Inhibitors Competitive Competes with substrate for active site Noncompetitive Binds to enzyme at a site other than the active site Feedback inhibition End product of pathway binds to an allosteric site on enzyme that catalyzes first reaction pathway Shuts down pathway so raw materials and energy aren t wasted Metabolism Total of all chemical reactions carried out by an organism Anabolic reactions anabolism expend energy to build up molecules Catabolic reactions catabolism Harvest energy by breaking down molecules Biochemical pathways Occur in a sequence Product of one reaction is a substrate for the next Many steps occur in the organelles Chapter Respiration Organisms can be classified based on how they obtain energy Autotrophs make their own food Heterotrophs obtain energy from other organisms All organisms use cellular respiration to extract energy from organic molecules Redox Electrons and energy Nicotinamide adenosine dinucleotide NAD NAD electron carrier accepts 2 electrons and 1 proton to become NAD and is reversible Respiration Aerobic final electron receptor is oxygen Anaerobic final electron acceptor is an inorganic molecule Fermentation final electron acceptor is an organic molecule C6H12O6 6O2 6CO2 6H20 energy G 686 kcal mol of glucose Electron carriers Many types of carriers can be used soluble membrane bound move within membrane All carriers can be easily oxidized and reduced Some carry electrons some electrons and proteins NAD acquires 2 electrons and a proton to become NADH ATP Cells use ATP to drive endergonic reactions G 7 3 kcal mol Two mechanisms for sythensis 1 Substrate level phosphorylation transfer phosphate group to ADP glycolysis 2 Oxidative phosphorylation ATP synthanse uses energy from a proton gradient Oxidation of glucose Complete oxidation of glucose proceeds in stages 1 Glycolysis 2 Pyruvate oxidation 3 Krebs cycle citric acid cycle 4 Electron transport chain chemiosmosis Glycolysis Converts 1 glucose 6 carbons to 2 pyruvate 3 carbons 10 steps Occurs in cytoplasm Net production of 2 ATP molecules by substrate level phosphorylation 2 NADH produced by the reduction of NAD NADH must be recycled For glycolysis to continue NADH must be recycled to NAD by either 1 Aerobic respiration Oxygen is available as the final electron acceptor Produces significant amount of ATP 2 Fermentation Occurs when oxygen is not available Organic molecule is the final electron acceptor Fate of pyruvate Depends on oxygen availability When oxygen is present pyruvate is oxidized to acetyl CoA which enters the krebs cycle o Aerobic respiration Without oxygen pyruvate is reduced in order to oxidize NADH back to NAD o Fermentation Pyruvate Oxidation In the presence of oxygen pyruvate is oxidized Occurs in the mitochondria in eukaryotes o Multienzyme complex called pyruvate dehydrogenase catalyzes the reaction Occurs at the plasma membrane in prokaryotes Products of pyruvate oxidation For each 3 carbon pyruvate molecule 1 CO2 o Decarboxylation 1 NADH 1 acetyl CoA which consists of 2 carbons from pyruvate attached to coenzyme A o Acetyl CoA proceeds to the Krebs cycle Krebs cycle Oxidizes the acetyl group from pyruvate Occurs in the matrix of the mitochondria Biochemical pathway of 9 steps in 3 segments 1 Acetyl CoA Oxaloacetate Citrate 2 Citrate rearrangement and decarboxylation 3 Regeneration of oxaloacetate For each acetyl CoA entering Release 2 molecules of CO2 Reduce 3 NAH to 3 NADH Reduce 1 FAD electron carrier to FADH 2 Produce 1 ATP Regenerate oxaloacetate So far Glucose has been oxidized to 6 CO2 4 ATP 10 NADH 2 FADH Electron carriers proceed to the electron transport chain Electron transfer has released 53 kcal mol of energy by gradual energy extraction Energy will be put to use to manufacture ATP Electron transport chain ETC A series of membrane bound electron carriers Embedded in the inner mitochondrial membrane Electrons from NADH and FADH2 are transferred to complexes of the ETC Each complex A proton pump creating proton gradient Transfers electrons to next carrier Chemiosmosis Accumulation of protons in the intermembrane space drives protons into the matrix via diffusion Membrane relatively impermeable to ions Most protons can only reenter matrix through ATP synthase Uses energy of gradient to make ATP from ADP P i Energy yield of respiration Theoretical energy yield 38 ATP per glucose for bacteria 36 ATP per glucose for eukaryotes Actual yield 30 ATP per glucose for eukaryotes Reduced yield is due to o o leaky inner membrane Use of the proton gradient for purposes other than ATP synthesis Regulation of respiration Example of feedback inhibition 2 key control points 1 In glycolysis o Phosphofructokinase is allosterically inhibited by ATP and or citrate 2 In pyruvate oxidation o Pyruvate dehydrogenase inhibited by high levels of NADH o Citrate synthetase inhibited by high levels of ATP Oxidation without O2 1 Anaerobic respiration Use of inorganic molecules other than O2 as final electron acceptor Many prokaryotes use sulfur nitrate carbon dioxide or even inorganic molecules 2 Fermentation Use of organic molecules as final electron acceptor Anaerobic respiration Methanogens CO2 is reduced to CH4 methane Found in diverse organisms including cows Sulfur bacteria Inorganic sulphate SO4 is reduced to hydrogen sulfide H2S Early sulfate reducers set the stage for evolution of photosynthesis Fermentation Reduces organic molecules in order to regenerate NAD 1 Ethanol fermentation occurs in yeast CO2 ethanol and NAD are produced 2 Lactic acid fermentation Occurs in animal cells especially muscles Electrons are transferred from NADH to pyruvate to produce lactic acid Catabolism of protein Amino acids undergo deamination to remove the amino group Remainder of the amino acid is converted to a molecule that enters glycolysis or the Krebs cycle Alanine is converted to pyruvate Aspartate is converted to oxaloacetate Catabolism of Fat Fats are broken down to fatty acids and glycerol Fatty acids are converted to acetyl groups by oxidation Oxygen dependent process The respiration of a 6 carbon fatty acid yields 20 more energy than 6 carbon glucose Evolution of metabolism Hypothetical timeline 1 Ability to store chemical energy in ATP 2 Evolution of glycolysis Pathway found in all living organisms 3 Anaerobic photosynthesis using H2S 4 Use of H2O in photosynthesis not H2S Begins permanent change in Earth s atmosphere 5 Evolution of nitrogen fixation 6 Aerobic respiration evolved most