Cell Bio - Exam 2

Cell Bio - Exam 2 - Cell Biology Exam 2 2.4 Biochemical...

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Cell Biology - Exam 2 2.4 Biochemical Energetics (A quick review) - Kinetic energy: energy of motion o Heat energy o Radiant (light) energy o Electrical energy: moving electrons or ions - Potential energy: stored energy o Energy in covalent bonds o Energy stored in a concentration gradient o Electrical potential: energy of charge separation - Biochemical Energetics o Gibb’s free energy equation: ΔG = ΔH – T ΔS G Free energy; energy available to do work H = Total energy in the bonds (a.k.a. enthalpy) T = temperature in degrees Kelvin S = entropy, measure of randomness or disorder A positive ΔG means you have to put energy into a reaction in order for the reaction to go forward: Endothermic A negative ΔG means that energy was released from the reaction: Exothermic o ΔG If ΔG is negative, the forward reaction will occur spontaneously, and energy will be released If ΔG is positive, the forward reaction will not occur spontaneously, energy will have to be added to the system in order for the forward reaction to occur - Energy Coupled Reactions: o Lets say: A ↔ B + x ΔG = +5 kcal/mol ( endothermic ) o But then, X ↔ Y + Z ΔG = -10 kcal/mol ( exothermic ) o Now couple the two reactions: A↔ B + Y + Z ΔG = -5 kcal/mol o Overall, this coupled reaction is exothermic. But the initial reaction is endothermic. Where does this energy come from?
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Adenosine triphosphate (ATP) – the energy currency molecule in the cell Phosphoanhydride bonds are high energy bonds Breaking them liberates ~7.3 kcal/mol o Hydrolysis of ATP to ADP + P is usually the exothermic reaction (-ΔG) that a cell couples to most endothermic synthetic reactions that have a positive ΔG In plain English: This is how cells use ATP for the energy needed to complete certain cellular tasks o Things the cell uses ATP for aka Endothermic Reactions powered by ATP hydrolysis “Generation of electric potential across a membrane (important for nerve function” WRONG!!!!. .. they mean the cell uses ATP to RESTORE the electric potential across the membrane - Activation Energies and Reaction Rates:
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o This reaction does not require energy between the free energy of the reactants is higher than that of the products (total = - ΔG) A reaction will occur spontaneously if G reactants > G products The highest point are the molecular intermediates o ΔG is the activation energy , or the difference in free energy between the reactants and the transition state o Catalysts increase the rate of reaction by lowering the activation energy - An enzyme: o Accelerates the rates of the reaction by specifically binding the transition state intermediate to thus stabilize it o Does NOT alter the change in free energy between reactants and products o Does NOT affect the equilibrium constant, K eq Chapter 3. Read pages 63-109 - Protein Structure and Function o Proteins are the most diverse of the macromolecules in terms of structure
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Cell Bio - Exam 2 - Cell Biology Exam 2 2.4 Biochemical...

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