Catabolism is the biochemical processes of metabolism by which molecules are broken down. Often catabolism is an oxidative process in which carbons have hydrogen atoms removed. CO2 is the most oxidized form of carbon. NADH is the primary electron acceptor for catabolic reactions.
The best source of energy for eukaryotic organisms are fats. Glucose offers a ratio 6.3 moles of ATP per carbon while saturated fatty acids offer 8.1 ATP per carbon. Also the complete oxidation of fats yields enormous amounts of water for those organisms that do not have adequate access to drinkable water. Camels and killer whales are good example of this, they obtain their water requirements from the complete oxidation of fats.
Photosynthesis is responsible for creating NADPH and ATP and the Calvin-Benson-Bassham cycle (CBB) uses those high energy molecules to drive the production of glyceraldehyde-3-phosphate (G-3-P). G-3-P can then be used to synthesize hexose sugars which are the primary source of nutrients for heterotrophs.
The electron transport chain (aka ETC) is a process in which the NADH and [FADH2] produced during glycolysis, β-oxidation, and other catabolic processes are oxidized thus releasing energy in the form of ATP. The mechanism by which ATP is formed in the ETC is called chemiosmotic phosphorolation.
The majority of the energy conserved during catabolism reactions occurs near the end of the metabolic series of reactions in the electron transport chain. The electron transport or respiratory chain gets its name from the fact electrons are transported to meet up with oxygen from respiration at the end of the chain.
Fermentation is the process by which living organisms recycle NADH→NAD+ in the absence of oxygen. NAD+ is a required molecule necessary for the oxidation of Glyceraldehyde-3-phosphate to produce the high energy molecule 1,3-bisphosphoglycerate. Fermentation occurs in the cytosol of cells.
Glycolysis is the catabolic process in which glucose is converted into pyruvate via ten enzymatic steps. There are three regulatory steps, each of which is highly regulated.
Organisms derive the majority of their energy from the Kreb's Cycle, also known as the TCA cycle. The Kreb's Cycle is an aerobic process consisting of eight definite steps. In order to enter the Kreb's Cycle pyruvate must first be converted into Acetyl-CoA by pyruvate dehydrogenase complex found in the mitochondria.
The pyruvate dehydrogenase complex links glycolysis to the TCA cycle (also known as the Krebs cycle or the citric acid cycle). It is a large multi-enzyme complex composed of three enzymes involving five cofactors. The pyruvate dehydrogenase complex oxidizes pyruvate to generate acetyl-coA.
