Lesson 5 Energy and Life PDF

Energy and Life Lesson : 5 Biol 101  OBJECTIVES Define metabolism and energy Differ between exergonic and endergonic reactions Know the function of Enzymes 2  Metabolism Metabolism is the co...

Energy and Life Lesson : 5 Biol 101  OBJECTIVES Define metabolism and energy Differ between exergonic and endergonic reactions Know the function of Enzymes 2  Metabolism Metabolism is the collection of chemical reactions that occur in an organism (catabolism + anabolism) Catabolic = breaking down molecules, releasing energy Anabolic = building molecules, consuming energy Enzymes catalyze reactions in all metabolic pathways which can be catabolic or anabolic Biol 101  Exergonic / Endergonic Reactions Exergonic chemical reaction is spontaneous, it doesn’t need energy Example : catabolic reactions, ATP hydrolysis Endergonic chemical reaction is nonspontaneous it requires an input of energy Example : anabolic reaction, ATP synthesis (regeneration) Biol 101  ATP (Adenosine TriPhosphate) Cycle ATP is the cell’s energy shuttle Hydrolysis of ATP is an exergonic reaction : ATPADP + P + Energy Synthesis (regeneration ) of ATP is an endergonic reaction: ADP + P + E ATP (The energy needed for ATP synthesis is provided by catabolism = Catabolic pathways drive regeneration of ATP) Biol 101  ATP’s Function ATP powers cellular work by coupling exergonic reactions (spontaneous) to endergonic reactions (needing energy) Through Energy Coupling, the exergonic process of ATP hydrolysis drives endergonic reactions by transfer of a phosphate group to specific reactants forming a phosphorylated intermediate that is more reactive. Biol 101  Enzymes Enzymes are macromolecules (proteins) acting as catalyst. Enzymes speed up reactions without being consumed. Each type of enzyme has a unique active site that combines specifically with its substrate, (the reactant molecule on which it acts) The enzyme changes shape slightly when it binds the substrate (inducted fit) E+ SE S  P+ E Biol 101  Enzymes and Activation Energy Enzymes speed up reactions by lowering the EA barrier (EA= activation energy = the energy necessary to break the bonds of the reactants) Lowering the EA barrier is done by: orienting substrates correctly, straining their bonds, providing a favorable microenvironment, or even covalently bonding with the substrate Biol 101  Regulation of Enzymes Activity Regulation could be either by activation, inhibition, or stabilizing of the enzyme’s activity The activity of the enzyme is affected by: 1. Environmental (physical) factors like: temperature, and pH… 2. Chemical factors like salt concentration, cofactors, inhibitors, enzyme concentration … 3. Allosteric regulators when Regulatory molecules, either activators or inhibitors, bind to specific regulatory sites, affecting the shape and function of the enzyme Biol 101  Environmental 1. Temperature and pH Each enzyme has an optimal temperature and pH Above a critical temperature enzyme activity falls rapidly because the enzyme unfolds (denatures) Change in pH affects as well the enzyme’s activity, the pH sensitivity is due to acidic and basic side groups of amino acids Biol 101  Chemical 2. Inhibitors Inhibitors reduce enzyme function There are two types of inhibitors: competitive and non-competitive Biol 101  Chemical 3. Activators Activators increase enzyme function There are 4 types of activators: o Cofactors are inorganic like metals in ionic forms ( zinc, iron, copper) o Coenzymes are organic molecules like vitamins o High Enzyme concentration o High Substrate concentration Biol 101  3. Allosteric Inhibitor/Allosteric Activators Allosteric Activators stabilize the active form of the enzyme. Allosteric Inhibitors stabilize the inactive form of the enzyme. Biol 101  4. Allosteric Cooperativity Cooperativity occurs between a substrate and one active site of an enzyme. The binding of one substrate can stimulate activity at other active sites of the enzyme. All active sites of the enzyme are then locked in active form. Biol 101  5. Allosteric Feedback Inhibition The end product of a metabolic pathway allosterically inhibits the enzyme used in the first step of the pathway. Biol 101 Biol 101