BIO 101 1st EditionLecture 13Outline of Last LectureI. Enzymesa. Catalystsb. Free Energy of ActivationII. Factors Affecting Enzyme ActivityIII. Control of MetabolismIV. Feedback InhibitionV. ATP and Cellular WorkOutline of Current LectureI. Cellular RespirationII. Redox Reactionsa. Oxidationb. ReductionIII. Four Stages of Respirationa. Glycolysisb. Transition to Mitochondriac. Krebs Cycled. Oxidative PhosphorylationChapter 9- Cellular RespirationCellular respiration- aerobic (requires O2) catabolism (breakdown) of organic (carbon based) nutrients (food)- Nutrients have potential energy stored in chemical bonds- Goal of cellular respiration is to convert to stable chemical energy in nutrients to a readily useable form= ATP- Strategy is to extract energy from nutrients in a stepwise manner- a series of chemical reactions= CATABOLIC PATHWAY- Overall chemical equation for the whole pathway=- During this pathway, the cell makes 36 ATPs/glucose- Each ATP made requires 7.3 kcal/mole of energy- Yield of respiration is therefore ~263/686 = ~38%- ~60% of the energy of glucose is lost (used to drive some endergonic reaction, or lost as heat)- ~405 is saved in form of ATPRedox Reactions- The cell get energy from glucose during cellular respiration using a series of OXIDATION/REDUCTION reactionOxidation=loss of electronsBIO 101 1st EditionReduction= gain of electrons- Called redox because these 2 kinds of reactions are always coupled in the cell- One molecule loses an electron (becomes oxidized) and the electron is gainedby another molecule (becomes oxidized) and the electron is gained by another molecule (becomes reduced)- The loss and gain of electrons can be easily thought of as loss and gain of whole H-atoms (because the electron is often accompanied by a proton= H-atom)- Easy to monitor oxidation as loss of H-atoms and reduction as gain of H-atomsOverview of Respiration- During respiration, glucose is broken down (to CO2) and oxidized (electrons stripped off)- Electrons (usually H-atoms) are removed in a series of REDOX reactions= catabolic pathway- Electrons from glucose are eventually transferred to O2 (which is the REDUCED to H2O) - Overall process is exergonic and releases energy in a stepwise manner- Some of the energy is captured in the form of ATPFour Stages of Respiration1. Glycolysis:- A catabolic pahway with 10 chemical reactions- Occurs in all living cells (ex of unity in life)- Although the overall respiration pathway requires O2, this first stage DOES NOT require oxygen- Occurs in cytoplasm- Overall pathway for glycolysis- Glucose (6 carbon) is split into 2 pyruvates (3 carbons)Glucose is partially OXIDIZED (some electrons are removed)- OXIDATION of glucose is catalyzed by enzymes called DEHYDROGENASESo Generally 2 H-atoms are removed by dehydrogenaseso Dehydrogenases require CO-ENZYMES to work (small organic non-protein molecules)o The coenzymes act as temporary carriers for the electrons that are removed during oxidation reactionso There are TWO important coenzymes that work with dehydrogenases during respirationBIO 101 1st EditionTwo Coenzymes that are required for Dehydrogenases1. Nicotinamide Adenine dinucleotide (NAD)- vitamin B derivative exists is 2 forms 2. Flavin adenine dinucleotide (FAD)- riboflavin derivative also exists in 2 forms- these coenzymes are only ACTIVE in their OXIDIZED FORMS (this is the form available to accept electrons)- glycolysis produces a NET GAIN of 2 ATPs per glucose molecule that enters the pathway- these 2 ATPs arise by SUBSTRATE LEVEL PHOSPHORYLATION- substrate level phosphorylation= direct transfer of a phosphate from an intermediate substrate in the pathway to ADP, making ATP- glycolysis also produces 2 NADHs (reduced coenzyme)- these will be important in the last stage of respiration in which ATP is generated by oxidative phosphorylation- OVERALL FOR GLYCOLYSISReactant products1 Glucose 2 pyruvates*can be used later to 2 ATPsmake ATP *2 NADH*2. Transition to Mitochondria: glycoslysis occurs in the cytoplasm- the rest of respiration occurs in the mitochondria - Pyruvate (from glycolysis) enters the matrix of mitochnodria- As it enters, it is further OXIDIZED and broken down- Pyruvate has 3-carbons- as it enters the mitochondria, one carbon is completely oxidized and pulled OFF of pyruvate, producing CO2BIO 101 1st Edition- The remaining 2-carbon group (called acetyl group) is carried into the mitochondria by a molecule called COENZYME A (CoA) acetyl+CoA=acetyl-CoA- The electrons removed from pyruvate are transferred to NAD+ NADH- the overall process is this:What goes in What are products2 pyruvates 2 acetyl-CoA*can be used later 2 CO2to make ATP *2 NADH*3. Krebs Cycle (Citric Acid Cycle)- Catabolic pathway- Occurs in matrix of mitochondria- Occurs only in presence of O2- 2 carbon acetyl group is COMPLETELY broken down and OXIDIZED to give 2 CO2- electrons are transferred to NAD+ and FAD to produce NADH and FADH2- is called a cycle because oxaloacetate (one of the beginning reactants) is regenerated by the reactionsWhat goes in Products2 acetyl groups 4 CO22 ATP(substrate level phos)*6 NADH**2 FADH2*4. Oxidative Phosphorylation- occurs on the inner mitochondrial membrane- uses electrons that were transferred to NADH and FADH2 in stages 1-3 (REDUCED COENZYMES)BIO 101 1st Edition- electrons carried by REDUCED COENZYMES are dropped at the ELECTRON TRANSPORT CHAIN (ETC)- electron transport chain= series of electron carrier molecules located on inner mitochondrial membrane- electrons from the reduced coenzymes (NADH and FADH2) are passedalong the chain and eventually to O2 (FINAL ELECTRON ACCEPTOR)- During some electron transfers along the electron transport chain, protons (H+) are pumped from the matrix into the inner membrane space creating a H+ gradient (proton gradient)Proton gradient= potential energy= PROTON MOTIVE FORCE- Protons can re-enter the matrix of mitochondria (down their electrochemical gradient) using a special transport protein called ATP synthase- transport protein for protons, but ALSO an ENZYME that catalyzes reaction: ADP+ phosphate ATP- As proton pass through ATP synthase, energy of proton gradient is harnessed to drive the endergonic reaction- *CHEMIOSMOSIS* - using energy of proton gradient to make ATP- for every NADH that drops electrons at electron transport chain, enough energy is captured to