Respiration can be defined as the oxidation of the end products of glycolysis with the storage of the energy in the form of ATP. Cellular respiration occurs when oxygen is available, and the products are carbon dioxide and water. There are three main pathways in the cellular respiration process. These are: pyruvate oxidation, the citric acid cycle, and the respiratory chain. Pyruvate oxidation in eukaryotic cells occurs inside the mitochondrion in the inner membrane, and in prokaryotes on the inner face of the plasma membrane.
These NADH and FADH2 molecules are oxidized during oxidation phosphorylation and the electron transport chain and generate water, H2O and ATP (Voet et al. 2006. p. 397). Intermediates formed from the citric acid cycle are important precursors and building blocks for producing important materials in an organism. These intermediates are drained from the TCA cycle in cataplerotic reactions to synthesize important products such as glucose, fatty acids, and amino acids. For example, gluconeogenesis, the synthesis of glucose, requires oxaloacetate that has been converted to malate, while fatty acid biosynthesis utilizes acetyl CoA, and amino acid biosynthesis utilizes oxaloacetate and α -ketoglutarate (Tymoczko, J. L., Berg, J. M., & Stryer, L. 2013. p. 339).
Glycolysis occurs in the cytosol of the cell and can be divided into three different phases, which include sugar activation, sugar cleavage, and lastly sugar oxidation and ATP formation. The first steps in glycolysis require ATP to get started, this can be thought of as the investment phase of glycolysis. Hexokinase strips a phosphate group from ATP and attaches it to the glucose creating glucose-6-phosphate. Phosphoglucoisomerase re arranges the existing molecule to from
This is achieved through a dehydration and hydration step with cis-Aconistase produced as an intermediate and the aconitase catalysing the overall reaction. The third step involves isocitrate undergoing decarboxylation and oxidation reactions to form alpha-ketoglutarate (Berg J.M et al., 2015). In step four, a second decarboxylation oxidation reaction occurs to form succinyl CoA from alpha-ketoglutarate. Step five involves splitting succinyl CoA to produce succinate and CoA. In step six, succinate is oxidised to fumurate and FADH2 is formed simultaneously (Ness B., 2017).
Glycolysis is an anaerobic respiration. The first step involves the breakdown of glucose. Phosphate groups are added to the glucose to make it a six carbon ring sugar phosphate. For this to happen, 2 ATP are required, this energizes the glucose. The glucose is now more reactive and so this six carbon sugar phosphate is then broken down, forming two, 3 carbon phosphates.
At step 5 NAD+ is converted into NADH + H+. The process works on glucose, a 6-C, until step 4 splits the 6-C into two 3-C compounds. Glyceraldehyde phosphate (GAP, also known as phosphoglyceraldehyde, PGAL) is the more readily used of the two. Dihydroxyacetone phosphate can be converted into GAP by the enzyme Isomerase. The end of the glycolysis process yields two pyruvic acid (3-C) molecules, and a net gain of 2 ATP and two NADH per glucose.
Finally, during TCA-8, NADH is formed and OAA is regenerated. The total numbers of products per acetyl CoA are: 2 CO2, 3 NADH, 1 FADH2, and 1 ATP. The numbers of products per glucose are: 4 CO2, 6 NADH, 2 FADH2, and 2 ATP. Specific enzymes exist for this process as well. First, Acetyl CoA is changed to Citrate by Citrate Synthase, then Citrate is changed to Isocitrate by Aconitase.
Each of these occurs in a specific region of the cell. The first step of cellular respiration is glycolysis, it occurs in the cytosol. Gylcolysis literally means the breakdown of glucose. The process of Glycolysis is both anaerobic without oxygen and aerobic with oxygen. Aerobic is when, in the cytosol converts 1 molecule of glucose into 2 molecules of pyruvate.
This is because the coenzyme is released by hydrolysis from the molecule so that it combines with another acetic acid molecule to begin the Krebs cycle again (Reece, Urry, Cain, Wasserman, Minorsky, & Jackson, 2011). The citric acid molecule undergoes an isomerisation of citrate in the second step in the process of the Krebs cycle in metabolism. Reece et al. (2011) defined isomer as “The isomer is one of several compounds with the same molecular formula but different structures and therefore different properties. There are three types of isomers are structural isomers, cis-trans isomers, and enantiomers” (p. 108).
Glycolysis splits apart a six glucose molecule (six carbon sugar) into three-carbon molecules of pyruvate. The presence of oxygen becomes an issue only in the processes that follow glycolysis. During glycolysis, two ATP molecules are produced. Also, under anaerobic conditions, the pyruvate is usually converted by fermentation into lactate or ethanol. Cellular respiration is a series of reactions, occurring under aerobic conditions, in which large amounts of ATP are produces.