Energy Systems

Reaction Location: Sarcoplasm

Type of Reaction: Anaerobic Coupled

By-products/effects: N/A

1.  ATP is broken down to release energy for muscle contraction. This leaves the by-products: adenosine diphosphate (ADP) and one phosphate (Pi) on its own.

2. Phosphocreatine (PC) stored in the muscle is broken down by the enzyme creatine kinase (releasing energy via this Exothermic Reaction) into Creatine and Phosphate (Pi)

3. Energy released in the breakdown of PC allows ADP and Pi to rejoin forming more ATP (Endothermic Reaction).  This newly formed ATP can now be broken down to release energy to fuel further activity.

Reaction location: Muscle Cell Sarcoplasm

Type of Reaction: Anaerobic Coupled

By-products/effects: Lactic Acid

1. The decrease in PC (Phosphocreatine) stores activates the enzyme glycogen phosphorylase to break down glycogen into glucose - this is then broken down further in a series of reactions called glycolysis.

2. During glycolysis, phosphofruktokinase (PFK) initiaties the partial breakdown of glucose into pyruvic acid.

3. The absence of oxygen means pyruvic acid is further broken down into lactic acid via lactate dehydrogenase (LDH).

Reaction Location: Muscle Sarcoplasm

Type of Reaction: Aerobic Coupled

By-Products/Effects: N/A

1. The presence of oxygen prevents the accumulation of lactic acid by diverting pyruvic acid further into the aerobic system.

2. Pyruvic acid combines with coenzyme A to form Acetyl Coenzyme A.

Reaction Location: Matrix of the Mitochondria

Type of reaction: 

By-Products/Effects: 

1. Acetyl Coenzyme A combines with Oxaloacetic acid to form Citric acid.

2. This is broken down further via a series of complex reactions in the matrix of the mitochondria where four events take place:

- CO2 produced and removed via the lungs

- Hydrogen atoms are removed in a process called oxidation

- Energy is produced to resynthesise two ATP molecules

- Oxaloacetic acid is regenerated.

Reaction Location: Mitochondria Cristae

Type of Reaction:

By-Products/Effects:

1. Hydrogen atoms combine with coenzymes NAD and FAD to form NADH and FADH.

2. NADH and FADH carried down the ETC where hydrogen is split into H+ and e-.

3. In the mitochondria cristae, three events take place:

- Hydrogen electron (e-) splits from hydrogen atom and passes down the ETC 

- This provides energy to resynthesise 34 ATP

- Hydrogen ion (H+) combines with oxygen to form H2O