physio lab 1 - INTRODUCTION Reactions take place when a...

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INTRODUCTION Reactions take place when a starting material, a reactant, is altered into a different material called the product. Reactions can proceed in a forward, backward, or bi- directional (both) manner. If the reaction breaks a large starting material into smaller ones, it is considered a catabolic reaction, whereas if a larger molecule is formed from smaller ones, it is known as an anabolic reaction. The sum of all chemical reactions that occur in the body is known as metabolism. A metabolic pathway involves many different reactions in a series of steps, where the product of one reaction acts as the reactant of the next, until the desired end products are made. The following are types of reactions utilized by the body in the metabolic pathway: hydrolysis (uses water to break bonds between molecules), condensation (links two molecules by generating water as a product), phosphorylation (addition of a phosphate group), dephosphorylation (removal of a phosphate group), oxidation (removal of electrons from a molecule), and reduction (addition of electrons to a molecule). The first law of thermodynamics states that energy in a closed system is constant. This means that in a metabolic reaction, if the products have less energy than the reactants, energy is released as another form, such as heat. Reactions that release energy can proceed spontaneously in the forward direction. On the other hand, in reactions that require energy, the products have more energy than the reactions and must obtain a certain amount of energy in order to enter the transition state and allow the reaction to proceed. This energy barrier is known as the reaction’s activation energy. An enzyme is a protein that acts as a biological catalyst to increase the rate of reaction by decreasing the energy barrier. Its activity is one of the most important 1
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regulatory features in human metabolism. An enzyme operates without altering the nature of the reaction or the reaction’s products. The substrate binds to the active site of the enzyme in a lock and key model, where the substrate’s shape complements the active site, or an induced fit model, where the substrate binding alters the shape of the enzyme. Some enzymes bind coenzymes, which are vitamins or vitamin derivatives that participate in the reaction. NAD and FAD are examples of coenzymes. The activity of an enzyme can be affected by many different factors such as the enzyme’s catalytic rate, enzyme concentration, substrate concentration, the affinity of the enzyme to the substrate, and the presence of allosteric or covalent regulators. In allosteric regulation, a modulator binds to the regulatory site of the enzyme and alters the shape of the active site, whereas in covalent regulation, a chemical group is chemically bonded to the enzyme. Enzyme activity can also be controlled through the pH or temperature of the enzyme’s environment. Usually, as the temperature of the environment increases, the activity of the enzyme increases so that the reaction proceeds at a faster rate. However,
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physio lab 1 - INTRODUCTION Reactions take place when a...

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