The human body’s Chemical energy

Cells get energy from food (e.g., carbohydrates and fats) indirectly by breaking them down liberating and catching their energy as “Adenosine triphosphate(ATP), which is a form of chemical energy for “Immediate” use in cellular functions. Cells cannot store ATP; therefore, the extra ATP generated is stored as the animal sugar “Glycogen” (Liver & muscles) and “Body fat” (Fatty acids)

The body has 4 main “Chemical” energy pathways that work as a “Car piston, typically located in the mitochondria, to fuel different body functions:

1. Adenosine triphosphate (ATP): it lasts for 2-3 seconds 

2. Phosphocreatine (ATP-Cr): it lasts for 8-10 seconds; the main function of phosphocreatine is to store excess energy and release it with its phosphate (P) molecule to “replenish” ATP when ADP starts to accumulate within the tissues. Phosphocreatine is used for “Emergency fuel” in muscle tissues   

3. Anaerobic respiration: it lasts for 2-3 minutes; this system is used when the phosphocreatine system is depleted. It uses “Glucose” only to yield (2-ATP from glucose and 3-ATP from glycogen) molecules via “Fermentation” in the “Cytoplasm” of cells, building lactic acid within the tissues. According to the work of the German Nobel Prize laureate Dr. Otto Warburg, cancer cells use anaerobic respiration exclusively 

4. Aerobic respiration: it lasts for > 3 minutes; oxygen is used by the electron transport chain in the inner wall of the “Mitochondria” to generate ATP from burning “Glucose, Fatty acids, & Alanin”. Oxygen is needed to burn fatty acids, unlike glucose which can be fermented. Aerobic respiration yields (36-ATP from glucose and 129-ATP from fat). Protein is NOT used as a fuel unless the body is in an emergency situation 


Selected references

1. Gilbert HF. Basic concepts in biochemistry. A student survival guide. 1999; McGraw-Hill Education / Medical; 2nd edition

2. Naik P. Essentials of biochemistry. 2012; Jaypee Brothers Medical Publications; 1st edition