chapter 8 lecture notes

Would stop what would happen cells would die cells

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Unformatted text preview: l Endergonic Reac1ons in Metabolism (+ΔG): Not spontaneous Must absorb free energy from the surroundings 6CO2 + 6H20 C6H1206 + 6O2 ΔG = 686 kcal/mol Key Point: energy release by an exergonic reaction is equal to the energy required by the reverse endergonic reaction Isolated System Equilibrium Glucose, O2 Open System Once equilibrium is reached, systems cannot do work If cells existed in isolated systems: All their metabolic reac,ons would stop What would happen? cells would die Cells exist in an open system: Metabolic reac,ons never reach equilibrium because: reactants and products move in and out of cells Glucose, O2 CO2, H20 Mul,step Open System CO2, H20 In cellular respira1on: glucose is broken down in a series exergonic reac,ons that power the work of the cell Products of reac,ons do not build up – rather become reactants in the next step * equilibrium is not reached-cells keep living ATP powers cellular work by coupling exergonic reac1ons to endergonic reac1ons A cell usually uses ATP as the immediate source of energy for: 1.  Mechanical Work: Example: contrac,on of muscle 2.  Transport Work: Example: 3.  Chemical Work: Example: pushing endergonic reac,ons such as the synthesis of proteins from AAs Purine Adenosine What type of reac1on is this? ΔG =  ­7.3 kcal/mol (standard condi,ons) or  ­13 kcal/mol (cellular condi,ons) Why does this hydrolysis reac1on release so much energy? “compressed spring” * In a test tube, the energy produced by the hydrolysis of ATP would be in the form of heat * Instead cells use the energy produced by the hydrolysis of ATP to do cellular work (e.g. mechanical, transport, and chemical) How does the cell do this? How ATP Drives Chemical Work: Example: Synthesis of the amino acid glutamine ΔG = 3.4 kcal/mol Endergonic reac,on – not spontaneous Glutamic Acid Ammonia Break into two steps Less stable intermediate * Ammonia dis...
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