BIO 101 1st Edition Lecture 12 Outline of Last Lecture I Metabolism a Metabolic Pathways II Classified Energetics a Catabolic pathways b Anabolic pathways III Energy a Kinetic b Potential IV Thermodynamics V Chemical reactions a Exergonic b Endergonic Outline of Current Lecture I Enzymes a Catalysts b Free Energy of Activation II Factors Affecting Enzyme Activity III Control of Metabolism IV Feedback Inhibition V ATP and Cellular Work Enzymes Biological catalysts proteins used to speed up chemical reactions in the cell Catalyst speeds up a reaction without being consumed in the reaction can be used over and over Consider the reaction A reactant B C products negative Free Energy of Activation amount of energy needed to reach the transition state an unstable state This reaction is energetically favorable exergonic But will not initiate without input of energy to allow A to reach transition state THEN it will go spontaneously and release energy In lab a reaction can go to transition state by heating BIO 101 1st Edition In cell enzymes are used to reach transition state quickly speed up reaction So the of a reaction determines if it will be spontaneous or not but will not predict how long it will take to initiate Enzyme speeds up initiation speed by lowering the free energy of activationit does not change the with help of an enzyme of the reaction in chemical reactions occurring The reactant s are referred to as the substrate for the enzyme The enzyme is a protein with a specific 3D shape It has a groove or pocket on the surface that is just right size shape charge to hold the SUBSTRATE The groove pocket on the enzyme that holds the substrate is called the ACTIVE SITE Enzyme Substrate Enzyme Substrate Complex o Binding of substrate by active site induces enzyme to change shape o This puts stress on bonds in the substrate and or brings 2 substrates into close proximity o The chemical reaction occurs in the active site o Products are released o Whole cycle occurs very quickly 1000 a reactions second o Once products are released enzyme can be used again Factors Affecting Enzyme Activity Cells control chemical reactions by controlling the ENZYMES that catalyze the reaction Factors that determine how well an enzyme works 1 Environmental conditions temperature pH ionic concentration 2 Cofactors and coenzymes small non protein molecules that are required for the activity of some enzymes May be inorganic cofactor ex iron zinc May be organic coenzyme ex most vitamins 3 Substrate concentration Substrate increases rate of the reaction until all active sites are filledthen enzyme is said to be saturated and reaction is at maximum rate 4 Enzyme inhibitors some chemcials can selectively decrease activity of certain enzymes Competitive inhibitors chemical looks like substrate and competes for active site BIO 101 1st Edition Noncompetitive inhibitor binds to another part of the enzyme NOT the active site changes the SHAPE of the enzyme so that it can no longer bind substrate 5 Allosteric regulation some complex enzymes are regulated both up and down by binding of small molecules to a specific site on the enzyme Allosteric site specific site where allosteric regulators bind and affect enzyme activity NOT the active sits usually at the place where subunits of the enzyme are connected Enzymes with allosteric sites are usually complex with more than one subunit called ALLOSTERIC ENZYMES Allosteric enzymes oscillate between an active form catalyzes chemical reaction and inactive form doesn t bind substrate does NOT catalyze reaction There are two kinds of allosteric regulators Allosteric activator stabilizes active form increases activity Allosteric inhibitor stabilizes inactive form decreases activity Control of Metabolism Metabolic pathways are a series of chemical reactions where the product of one is the substrate for the next Pathways can be controlled by controlling the activity of any ONE enzyme in the pathway ie don t have to control ALL the individual reactions because they are connected Feedback Inhibition an example of controlling a pathway In feedback inhibition the end product of the pathway is an allosteric inhibitor of an enzyme that functions early in the pathway usually enzyme 1 Example is the metabolic pathway in which the amino acid Threonine is converted to the amino acid isoleucine at any given time cell need both of these amino acids to make proteins a balance is needed if too much isoleucine starts to accumulate the cell will run out of threoninethen isoleucine binds to the inactive form of enzyme 1 and inhibits it this allows threonine to accumulate BIO 101 1st Edition self controlling pathway because the end product regulates its own synthesis good mechanism when beginning reactant final product ratio is important ATP and Cellular Work Cell does work ex Endergonic chemical reactions mechanical work movement transport of substances across membrane Usual immediate source of energy for cellular work is adenosine triphosphate ATP energy currency of cell How does releasing a phosphate from ATP or ADP allow the cell to do work the phosphate is transferred to another molecule and that molecule becomes energized ex ATP powers muscle movement by transferring a phosphate group to contractile proteins they become energized and then can move 10 million ATPs are consumed and regenerated per cell per second regeneration of ATP is an endergonic reaction 2 basic ways to provide energy to regenerate ATP cellular respiration catabolic pathway and photosynthesis light energy