Energy Systems Flashcards
Define adenosine triphosphate (ATP)
A high energy compound which is the only immediately available source of energy for muscular contraction
Explain the ATP-PC system
The ATP-PC system kicks in during very high intensity activity after the first two seconds of intense exercise depletes the original ATP stores. ATP levels fall dramatically and ADP and P levels rise. This triggers the release of creatine kinase, an enzyme which catalyses the breakdown of the immediately available fuel phosphocreatine (PC).
ATP-PC system
Type of reaction
Site of reaction
Food fuel used
Controlling enzyme
ATP yield
By-products
Intensity of activity
Duration of system
Type - anaerobic
Site - sarcoplasm
Fuel - phosphocreatine
Enzyme - creatine kinase
Yield - 1 mole of PC yields 1 mole of ATP (1:1)
By-products - none
Intensity - very high intensity (100m sprint)
Duration - 2-10 seconds
Strengths and weaknesses of the ATP-PC system
Strengths:
• no delay for oxygen
• PC readily available in muscle cell
• simple and rapid breakdown of PC and resynthesis of ATP
• provides energy for very high intensity activities
• no fatiguing by-products and simple compounds aid fast recovery
Weaknesses:
• Low ATP yield and small PC stores lead to rapid fatigue after 8-10 seconds
Explain the glycolytic system
The glycolytic system kicks in during high intensity activity after the first ten seconds of intense activity exhausts the PC stores and ATP levels fall. ADP and P levels rise again and trigger the release of phosphofructokinase (PFK), an enzyme which catalyses the breakdown of the next available fuel: glucose.
Glycolytic system
Type of reaction
Site of reaction
Food fuel used
Controlling enzyme
ATP yield
By-products
Intensity of activity
Duration of activity
Reaction - anaerobic
Site - sarcoplasm
Fuel - glycogen/glucose
Enzyme - GPP, PFK, LDH
ATP yield - 1 mole of glycogen yields 2 moles of ATP (1:2)
by-products - lactic acid
Intensity - very high intensity (200-400m track events)
Duration of system - up to 3 mins depending on intensity
Strengths and weaknesses of the glycolytic system
Strengths:
• no delay for oxygen and large fuel stores in the liver, muscles and blood stream
• relatively fast fuel breakdown for ATP resynthesis
• provides energy for high intensity activities for up to three minutes
• lactic acid can be recycled into fuel for further energy production
Weaknesses:
• fatiguing by-product lactic acid reduces pH and enzyme activity
• relatively low ATP yield and recovery can be lengthy
Describe the aerobic system
The aerobic system kicks in during low to moderate intensity activity as the arrival of sufficient oxygen enables continued energy production. The aerobic system utilities around 95 per cent of the potential energy in glucose through three distinct stages: aerobic glycolysis, Krebs cycle, electron transport chain (ETC)
Explain the aerobic glycolysis stage of the aerobic energy system
Aerobic glycolysis in the sarcoplasm converts glucose into pyruvic acid with the enzyme PFK catalysing the reaction. This releases enough energy to resynthesise two moles of ATP. Converting glycogen into glucose (by enzyme GPP) maintains this process for extended periods of time. As oxygen is now in sufficient supply, the pyruvic acid is no longer converted into lactic acid. It goes through a link reaction catalysed by coenzyme A, which produces acetyl CoA. This allows access to the mitochondria.
Explain the Krebs’s cycle stage of the aerobic energy system
Acetyl CoA combines with oxaloacetic acid to form citric acid, which is oxidised through a cycle of reactions, known as the Krebs’s cycle. CO2, hydrogen and enough energy to resynthesise two moles of ATP are released. This process occurs in the matrix (intracellular fluid) of the mitochondria
Explain the electron transport chain stage of the aerobic energy system
The hydrogen atoms are carried through the electron transport chain along the cristae of the mitochondria by NAD and FAD, splitting into ions (H+) and electrons (H-). Hydrogen ions are oxidised and removed as H2O. Pairs of hydrogen electrons carried by NAD (NADH2) release energy to resynthesise 30 moles of ATP and those carried by FAD (FADH2) release enough energy to resynthesise 4 moles of ATP. The overall yield of the ETC is 34 moles of ATP
Aerobic system
Type of reaction
Site of reaction
Food fuel used
Controlling enzyme
ATP yield
By-products
Intensity of activity
Duration of system
Type - aerobic
Site - sarcoplasm, matrix and cristae
Fuel - glycogen, glucose and triglycerides
Enzyme - GPP, PFK, co-enzyme A and lipase
Yield - 1 mole of glycogen yields up to 38 moles of ATP (1:38)
By-products - CO2 and H2O
Intensity - low-moderate intensity (e.g. marathon)
Duration - three minutes onwards
Strengths and weaknesses of the aerobic energy system
Strengths:
• large fuel stores
• high ATP yield and long duration of energy production
• no fatiguing by-products
Weaknesses:
• delay for oxygen delivery and complex series of reactions
• slow energy production limits activity to sub-maximal intensity
• triglycerides or FFAs demand around 15% more O2 for breakdown
