BIO 101 1st EditionLecture 12Outline of Last LectureI. Metabolisma. Metabolic PathwaysII. Classified Energeticsa. Catabolic pathwaysb. Anabolic pathwaysIII. Energya. Kineticb. Potential IV. ThermodynamicsV. Chemical reactionsa. Exergonicb. EndergonicOutline of Current LectureI. Enzymesa. Catalystsb. Free Energy of ActivationII. Factors Affecting Enzyme ActivityIII. Control of MetabolismIV. Feedback InhibitionV. ATP and Cellular WorkEnzymesBiological catalysts- proteins used to speed up chemical reactions in the cellCatalyst= speeds up a reaction without being consumed in the reaction- can be used over and overConsider the reaction: A (reactant)B + C (products)= negativeFree 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 heatingBIO 101 1st Edition- In cell, enzymes are used to reach transition state quickly: speed up reactionSo 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 activation- it does not change the of the reaction in chemical reactions occurring with help of an enzyme 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 onthe 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 Complexo Binding of substrate by active site induces enzyme to change shapeo This puts stress on bonds in the substrate and/or brings 2 substrates into close proximityo The chemical reaction occurs in the active siteo Products are releasedo Whole cycle occurs very quickly 1000’a reactions/secondo Once products are released, enzyme can be used again Factors Affecting Enzyme Activity- Cells control chemical reactions by controlling the ENZYMES that catalyze thereaction- Factors that determine how well an enzyme works1. Environmental conditions- temperature, pH, ionic concentration2. 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 vitamins3. Substrate concentrationSubstrate increases rate of the reaction until all active sites are filled- then enzyme is said to be saturated and reaction is at maximum rate4. Enzyme inhibitors- some chemcials can selectively decrease activity ofcertain enzymes- Competitive inhibitors- chemical looks like substrate and competes for active siteBIO 101 1st Edition- Noncompetitive inhibitor- binds to another part of the enzyme (NOT the active site)- changes the SHAPE of the enzyme so thatit can no longer bind substrate5. 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 andaffect 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 activityAllosteric inhibitor- stabilizes inactive form: decreases activityControl 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 threonine- then, isoleucine binds to the inactive form of enzyme #1 and inhibits it- this allows threonine to accumulateBIO 101 1st Edition- self-controlling pathway because the end product regulates its own synthesis- good mechanism when beginning reactant/final product ratio is importantATP and Cellular WorkCell does work: ex. Endergonic chemical reactions, mechanical work-movement, transport of substances across membraneUsual immediate source of energy for cellular work is adenosine triphosphate (ATP)= energy currency of cellHow 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 energizedex: ATP powers muscle movement by transferring a phosphate group to contractile proteins- they become energized and then can move10 million ATPs are consumed and regenerated per cell per secondregeneration of ATP is an endergonic reaction 2 basic ways to provide energy to regenerate ATP:cellular respiration(catabolic pathway) and photosynthesis (light