used to make ATP

Substrate: Protein

used very minimally to power metabolism

converted into glucose via gluconeogenesis, converted into FFA’s via lipogenesis

Primary Use: build, maintain, and repair tissues and to create hormones, enzymes, and other crucial molecules important for metabolism

Energy Production

The rate and means of ATP production are controlled by substrate availability and enzyme activity

Substrate Availability

mass action effect

substrate availability affects metabolic rate

more availability substrate= higher pathway activity

excess of given substrate = cells relying on that substrate more than on others

Enzyme Activity: Enzymes

Do not start chemical reactions or set ATP yield

Do facilitate breakdown (catabolism) of substrates

lower the activation energy for a chemical reaction

end with the suffix -ase

specific enzymes required for each step in a biochemical pathway - more enzyme activity typically enables more breakdown of substrates

Enzyme Activity: rate-limiting enzyme

can create bottleneck at an early step

activity is influenced by negative feedback

slows overall reaction, prevents runaway reaction

What are the 3 synthetic pathways?

ATP-PCr system (anaerobic metabolism)

glycolytic system (glycolysis; anaerobic metabolism)

Oxidative system (oxidative phosphorylation; aerobic metabolism)