Exam#2 ReviewBioenergetics: -Overview: a. Cells require energy -Cells use sunlight / electromagnetic radiation (photosynthesis) or chemical nutrients with high potential energy (cellular respiration) b. These external sources of E are converted into a chemical E carrier: adenosine triphosphate (ATP) -ATP is generated from ADP and inorganic phosphate (Pi) -Cells use the E released during hydrolysis of the high E phosphoanhydride bond in ATP to power its other processes2 processes: Aerobic oxidation -Occurs in mitochondria of eukaryotic cells -Sugars (carbohydrates) and fatty acids (hydrocarbons) - both derived from digestion of food- contain E in there chemical bonds-These are oxidized and the E released from there chemical bonds is converted into the terminal phosphoanhydride bond of ATP 2. Photosynthesis -Chloroplasts of plant cells, and some bacteria -Radiant E of light is absorbed by pigments and used to make ATP and carbohydrates -Uses CO2 as a substrate and generates O2 and carbohydrates as a product Chemiosmosis: A mechanism common to mitochondria, bacteria and chloroplasts -Proton electrochemical gradient is generated across membrane driven by E released as electrons travel through an electron transport chain -The E stored in this gradient = proton motive force; that is used directly to power the synthesis of ATP and other E-requiring processesAerobic Oxidation-Hydrocarbon (fatty acids) and carbohydrates (sugar) with energy stored in the chemical bonds are combusted and this is coupled to ATP synthesis -Comprised of multiple steps that are catalyzed by specific proteins Glucose Oxidation Conversion in cytosol of (1) 6-carbon glucose molecule to (2) 3- carbon pyruvate molecules [glycolysis] Pyruvate oxidation to CO2 in the mitochondrion via a 2-carbon acetyl CoA intermediate [Citric Acid Cycle]Electron transport chain to generate a proton motive force ATP synthesis in the mitochondiron [Oxidative phosphorylation]Substrate Level Phosphorylation vs. Oxidative PhosphorylationSubstrate Level Phosphorylation: Formation of ATP from ADP and Pi catalyzed by cytosolic enzymes in reactions that do NOT depend on a proton-motive force or molecular oxygen C-C [chemical bond] ----> AT~P [chemical bond] Oxidative Phosphorylation: The phosphorylation of ADP to from ATP driven by the transfer of electrons to oxygen (O2). Involves the generation of a proton-motive force during electron transport and its subsequent use to power ATP synthesis C-C [chemical bond] --> Reducing power [e-] --> Proton motive Force --> AT~P [bond] Stage I: GLYCOLYSIS Glycolytic Pathway: Occurs in cytosol Does NOT require oxygen: Anaerobic glucose catabolism (Biological breakdown of complex to simpler substances)Converts (1) glucose into (2) pyruvate molecules -The free E released in this process is used to form the high E compounds: ATP and NADPHa. 4 ATP molecules are generated: -Substrate-level phosphorylation: Requires initial input of 2ATP molecules that are used to make 2ADP molecules that will go on to generate 4ATP molecules -Glycolysis yields net of: (2) ATP molecules/ glucose molecule b. Chemical equation for glucose --> 2 pyruvate c. In reaction #6: The (4) e-’s and (2) of the H+’s are transferred to (2) molecules of NAD+ -Used to produce the reduced form: NADH 2H+ + 4e- + 2NAD+ ---> 2NADH*Reducing power of NAD and FAD -Some of the energy released in the early stages of oxidation (Stage I and Stage II) is temporarily stored in the reduced coenzymes: NADH and FADH2-These are energy carriers that carry high-energy electrons that subsequently drive the electron transport chain So the complete overall equation for glycolysis: C6H12O6 + 2NAD+ + 2ADP + 2Pi --> 2C3H4O3 + 2NADH + 2ATP +2H+ + 2H2O*At this point, only some of the E available has been used to produce ATP, the rest is stored in the chemical bonds of the pyruvate molecule and some in the high E electrons of NADH Allosteric regulation of glucose metabolism -Stages I and II are both closely regulated so as to produce only the needed amount of metabolites (intermediates) and not excess -Glycolysis is regulated by slowing down or speeding up certain steps in the pathway; controlled by three allosteric glycolytic enzymes Allostery: Any change in a proteins 3º or 4º structure, induced by the non-covalent binding of a ligand Allosteric protein: Have multiple binding sites for ligands. Allosteric change in activity can either be positive or negative Three steps that are rate limiting and irreversible (- -Step 1: Hexokinase is inhibited by its product: glucose 6-phosphate -Step 10: Pyruvate kinase is inhibited by ATP (glycolysis is slowed down when ATP concentrations are too high) -Step 3: Phosphofructokinase -1: Principal rate-limiting enzyme of the pathway; Allosterically controlled by many molecules -Inhibited by ATP and citrate -Activated by AMP, fructose 2,6-biphosphate, and Insulin Anaerobic vs. Aerobic Metabolism of Glucose ~What happens to the pyruvate that was formed in glycolysis depends on whether or not there is oxygen present Anaerobic: In absence of oxygen, the products of glycolysis remain in the cytoplasm. The 2NADH molecules that were produced during glycolysis are oxidized and regenerated back into NAD+. And the only chemical bond energy that is converted to ATP chemical bond Energy, is the net gain of 2 ATP that occurred in glycolytic pathway -In yeast this process = Fermentation -In animals: Pyruvate is converted to lactic acid Aerobic: (~Cellular Respiration) - In the presence of oxygen, there is a transfer of chemical bond energy (pyruvate via pyruvate transporter) and reducing power (NADH via electron shuttle) to mitochondrion matrix -Reactions in the mitochondria (II-IV) generate 28 more ATP moleculesTransportation of products from glycolysis into mitochondria (Products of glycolysis in the cytoplasm must get to mitochondria for steps II-IV) Pyruvate -Move through outer membrane via semi-permeable porins -Move through inner membrane (impermeable) via pyruvate uniporter (protein transporter) into the matrix *Fatty acid CoA (the stage I product of fatty acid) is also transported through the outer membrane first via a semi-permeable porin. And then through a specific fatty