Chapter 7 Harvesting Energy

7.1 Overview of Respiration Autotrophs-photosynthesize-use sunlight and convert it to chemical energy Ex: plants, algae and some bacteria Heterotrophs-live on energy produced by autotrophs Ex: animals, fungi, most protists and some bacteria How is harvesting actually done? 1. Digestion 2. Catabolism (carbs, proteins and fats)

7.1 cont’d C 6 H 12 O 6 + 6O 2  6CO 2 + 6H 2 O + Energy (heat or ATP) 1.Change in free energy in -720 kcal/mole 2.Results from breaking of the six C-H bonds in glucose 3.(-) sign indicates products possess less free energy than reactants Electron carriers (NAD+) play a critical role in energy metabolism- during respiration, glucose is oxidized to CO 2. If electrons were given directly to O 2, the reaction would be combustion. The ability to supply high energy electrons is critical to both energy metabolism and the biosynthesis of organic molecules. ATP is used for two major reasons 1.Movement 2.To drive endergonic reactions Enzymes that catalyze endergonic reactions have two binding sites; one for reactant and the other for ATP. The ATP site splits the ATP, releasing 7.3 kcal of energy; this energy pushes reaction “uphill” thus driving the reaction. (these events are coupled)

7.2 Glycolysis: Splitting Glucose Stage One: Glycolysis-occurs in the cytoplasm of the cell Initial breakdown of glucose into two molecules of pyruvate (pyruvic acid) 1. Glucose priming-glucose has two high energy phosphates added to it; this process requires energy. 2. Cleavage- glucose is split into two (3) carbon sugar phosphate molecules. 3. Energy harvesting reactions- the two (3) carbon sugars are converted into two pyruvate molecules. As a result of this process, energy-rich hydrogen is harvested as NADH and two ATP molecules are formed. hill.com/sites/ /student_view0/chapter25/animation__how_glycolysi s_works.html

7.3 The Oxidation of Pyruvate Stage Two-occurs in the mitochondria Oxidation of Pyruvate-pyruvate is oxidized in a single “decarboxylation” reaction that cleaves off one of pyruvate’s three carbons. This carbon is released as CO 2 This reaction produces a molecule of NADH which is later used to produce ATP This reaction also produces Acetyl Co-A which is the starting material in the Krebs cycle If ATP is needed, Acetyl Co-A is funneled into the Krebs cycle; if it is not needed, ATP is funneled into lipid synthesis.

7.4 The Krebs Cycle-series of nine reactions with nine intermediates 1.Condensation The two carbon group from acetyl Co-A joins with a four carbon molecule, oxaloacetate, to form a six carbon molecule called citrate. 2. & 3. Isomerization A water molecule is removed from one carbon then added to another carbon. As a result and H and an OH change positions The product is an isomer of citrate called isocitrate 4.The First Oxidation First energy yielding step; isocitrate undergoes an oxidative decarboxylation; this yields a pair of electrons that reduce NAD+ to NADH The oxidized intermediate is decarboxylated; CO2 is formed and yields a five carbon molecule called α- ketoglutarate 5. The Second Oxidation α-ketoglutarate is decarboxylated by a multi-enzyme complex forming succinyl CoA Two electrons are extracted and they reduce another molecule of NAD+ to NADH

Stage Three 6. Substrate level phosphorylation Bond between succinyl Co-A is cleaved Energy released drives phosphorylation of GDP to GTP (readily converted to ATP) Succinate is what remains 7. Third Oxidation Succinate is oxidized to fumarate Energy reduces FAD to FADH 2 8. & 9. Regeneration of oxaloacetate H2O is added to fumarate, forming malate Malate is oxidized to form oxaloacetate Two e- reduce NAD+ to NADH Cycle starts again hill.com/sites/ /student_view0/chapter25/animation__how_the_krebs_cycle_works__qui z_1_.html

7.5 ETC and Chemiosmosis Stage Four The Electron Transport Chain Series of five membrane associated protein (multi-enzyme complex) Electrons are delivered by NADH and FADH2 and are passed from protein to protein along the chain ETC use e- harvested in aerobic respiration to pump a large number of protons across the inner mitochondrial membrane. The subsequent re-entry into the matrix drives the synthesis of ATP by chemiosmosis. hill.com/sites/ /student_view0/chapter25/animation__electron_tran sport_system_and_atp_synthesis__quiz_1_.html

7.6 Energy Yield Summary of Cellular Respiration Glycolysis = 2 ATP Krebs Cycle = 2 ATP ETC = 32 ATP _______ 36 ATP (Theoretical) 30 ATP (Actual) 7.7 Regulation of Aerobic Respiration Regulation of aerobic respiration depends on amount of ATP. Two feedback inhibition points are in the system; one in glycolysis and one in the Krebs cycle.

No Oxygen Available Glycolysis Oxygen Available 2ATP Pyruvate Ethanol or Lactic acidOxidation of Pyruvate Fermentation fermentation Krebs Cycle 2ATP Ethanol & CO 2 Lactic Acid (yeast)(muscle cells) ETC 32 ATP Yield = 2 ATP Yield = 36 ATP Actual = 30 ATP

7.8 Oxidation Without O 2 In the presence of oxygen, cells can generate a large amount of ATP. In the absence of oxygen, some organisms can respire anaerobically using inorganic molecules as the final electron acceptor for the ETC. 1.Methanogens- Archaea- use CO 2 as their final electron acceptor and produce CH 4. 2.Sulfur bacteria- derive energy from the reduction of inorganic sulfates to hydrogen sulfide. 3.Fermentation- rely on glycolysis to produce ATP a.Ethanol- yeast cells- produce CO 2 and alcohol. b.Lactic acid-muscles- produce lactic acid

7.9 Catabolism of proteins and fats Respiration of Proteins 1. broken down into amino acids 2. amine group removed by deamination 3. remaining carbon chain in converted into a compound that can take part in glycolysis or Krebs. Respiration of Fats 1. broken down into fatty acids and glycerol 2. fatty acids are oxidized in matrix of mitochondria 3. a six carbon fatty acid yields 20% more ATP

7.10 Evolution of Metabolism 1.Degradation- breaking down organic molecules that were abiotically produced, that is carbon-containing molecules formed by inorganic processes. 2. Glycolysis- initial breakdown of glucose. 3.Anoxygenic photosynthesis- organisms used light to pump protons out of their cells and use the resulting proton gradient to power the making of ATP. 4.Oxygen-forming photosynthesis- employs H 2 O rather than H 2 S as a source of hydrogen atoms and their associated electrons. 5.Nitrogen fixation- obtains N 2 from nitrogen gas by breaking the nitrogen triple bonds. 6.Aerobic respiration- employs the same kind of proton pumps as photosynthesis and is thought to have evolved as a modification of the basic photosynthetic machinery.