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neurologyYou need to know

• Adenosine triphosphate (ATP) is described as the body’s energy currency because it transfers usable energy directly to energy-requiring processes such as muscle contraction.
• ATP consists of adenosine and three phosphate groups; hydrolysis removes the terminal phosphate to form adenosine diphosphate (ADP), inorganic phosphate and usable energy.
• ATPase is the enzyme that catalyses the exothermic hydrolysis of ATP, while ATP resynthesis is an endothermic reaction requiring an input of energy.
• Energetically coupled reactions use energy released by an exothermic reaction to drive an endothermic reaction, such as using energy from fuel breakdown to resynthesise ATP from ADP and inorganic phosphate.
• The ATP-PC system resynthesises ATP anaerobically by transferring a phosphate group from phosphocreatine to ADP, in a reaction catalysed by creatine kinase.
• The ATP-PC system provides ATP very rapidly but has a small capacity because phosphocreatine stores are limited, so it predominates during maximal efforts lasting approximately 10 seconds.
• Phosphocreatine stores are replenished during recovery using energy supplied mainly by the aerobic system, allowing the ATP-PC system to contribute again during repeated exercise.
• Anaerobic glycolysis breaks down muscle glycogen or glucose without directly requiring oxygen and produces a small but rapid supply of ATP.
• Glycogen phosphorylase initiates the breakdown of glycogen, phosphofructokinase regulates an important stage of glycolysis, and lactate dehydrogenase converts pyruvate to lactate when the rate of glycolysis exceeds aerobic processing.
• Anaerobic glycolysis produces a net yield of two ATP from each glucose molecule, although starting with stored glycogen avoids one ATP-consuming step and can produce a net yield of three ATP.
• Anaerobic glycolysis predominates during high-intensity activity that lasts longer than the ATP-PC system can sustain, but the accumulation of hydrogen ions contributes to reduced muscle pH and fatigue.
• Buffering systems resist changes in pH by removing or neutralising hydrogen ions, helping to delay fatigue during intense anaerobic exercise.
• The aerobic system uses oxygen and takes place mainly in the mitochondria through aerobic glycolysis, the link reaction, the Krebs cycle and the electron transport chain.
• During aerobic glycolysis, glucose is converted to pyruvate; pyruvate then combines with coenzyme A to form acetyl coenzyme A before entering the Krebs cycle.
• In the Krebs cycle, acetyl coenzyme A combines with oxaloacetic acid to form citric acid, and subsequent reactions regenerate oxaloacetic acid while releasing carbon dioxide and transferring hydrogen and electrons to carrier molecules.
• The electron transport chain uses electrons and hydrogen carried from earlier stages to create the conditions for oxidative phosphorylation, producing most of the ATP made aerobically, with water formed when oxygen acts as the final electron acceptor.
• The aerobic system resynthesises ATP more slowly than the anaerobic systems but has a much larger capacity, so it predominates during prolonged, lower-intensity exercise.
• The energy continuum describes how all three energy systems contribute to ATP resynthesis at the same time, although one system is usually predominant according to the demands of the activity.
• Increasing exercise intensity raises reliance on the ATP-PC and glycolytic systems, while increasing duration generally raises reliance on the aerobic system; crossing the anaerobic threshold causes a rapid increase in anaerobic contribution and lactate accumulation.
• Work-to-recovery ratio, the intermittent or continuous nature of activity, and aerobic and anaerobic fitness levels affect energy-system predominance and the speed of recovery between efforts.

• Explain why ATP is an energy currency by linking ATP hydrolysis to energy transfer and ATP resynthesis to the breakdown of energy-rich fuels.
• Illustrate an energetically coupled reaction by showing how an exothermic reaction supplies the energy needed for the endothermic resynthesis of ATP.
• Trace ATP resynthesis in the ATP-PC system, identifying phosphocreatine, ADP and creatine kinase and explaining its rapid rate and limited capacity.
• Trace anaerobic glycolysis from glycogen or glucose to pyruvate and lactate, identifying the roles of glycogen phosphorylase, phosphofructokinase and lactate dehydrogenase.
• Trace aerobic ATP resynthesis through aerobic glycolysis, the link reaction, Krebs cycle and electron transport chain, including the roles of mitochondria, coenzyme A and oxygen.
• Compare the ATP-PC, glycolytic and aerobic systems by their oxygen requirement, rate of ATP resynthesis, capacity, fuels, by-products and predominant exercise conditions.
• Interpret energy-continuum graphs by identifying changes in the relative contribution of each energy system as exercise intensity and duration change.
• Analyse an exercise or sport by using its intensity, duration, work-to-recovery ratio and intermittent or continuous pattern to justify which energy system is predominant.
• Critically evaluate energy-system use by recognising that no system works alone and by explaining how fitness, recovery and buffering can alter each system’s contribution.