A way to transform energy to a useable form for organisms. Cellular Respiration Chapter 7 AP Biology A way to transform energy to a useable form for organisms. ATP

powers most cellular work Life is Work! Sun: ultimate source of energy Photosynthesis: takes light E and converts it to food, autotrophs Cellular Respiration: uses the food energy and converts it to ATP, autotrophs and heterotrophs Generates ATP & Releases heat Excess free energy results in growth & storage Light energy ECOSYSTEM CO2 + H2O Photosynthesis in chloroplasts Cellular respiration in mitochondria Organic molecules + O2 ATP powers most cellular work Heat energy

Redox Reactions Reduction Oxidation Gain of electrons Oxidizing Agent (electron acceptor) Oxygen: the final electron acceptor! Oxygen is strongly electronegative, as the e- leaves glucose, & goes to oxygen, free E is released Oxidation Loss of electrons Reducing Agent (electron donor) Glucose Oxidized in steps using a coenzyme (NAD+) and hydrogen atoms to strip the electrons from glucose & release E becomes oxidized becomes reduced

NAD+ Energy harvest and the Electron Transport Chain (ETC) NAD+ - nicotinamide adenine dinucleotide is a coenzyme that transports electrons from glucose to the electron transport chain to make ATP NAD+ is reduced to NADH + H+ (remove a pair of H atoms from food molecule, oxidized) NADH Carries electrons to the ETC (electron transport chain) to release free energy Glucose is broken down in a series of steps to slowly harvest the free energy from “falling” electrons more efficiently The e- travel with a H+ The H+ ‘s ride along on NAD+

Stages of Cellular Respiration C6H12O6 + O2  6CO2 + 6H2O + ATP 09_06CellularRespiration.mpg Glycolysis Oxidize Glucose Make Pyruvate Citric Acid Cycle (aka Krebs Cycle) Oxidize Pyruvate to Acetyl CoA Regenerate C molecules, give off CO2 Oxidative Phosphorylation (aka Electron Transport) Chemiosmosis ATP Synthesis Cytosol 2 ATP Mitochondrial matrix 2 ATP Inner Mitochondrial Membrane 32 ATP

Electrons carried via NADH Electrons carried via NADH and FADH2 Fig. 9-6-3 Electrons carried via NADH Electrons carried via NADH and FADH2 Oxidative phosphorylation: electron transport and chemiosmosis Glycolysis Citric acid cycle Glucose Pyruvate Mitochondrion Cytosol Figure 9.6 An overview of cellular respiration ATP ATP ATP Substrate-level phosphorylation Substrate-level phosphorylation Oxidative phosphorylation

Glycolysis: breaking glucose into two 3 C pyruvate molecules Substrate Level Phosphorylation small amounts of ATP, made by transferring P group from substrate to ADP Occurs in the cytosol Used in fermentation and respiration, ancient process Converts glucose (6C)  2 pyruvate (3C) (pyruvic acid) Uses 2 ATP – energy investment Produces 4 ATP + 2 NADH – energy payoff NET production = 2 ATP + 2 NADH

Between Glycolysis and Citric Acid Cycle Most of glucose energy is stored in Pyruvate Pyruvate’s carboxyl group (already oxidized) broken off and released as CO2 WASTE! Follow the Carbon: Now the 2 C fragment is oxidized (e- removed) and the e- are transferred to NAD+ Enzyme conversion of remaining C to acetyl CoA http://access.mmhs.ca/docs/Science/MMHS%20Web%20Folder/Kamla/conversiona.jpg

Citric Acid Cycle – Krebs Cycle complete energy-yielding oxidation of organic molecules Substrate Level Phosphorylation Small amounts of ATP Occurs in the Mitochondrial Matrix Converts 2 Acetyl CoA  6 NADH, 2 FADH2, 2 ATP and 4CO2 The CAC must turn twice for each molecule of glucose See pg 142-143 http://drchadedwards.com/wp-content/uploads/2010/02/krebs_cycle1.gif

Electron Transport Chain Oxidative Phosphorylation lots of ATP Electrons from food carried in NADH & FADH2 move down ETC & release energy Electroneg. Oxygen pulls e- Occurs in the inner mitochondrial membrane Electrons stored in NADH and FADH2 from glycolysis and the CAC are transported to the ETC where ~ 32 ATP are created NADH + FADH2 + O2  ATP + H2O http://www.molvray.com/sf/exobio/images/electron_chain.jpg

Chemiosmosis & Electron Transport Proteins carry electrons through the ETC while H+ pumps (oxidizing NADH to NAD+) pump H+ out into the cristae The H+’s create an electrochemical gradient As H+’s pass through the enzyme ATP synthase, ATP is made powered by flow of H+ across the membrane

Process Where? Phosphorylation Input Output 1. Glycolysis 2. Pyruvate  Acetyl CoA 3. Citric Acid Cycle (Kreb’s) 4. Electron Transport Chain (ETC) TOTAL

Mitochondria

Process Where? Phosphorylation Input Output 1. Glycolysis Cytosol Substrate Level 2 ATP + Glucose 4 ATP + 2 NADH + 2 pyruvate 2. Pyruvate  Acetyl CoA Mitochondrial Matrix N/A 2 pyruvate 2 CO2 + 2 NADH + 2 Acetyl CoA 3. Citric Acid Cycle (Kreb’s) 2 Acetyl CoA 6 NADH + 2 FADH2 + 2 ATP + 4CO2 4. Electron Transport Chain (ETC) Inner Mitochondrial Membrane Oxidative 10 NADH + 2 FADH2 + O2 ~ 32 ATP + H2O TOTAL Cytosol + Mitochondria Glucose + O2 H2O + CO2 + 36 ATP

Anaerobic Respiration (ETC) Fermentation (no ETC) CYTOSOL Uses Glycolysis and the ETC, but O2 is not the final e- acceptor One ex: sulfate reducing bacteria use the SO42- ion at the end of the ETC, a by-product is H2S (icky smell, thermal vent bacteria) Not as efficient as aerobic respiration Fermentation Oxidizes food w/out O2 & w/out Cellular Respiration. Still uses glycolysis & NAD+ to generate ATP from food source Alcoholic or Lactic Acid Fermentation are most common

Fermentation: Glycolysis then: Lactic Acid 1. Pyruvate is reduced directly by NADH to form lactate (lactate is the form lactic acid takes when it gains e-) 2. Human muscle cells do this when O2 is scarce Summary Glycolysis – glucose  2 pyruvate 2 pyruvate  2 Lactate 09_18FermentationOverview_A.swf Alcoholic CO2 released from pyruvate then converted to acetaldehyde Acetaldehyde reduced by NADH to ethanol Summary Glycolysis – glucose  2 pyruvates 2 Pyruvate  Ethanol + CO2

What is the evolutionary significance of Glycoysis? Glycolysis: a metabolic pathyway that breaks down glucose to produce pyruvate and ATP w/out O2 and w/out a membrane bound organelle, it just takes place in the cytosol of a cell. Likely the first way to generate cellular energy from food sources. Would have worked when earth did not have an O2 rich atmosphere and when eukaryotic cells didn’t exist! How cool is that?

Respiration vs. Fermentation Aerobic Respiration O2 Mitochondria Electron Acceptor is O2 ~36-38 ATP (depends on amt of O2 available to the cell.) Free Energy becomes available for metabolism by the converstion of ATP to ADP & inorganic phosphate Anaerobic Respiration No O2 Cytosol ETC w/ alternative final electron acceptors ATP production variable Fermentation (a type of anaerobic metabolism) Electron Acceptors are Ethanol or Lactate 2 ATP

Heterotrophs don’t eat just glucose Amino acids Sugars Glycerol Fatty Glycolysis Glucose Glyceraldehyde-3- P Pyruvate Acetyl CoA NH3 Citric acid cycle Oxidative phosphorylation Fats Proteins Carbohydrates Figure 9.19 Proteins, Lipids and Carbs may enter the process of respiration at various locations Glucose provides the most direct ATP

Feedback Mechanisms & Respiration Regulation Glucose Glycolysis Fructose-6-phosphate Phosphofructokinase Fructose-1,6-bisphosphate Inhibits Pyruvate ATP Acetyl CoA Citric acid cycle Citrate Oxidative phosphorylation Stimulates AMP + – Figure 9.20 Allosteric regulation of enzymes control cellular respiration by either preventing an enzyme from catalyzing a reaction OR by allowing an enzyme to catalyze a reaction.

Concept Check What would happen if a disulfide bridge in cytochrome C did not form correctly in a cell?