Chapter 9 Cellular Respiration: Harvesting Chemical Energy

Principles of Energy Harvest Photosynthesis vs. Cellular respiration

Principles of Energy Harvest Photosynthesis Cellular respiration EndergonicExergonic Products: O 2,Products: CO 2, C 6 H 12 O 6 H 2 O, ENERGY Reactants: CO 2,Reactants: O 2, H 2 O, ENERGYC 6 H 12 O 6 ChloroplastsMitochondria

Principles of Energy Harvest Cell respiration is catabolic Breaks down glucose Photosynthesis is anabolic Synthesizes glucose

Redox reactions Oxidation - Reduction Oxidation is e- or H loss Reduction is e- or H gain Reducing agent: e- donor Oxidizing agent: e- acceptor

Oxidizing agent in respiration NAD+ (nicotinamide adenine dinucleotide) Removes electrons from food (series of reactions) NAD+ is reduced to NADH Enzyme action: dehydrogenase Oxygen is the eventual e- acceptor

Electron transport chains Electron carrier molecules (membrane proteins) Shuttles electrons that release energy used to make ATP Sequence of reactions that prevents energy release in 1 explosive step Electron route: food---> NADH ---> electron transport chain ---> oxygen

Cellular respiration summary Glycolysis: cytosol; degrades glucose into pyruvate Kreb’s Cycle: mitochondrial matrix; pyruvate into carbon dioxide Electron Transport Chain: inner membrane of mitochondrion; electrons passed to oxygen

Glycolysis ALLThe First Stage of Respiration for ALL living organisms, anaerobes or aerobes, is called Glycolysis and takes place in the Cytosol. 1 Glucose ---> 2 pyruvate molecules

Net Result 2 Pyruvic Acid 2 ATP per glucose (4 – 2 = 2) 2 NADH In summary, glycolysis takes one glucose and turns it into 2 pyruvates (molecules of pyruvic acid), 2 NADH and a net of 2 ATP.

Glycolysis Glucose (6 carbons) Pyruvic Acid (3 Carbons) 2 ATP’s supply the activation energy 4 ATP’s are produced 4 ATP Yield = 2 ATP Net Gain 2 NAD e- 2 NADH

Glycolysis Energy investment phase: cell uses ATP to phosphorylate fuel Energy payoff phase: ATP is produced by substrate-level phosphorylation and NAD+ is reduced to NADH by food oxidation Net energy yield per glucose molecule: 2 ATP plus 2 NADH; no CO 2 is released; occurs aerobically or anaerobically (no O 2 used) 1 Glucose ---> 2 pyruvate molecules

In order for Aerobic Respiration to continue the Pyruvic acid is first converted to Acetic Acid by losing a carbon atom and 2 oxygens as CO 2. The Acetic acid then must enter the matrix region of the mitochondria. The CO 2 produced is the CO 2 animals exhale when they breathe. Mitochondrion

The Krebs Cycle (AKA the Citric Acid Cycle, Tricarboxylic Acid Cycle) Sir Hans Adolf Krebs Produces most of the cell's energy in the form of NADH and FADH 2 … not ATP Does NOT require O 2

Kreb’s Cycle Each pyruvate is converted into acetyl CoA (x 2): CO2 is released NAD+ ---> NADH coenzyme A (from B vitamin), makes molecule very reactive From this point, each turn 2 C atoms enter (pyruvate) and 2 exit (carbon dioxide) Creates NADH + FADH 2 + ATP

Kreb’s Cycle “The cycle”: Oxaloacetate is regenerated For each pyruvate that enters (x2): 3 NAD+ reduced to NADH 1 FAD+ reduced to FADH2 (riboflavin, B vitamin) 1 ATP molecule Requires O 2, creates NADH + FADH 2 + ATP

Krebs cycle Summary Occurs in matrix of mitochondrion As a result of one turn of the Krebs cycle the cell makes: 1 FADH 2 3 NADH 1 ATP However, each glucose produces two pyruvic acid molecules…. So the total outcome is: 2 FADH 2 6 NADH 2 ATP

Oxidative Phosphorylation Occurs in inner mitochondrial membrane Only phase that requires O 2 Requires NADH or FADH 2 ADP and P O 2

Electron transport chain

The Chemiosmotic Hypothesis proposes that the Electron Transport Chain energy is used to move H + (protons) across the cristae membrane, and that ATP is generated as the H + diffuse back into the matrix through ATP Synthase.

Electron transport chain Chemiosmosis: energy coupling mechanism ATP synthase (enzyme): produces ATP using H+ gradient (proton-motive force) pumped into the inner membrane space from the electron transport chain harnesses the flow of H+ back into the matrix to phosphorylate ADP to ATP (oxidative phosphorylation) Cytochromes carry electron carrier molecules (NADH & FADH 2 ) down to oxygen

Review: Cellular Respiration 1.Glycolysis: 2 ATP (substrate-level phosphorylation) 2.Kreb’s Cycle: 2 ATP (substrate-level phosphorylation) 3.Electron transport & oxidative phosphorylation: 2 NADH (glycolysis) = 6ATP 4.2 NADH (acetyl CoA) = 6ATP 6 NADH (Kreb’s) = 18 ATP 2 FADH2 (Kreb’s) = 4 ATP 38 TOTAL ATP/glucose 38 molecules ATP/glucose molecule (theoretically!)

How other nutrients enter the catabolic pathway

Control of Glucose Catabolism

Theoretical ATP Yield of Aerobic Respiration Usually Said to be 36 ATP But…

Why can’t we agree?

Related metabolic processes Fermentation: 1.Alcohol: pyruvate to ethanol 2.Lactic acid: pyruvate to lactate Facultative anaerobes (yeast/bacteria) Beta-oxidation lipid catabolism

Two Types of Cellular Respiration There are two types of Respiration: Anaerobic Respiration and Aerobic Respiration Some organisms use the Anaerobic Respiration pathway, and some organisms use the Aerobic Respiration pathway.

Anaerobic Respiration: Alcoholic Fermentation is carried out by yeast, a kind of fungus.

Alcoholic Fermentation C 6 H 12 O 6 2 C 2 H 5 OH + 2 CO 2 (Ethyl Alcohol or Ethanol) As a result of Alcoholic Fermentation, Glucose is converted into 2 molecules of Ethyl Alcohol and 2 Molecules of Carbon Dioxide.

Alcoholic Fermentation Glucose (6 carbons) Pyruvic Acid (3C) 2 ATP’s supply the activation energy 4 ATP’s are produced 4 ATP Yield = 2 ATP Net Gain 2 NAD e- 2 NADH 2 NAD e- CO 2 Ethyl Alcohol (2C) (C 2 H 5 OH) Glycolysis Released into the environment

Anaerobic Respiration: Lactic Acid Fermentation Occurs in animals Uses only Glycolysis. Does NOT require O 2 Produces ATP when O 2 is not available. Carried out by human muscle cells under oxygen debt. Lactic Acid is a toxin and causes fatigue, soreness and stiffness in muscles. Diffuses into blood, detoxified by liver.

Lactic Acid Fermentation Glucose (6 carbons) Pyruvic Acid (3C) 2 ATP’s supply the activation energy 4 ATP’s are produced 4 ATP Yield = 2 ATP Net Gain 2 NAD e- 2 NADH 2 NAD e- Lactic Acid (3C) Glycolysis