Cellular Respiration | Conversion Of Energy From Nutrients Into ATP

Cellular respiration is an exothermic redox reaction which releases heat. During cellular respiration, sugar is broken down into CO2 and H2O, also with ATP is made that can then be used for cellular work. Respiration is the main keyway a cell releases chemical energy to fuel cellular activity. 

A set of metabolic reactions that take place in the cell of organisms to convert biochemical energy from nutrients into adenosine triphosphate(ATP), and then release the waste products. The biochemical reaction pathways by which cells release the energy from the chemical bonds of food molecules and provide that energy for the metabolism. 


     C6H12O6  + 6O2 ——————-> 6CO2 + 6H2O + 38 ATP

The chemical energy stored in ATP can be used to drive processes that require energy, including biosynthesis, locomotion, or transportation of molecules across the cell membranes.

Aerobic Respiration: Cellular Respiration

  • Glucose:

Glucose is a carbohydrate, and it is the most important simple sugar required in human metabolism. Glucose is called a simple sugar or a monosaccharide because it is one of the smallest units which has the characteristics of this type of carbohydrates.

  • Glycolysis:

Glycolysis, part of cellular respiration, is a series of reactions that constitute the first phase of the carbohydrate catabolism, catabolism meaning the break down of larger into smaller molecules. In glycolysis, glucose breaks down and forms pyruvate with the production of two molecules of ATP.

   Glucose + 2 NAD+ 2 ADP → 2 pyruvate+ 2 NADH + 2 ATP + 2 H2O + heat

  • The TCA (Tricarboxylic Acid) Cycle:

The tricarboxylic acid cycle (TCA cycle) is a series of enzyme-catalyzed chemical reactions that is a vital part of aerobic respiration in cells. The net gain of high-energy compounds from one cycle(one pyruvate molecule) is 3 NADH, 1 FADH2, and 1 GTP; the GTP may be used to produce ATP. Thus, the total yield from 1 glucose molecule (2 pyruvate molecules) is 6 NADH, 2 FADH2, and 2 ATP.

  • Electron Transport Chain:

This cycle deposits energy in the reduced coenzymes which transfer that energy through the chain called the electron transport chain. Occurs in the cristae of the mitochondria the folded membranes inside the chloroplast of the cell. Electrons from hydrogen are carried by NADH and passed down an ETC to result in the production of ATP. ETC results in the production of 32 ATPs for each glucose.

  • Adenosine Triphosphate:

It is a high-energy molecule that stores the energy we need to do everything. It is present in the cytoplasm and nucleoplasm of each and every cell, and essentially all the mechanisms that require energy for operation, obtain it directly from the stored ATP in the cell. For aerobic respiration, glycolysis is also a source of ATP production, but the more productive process in the tiny energy factories called mitochondria plays a significant role.

  • Fermentation:

One of two pathways of anaerobic respiration in cells is the Fermentation pathway, producing ethanol and the other path producing lactate. Both fermentation processes restore the necessary NADH for glycolysis to proceed with the net yield of 2 ATP molecules per glucose. In lower oxygen concentrations, a partial breakdown of sugar occurs which results in less amount of energy, enough to keep a cell alive or working for a while, but not as efficiently As higher concentrations of oxygen. This process is called fermentation. In yeast cells, fermentation results in the production of 2 ATP molecules and a waste product, ethyl alcohol.

  • Anaerobic Respiration:

The respiration in which using electron acceptors other than molecular oxygen(O2) is known as anaerobic respiration. Even though oxygen is not the final electron acceptor, the process still uses a respiratory ETC. In anaerobes, other less-oxidizing substances such as sulfates, nitrates, sulfur (S), or fumarate is used. These electron acceptors have smaller reduction potentials than O2, meaning that less energy is released per molecule get oxidized.

Anaerobic respiration takes place in the fluid portion of the cytoplasm when the bulk of the energy yield of aerobic respiration takes place in the mitochondrial part. Anaerobic respiration leaves a lot of energy in ethanol or lactate molecules that the cell cannot use and must excrete.

Read More-

Cell Cycle or Cell Division Cycle | Mitosis & Meiosis 

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