BIOLOGY 111 1st Edition Lecture 10 Outline of Last Lecture I Osmosis II Tonicity III Osmoregulation IV Metabolism V Gibbs Free Energy Outline of Current Lecture I Equilibrium A Open vs Closed systems B Exergonic reactions and Endogonic reactions II ATP III Catalyst A Enzyme and Ribozymes B Activation Energy and Transition State IV Enzymes A Purpose B Active Site and Induced Fit C Environment factors V Inhibitors A Competitive vs Noncompetitive inhibitor B Feedback inhibitor These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute Current Lecture Equilibrium Closed systems will reach equilibrium G 0 And once the system reaches equilibrium the reaction will usually stop and not continue to function Open systems will never reach equilibrium G 0 because there is a continuous flow of energy The reactants and products cycle continuously An example of this would be cells because they experience a constant flow of materials In cells processes with very large negative G s are usually broken down in smaller steps where energy can be captured in manageable chunks Metabolism is also something that is never at equilibrium Exergonic reaction net release of free energy G 0 energy moves outward occurs spontaneously G reactants products don t require work Endergonic reaction absorbs stores free energy from its surroundings G 0 energy moves inward does not occur spontaneously G reactants products require work Cells do three main kinds of work 1 Chemical work pushing of endergonic reactions don t occur spontaneously 2 Transport work pumping substances across membranes against the direction of spontaneous movement 3 Mechanical work i e movement by cilia or flagella contraction of muscle cells energy coupling use of an exergonic process to drive an endergonic one ATP is responsible for mediating most energy coupling in cells and is also usually the immediate source of energy the key to coupling exergonic and endergonic reactions is the formation of a phosphorylated intermediate that is more reactive less stable than an unphosphorylated molecule Phosphorylated intermediate the molecule receiving the phosphate group from the ATP and is covalently bonded explained next Phosphorylation phosphate directly transferred to glucose ATP adenosine triphosphate contains sugar ribose nitrogenous base adenine and a chain of three phosphate groups mediates energy coupling main source of energy hydrolysis breaks the bonds between the phosphate groups and adds water to the terminal phosphate bond creating ADP adenosine diphosphate ATP water hydrolysis ADP phosphate Hydrolysis of last phosphate on ATP G 7 3 kcal mol The energy ATP releases on losing a phosphate group is somewhat greater than energy most other molecules could deliver Catalyst agent that speeds up the rate of a chemical reaction without being consumed during the reaction Enzymes most common protein catalysts in living cells Ribozymes RNA molecules with catalytic properties enzymes are more common than ribozymes as catalysts Activation Energy EA the energy required to start a reaction and get it to the transition state this is often supplied in the form of heat from the surroundings Transition State when molecules have absorbed enough energy for the bonds to break making the reactants be in their most unstable condition Enzymes Speed up reactions by lower the activation energy barrier these do not affect the G or equilibrium Channels the reaction in certain directions most are reversible catalyzing forward or backwards depending on which direction has negative G Allow the cell to control the reactions Bind to substrates Active Site pocket or a groove on the surface of an enzyme where catalysis occurs capable of lowering EA and speed up a reaction by 1 Orienting substrates correctly 2 Bonding the substrate 3 Providing a favorable microenvironment Induced fit brings chemical groups of the active site into positions that enhance their ability to catalyze the chemical reaction the enzyme actually changes shape so that the active sit can enfold the substrate Affected by environmental factors some enzymes work better under certain circumstances than others because these optimal conditions favor the most active shape for enzyme molecules Temperature the rate of enzymatic reaction increases with increasing temperature because substrates collide with active sites more frequently when molecules move more rapidly Above that temperature however the speed of the enzymatic reaction drops sharply because it denatures pH the optimal most enzymes fall in the range of pH 6 8 pepsin stomach enzyme prefers pH 2 and trypsin intestinal enzyme prefers pH 8 Cofactor non protein enzyme helper that is usually an inorganic ion that permanently binds to the enzyme or temporarily binds to the substrate Coenzyme an organic cofactor that participate in a reaction and remain unchanged afterwards Prosthetic Groups small molecules permanently attached to the enzyme and help catalyze Inhibitors Competitor inhibitor reduce the productivity of enzymes by blocking substrates from entering active sites They fight for the active site If increase the concentration of a substrate there will be less competitive inhibition If you decrease the concentration of a substrate there will be more competitive inhibition Examples include Toxins Poisons Pesticides Antibiotics Noncompetitive inhibitor do not directly compete with the substrate to bind to the enzyme at the active site Will bind to the allosteric site and alter the structure of the enzyme so it cannot carry out the reaction The concentration of substrate does not matter like in a competitive inhibitor Feedback inhibition the end product of a metabolic pathway allosterically inhibits the enzyme for a previous step in the pathway