Lecture 6 The ATP-PCr System

Learning Outcomes

  • Describe the chemical structure of adenosine triphosphate (ATP) and its contribution to biological work.

  • List three functions of ATP in muscle.

  • Describe the ATP-PCr immediate energy system.

  • List the advantages and disadvantages of the ATP-PCr system.

Energy Storage: Adenosine Triphosphate (ATP)

  • ATP: energy currency of cells, from breakdown of macronutrients.

  • High-energy bonds in ATP store potential energy.

  • Bioenergetics: Conversion of substrates to usable energy.

  • ATP powers biological work; it is stored in limited quantities (80-100g), enough for 2-3 seconds of effort.

  • Continuous resynthesis of ATP is essential to maintain energy levels.

Chemical Structure of ATP

  • Structure of ATP consists of:

    • Adenine

    • Ribose

    • Inorganic phosphates

  • Hydrolysis of ATP releases free energy, converting ATP to ADP and Pi.

Hydrolysis of ATP

  • ATP is stored in small amounts and is hydrolyzed to release energy.

  • This process does not require oxygen (anaerobic) and occurs instantly.

  • ADP is a by-product and less useful as an energy source.

  • Synthesis of ATP occurs via phosphorylation: ADP + Pi + energy → ATP.

  • Hydrolysis yields 7.3 kcal/mol, reflecting an exergonic reaction.

Catabolism-Anabolism Interactions

  • ATP is reconstructed from ADP/Pi through the oxidation of macronutrients.

  • Rebuilding ATP requires energy, while hydrolysis releases energy for biological work.

Function of ATP in Muscle

  • Myosin ATPase catalyzes ATP hydrolysis, facilitating muscle contraction.

  • Cross-bridge formation occurs with ADP and Pi bound to myosin.

  • ATP binding to myosin leads to detachment from actin after the power stroke.

  • ATP is also crucial for active transport, specifically pumping calcium back into the sarcoplasmic reticulum.

Cross-Bridge Cycle

Basic Energy Systems

  • Beginning of muscular movement rapidly activates several systems for energy transfer

  • Three metabolic pathways for ATP synthesis:

    • ATP-PCr system (anaerobic)

    • Glycolytic system (anaerobic)

    • Oxidative system (aerobic)

ATP-PCr System

Function: maintains ATP levels in early exerc

  • ATP stores are quickly depleted; muscles contain more phosphocreatine (PCr) than ATP.

  • PCr donates Pi to ADP to regenerate ATP and is hydrolyzed at the start of intense exercise.

  • Creatine Kinase (CK) catalyzes this reaction, increasing with high ADP levels and being inhibited by ATP.

  • The ATP-PCr system supports energy needs for 3-15 seconds of maximal exercise.

Changes in Muscle Energy Stores

  • Observation of ATP and PCr levels in type 2 muscle fibers during a 14-second sprint effort.

Advantages/Disadvantages of ATP/PCr System

  • Advantages:

    • ATP can be rapidly regenerated.

    • Phosphocreatine stores replenish in ~3 minutes.

    • No fatiguing by-products.

  • Disadvantages:

    • Limited supply of PC in the body.

    • Regeneration requires the presence of o2.

    • Supplementation can enhance ATP-PCr performance for explosive movements.

Use of Supplements for ATP-PCr System

  • Primary use of creatine is to enhance skeletal muscle performance.

  • 2/3 of creatine is stored as PCr, aiding rapid ATP regeneration.

  • Supplementation can increase PCr availability, peak power output, and delay fatigue.

Activities Utilizing ATP-PCr System

  • golf, weightlifting, baseball, volley ball (specific)

Training the ATP-PCr System

  • Anaerobic training influences the ATP-PCr system; it is least adaptable to training.

  • Activities focusing on maximum muscle force utilize ATP-PCr significantly.

  • Max effort activities (3-10 seconds) enhance ATP and PCr breakdown.

  • Recommended work:rest ratio of 1:10; substantial rest improves strength and reduces fatigue.

Page 17: Case Study: 100m Sprint

  • Evaluation of energy systems contributing to ATP production during a 100m sprint completed in 10.72 seconds by an 18 yr old male.