BIOL 1411 1st Edition Lecture 10 Outline of Last Lecture I Cytoplasmic Receptors II Transduction and Amplification of Signal III Direct cell to cell interaction and communication Outline of Current Lecture I Energy Requirements of Cell II ATP III Enzymes Current Lecture I Ability to acquire and transform energy from one form to another is a characteristic of life Anabolic reactions simple molecules complex molecules Catabolic reactions complex simpler ones Thermodynamics o 1st Law of Thermodynamics energy is neither created nor destroyed o 2nd Law when energy is converted form one form to another some of that energy becomes unavailable to do work no reaction is 100 efficient Entropy disorder in a system is increasing in the universe Total Energy usable energy unusable energy entropy o Enthalpy H free energy G entropy S o H G TS T absolute temp o G H TS o G H T S If delta G is negative free energy is released exergonic If delta G is positive free energy is consumed Endergonic If free energy is not available the reaction does not occur Energy releasing reactions occur spontaneously and always increase disorder in the system Exergonic o Releases energy G o Catabolic reactions complex simpler o Spontaneous Endergonic o Consume free energy 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 o Anabolic reactions simple molecules complex o Is a localized decrease in entropy o Not spontaneous Chemical Equilibrium forward and reverse reactions occur at the same time G Cells are an example of an open system Living organisms are highly ordered Do organisms violate the 2nd law of thermodynamics no living organisms must have a constant supply of outside energy to maintain order open system Endergonic reactions are coupled to exergonic reactions in ordered metabolic pathways II ATP Releases a large amount of energy when hydrolyzed to ADP and Pi G 7 3 kcal mol exergonic Bioluminescence o Luciferin O2 ATP Oxyluciferin AMP PPi Light o Enzyme Luciferarse ATP couples exergonic and endergonic reactions in the cell Even thermodynamically favored chemical reactions require some energy to get them started activation energy Enzymes are proteins that act as catalysts for biological reactions o The enzyme is not altered by the reactions o Act as a framework in which reactions can take place o Bring reactants together and increase their free energy III Enzymes Are highly specific for their substrates o Substrate molecules bind to the active site of the enzyme 3 D shape of the enzyme determines the specificity Enzyme Substrate complex ES o Is held together by hydrogen bonds electrical attraction or covalent bonds Enzyme E may change when bound to the substrate induced fit but returns to its original form o E S ES E P Enzymes only lower the energy barrier for reactions o Final equilibrium doesn t change o G doesn t change How Enzymes Work o An enzyme may use one or more mechanisms to catalyze a reaction Orienting the substrates to react Inducing strain in the bonds of the substrates Temporarily adding chemical groups o o o Acid Base catalysis enzyme side chains transfer H to or from the substrates causing a covalent bond to break Covalent Catalysis a function group can covalently bond with substrate Metal ion catalysis metals on side chains lose or gain electrons Reaction Rate There is a max rate for any given enzyme that depends on the substrate concentration Enzyme concentration is usually much lower than concentration of a substrate If all enzyme is bound to substrate max reaction rate Enzymatic Pathways are interconnected Inhibitors naturally occurring molecules that bind to the enzyme and slow reaction rates Competitive inhibitors compete with the natural substrate for binding sites Noncompetitive inhibitors bind to the enzyme at a different site and alter active site often function as metabolic regulators Reversible inhibitor bonds non covalently to the enzyme Irreversible inhibitor covalently bonds to side chains of the enzyme