ATP ENERGY PRODUCTION

Energy The body needs a constant supply of energy to perform every day tasks such as respiration and digestion. Energy is the capacity to perform work and is measured in joules or calories.

Calorie, Joule and Watt Calorie is the amount of heat energy needed to raise the temperature of 1 gram of water through 1oC. A Kilocalorie (kCal)is 1000 calories. Joule = 4.2 kCal. A Watt is equivalent to the use of one joule per second. Power is the work performed per unit of time and is measured in watts.

Work Work is defined as force x distance. It can be measured in calories and joules. Food Food is chemical energy. It is converted into movement (kinetic energy). Or is stored as potential energy.

Energy release in the body Energy release in the body is complicated. There is only one usable form of energy in the body – adenosine triphosphate (ATP). All food we eat has to be converted into ATP. ATP is a high energy phosphate compound made up of adenosine and 3 phosphates. The bonds that hold the compound together are a source of a lot of potential energy. ATP = adenosine-phosphate-phosphate-phosphate

When a compound is broken down( the bonds between the molecules are broken) the energy is released. ATP is broken down to adenosine diphosphate (ADP) and free phosphate, releasing the stored energy. ATP → ADP + P + Energy The energy released from the breakdown of ATP to ADP and P is converted to kinetic and heat energy.

Methods of ATP production Once ATP has been broken down to release energy it has to be put back. There are three ways that this is achieved in the human body: 1 The phosphocreatine system (ATP/PC) or alactic system. 2 The lactic acid system or glycolysis. 3 The aerobic system. Each method is good at supplying energy for particular energy demands and duration. Systems 1 and 2 are anaerobic they take place without oxygen System 3 is aerobic: it requires oxygen to work.

ATP Production by Phosphocreatine or Alactic System Phosphocreatine is a high- energy phosphate compound. It is found in the sarcoplasm of the muscle. Potential energy is stored in the bonds of the compound. Phosphocreatine → P+ Creatine + Energy creatine kinase

Creatine kinase is activated when the level of ADP in the muscle cell increases. It is when the stores of ATP start to diminish. The energy released by the breakdown of PC is used to convert ADP to ATP. Energy has to be liberated by the breakdown of PC before ATP can be formed. Stores of PC in the muscles are enough to sustain all out effort for about ten seconds.

This is the only system capable of producing ATP quickly. During activities that demand large amounts of energy over a short period of time e.g...... As PC is stored in the muscle it is readily accessible as an energy source. Energy for ATP can be obtained extremely quickly. No fatiguing by products are released.

ATP production by the lactic acid system or Glycolysis Also anaerobic taking place in the sarcoplasm. The energy needed comes from the food we eat. It involves the partial breakdown of glucose. Breakdown of PC does not rely on the availability of oxygen. It is much more complex than Phosphocreatine. It therefore stores more energy.

Glucose is broken down anaerobically (in absence of oxygen). Because there is no O2 lactic acid is formed. Breakdown of bonds in glucose release energy. The energy is used to synthesise ATP. The lactic acid system takes longer to produce energy than the ATP/PC system. It supplies energy for high intensity activities for about a minute. The 400m is a good example. What causes fatigue from this system?

Outline of Lactic Acid System Production of energy for resynthesis of ATP

Fatigue When glycogen is broken down anaerobically lactic acid is produced. If lactic acid accumulates it lowers the pH. The drop in pH affects the action of phosphofructokinase. It also affects lipoprotein kinase that breaks down fat. The body’s ability to synthesise ATP is temporarily reduced causing fatigue.

Production of ATP using the Aerobic System The aerobic system needs oxygen. At the onset of exercise there isn’t enough O2 to break down food fuels. So the 2 anaerobic systems are used. As heart rate and rate of ventilation increase more oxygen gets to the working muscles. Within 1-2 minutes the muscles are being supplied with enough O2 to allow effective aerobic respiration.

Stage 1:Aerobic glycolysis Aerobic glcolysis is the same as anaerobic glycolysis. Glucose is broken down to pyruvic acid. As O2 is now present the reaction can proceed further than in anaerobic glycolysis. Lactic acid is not produced. Two molecules of ATP are synthesised at this stage.

Stage 2: The TCA/Citric acid/Krebs’ Cycle The pyruvic acid produced in the 1st stage diffuses into the matrix of the mitochondria. A complex cyclical series of reactions now occurs. During the cycle three important things happen: 1.carbon dioxide is formed. 2.oxidation takes place-hydrogen is removed from the compound. 3.Sufficient energy is released to synthesis 2 molecules of ATP.

Stage 3:The Electron transport chain/electron transport system The H2 atoms removed in stage 2 are transported by coenzymes to the inner membrane of the mitochondria. The electrons are passed along by electron carries combining with O2 and H2 ions to form water. Energy is released which combines ADP with phosphate to form ATP. The energy yield from the electron tranport chain forms 34 molecules of ATP. The total yield of ATP from aerobic respiration is therefore 38 molecules of ATP.

Mitochondrion

Mitochondrion Krebs cycle Electron transport chain ATP synthase Pathways (e.g. b-oxidation)

Differences betweeen aerobic and anaerobic ATP production McArdle, Katch&Katch term three energy systems: immediate energy system (ATP/PCr) short-term energy system (Glycolysis) long-term energy system (aerobic)

The aerobic system of synthesising ATP is the most efficient. The byproducts (CO2 and H2O) are easily expelled from the body. However the reactions involved in this system depend on the availability of O2.