Lecture 11Outline of Last Lecture I. Chemical ReactionsII. Exergonic ReactionsIII. Endergonic ReactionsIV. EnzymesV. Enzyme-Substrate ComplexVI. Factors Affecting Enzyme ActivityVII. Control of MetabolismVIII. ATPOutline of Current Lecture I. Cellular RespirationII. Redox ReactionsIII. Overview of RespirationIV. First Two Stages of RespirationCurrent LectureI. Cellular Respirationa. The aerobic catabolism or organic nutrientsb. Requires O2 and carbon-based foodc. Nutrients have potential energy stored in chemical bondsd. Goal of cellular respiration is to convert the stable chemical energy in nutrients to a readily usable form  ATPe. Accomplish in a stepwise manner  catabolic pathwaysi. Chemical equation: C6H12O6 + O2  CO2 + H2Oii.∆ G = -686 kcal/molef. Cell makes 36 ATPs/glucose BIOL 101 1st Editiong. Each ATP requires 7.3 kcal/mole of energyh. Yield of respiration is approximately 38%i. 60% of energy is lostj. 40% is stored in ATPII. Redox Reactionsa. Cells get energy from glucose during cellular respiration using a series of oxidation/reduction reactions (Redox)i. Oxidation  Loss of electronsii. Reduction  gain of electronsb. Two types of reactions are always coupled togetherc. One molecule loses an electron (becomes oxidized) and the electron is gained by another molecule (becomes reduced)d. The loss and gain of electrons can be easily thought of as loss and gain of whole H-atoms e. Easy to monitor oxidation as loss of H-atoms and reduction as gain of H-atomsIII. Overview of Respirationa. Glucose is broken down to CO2 and oxidized (stripped of electrons)b. Electrons (usually H-atoms) are removed in a series of redox reactions  catabolic pathwaysc. Electrons from glucose are eventually transferred to O2  then reduced to H2Od. Overall process is exergonic and releases energy in stepwise mannere. Energy is then captured in the form of ATPIV. First Two Stages of Respirationa. Glycolysis:i. Catabolic pathways with 10 chemical reactionsii. Occurs in all living cells (unity in life)iii. Although the overall respiration pathway requires O2, this first stage does not require oxygeniv. Occurs in cytoplasmv. Overall pathway for glycolysis1. Glucose  10 reactions  2 pyruvates2. (C6H12O6)       (C3H4O3)vi. Glucose (6 carbon) is split into 2 pyruvates (3 carbons)vii. Glucose is partially oxidized (some electrons are removed)viii. Catalyzed by enzymes called dehydrogenases1. Generally 2 H-atoms are removed by dehydrogenases2. Require co-enzymes to work3. Act as temporary carriers for the electrons that are removed during oxidation reactions4. Two important coenzymes that work with dehydrogenases during respirationa. Nicotinamide Adenine Dinucleotide (NAD)i. Exists in 2 formsii. NAD+  NADHb. Flavin Adenine Dinulceotide (FAD)i. Exists in 2 formsii. FAD  FADH5. Enzymes are only active in their oxidized forms (form available to accept electrons)ix. Glycolysis produces a net gain of 2 ATPs per glucose molecule that enters the pathwayx. These 2 ATPs arise by “substrate level phosphorylation”  direct ransfer of a phosphate from an intermediate in substrate in the pathway to ADP, making ATPxi. Glycolysis also produces 2NADHs (reduced coenzyme) – these will be important in the last stage of respiration in which ATP is generated by “oxidative phosphorylation”xii. Overall:1. Reactant = 1 glucose2. Products = 2 pyruvates, 2 ATPS, 2 NADH *can be used later to make ATPb. Transition to Mitochondriai. Rest of respiration occurs in mitochondriaii. Pyruvate (from glycolysis) enters the matrix of the mitochondria, further oxidizing and breaking it downiii. Pyruvate has 3 carbons  one carbon is completely oxidized in mitochondria, producing CO2iv. The remaining 2-carbon group (acetyl group) is carried into the mitochondria by a molecule called “coenzyme A” v. The electrons removed from pyruvate are transferred to NAD+  NADH reduced coenzymevi. Overall process:1. Pyruvate  CoA, NAD+, NADH, CO2  acetyl-CoA2. (Cytoplasm)          (Mitochondrial matrix)vii. Overall:1. Reactants = 2 pyruvates2. Products = 2 acetyl-CoA, 2 CO2, 2 NADH *can be used later to make