Tag: bio-chemistry

Cellular respiration is a set of metabolic reactions and processes that take place in the cells of organisms to convert biochemical energy from nutrients into adenosine triphosphate (ATP), and then release waste products. The reactions involved in respiration are catabolic reactions, which break large molecules into smaller ones, releasing energy in the process, as weak so-called "high-energy" bonds are replaced by stronger bonds in the products. Respiration is one of the key ways a cell releases chemical energy to fuel cellular activity.  The chemical energy stored in ATP (its third phosphate group is weakly bonded to the rest of the molecule and is cheaply broken allowing stronger bonds to form, thereby transferring energy for use by the cell) can then be used to drive processes requiring energy. Since the cellular respiration happens inside mitochondria, and glucose being given out as a by-product, glucose is produced inside and outside mitochondria.

Oxidation is a chemical process that, loosely defined, involves removing electrons from particular areas of a molecule. In biochemical processes, oxidation generally results in the release of energy. The glucose molecule contains stored energy in its bonds, just as other nutrient molecules do, including starch, proteins and fats. When you consume food that contains glucose, you digest the food and absorb the glucose into your bloodstream. From there, cells take up the glucose and either store it for later use or chemically burn it to provide energy. Oxidation of glucose is analogous to burning wood in many ways: It releases chemical energy. The complete aerobic oxidation of glucose is coupled to the synthesis of as many as 36 molecules of ATP.

For every molecule of glucose, two molecules of acetyl-CoA enter the Krebs cycle, each producing one GTP (which is readily converted to ATP) through substrate-level phosphorylation. Thus, a total of 2 ATP molecules are obtained directly per glucose molecule from the Krebs cycle.

3-phosphoglyceric acid is an intermediate in glycolysis. Its oxidation involves conversion to pyruvate and subsequent entry into the Krebs cycle and ETC, yielding approximately 16 ATP.

Both ATP and Glucose oxidation are energy releasing or exergonic processes as the value of $\delta$G is negative

The process of glycolysis in respiration requires glucose as the primary substrate to be oxidised. Any other substrate is first converted to glucose before it can enter glycolysis. Certain substrates like ketogenic amino acids, amylose, glycogen need to be converted to glucose first at a cost of some energy in the form of ATP. Hence their net yield of ATP is less than that of glucose as a substrate.

In eukaryotic cells, Complete breakdown of one glucose molecule in to carbon dixoide and water using oxygen produces 36 ATP molecules.

One NADH$ _2$/NADPH$ _2$ yields 3 ATP during electron transport chain process.

Oxidation of palmitic acid yields 7 NADH + 7 FADH2 + 8 acetyl-CoA in 7 cycles of mitochondrial beta-oxidation. Every acetyl-CoA yields 3 NADH + 1 FADH2 + 1 GTP (=ATP) during Krebs cycle. An average production of 3 ATP/NADH and 2 ATP/FADH2 using the respiratory chain, We get  131 ATP molecules. However, you have to use 2 ATP molecules for the initial activation of every fatty acid that is going to be oxidized in the mitochondria.

During the Krebs cycle, the net yield obtained was 6 molecules of NADH + H+, 2 molecules of FADH2, 4 carbon dioxide molecules, and two molecules of ATP.