MCB Exam 2 02 10 2014 Exam 2 LECTURE 9 Metabolism the sum of all chemical activity in the cell catabolism takes molecules and breaks them down releases energy final products used as precursors for new molecules ex food biosynthesis takes precursors and makes macromolecules require energy and get it from catabolic reactions the more stable a molecule is less reactive it is the carbon and hydrogen in food molecules are not in most stable form which makes them reactive most stable form of carbon is C02 and most stable form of h is h20 large organic molecules like glucose are broken down to co2 and h20 by combining with oxygen c and h are oxidized oxidation reactions use it now use it later lose it as heat spread out over multiple reactions harness more of the energy not dissipated as heat each oxidation reaction controlled by specific reaction Redox Reactions and Coenzymes removing electrons are not lost they are transferred to a molecule which is reduced OIL RIG oxidation and reduction reactions must balance most electrons transferred are in form of 2 hydrogen atoms E is held in transferred electrons recipients of electrons are associated with enzymes called cofactors or coenzymes these coenzymes are only temporary carriers 2 main coenzymes in biological oxidation accept 2H NAD reduced to NADH reversible FAD reduced to FADH2 ATP all the energy harnessed from the oxidation of food sources is used to make ATP the most common energy currency for the cell adenosine triphosphate energy comes from repulsion of negative charges hydrolysis of ATP yields ADP inorganic phosphate and energy ATP hydrolysis exergonic is coupled to the endergonic reaction the reaction that requires energy uses the energy provided upon hydrolysis of ATP glucose glucose 6 phosphate delta G 3 ATP adp p delta G 7 4 ATP when ATP releases energy it also releases inorganic phosphate This inorganic phosphate then may be used to form a phosphorylated intermediate LECTURE 10 Metabolism II Cellular Respiration Energy from food ATP breakdown glucose to CO2 and H2O 3 different phases glycolysis pyruvate oxidation and krebs cycle electron transport and oxidative phosphorylation chemiosmosis Phase 1 Glycolysis breaking of a sugar molecule starts with a 6 carbon sugar glucose ends with two 3 carbon molecules pyruvate endergonic up to production of first 3 carbon molecules uses cell s store of ATP occurs in the cytoplasm of all living cells steps 1 and 3 are endergonic energy investment phase after step 4 everything happens twice steps 6 7 and 10 are exergonic step 6 s energy is harnessed and saved for later 2 SLP reactions put in 2 ATP makes 4 ATP net 2 ATP problems at the end of glycolysis molecules are still not at their lowest energy state some of our energy is being held in NADH NAD is being used up and not replaced oxygen is present aerobic respiration oxygen is absent with an alternative terminal electron acceptor anaerobic respiration oxygen is absent without a terminal electron acceptor fermentation Aerobic Respiration carbon source 2 molecules of pyruvate completely converted to CO2 pyruvate molecules first converted to acetyl coA which then enter the Krebs all c h bonds converted to c o bonds 6 co2 released more energy transferred to NAD and FAD makes NADH and FADH2 another SLP reaction in krebs cycle occurs in mitochondria of eukaryotes or cytoplasm and plasma membrane of prokaryotes mitochondrion outer membrane separates from cytoplasm half lipid and half protein porins passes small molecules inner membrane site of ATP generation 70 protein impenetrable to ions and small molecules except by transporters intermembrane space composition of ions and small molecules is the same as the cytoplasm cristae sacs of inner membrane joined to the rest of the inner membrane matrix krebs enzymes dna ribosomes Phase 2 Pyruvate Oxidation and Krebs Cycle citric acid cycle takes place in the mitochondrial matrix Probl ems at the end of Krebs cycle still haven t replaced NAD more NADH is made now you have FADH2 that needs to be reoxidized still haven t transferred energy carried by cofactors to ATP aerobic respirationrequires oxygen krebs cycle does not krebs cycle is coupled to the third pathway which does require oxygen The ETC LECTURE 11 ETC Fermentation Electric Transport Chain prokaryotes cytoplasmic membrane eukaryotes inner mitochondrial membrane NADH complex I accepts 2 e of NADH and oxidizes NAD and a free proton H use energy to move protons against the concentration gradient matrix intermembrane space Complex 1 and Complex 3 electron carrier ubiquinone C 3 and C 4 electron carrier Cyt C Final electron acceptor Oxygen accepts electrons from C 4 and combines with hydrogens in matrix to make H2O FADH2 Complex 2 does not pump protons into space like 1 3 and 4 does uses ubiquinone to transfer to 3 ATP is not produced directly by the ETC but instead via the proton gradient generated during electron transport through the ETC therefore indirect If drug inhibits ATP Synthase ATP synthase acts as a proton channel in the inner mitochondrial membrane If that channel were inhibited protons would still be pumped out of the matrix by the ETC but would be unable to flow back in causing the pH to rise Respiration via the ETC derives more ATP energy from glucose because the potential energy drop between the start and end is much greater than for fermentation Electrochemical Gradient high concentration of protons in intermembrane space than matrix pH is different Energy decreases from C 1 C 4 electrical difference in charge more charged to intermembrane space charged to matrix and chemical components pH 7 to space pH 8 to matrix Chemiosmosis Oxidative Phosphorylation ATP synthase allows a small channel where protons can pass through not part of ETC turning molecular motor by flow of protons produces ATP from ADP P the larger the gradient more protons pumped through space 3 ATP per NADH 2 ATP per FADH2 Aerobic Respiration Glucose 6O2 6CO2 6H2O glycolysis 4 ATP from ATP and NADH TCA cycle 2 ATP from GTP 24 ATP from 8 NADH 4 ATP from 2 FADH2 36 molecules of ATP per glucose Path of energy Electrons in glucose to make ATP SLP in both glycolysis and Krebs Most electrons transferred to cofactors which carry them to the ETC which uses them to make a proton gradient ATP Synthase Proteins Amino Acids to make ATP by Acetyl CoA Fats Glycerol to Glycolysis and Fatty Acids to make ATP by Acetyl CoA Fermentation ATP comes from glycolysis pyruvate undergoes