Presentation on theme: "How Cells Harvest Chemical Energy"— Presentation transcript:
1 How Cells Harvest Chemical Energy Chapter 6How Cells Harvest Chemical Energy1
2 BREATHING VERSUS RESPIRATION Alternation of inhalation and exhalation.Exchange of gases in which organisms obtain oxygen from the air (or water) and release carbon dioxide.Exchange occurs in lungs (or gills).CELLULAR RESPIRATION:Harvesting of energy from food molecules by cells.Aerobic process (requires oxygen).Occurs inside cells (cytoplasm and mitochondria).“Respiration” comes from Latin word for breathing.Breathing and cellular respiration are closely related, but not the same processes.
4 CELLULAR RESPIRATION BANKS ATP REACTION: C6H12O O > 6CO H2O + ENERGY(Glucose) (Oxygen) (Carbon dioxide) (Water)What happens to the energy in glucose or other food molecules?Only about 40% of energy is turned into ATPThe rest is lost as metabolic heat.One ATP molecule has about 1% of the chemical energy found in glucose.
5 ENERGY CONVERSIONS ARE INEFFICIENT Second Law of Thermodynamics By Comparison Living Organisms Are Efficient
6 THREE MAJOR CATABOLIC PATHWAYS IN LIVING ORGANISMS CATABOLISM:Process of splitting larger molecules to smaller ones. Catabolic reactions are exergonic and release free energy.THREE MAJOR CATABOLIC PATHWAYS IN LIVING ORGANISMSA. Aerobic (Cellular) respirationB. Anaerobic respirationC. Fermentation
7 MAJOR CATABOLIC PATHWAYS A. Aerobic (Cellular) respiration: Requires oxygen.Most commonly used catabolic pathway.Over 30 reactions. Used to extract energy from glucose molecules.Final electron acceptor: Oxygen.Most efficient: 40% of glucose energy is converted into ATP.REACTION:C6H12O O > 6CO H2O + ENERGYGlucose Oxygen Carbon dioxide Water
8 THREE MAJOR CATABOLIC PATHWAYS B. Anaerobic respiration: Does not require oxygen.Used by bacteria that live in environments without oxygen.Final electron acceptor: Inorganic molecule.Very inefficient: Only 2% of glucose energy is converted into ATP.Final products: Carbon dioxide, water, and other inorganic compounds.
9 THREE MAJOR CATABOLIC PATHWAYS C. Fermentation: Does not require oxygen.Used by yeast, bacteria, and other cells when oxygen is not available.Final electron acceptor: Organic molecule.Very inefficient: Only 2% of glucose energy is converted into ATP.Products depend on type of fermentation:Lactic acid fermentation: Used to make cheese and yogurt. Carried out by muscle cells if oxygen is low.Alcoholic fermentation: Used to make alcoholic beverages. Produces alcohol and carbon dioxide.
10 II. Hydrogen carriers shuttle electrons in REDOX reactions Oxidation:Partial or complete loss of electrons or H atoms.When a molecule is oxidized it loses energy.Reduction:Partial or complete gain of electrons or H atoms.When a molecule is reduced it gains energy.REDOX Reactions:Reactions in which both oxidation and reduction occur.Characteristic of many cell processes, including aerobic respiration and photosynthesis.
11 Cellullar Respiration is a Redox Process: Involves Both Oxidation and Reduction Glucose is oxidized to carbon dioxide.Oxygen is reduced to water.
12 III. Redox reactions in living organisms Cellular Respiration: Macromolecules oxidized to release energy (686 kcal/mole) which is used to synthesize ATPC6H12O O > 6CO H2O + ENERGYGlucose Oxygen (oxidized) (reduced)Photosynthesis: CO2 is reduced ; requires energy to drive the reaction forward6CO H2O + ENERGY ---> C6H12O O2Carbon Water (reduced) (oxidized)Dioxide High Energy
13 IV. Hydrogen carriers shuttle electrons in redox reactions 1. Dehydrogenase: Removes hydrogen atoms (with their electrons) from organic molecules and transfers them to an electron carrier.2. Electron Carrier Molecules:NAD+: (Nicotinamide adenine dinucleotide) Coenzyme that accepts and transfers most H and the high energy electrons released by redox reactionsReductionNAD+ + 2H > NADH + H+(2H+ & 2e-)FADH2 (Flavin adenine dinucleotide): Secondary H carrier, related to NADH.
14 Dehydrogenase and Hydrogen Carriers Shuttle Electrons in Redox Reactions
15 IV. Electrons “fall” from Hydrogen Carriers to Oxygen in the Electron Transport Chain NADH: (Nicotinamide andenine dinucleotide) : Delivers H and the high energy electrons released by redox reactions to electron carrier molecule of chain.Electron transport chain: Proteins on inner mitochondrial membrane that accept H and use high energy electrons to produce ATP.
16 As Electrons “Fall” From Hydrogen Carriers to Oxygen, Energy is Released
17 Two different means of ATP production: 1. Substrate-level phosphorylation:Generates a small amount of ATP during cellular respiration.Simple process, does not require membranes.Phosphate group is directly transferred from an organic molecule to ADP to make ATP.Occurs in first two stages of aerobic respiration:GlycolysisKreb’s cycle
18 2. Oxidative phosphorylation (Chemiosmosis): Two different means of ATP production:2. Oxidative phosphorylation (Chemiosmosis):Generates most of ATP made during cellular respirationComplex process, requires mitochondrial membranes.Energy released from exergonic reactions of electron transport is used to pump H+ ions across membrane, creating a concentration gradient (potential energy).Chemiosmosis: ATP is made by ATP synthase on mitochondrial membranes, as H+ flow down concentration gradient.Occurs in last stage of aerobic respiration.Requires the presence of OXYGEN
19 Two Mechanisms of ATP Synthesis: Oxidative and Substrate Level Phosphorylation
20 V. Three Stages of Cellular Respiration A. GlycolysisB. Kreb’s CycleC. Electron Transport Chain & Chemiosmosis
22 A. Glycolysis: “Splitting sugar” Occurs in the cytoplasm of the cellDoes not require oxygen9 chemical reactionsNet result: Glucose molecule (6 carbons each) is split into two pyruvic acid molecules of 3 carbons each.Yield per glucose molecule:2 ATP ( Substrate-level phosphorylation)2 NADH + 2 H+(2 ATP are “invested” to get 4 ATP back)Pyruvic acid diffuses into mitochondrial matrix where all subsequent reactions take place.
23 Glycolysis: “Splitting” of Glucose into Two Molecules of Pyruvic Acid
24 Conversion of Pyruvate to Acetyl CoA Before entering the next stage, pyruvic acid (3C) must be converted to Acetyl CoA (2 C).A carbon atom is lost as CO2.Yield per glucose molecule: 2 NADH H+
26 Occurs in the matrix of the mitochondrion A cycle of 8 reactions B. Kreb’s CycleOccurs in the matrix of the mitochondrionA cycle of 8 reactionsReaction 1: Acetyl CoA (2C) joins with 4C molecule (oxaloacetic acid) to produce citric acid (6C).Reactions 2 & 3: Citric acid loses 2C atoms as CO2.Reactions 4 & 5: REDOX reactions produce NADH and FADH2.Reactions 6-8: Oxaloacetic acid is regenerated.
29 B. Kreb’s CycleCarbons are released as CO2Yield per glucose molecule:2 ATP (substrate-level phosphorylation)6 NADH H+2 FADH2
30 C. Electron Transport Chain & Chemiosmosis Most ATP is produced at this stageOccurs on inner mitochondrial membraneElectrons from NADH and FADH2 are transferred to electron acceptors, which produces a proton gradientProton gradient used to drive synthesis of ATP.Chemiosmosis: ATP synthase allows H+ to flow across inner mitochondrial membrane down concentration gradient, which produces ATP.Ultimate acceptor of H+ and electrons is OXYGEN, producing water.
31 Electron Transport & Chemiosmosis: Generates Most ATP Produced During Cellular Respiration
32 NOTE: The electron transport chain ONLY works when OXYGEN is available at the end of the chain to accept the electrons and H+ to form water.
33 C. Electron Transport Chain & Chemiosmosis Yield of ATP through Chemiosmosis:Each NADH produces 3 ATPEach FAHD2 produces 2 ATP2 NADH (Glycolysis) x 3 ATP = 6 ATP2 NADH (Acetyl CoA) x 3 ATP = 6 ATP6 NADH (Kreb’s cycle) x 3 ATP = 18 ATP2 FADH2 (Kreb’s cycle) x 2 ATP = 4 ATP________________ATPThese ATPs are made by oxidative phosphorylationor chemiosmosis.
34 VIII. Total Energy from cellular respiration Substrate OxidativeProcess Phosphoryl e-Carrier Phosphoryl TOTALGlycolysis 2 ATP NADH ---> ATP ATPAcetyl CoA NADH ---> 6 ATP ATPFormationKreb’s ATP NADH ---> 18 ATP2 FADH2 ---> 6 ATP ATP__________Total yield per glucose : ATP
36 Many poisons interrupt cellular respiration Electron transport chain blockers:Rotenone: PesticideCyanideCarbon monoxideATP synthase inhibitorsOligomycin: Antifungal drug. Used on skin.Uncouplers: Make mitochondrial membrane leaky to H+ ions. Abolishes H+ gradient, can’t make ATP through chemiosmosis.Dinitrophenol (DNP): Used in 1940s as weight loss drug.
37 Effects of Various Poisons on the Electron Transport Chain
38 Yeasts normally use aerobic respiration to process food. FERMENTATION OCCURS WHEN OXYGEN IS NOT AVAILABLEYeasts normally use aerobic respiration to process food.If oxygen is not available, they use fermentation, which is less efficient.Types of fermentation:Alcoholic fermentationGlucose ----> 2 pyruvate ----> 2 Ethanol CO2Lactic acid fermentationGlucose ----> 2 pyruvate ----> 2 Lactic acids
40 Alcoholic and Lactic Acid Fermentation: An Alternative to Aerobic Respiration
41 ORGANISMS CAN BE CLASSIFIED BASED ON THEIR OXYGEN REQUIREMENTS Strict aerobes: Require oxygen for survival. All large organisms are aerobes.Examples: Humans, dogs, insects.Strict anaerobes: Grow only in the absence of oxygen. Are poisoned by oxygen.Examples: Bacteria that live in soil and animal intestines.Facultative anaerobes: Grow with/without oxygen. Grow better with oxygen.Examples: Yeast and many bacteria.
42 All Food Molecules are Fed into The Catabolic Pathway of Aerobic Respiration