Whether it is the huge set of bodily processes such as cell metabolism, enzyme and hormone synthesis, muscular activity, brain function, and transport of substances or accomplishing a range of daily chores, exercises, and sports, our body needs energy on an ongoing basis. Understanding the chemical processes involved in the conversion of nutrients into energy is critical to maintain balance in the energy intake and expenditure equation.
The Science of Energy Production
Despite the type and amount of nutrients provided to the body and fluctuations in our activity levels, our cells must adapt and produce energy continuously. When we consume foods, they are broken down into smaller units by various biochemical reactions involving enzymatic activity. The protein foods get broken down into amino acids, carbohydrates into simpler glucose molecules, and fats get converted into fatty acids.
These basic nutrient components are then circulated via blood vessels to different cells of the body. Each cell contains an energy power station in the form of mitochondria. Here the chemical bonds of the fuel molecules undergo a series of oxidation-reduction reactions. Every fuel that goes into our body - carbohydrate, fat or protein - must get converted into a compound called acetyl coenzyme A, before it can be metabolized in the mitochondria. The energy produced is stored as ATP, or adenosine tri phosphate, in the mitochondria. These ATP molecules work as carriers of chemical energy across our body. ATP consists of one adenosine unit attached to three phosphate groups by high energy chemical bonds. Whenever a cell requires energy, the stored energy in ATP is released by breaking the ATP molecule into ADP, or adenosine di phosphate, and inorganic phosphorus. The energy released helps the cells perform their specific roles.
For example, ATP breakdown in a muscle cell will produce energy for muscular contractions. In immune cells, it may help to kill invading bacteria. Since our cells can store only a small quantity of ATP, the body replenishes the ATP stores by adding the phosphate group back to the ADP molecule to create ATP through a process called phosphorylation. This inter-conversion of ATP into ADP and later back into ATP forms the crux of our energy system.
Carbohydrates as Energy Source
Carbohydrates get converted into glucose. Any glucose not needed right away gets stored in the muscles and the liver in the form of glycogen. Once these glycogen stores are filled up, any extra gets stored as fat. During exercise, our body uses the stored glycogen reserves as an easy source of energy - the duration and intensity of exercise being the key regulating factors.
If we are not consuming enough carbohydrates, then our body may have to use proteins for energy production. Relying on protein, as opposed to carbohydrates, may interfere with the primary roles of proteins as building blocks of muscle, tissue, and bone. The glucose released by the breakdown of carbohydrates follow two major metabolic pathways:
results in the production of two molecules each of ATP and pyruvic acid. The end product, pyruvic acid, may get transformed into acetyl coenzyme A and enter Krebs’ cycle in presence of oxygen or get converted into lactic acid during heavy exercises (anaerobic). The energy produced through glycolysis is quick but inefficient and is often used by our body during ‘fight or flight’ situations or under emergency only.
or citric acid cycle comprises a series of enzyme and coenzyme reactions undertaken in presence of oxygen, resulting in the generation of thirty six units of ATP from a single glucose molecule. Carbon dioxide and water are the end products. The entire process is considered to be a highly efficient aerobic energy production mechanism. No doubt that glucose is the preferred energy source for most cells.
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