Energy systems
Encyclopedia
There are three sources of Adenosine triphosphate
(ATP), the body's main energy source on the cellular level.
to glucose
. Then, with enzymes, glucose is broken down anaerobically to produce lactic acid; this process creates enough energy to reform ATP molecules, but due to the detrimental effects of lactic acid and H+ ions building up and causing the pH of the blood to become more acidic, this system cannot be relied on for extended periods.
Glycolysis - The first stage is known as glycolysis, which produces 2 ATP molecules, a reduced molecule of NAD (NADH), and 2 pyruvate molecules which move on to the next stage - the Krebs cycle. Glycolysis takes place in the cytoplasm of normal body cells, or the sarcoplasm of muscle cells.
The Krebs Cycle - This is the second stage, and the products of this stage of the aerobic system are a net production of 1 ATP, 1 carbon dioxide
Molecule, three reduced NAD molecules, 1 reduced FAD molecule (The molecules of NAD and FAD mentioned here are electron carriers, and if they are said to be reduced, this means that they have had a H+ ion added to them). The things produced here are for each turn of the Krebs Cycle. The Krebs cycle turns twice for each molecule of glucose that passes through the aerobic system - as 2 pyruvate molecules enter the Krebs Cycle. In order for the Pyruvate molecules to enter the Krebs cycle they must be converted to Acetyl Coenzyme A. During this link reaction, for each molecule of pyruvate that gets converted to Acetyl Coenzyme A, an NAD is also reduced. This stage of the aerobic system takes place in the matrix of the cells' mitochondria.
Oxidative Phosphorylation - This is the last stage of the aerobic system and produces the largest yield of ATP out of all the stages - a total of 34 ATP molecules. It is called 'Oxidative Phosphorylation' because oxygen is the final acceptor of the electrons and hydrogen ions that leave this stage of aerobic respiration (hence oxidative) and ADP gets phosphorylated (an extra phosphate gets added) to form ATP (hence phosphorylation).
This stage of the aerobic system occurs on the cristae (infoldings on the membrane of the mitochondria). The NADH+ from glycolysis and the Krebs cycle, and the FADH+ from the Krebs cycle pass down electron carriers which are at decreasing energy levels, in which energy is released to reform ATP. Each NADH+ that passes down this electron transport chain provides enough energy for 3 molecules of ATP and each molecule, and each molecule of FADH+ provides enough energy for 2 molecules of ATP. If you do your math this means that 10 total NADH+ molecules allow the rejuvenation of 30 ATP, and 2 FADH+ molecules allow for 4 ATP molecules to be rejuvenated (The total being 34 from oxidative phosphorylation
, plus the 4 from the previous 2 stages meaning a total of 38 ATP being produced during the aerobic system). The NADH+ and FADH+ get oxidized to allow the NAD and FAD to return to be used in the aerobic system again, and electrons and hydrogen ions are accepted by oxygen to produce water, a harmless by-product.
Adenosine triphosphate
Adenosine-5'-triphosphate is a multifunctional nucleoside triphosphate used in cells as a coenzyme. It is often called the "molecular unit of currency" of intracellular energy transfer. ATP transports chemical energy within cells for metabolism...
(ATP), the body's main energy source on the cellular level.
- ATP-PC system (Phosphogen system) - This system is used only for very short durations of up to 10 seconds. The ATP-PC system neither uses oxygenOxygenOxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
nor produces lactic acidLactic acidLactic acid, also known as milk acid, is a chemical compound that plays a role in various biochemical processes and was first isolated in 1780 by the Swedish chemist Carl Wilhelm Scheele. Lactic acid is a carboxylic acid with the chemical formula C3H6O3...
if oxygen is unavailable and is thus said to be alactic anaerobic. This is the primary system behind very short, powerful movements like a golf swing, a 100 m sprint or powerlifting.
- Anaerobic system (Lactic Acid system) - Predominates in supplying energy for exercises lasting less than 2 minutes. Also known as the Glycolytic System. An example of an activity of the intensity and duration that this system works under would be a 400 m sprint.
- Aerobic system - This is the long duration energy system. By 5 minutes of exercise the O2 system is clearly the dominant system. In a 1 km run, this system is already providing approximately half the energy; in a marathonMarathonThe marathon is a long-distance running event with an official distance of 42.195 kilometres , that is usually run as a road race...
run it provides 98% or more.
ATP-PC system
Creatine phosphate, also known as ATP-PC or ATP-CP system, is the first source of energy our body uses; it works by forming ATP and then by breaking down a creatine phospction, but is mainly used for resynthesising ATP and to maintain a constant supply of energy. These reactions occur very rapidly and only last up to high intensity (this only lasts for a short period of time). The ATP-PC system is for short bursts of energy but is burnt out in 10 seconds. As the ATP-PC only lasts for around 10 seconds it is optimal for sports that require fast bursts of energy.Anaerobic system
The lactic acid or anaerobic glycolysis system converts glycogenGlycogen
Glycogen is a molecule that serves as the secondary long-term energy storage in animal and fungal cells, with the primary energy stores being held in adipose tissue...
to glucose
Glucose
Glucose is a simple sugar and an important carbohydrate in biology. Cells use it as the primary source of energy and a metabolic intermediate...
. Then, with enzymes, glucose is broken down anaerobically to produce lactic acid; this process creates enough energy to reform ATP molecules, but due to the detrimental effects of lactic acid and H+ ions building up and causing the pH of the blood to become more acidic, this system cannot be relied on for extended periods.
Aerobic system
- Glycolysis
- The Krebs Cycle
- Oxidative Phosphorylation
Glycolysis - The first stage is known as glycolysis, which produces 2 ATP molecules, a reduced molecule of NAD (NADH), and 2 pyruvate molecules which move on to the next stage - the Krebs cycle. Glycolysis takes place in the cytoplasm of normal body cells, or the sarcoplasm of muscle cells.
The Krebs Cycle - This is the second stage, and the products of this stage of the aerobic system are a net production of 1 ATP, 1 carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
Molecule, three reduced NAD molecules, 1 reduced FAD molecule (The molecules of NAD and FAD mentioned here are electron carriers, and if they are said to be reduced, this means that they have had a H+ ion added to them). The things produced here are for each turn of the Krebs Cycle. The Krebs cycle turns twice for each molecule of glucose that passes through the aerobic system - as 2 pyruvate molecules enter the Krebs Cycle. In order for the Pyruvate molecules to enter the Krebs cycle they must be converted to Acetyl Coenzyme A. During this link reaction, for each molecule of pyruvate that gets converted to Acetyl Coenzyme A, an NAD is also reduced. This stage of the aerobic system takes place in the matrix of the cells' mitochondria.
Oxidative Phosphorylation - This is the last stage of the aerobic system and produces the largest yield of ATP out of all the stages - a total of 34 ATP molecules. It is called 'Oxidative Phosphorylation' because oxygen is the final acceptor of the electrons and hydrogen ions that leave this stage of aerobic respiration (hence oxidative) and ADP gets phosphorylated (an extra phosphate gets added) to form ATP (hence phosphorylation).
This stage of the aerobic system occurs on the cristae (infoldings on the membrane of the mitochondria). The NADH+ from glycolysis and the Krebs cycle, and the FADH+ from the Krebs cycle pass down electron carriers which are at decreasing energy levels, in which energy is released to reform ATP. Each NADH+ that passes down this electron transport chain provides enough energy for 3 molecules of ATP and each molecule, and each molecule of FADH+ provides enough energy for 2 molecules of ATP. If you do your math this means that 10 total NADH+ molecules allow the rejuvenation of 30 ATP, and 2 FADH+ molecules allow for 4 ATP molecules to be rejuvenated (The total being 34 from oxidative phosphorylation
Phosphorylation
Phosphorylation is the addition of a phosphate group to a protein or other organic molecule. Phosphorylation activates or deactivates many protein enzymes....
, plus the 4 from the previous 2 stages meaning a total of 38 ATP being produced during the aerobic system). The NADH+ and FADH+ get oxidized to allow the NAD and FAD to return to be used in the aerobic system again, and electrons and hydrogen ions are accepted by oxygen to produce water, a harmless by-product.
How they work
Aerobic and anaerobic systems usually work concurrently. When describing activity it is not which energy system is working but which predominates.Further reading
- Exercise Physiology for Health, Fitness and Performance. Sharon Plowman and Denise Smith. Lippincott Williams & Wilkins; Third edition (2010). ISBN 978-0781779760.