Energy and Cellular Respiration

We need energy to perform our daily activities and we get this energy from cell through cellular respiration from food molecules. In general, the food molecule glucose used as metabolic fuel in cellular respiration, but amino acids and fatty acids can also be used as metabolic fuels when stored glucose in our body become depleted.rnWe can found the metabolic glucose from carbohydrate sources such as wheat, rice, potatoes, legumes, honey, fruits etc, amino acids from protein sources such as meat, egg, fish, soya bean etc, and fatty acid from animal fat and different type of oil. Usually daily energy requirement is made up of 50% carbohydrate, 35% fat, and 15% protein. Daily average requirement of carbohydrate is 400-600 gm, protein is 70-100 gm and fat is 10-20 gm. Each gram of carbohydrate provides 4 Kcal energy, each gram of protein provides 4 Kcal energy and each gram of fat provides 9 Kcal energy.rnThe metabolic fuels generate energy via the three stages of cellular respiration that are glycolysis, TCA cycle and electron transporat chain. At first fuel molecules enters into glycolysis pathway, and generates Acetyl CoA, NADH and energy molecule in the form of ATP. There are two types of glycolysis present, one is aerobic glycolysis and another is anaerobic glycolysis. Both type of glycolysis occur in cytoplasm of cell. Oxygen is necessary in aerobic glycolysis but anaerobic glycolysis occurs without participation of oxygen that is a valuable energy sourec during deprived of sufficient oxygen such as during heavy exercise, in hypoxic state, and in shock. When the principle fuel glucose is depleted and energy needed, fat are degraded into fatty acids. Fatty acids are oxidized by the process of β-oxidation producing acetyl CoA. Amino acids are used as fuel only if glucose and fat reserves in our body are depleted. Amino acids are converted into acetyl CoA by the process of transamination. Next, Acetyl CoA produced NADH, FADH2 and energy via the TCA cycle. TCA cycle is the second stage of cellular respiration, occurs in the mitochondria of cell and required oxygen. Finally, NADH and FADH2 provides large amount of energy through the electron transport chain. It is the last stage of cellular respiration, occurs within the mitochondria and need oxygen. By these three stages, cell generates a large amount of energy, body store this energy and utilize in appropriate amounts in different type of energy consuming daily activities including muscle contraction, nerve impulse conduction, active transport, synthesis, and so on. cellular respiration