Chapter 6
Energy Energy is the ability to do work or bring about a change Kinetic Energy: Energy of motion Potential Energy: Stored energy Energy transactions must follow the laws of Thermodynamics 1 st : Energy cannot be created or destroyed, only changed to different forms 2 nd : Energy has a tendency to become more random and less organized
Entropy Entropy is a term referring to disorganization. Entropy is a natural state. Therefore, all forms of energy will naturally pursue entropy. An input of energy is always required to build molecules because you are decreasing the randomness/increasing the order in the system. Therefore, a living organism is merely a temporary repository of energy They constantly lose energy due to entropy, so they are constantly in need of energy
Metabolism Metabolism is the compilation of all chemical reactions that occur in a cell. Each reaction has a reactant and a product A + B C + D Reactants (A, B): substances that participate in a reaction. Products (C, D): substances that form as a result of a reaction.
Metabolism Exergonic Reactions are reactions in which more energy is in the reactants than the products Energy is released (Explosion, respiration) Endergonic reactions are reactions in which more energy is in the products than the reactants Energy is stored (Cooking, photosynthesis) A coupled reaction is when an exergonic reaction s released energy drives an endergonic reaction.
ATP The most common molecule of stored energy, available as an immediate power source, is Adenosine Triphosphate, or ATP ATP is a type of nucleid acid. It contains the nucleotide adenine and three phosphate group (triphosphate) Adenine can hold two phosphates easily, but three is difficult. In order to hold the third phosphate, a highenergy bond is required As long as the ATP holds the third phosphate, it holds this input of energy.
ATP ATP (with three phosphates) is a unit of potential energy. When the ATP releases it s third phosphate into an enzyme, the potential energy takes the form of kinetic energy The third phosphate is released with such force that binding with an enzyme causes the enzyme to change shape The ATP now becomes an ADP (adenosine diphosphate).
ATP Using ATP as an energy carrier has three advantages It s a common currency of energy that works the same in any organism The amount of energy stored in ATP is sufficient to run most biological functions, so little energy is wasted When ATP releases it s energy, it does so with a purpose (usually to power an endergonic reaction)
Enzymes An enzyme is a protein that functions as a natural, organic catalyst Catalysts speed up chemical reactions without adding any new elements or chemicals to the reaction The reactants in the reaction that the enzyme helps to function are called substrates Enzymes allow reactions to occur millions of times faster than would otherwise Enzyme equation: E + S ES E + P Enzymes don t become part of the reaction; they just facilitate the reaction
Enzymes Enzymes lower the activation energy The activation energy is the amount of energy required for a reaction to occur Enzymes lower that amount of energy without changing the reaction Enzymes control reactions (they only occur in the presence of enzymes) Enzymes reduce the total amount of energy cells use Enzymes speed up the metabolic processes of the cell
Induced fit model A substrate reacts with an enzyme because the substrate is a perfect fit The location of the enzyme where the substrate fits is called the activation (active) site When the substrate reacts with the active site, it alters the shape of the enzyme temporarily This alteration allows the enzyme to act as a catalyst, and only when the substrate is present
Factors affecting Enzymes Substrate Concentration In order for an enzyme to cause a reaction, the enzyme and substrate must come into contact The more substrates in the cell, the more reactions can occur If the active sites of the enzymes are constantly filled, however, there is no way for the rate to increase
Factors affecting Enzymes Temperature Warmer temperatures cause molecules to move faster, which means the likelihood of substrate/enzyme contact increases If the temperature raises too high, the bonds that hold the protein together fail. This is called denaturing ph Each enzyme has a narrow ph range where it can function Denaturing can also occur if the ph of a cell becomes too low or too high
Factors affecting Enzymes Cofactors Cofactors are molecules that attach to a second active site on an enzyme Cofactors turn an enzyme on Many enzymes can only work if the cofactor is attached to its active site If the concentration of substrate is high, but the concentration of cofactor is low, the enzyme still won t react with the substrates
Factors affecting Enzymes Cofactors There are two types of main cofactors Vitamins Vitamins are trace amounts of material in our diets that act as cofactors for multiple enzymes Phosphorylation Many hormones are activated by phosphorylation Phosphorylation is attaching a phosphate molecule to an enzyme, making it active Hence, most enzymes require an input from an ATP s third phosphate to be activated.
Factors affecting Enzymes Enzyme inhibition Enzymes can be prevented from working as well The enzyme only runs one reaction for every substrate interaction If the substrate does not leave the active site, the enzyme cannot restart a reaction Competitive inhibition Enzymes also have an allosteric inhibitor site, which is like a cofactor except it turns an enzyme off when it would normally be on. Noncompetitive inhibition Most poisons and medicines on the planet are enzyme inhibitors