Cellular Respiration: Harvesting Chemical Energy Chapter 9 Biology – Campbell Reece

Harvesting Energy Release stored energy by breaking down complex molecules in catabolic processes Release stored energy by breaking down complex molecules in catabolic processes –Fermentation – break down sugars without oxygen –Aerobic (Cellular) Respiration – break down of organic compounds (carbohydrates, fats, and proteins) with oxygen C 6 H 12 O 6 + 6O 2 → 6CO 2 + 6H 2 O + energy C 6 H 12 O 6 + 6O 2 → 6CO 2 + 6H 2 O + energy

Redox Reactions A.K.A. oxidation-reduction reactions A.K.A. oxidation-reduction reactions Oxidation – the loss of electrons Oxidation – the loss of electrons Reduction – the addition of electrons Reduction – the addition of electrons

The Stages of Cellular Respiration 1. Glycolysis –Occurs in the cytosol 2. The citric acid cycle (Krebs Cycle) –Occurs in the mitochondrial matrix 3. Oxidative phosphorylation: electron transport and chemiosmosis –Occurs on the inner membrane of the mitochondrion

Substrate-level Phosphorylation ATP synthesis in glycolysis and the citric acid cycle occurs when an enzyme transfers a phosphate from a substrate molecule to ADP ATP synthesis in glycolysis and the citric acid cycle occurs when an enzyme transfers a phosphate from a substrate molecule to ADP

Glycolysis “sugar splitting” “sugar splitting” Glucose is split into two three-carbon sugars, which are converted to pyruvate Glucose is split into two three-carbon sugars, which are converted to pyruvate Two phases: Two phases: –Energy investment – 2 ATP are used –Energy payoff – 4 ATP produced + 2 NADH

Glycolysis

Glycolysis Overview Inputs: Inputs: –Glucose –2 ATP Outputs: Outputs: –Pyruvate –4 ATP –2 NADH

After Glycolysis If oxygen is present, the pyruvate enters the mitochondrion If oxygen is present, the pyruvate enters the mitochondrion In prokaryotic cells, the next step occurs in the cytosol In prokaryotic cells, the next step occurs in the cytosol If oxygen is not present… If oxygen is not present…

Citric Acid Cycle A.K.A. Krebs Cycle A.K.A. Krebs Cycle Pyruvate is converted to acetyl coenzyme A (acetyl CoA) Pyruvate is converted to acetyl coenzyme A (acetyl CoA) –CO 2 is released –NADH is produced The acetyl CoA enters the citric acid cycle The acetyl CoA enters the citric acid cycle The cycle runs twice for each glucose molecule The cycle runs twice for each glucose molecule

Citric Acid Cycle Overview Inputs: Inputs: –2 pyruvate/ acetyl CoA Outputs: Outputs: –6 CO 2 –8 NADH –2 FADH 2 –2 ATP

Electron Transport Chain A collection of molecules imbedded in the inner membrane of the mitochondrion (bound in multiprotein complexes I through IV) A collection of molecules imbedded in the inner membrane of the mitochondrion (bound in multiprotein complexes I through IV) Electrons are transferred from the NADH to the first molecule in the chain Electrons are transferred from the NADH to the first molecule in the chain The electrons are passed from complex I to complex II and then continue down the chain The electrons are passed from complex I to complex II and then continue down the chain

Electron Transport Chain At the end of the chain, the electrons are passed to oxygen which then picks up a pair of hydrogen ions, forming water At the end of the chain, the electrons are passed to oxygen which then picks up a pair of hydrogen ions, forming water FADH 2 adds electrons to the chain starting at complex II FADH 2 adds electrons to the chain starting at complex II Complexes I, III, and IV pump H+ from the mitochondrial matrix into the intermembrane space resulting in a higher concentration on one side Complexes I, III, and IV pump H+ from the mitochondrial matrix into the intermembrane space resulting in a higher concentration on one side

Electron Transport Chain

Chemiosmosis The energy released by the electron transport chain is used to power the process of ATP synthesis (energy coupling) The energy released by the electron transport chain is used to power the process of ATP synthesis (energy coupling) Chemiosmosis uses energy stored in the form of a hydrogen ion gradient across a membrane to synthesize ATP Chemiosmosis uses energy stored in the form of a hydrogen ion gradient across a membrane to synthesize ATP ATP synthase is an enzyme embedded in the inner membrane of the mitochondria that makes ATP from ADP and inorganic phosphate ATP synthase is an enzyme embedded in the inner membrane of the mitochondria that makes ATP from ADP and inorganic phosphate

ATP Synthase and the ETC

ATP Synthase When the rotor of the ATP synthase turns in one direction, ATP is hydrolyzed When the rotor of the ATP synthase turns in one direction, ATP is hydrolyzed When it turns the other direction, ATP is synthesized When it turns the other direction, ATP is synthesized The H+ ions pass through the ATP synthase providing energy to power ATP synthesis The H+ ions pass through the ATP synthase providing energy to power ATP synthesis

Electron Transport Chain Inputs: Inputs: –10 NADH –2 FADH 2 –6 O 2 Outputs: Outputs: –~32 ATP –6 H 2 O

How much ATP?

Anaerobic Respiration and Fermentation Generate ATP without oxygen Generate ATP without oxygen Certain prokaryotes that live in environments without oxygen use anaerobic respiration (some use a sulfate ion as the final electron acceptor) Certain prokaryotes that live in environments without oxygen use anaerobic respiration (some use a sulfate ion as the final electron acceptor) Fermentation lacks any electron transport chain Fermentation lacks any electron transport chain –Consists of glycolysis plus reactions that regenerate NAD+

Types of Fermentation Alcohol fermentation – pyruvate is converted to ethanol, producing 2 ATP and 2 CO 2 Alcohol fermentation – pyruvate is converted to ethanol, producing 2 ATP and 2 CO 2 –Used in brewing, winemaking, baking Lactic acid fermentation – pyruvate is converted to lactic acid, producing 2 ATP Lactic acid fermentation – pyruvate is converted to lactic acid, producing 2 ATP –Used to make cheese and yogurt –Human muscle cells use LAF when oxygen is scarce

Types of Fermentation