biology metabolism

What is metabolism? All living things must have an unceasing supply of energy and matter. The transformation of this energy and matter within the body is called metabolism. Metabolism includes two different types: catabolism and anabolism. Catabolism is destructive metabolism. Typically, in catabolism, larger organic molecules are broken down into smaller constituents. This usually occurs with the release of energy. Anabolism is constructive metabolism. Typically, in anabolism, small precursor molecules are assembled into larger organic molecules. This always requires the input of energy. Anabolism is the synthesis of complex molecules from precursors. This includes synthesis of proteins, carbohydrates, nucleic acids and lipids, usually from their building block monomers. Catabolism is the breakdown of complex molecules into smaller precursors from which they are synthesized. It is a reversed process of anabolism. When cells have excess resources such as food and extra energy, anabolism occurs to store unused nutrients for later use. When cells are deficient for food or energy, catabolism occurs to break down the stored nutrients for the body to use. 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. There are two phases of Glycolysis. The first is known as the "priming phase," because it requires an input of energy in the form of 2 ATPs per glucose molecule. The second phase is known as the "pay off phase,” because energy is released in the form of 4 ATPs, 2 per glyceraldehyde molecule. The end result of Glycolysis is two new pyruvate molecules which can then be fed into the Citric Acid cycle (also known as the Kreb's Cycle) if oxygen is present, or can be reduced to lactate or thanol in the absence of of oxygen using a process known as Fermentation. The Kreb’s cycle is the process through which aerobic cellular metabolism occurs. Hans Krebs received the 1953 Nobel Prize in Medicine for his “discovery” of the citric acid cycle. This cycle involves a series of reactions involving a (1) a substrate, Oxaloacetate, that is modified in every reaction, (2) Acetyl–CoA, from which energy is extracted, (3) energy transport reactants, which collect the extracted energy, and (4) the controlling enzymes, which regulate the steps of the cycle. This cycle is ubiquitous in living organisms, single and multi-celled, both plants and animals — including humans. Organizationally, the process is often divided into 8 steps, one for each controlling enzyme, usually beginning with the combination of the Oxaloacetate substrate to the Acetyl–CoA, which is produced from either glycolysis or pyruvate oxidation. Below is a picture of the Kreb’s Cycle Glycolysis occurs within almost all living cells and is the primary source of Acetyl-CoA, which is the molecule responsible for the majority of energy output under aerobic conditions. The first phase of Glycolysis requires an input of energy in the form of ATP (adenosine triphosphate). Because the next portion of Glycolysis requires the molecule D-Glyceraldehyde-3-phosphate to continue Dihydroxyacetone phosphate is converted into D-Glyceraldehyde-3-phosphate by the enzyme Triose phosphate isomerase (Class: Isomerase) Carbohydrate metabolism begins with digestion in the small intestine where monosaccharaides are absorbed into the blood stream. Blood sugar concentrations are controlled by three hormones: insulin, glucagon, and epinephrine. If the concentration of glucose in the blood is too high, insulin is secreted by the pancreas. Insulin stimulates the transfer of glucose into the cells, especially in the liver and muscles, although other organs are also able to metabolize glucose. In the liver and muscles, most of the glucose is changed into glycogen by the process of glycogenesis (anabolism). Glycogen is stored in the liver and muscles until needed at some later time when glucose levels are low. If blood glucose levels are low, then epinephrine and glucagon hormones are secreted to stimulate the conversion of glycogen to glucose. This process is called glycogenolysis (catabolism). If glucose is needed immediately upon entering the cells to supply energy, it begins the metabolic process called glycolysis (catabolism). The end products of glycolysis are pyruvic acid and ATP. Since glycolysis releases relatively little ATP, further reactions continue to convert pyruvic acid to acetyl CoA and then citric acid in the citric acid cycle. The majority of the ATP is made from oxidations in the citric acid cycle in connection with the electron transport chain. According to the website (UCDavischemwiki) the following picture describes the electron transport chain.
I (NADH-ubiquinone oxidioreductase): An integral protein that receives electrons in the form of hydride ions from NADH and passes them on to ubiquinone
II (Succinate-ubiquinone oxidioreductase aka succinate dehydrogenase from the TCA cycle): A peripheral protein that receives electrons from succinate (an intermediate metabolite of the TCA cycle) to yield fumarate and [FADH2]. From succinate the electrons are received by [FAD] (a prosthetic group of the protein) which then become [FADH2]. The electrons are then passed off to ubiquinone.
Q (Ubiquinone/ ubiquinol): Ubiquinone (the oxidized form of the molecule) receives electrons from several different carriers; from I, II, Glycerol-3-phosphate dehydrogenase, and ETF. It is now the reduced form (ubiquinol) which passes its electron off to III.
III (Ubiquinol-cytochrome c oxidioreductase): An integral protein that receives electrons from ubiquinol which are then passed on to Cytochrome c
IV (Cytochrome c oxidase):An integral protein that that receives electrons from Cytochrome c and transfers them to oxygen to produce water within the mitochondria matrix.
ATP Synthase: An integral protein consisting of several different subunits. This protein is directly responsible for the production of ATP via chemiosmotic phosphorylation. It uses the proton gradient created by several of the other carriers in the ETC to drive a mechanical rotor. The energy from that rotor is then used to phosphorylate ADT to ATP. (UCDavischemwiki) During strenuous muscular activity, pyruvic acid is converted into lactic acid rather that acetyl CoA. During the resting period, the lactic acid is converted back to pyruvic acid. The pyruvic acid in turn is converted back to glucose by the process called gluconeogenesis (anabolism). If the glucose is not needed at that moment, it is converted into glycogen by glycogenesis. You can remember those terms if you think of "genesis" as the formation-beginning. Free energy describes whether a reaction will occur spontaneously. The First Law of Thermodynamics states that energy is conserved: energy can neither be created nor destroyed. The Second Law of Thermodynamics states that the work produced from a given energy can never be 100% efficient. In metabolism, reactions which are spontaneous are favorable because these run automatically and release free energy. Every reaction has an activation energy, which describes an energy barrier that is overcome every time the reaction occurs. Most of the reactions in the cell require enzymes. Enzymes are proteins to speed up reactions by grabbing onto reactants to bring them closer together. Reactants which are closer together can reach activation energy more easily. Thus, enzymes lower activation energy and speed up the reaction. ATP is the energy currency of all cells. Most of the reactions in the cell require ATP. ATP is energy rich. When the energy is used by a reaction, ATP breaks up into ADP and Pi. In order to use the energy again, ADP and Pi must be changed back into ATP. This requires energy. Non-spontaneous reactions requires energy, and this is often done by coupling this reaction with an ATP breaking down reaction, the combined free energy will be negative and therefore enables the overall reaction. Cellular respiration is a series of metabolic processes which all living cells use to produce energy in the form of ATP. In cellular respiration, the cell breaks down glucose to produce large amounts of energy in the form of ATP. Cellular respiration can take two paths: aerobic respiration or anaerobic respiration. Aerobic respiration occurs when oxygen is available, whereas anaerobic respiration occurs when oxygen is not available. The two paths of cellular respiration share the glycolysis step. Aerobic respiration has three steps: glycolysis, Krebs cycle, and oxidative phosphorylation. During glycolysis, glucose is broken down into pyruvate and produces 2 ATP. The Krebs cycle is also known as TCA cycle which contains a series of Redox reactions to convert pyruvate into CO2 and produce NADH and FADH2. During oxidative phosphorylation, NADH and FADH2 are used as substrate to generate a pH gradient on mitochondria membrane which is used to generate ATP via ATP synthase. Anaerobic respiration contains two steps: glycolysis and fermentation. Fermentation regenerates the reactants needed for glycolysis to run again. Fermentation converts pyruvate into ethanol or lactic acid, and in the process regenerates intermediates for glycolysis.

Work cited

Benson, Darik. "Electron Transport Chain." - Chemwiki. N.p., n.d. Web. 13 Apr. 2014.