AN1. Anabolism and catabolism is the first major step before respiration occurs. Because our ingested glucose is normally in aggregates or large chains, the body must break down the large polymer down into single glucose monomers for absorption, and this process is known as catabolism. Catabolism is also used when stored chains of glucose are broken down for use.
Anabolism is used when glucose needs to be stored. Individual glucose monomers are chained together through dehydration synthesis to form glucose chains, which are stored for later use.



2. Overview of cellular respiration process. The entire process is split into 3 parts: Glycolysis, Citric acid cycle and Oxidative Phosphorylation. Only Glycolysis occurs outside the mitochondrion. The purpose of splitting up the reaction is to split up the potential energy in glucose into smaller units of energy, which then can be used to drive individual cellular endergonic reactions, such as phosphorylating ADP into ATP.




3. Glycolysis takes place as the first step in cellular respiration. Glucose is reduced through a series of steps where its potential energy is used to make ATP or added to the electron transport chain. The rearranging of atoms in each step of glycolysis is done by enzymes, which break and attach bonds. Glucose first goes through an energy investment phase, where ATP is coupled with enzymes to transform glucose into two 3-carbon chain molecules. This is followed by the energy pay-off phase, where the 3-carbon sugars give off energy through exergonic reactions. This exergonic energy is coupled with the endergonic reaction of attaching inorganic phosphates with ADP, thus remaking ATP. At the same time, glucose is oxidized by NAD+ molecules. The NAD+ is reduced to its neutral charge with an extra hydrogen attached: NADH.




4. The end product of glycolysis, pyruvate, is converted into acetyl CoA as it enters the mitochondrion. This is to prepare the molecule for the citric acid cycle. The Coenzyme A attaches after pyruvate loses a carbon dioxide, but the bond between the CoA and acetyl molecule is very weak. Pyruvate also becomes oxidized once more by NAD+ before attaching to CoA.




5. The citric acid cycle functions as a process of mass oxidation. It is a cycle because what is left of the citrate is eventually joined by another acetyl CoA group, which originates from the pyruvate. For every molecule of glucose, two pyruvates will be made, and thus will cause the citric acid cycle to "cycle" twice. For each cycle, there will be a stage where exergonic energy is yielded to couple the endergonic reaction of ATP synthesis. Furthermore, large amounts of electrons and hydrogen atoms are oxidized from the initial citrate, and taken to the electron transport chain/oxidation phosphorylation stage.




6. The NADH electron carriers which previously oxidized electrons from the remains of glucose now deposits their electrons into the electron transport chain. This electron transport chain allows the high potential energy electrons to fall down the energy gradient slowly to indirectly allow controlled release of usable energy. To do this, the NADH drops off electrons at the "top" of the electron transport chain, where the electrons are passed along the chain of membrane proteins through oxidation and reduction. This process lowers the electron's potential energy. The lost potential energy is used to power the membrane protein pumps to pump hydrogen ions out into the intermembrane space. Doing so creates a chemical gradient of concentrated hydrogen ions in the intermembrane space. With this gradient setup, the free flow of hydrogen ions back into the membrane can then be used to do work.




7. Hydrogen ions flow naturally back into the mitochondrial matrix due to the set up of a gradient on both sides of the mitochodrion. This natural flow of energy is harnessed by the ATP synthase transmembrane protein, which synthesizes ATP from ADP and inorganic phosphate as hydrogen ions flow in.


If we look at the big picture, the glucose molecule with high potential energy is broken apart, and energy is taken away from the glucose mainly in the form of electrons. The energy from the electrons sets up a chemiosmotic gradient to do work with. This energy is coupled with the endergonic reaction of ATP synthesis.