ATP

Examples of ATP in the following topics:

• Muscle Metabolism

  • Muscle contractions are fueled by adenosine triphosphate (ATP), an energy-storing molecule.
  • Four potential sources of ATP power muscle contractions.
  • The reaction of phosphocreatine + ADP to ATP + creatine is reversible.
  • During periods of rest, the store of phosphocreatine is regenerated from ATP.
  • Mitochondria in the muscle fibers can convert pyruvate into ATP in the presence of oxygen via the Krebs Cycle, generating an additional 30 molecules of ATP.

• Internal Respiration

  • Glycolysis: The breakdown of glucose into pyruvate, ATP, H2O, and heat.
  • Oxidative Phosphorylation: Produces ATP from NADH, oxygen, and H+.
  • The oxygen plays the role of electron receptor in an electron transport chain to produce ATP.
  • $Glucose + 6 Oxygen -> 6 Carbon Dioxide + 6 Water + 38 ATP$
  • This process is very inefficient compared to aerobic respiration, as without oxidative phosphorylation, the cell cannot produce nearly as much ATP (2 ATP compared to 38 during cellular respiration).

• Creatine Supplementation

  • Creatine supplements may increase anaerobic exercise performance by augmenting phosphocreatine levels and ATP availability.
  • This is a reflection of the differential energy pools used for anaerobic versus aerobic respiration, specifically the prioritization of use of phosphocreatine as an ATP pool for Type II muscles, which are primarily used during anaerobic exercise.
  • Phosphocreatine is an important source of energy-rich phosphate groups that can be added to available ADP to resynthesize ATP for muscle contractions.

• Rigor Mortis

  • After death, cellular respiration in organisms ceases to occur, depleting the corpse of oxygen used in the making of adenosine triphosphate (ATP).
  • ATP is no longer provided to operate the SERCA pumps in the membrane of the sarcoplasmic reticulum; these pumps move calcium ions into the terminal cisternae.
  • This release of calcium is caused by the loss of ATP-mediated function of calcium pumps of the sarcoplasmic reticulum, due to ATP depletion in the absence of cellular respiration.

• Energy Requirements

  • Cardiac cells contain numerous mitochondria, which enable continuous aerobic respiration and production of adenosine triphosphate (ATP) for cardiac function.
  • Cardiomyocytes contain large numbers of mitochondria, the powerhouse of the cell, enabling continuous aerobic respiration and ATP production required for mechanical muscle contraction.
  • Cardiac muscle cells contain larger amounts of mitochondria than other cells in the body, enabling higher ATP production.
  • Recycling lactate is very energy-efficient in the nutrient-deprived myocardium, since one NAD+ is reduced to NADH and H+ (equal to 2.5 or 3 ATP) when lactate is oxidized to pyruvate.

• Muscle Fatigue

  • Long-term muscle use requires the delivery of oxygen and glucose to the muscle fiber to allow aerobic respiration to occur, producing the ATP required for muscle contraction.
  • In aerobic respiration, pyruvate produced by glycolysis is converted into additional ATP molecules in the mitochondria via the Krebs Cycle.
  • Depletion of required substrates such as ATP or glycogen within a muscle result in fatigue as the muscle is not able to generate energy to power contractions.
  • With aging, levels of ATP, CTP, and myoglobin begin to decline, reducing the muscle's ability to function.

• Slow-Twitch and Fast-Twitch Muscle Fibers

  • The ATP required for slow-twitch fiber contraction is generated through aerobic respiration (glycolysis and Krebs cycle), whereby 30 molecules of ATP are produced from each glucose molecule in the presence of oxygen.
  • Unlike slow-twitch fibers, fast twitch-fibers rely on anaerobic respiration (glycolysis alone) to produce two molecules of ATP per molecule of glucose.

• Catabolic-Anabolic Steady State

  • The chemical reaction where ATP changes to ADP supplies energy for this metabolic process.
  • ATP, a high energy molecule, couples anabolism by the release of free energy.

• Microscopic Anatomy

  • The myosin head also binds to ATP, the source of energy for muscle movement.
  • When ATP binds to myosin, it separates from the actin of the myofibril, which causes a contraction.

• Homeostatic Responses to Shock

  • Shock is irreversible at this point since a large amount of cellular ATP has been degraded into adenosine in the absence of oxygen as an electron receptor in the mitochondrial matrix.
  • Because cells can only produce adenosine at a rate of about 2% of the cell's total need per hour, even restoring oxygen is futile at this point because there is no adenosine to phosphorylate into ATP.