BIOL 1st Edition Lecture 10 Outline of Last Lecture I Metabolism II Metabolic Pathways III Types of Pathways IV Energy V Energy with Chemical Reactions Outline of Current Lecture I Chemical Reactions II Exergonic Reactions III Endergonic Reactions IV Enzymes V Enzyme Substrate Complex VI Factors Affecting Enzyme Activity VII Control of Metabolism VIII ATP Current Lecture I II Chemical Reactions a Reactant molecules form to products i Written as reactants products b Chemical reactions proceed with change in free energy G i Free energy G is the amount of energy available to do work ii Free energy includes enthalpy and entropy factors lecture 9 iii Written as G H T S where G is the change in free energy H the change in enthalpy and T S is the change in entropy iv G determines whether the reaction is spontaneous Exergonic Reactions is a Spontaneous b Reactants have more bond energy H than products i Energy is released c S increases during the reaction because products are more disordered d G is the maximum amount of work that reaction can do e III Endergonic Reactions a Not spontaneous b Reactants have less bond energy H than products energy is consumed c S tends to decrease during the reaction products are more ordered d G is the minimum amount of work required to make a reaction go e IV Enzymes a Biological catalysts made from proteins that speed up chemical reactions in the cell b Catalyst speeds up a reaction without being used in the reaction over and over c Enzymes are used to bring the reaction to the transition state d Enzymes speed up the reaction but don t change the free energy G e Chemical reactions utilizing enzymes refer to the reactants as substrate i Substrate is held in a 3 D pocket in the enzyme specific to its shape ii This pocket is referred to as the active site V Enzyme Substrate Complex a Binding the substrate and the active site induces the enzyme to change shape b This stresses the bonds in the substrates or brings the two of them together c Chemical reactions occur in the active site d Products are released allowing the enzyme to catalyze another reaction e Occurs very quickly VI Factors Affecting Enzyme Activity a Environmental conditions i Temperature ii pH iii Ionic concentration b Cofactors and coenzymes i Small non protein molecules that are required for the activity of some enzymes ii Inorganic iron zinc or organic vitamins c Substrate concentration i Higher concentration increases the rate of reaction ii When all active sites are filled the solution has reached saturation iii Saturation maximum rate of reaction d Enzyme inhibitors i Competitive inhibitors chemical that looks like an enzyme and competes for the active site ii Noncompetitive inhibitor binds to another part of the enzyme and changes its shape so it can t bind with substrate e Allosteric regulations i Some enzymes are regulated by the binding of small molecules to a specific site on the enzyme 1 Allosteric site where these molecules are bonded NOT the active site ii These enzymes usually have more than one subunit and are called allosteric enzymes iii Allosteric enzymes oscillate between an active form catalyzes chemical reaction and an inactive form doesn t bind to the substrate or catalyze the reaction iv Two types of regulators 1 Allosteric activator stabilizes active form increasing activity 2 Allosteric inhibitor stabilizes inactive form decreasing activity VII Control of Metabolism a Metabolic pathways are a series of chemical reactions in which the product of one reaction becomes the reactant for the next b Can be controlled by controlling one enzyme VIII c Feedback Inhibition example of controlling a pathway i The end product of the pathway is an allosteric inhibitor of an enzyme that functions early in the pathway enzyme 1 usually ii Ex Threonine converting to Isoleucine 1 Cell needs both amino acids to make proteins 2 If too much isoleucine is present the cell runs our of threonine so the isoleucine binds to the inactive form of enzyme 1 and inhibits it allowing threonine to accumulate 3 This pathway is self controlling because the end product regulates its own synthesis 4 Good mechanism for reactions that have an important product to reactant ratio ATP a Adenosine triphosphate ATP is the usual immediate source for cellular work b ATP and ADP release phosphates causing the molecule to become energized and allowing the cell to do work c The regeneration of ATP is an endergonic reaction through two ways i Cellular respiration catabolic pathway ii Photosynthesis light energy