Respiration part 2 Feedback inhibition of glucose oxidation metabolic pathways Fermentation 1 Students will understand how energy is transformed from chemical or solar energy into the universal power source of cells ATP Focus Respiration oxidation of glucose control of rate of energy pathways 2 Cells control metabolic pathways with positive and negative feedback In energy producing processes it s not the intermediates that feed back to regulate enzymes it s the cell s Remember ATP ADP AMP cAMP Low energy indicators High energy indicators High cAMP High ATP High NAD High NADH High FADH High FADH2 Generally stimulate positive feedback Generally repress negative feedback 3 Multiple steps of the glucose oxidation pathway are regulated by energy levels phosphofructokinase Catalyzes step 3 of glycolysis Substrates fructose 6 phosphate and ATP Why regulate here First step of glycolysis requires energy INVESTMENT a commitment step 4 ATP inhibits phosphofructokinase via allosteric inhibition ATP is one of two substrates binds here first not phosphorylation Two ATP binding sites Higher affinity for active site If all actives sites are full ATP will bind regulatory sites Feedback inhibition why ATP is ALSO the regulatory molecule Negative feedback 5 ATP inhibits phosphofructokinase via allosteric inhibition 6 Graph the relationship between the concentration of ATP cAMP and phosphofructokinase activity Available ATP binds to ACTIVE SITE Rate of reaction catalyzed by Phosphofructokinase Active sites FULL ATP binds to REGULATORY SITE Inhibits enzyme Low ATP high cAMP high ATP low cAMP 7 Multiple steps of the glucose oxidation pathway are regulated by energy levels phosphofructokinase Catalyzes pyruvate processing Substrates pyruvate NAD CoA Regulated by inhibition via phosphorylation Pyruvate dehydrogenase High NADH and Acetyl CoA inhibits High NAD and CoA stimulates 8 Remember that NAD and NADH are related Chemical reaction catalyzed by the enzyme has THREE substrates and three products Pyruvate NAD CoA Acetyl CoA NADH CO2 reaction cannot occur without NAD 9 Cells control metabolic pathways with built in feedback Pyruvate processing Pyruvate Dehydrogenase active PD kinases PD phosphetases active P P Pyruvate Dehydrogenase P P inactive 10 Cells control metabolic pathways with built in feedback Pyruvate processing Pyruvate Dehydrogenase active PD kinases active PD phosphetases P P Pyruvate Dehydrogenase P P inactive 11 Pyruvate Dehydrogenase is a HUGE multienzyme complex Multiple active sites Multiple sites for phosphorylation It is partially phosphorylated most of the time low energy high substrates high energy high products activate phosphetases activate kinases Lower levels of phosphorylation FASTER Higher levels of phosphorylation SLOWER Yikes 12 Which graph best indicates the relationship between cellular NADH levels and pyruvate dehydrogenase phosphorylation levels Phosphetases active Amount of phosphorylation on pyruvate dehydrogenase Low NADH high NAD High NADH low NAD 13 Which graph best indicates the relationship between cellular NADH levels and pyruvate dehydrogenase activity Rate the reaction is catalyzed by pyruvate dehydrogenase High levels of phosphorylation PD is inactive Low levels of phosphorylation PD is most active Low NADH high NAD High NADH low NAD Challenge create graphs that describe the relationship between NAD CoA or AMP levels in the cell and pyruvate dehydrogenase activity 14 Multiple steps of the glucose oxidation pathway are regulated by energy levels isocitrate dehydrogenase phosphofructokinase Catalyzes step 3 Pyruvate dehydrogenase Substrates NAD and isocitrate Regulated by competitive inhibition by NADH 15 Isocitrate dehydrogenase regulated by NAD and NADH via competitive inhibition Chemical reaction catalyzed by this enzyme Isocitrate NAD ketoglutarate NADH concentration dependent process NAD competes with NADH for the active site 16 Which graph best indicates the relationship between cellular NAD levels and isocitrate dehydrogenase activity Rate the reaction is catalyzed by isocitrate dehydrogenase NADH outcompetes NAD for the active site NAD outcompetes NADH for active site Low NADH high NAD High NADH low NAD Challenge create graphs that describe the relationship between NADH levels in the cell and isocitrate dehydrogenase activity 17 Oxidative phosphorylation requires Oxygen Oxygen pulls electrons out of last member of the chain 18 Oxidative phosphorylation requires Oxygen All redox reactions None require an enzyme All exergonic Q is structurally similar to PQ AKA Coenzyme Q10 a popular supplement Anaerobic respiration alternative electron acceptor NOT fermentation Still oxidize glucose fill NADH FADH2 S becomes H2S X Still use ETC Consequences X Fermentation only glycolysis occurs normally NADH is oxidized again by the ETC Without the ETC all the NADH in the cell stays reduced 21 Fermentation oxidizes NADH so glycolysis can continue 22 These energy pathways do not exist in isolation each green line is a different chemical reaction connected to energy pathways 23 You should be able to For each of the four steps of respiration tell me The big picture what s the point of the first three steps glycolysis pyruvate processing citric acid cycle What s the point of the fourth step ETC and chemiosmosis How are they interrelated Where in the cell each of the fours steps occurs Which enzymes are regulated and how The overall equation of respiration and how glucose C 6H12O6 is converted into CO2 and H2O Why the first three steps MUST occur simultaneously with the fourth step i e why do the three metabolic pathways stop if we have no oxygen Looking at the metabolic pathways and electron transport chains Predict the effects of artificially blocking any enzyme ETC element in these pathways Reminder there are other metabolic pathways that feed into this one so you won t DIE if you block any step of glycolysis Remember that you can live just fine on a high protein high fat diet just ask anyone who does Atkins 24 You should be able to Explain the difference between inhibition of an enzyme via Phosphorylation covalent modification of enzyme primary structure that alters active site shape Requires an enzyme to put on and a different enzyme to take off competitive inhibition substrate competes with something else for active site Inhibition can be overcome when substrate concentration is high allosteric regulation inhibitor molecule binds to regulatory site alters active site