Cellular Respiration and Enzymes

• In first step of glycolysis, glucose is converted in to glucose -6- phosphate by the enzyme Hexokinase or Glucokinase.
  
• Hexokinase is available for all cell where as Glucokinase acts only for liver cell.
• It also require magnesium as cofactor.
• Hexokinase is the major regulatory enzyme of Glycolysis.

Pyruvate is the end product of glycolysis, which is the initial common pathway for cellular respiration that occurs in the cytoplasm. Glycolysis does not require oxygen, meaning pyruvate is formed irrespective of whether oxygen is present or absent.

Complete aerobic respiration of pyruvic acid into carbon dioxide and water releases the maximum amount of energy through the citric acid cycle and oxidative phosphorylation. Earlier steps like glycolysis or partial fermentation retain much of the energy within intermediate organic molecules.

Glycolysis, part of cellular respiration, is a series of reactions that constitute the first phase of most carbohydrate catabolism, catabolism meaning the breaking down of larger molecules into smaller ones. The word glycolysis is derived from two Greek words and means the breakdown of something sweet. Glycolysis breaks down glucose and forms pyruvate with the production of two molecules of ATP. The pyruvate end product of glycolysis can be used in either anaerobic respiration if no oxygen is available or in aerobic respiration via the TCA cycle which yields much more usable energy for the cell.

Glycolysis produces a gross total of 4 ATP and a net total of 2 ATP per glucose molecule, regardless of the presence of oxygen.

Glycolysis is also known as E.M.P. pathway which stands for Embden - Meyerhof - Parnas Pathway, which was discovered by Gustav Embden, Otto Meyerhof, and Jakub Karol Parnas. Glycolysis splits a 6-carbon sugar, glucose, into two molecules of 3-carbon pyruvate in a series of steps, each catalyzed by a particular enzyme. Glycolysis takes place in the cytoplasm (cytosol) of all living cells, not in mitochondria, and does not require the presence of oxygen. Therefore, glycolysis is also known as cytoplasmic respiration. 

During aerobic respiration, one molecule of glucose is oxidized with the help of six oxygen molecules to produce six molecules of carbon dioxide. Six molecules of water are also produced in the process. During aerobic respiration ATP is produced by the processes of substrate level phosphorylation and oxidative phosphorylation. Combined together these processes produce 38 molecules of ATP by phosphorylating 38 molecules of ADP.

Glycolysis produces NADH, but it does not produce FADH2. FADH2 is produced in the Krebs cycle.

Cellular respiration is a complex process that involves multiple pathways. The first step is the glycolysis of glucose which is then followed by Krebs' cycle and ETS in the end. The end products of respiration is CO$ _2$ and H$ _2$O along with release of energy in the form of ATP. Glucose breakdown first starts with glycolysis.

The first step of cellular respiration is the process of glycolysis, a process in which there is breakdown of an organic substance like glucose to pyruvic acid. There is stepwise oxidation of the substrate with the release of energy.

In glycolysis, glucose undergoes partial oxidation to form two molecules of pyruvic acid in a multi-step process catalyzed by various enzymes. In which 2 ATP molecules are obtained and NAD$^+$ into 2 molecules NADH when 2 moles of 1,3-diphosphoglyceraldehyde converts into two moles of 1,3 diphosphoglyceric acid.

Cellular respiration aims at producing energy in the form of ATP and occurs in every living cell. The respiration starts with glycolysis, a stepwise process that oxidises respiratory substrate like glucose. Oxidation is in the form of removal of hydrogen and there is no external electron acceptor present.

Phosphorylation is the addition of a phosphate group to an organic molecule.

Glycolysis is also known as EMP pathway on the name of the scientist who discovered it and they were Embden, Mayerhoff and Parnas.