Overview Of Aerobic Cellular Respiration Cellular respiration: the process that releases energy (ATP) by breaking down glucose and other food molecules in the presence of oxygen 3 phases Glycolysis Krebs cycle The electron transport chain

Cellular Respiration

NAD+ and the Electron Transport Chain In cellular respiration, glucose and other organic molecules are broken down in a series of steps Electrons from organic compounds are usually first transferred to NAD+, a coenzyme As an electron acceptor, NAD+ functions as an oxidizing agent during cellular respiration Each NADH (the reduced form of NAD+) represents stored energy that is tapped to synthesize ATP Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

2 e– + 2 H+ 2 e– + H+ Dehydrogenase Nicotinamide (reduced form) Fig. 9-4 2 e– + 2 H+ 2 e– + H+ NADH H+ Dehydrogenase Reduction of NAD+ NAD+ + 2[H] + H+ Oxidation of NADH Nicotinamide (reduced form) Nicotinamide (oxidized form) Figure 9.4 NAD+ as an electron shuttle

It starts… Cell Respiration starts with the food you eat. Foods are mechanically and chemically broken down throughout your digestive system. Amylase – Enzyme in saliva that breaks down starches

Step 1: Glyco-lysis: breaking glucose

Stage 1- Glycolysis (Glyco) and (lysis)- Breakdown of glucose Occurs in the cytoplasm Anaerobic (no oxygen required) Breaks glucose into 2 molecules called pyruvate 2 ATPs required to start the reaction 4 ATPs are produced. Net Gain = 2 ATPs

Substrate Level Phosphorylation Fig. 9-7 Substrate Level Phosphorylation Substrate-level phosphorylation is the enzyme catalyzed formation of ATP by direct transfer of a phosphate group to ADP from an intermediate substrate (substance) in catabolism. IE: When an enzyme breaks a phosphate group off a molecule (substrate) and reattaches it to ADP to create ATP. Enzyme Enzyme Figure 9.7 Substrate-level phosphorylation

Substrate Level Phosphorylation Fig. 9-7 Substrate Level Phosphorylation A small amount of ATP is formed in glycolysis and the citric acid cycle by substrate-level phosphorylation . Enzyme Enzyme Figure 9.7 Substrate-level phosphorylation

Butterflies Walk your turtle through the process of Glycolysis

Review What 2 molecules are produced at the end of glycolysis? How many carbons are in the two molecules produced at the end of glycolysis?

Objectives: Describe the major events in Glycolysis Summarize the events of the Krebs Cycle Distinguish between Glycolysis and Aerobic Respiration Summarize the reactants and products of cellular respiration

Shoulder Partners

7.2 The Krebs cycle and Electron Transport Aerobic Respiration

Mitochondria

Krebs Cycle (Citric Acid Cycle)

Stage 2: Krebs Cycle Krebs cycle Takes place in matrix of mitochondria The Krebs cycle occurs twice Once for each pyruvate; twice for each glucose Remember 2 pyruvate =1 glucose

The Krebs Cycle Aerobic (requires oxygen) Breaks pyruvic acid down First, into Acetyl CoA Then, into CO2 and Hydrogen Yields 2 ATPs and high-energy electrons (NADH and FADH2) for the electron transport chain

Substrate Level Phosphorylation Fig. 9-7 Substrate Level Phosphorylation A small amount of ATP is formed in glycolysis and the citric acid cycle by substrate-level phosphorylation . Enzyme Enzyme Figure 9.7 Substrate-level phosphorylation

Turtles Walk your butterfly through the process of the Krebs cycle

The E.T.C. (electron transport chain)

Step 3: The Electron Transport Chain Occurs along the inner membrane of the mitochondria (Cristae) Uses high-energy electrons from NADH and FADH2 (produced during the Krebs Cycle) to pump H+ from the matrix to the intermembrane space Hydrogen electrons are transferred along the ETC to Oxygen (final electron acceptor)  Water

NADH and FADH2 NADH and FADH2 passes the electrons to the electron transport chain O2 pulls electrons down the chain in an energy- yielding tumble The energy yielded is used to regenerate ATP Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Chemiosmosis: The Energy-Coupling Mechanism Electron transfer in the electron transport chain causes proteins to pump H+ from the mitochondrial matrix to the intermembrane space H+ then moves back across the membrane, passing through channels in ATP synthase ATP synthase uses the exergonic flow of H+ to drive phosphorylation of ATP This is an example of chemiosmosis, the use of energy in a H+ gradient to drive cellular work Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Oxidative Phosphorylation The process of creating ATP using energy from redox reactions in the ETC Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Oxidative Phosphorylation The process that generates most of the ATP is called oxidative phosphorylation because it is powered by redox reactions Makes ~32 ATP This requires the presence of Oxygen as the final electron acceptor Accounts for 90% of ATP generated Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Electron transport chain 2 Chemiosmosis Fig. 9-16 H+ H+ H+ H+ Protein complex of electron carriers Cyt c V Q   ATP synthase  2 H+ + 1/2O2 H2O FADH2 FAD NADH NAD+ ADP + P ATP Figure 9.16 Chemiosmosis couples the electron transport chain to ATP synthesis i (carrying electrons from food) H+ 1 Electron transport chain 2 Chemiosmosis Oxidative phosphorylation

An Accounting of ATP Production by Cellular Respiration During cellular respiration, most energy flows in this sequence: glucose  NADH  electron transport chain  proton-motive force  ATP About 40% of the energy in a glucose molecule is transferred to ATP during cellular respiration, making about 38 ATP Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig. 9-17 CYTOSOL Electron shuttles span membrane MITOCHONDRION 2 NADH or 2 FADH2 2 NADH 2 NADH 6 NADH 2 FADH2 Glycolysis Oxidative phosphorylation: electron transport and chemiosmosis 2 Pyruvate 2 Acetyl CoA Citric acid cycle Glucose + 2 ATP + 2 ATP + about 32 or 34 ATP Figure 9.17 ATP yield per molecule of glucose at each stage of cellular respiration About 36 or 38 ATP Maximum per glucose:

That moment when… Mitochondria goes from being the power house of the cell to being the oxidative phosphorylation center of the cell

Butterflies Explain how the ETC runs to your turtles

Overall Cellular Respiration breaks down C6H12O6. It produces H2O and CO2 It can produce 36-38 ATPs Net Gain 2 GLYCOLYSIS 2 KREBS CYCLE 32-34 ETC

Cellular Respiration (aerobic)

Turtles Walk your butterfly through the process of cellular respiration

Butterflies Walk your turtle through the process of cellular respiration

What if there is no Oxygen?

Anaerobic respiration Not enough oxygen for aerobic respiration Fermentation-releases energy from food molecules by producing ATP in the absence of oxygen. (Anaerobic = no oxygen) Two types: alcoholic fermentation, lactic acid fermentation

Lactic acid fermentation Alcoholic fermentation No oxygen Occurs in muscles Pyruvates lactate Occurs so muscles can continue making ATP Get lactate build up in muscles Causes burning sensation No oxygen Pyruvate  carbon dioxide & ethanol Seen in yeast and fungus Used to make beverages, food, makes dough rise

Fermentation Anaerobic respiration uses an electron transport chain with an electron acceptor other than O2, for example sulfate Fermentation uses phosphorylation instead of an electron transport chain to generate ATP Fermentation consists of glycolysis plus reactions that regenerate NAD+, which can be reused by glycolysis Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

alcohol fermentation In alcohol fermentation, pyruvate is converted to ethanol in two steps, with the first releasing CO2 Alcohol fermentation by yeast is used in brewing, winemaking, and baking Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

lactic acid fermentation In lactic acid fermentation, pyruvate is reduced to NADH, forming lactate as an end product, with no release of CO2 Lactic acid fermentation by some fungi and bacteria is used to make cheese and yogurt Human muscle cells use lactic acid fermentation to generate ATP when O2 is scarce Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Anaerobic Organisms Obligate anaerobes carry out fermentation or anaerobic respiration and cannot survive in the presence of O2 Yeast and many bacteria are facultative anaerobes, meaning that they can survive using either fermentation or cellular respiration In a facultative anaerobe, pyruvate is a fork in the metabolic road that leads to two alternative catabolic routes Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Ethanol or lactate Citric acid cycle Fig. 9-19 Glucose Glycolysis CYTOSOL Pyruvate O2 present: Aerobic cellular respiration No O2 present: Fermentation MITOCHONDRION Ethanol or lactate Acetyl CoA Figure 9.19 Pyruvate as a key juncture in catabolism Citric acid cycle

The Evolutionary Significance of Glycolysis Glycolysis occurs in nearly all organisms Glycolysis probably evolved in ancient prokaryotes before there was oxygen in the atmosphere Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

The Versatility of Catabolism Catabolic pathways funnel electrons from many kinds of organic molecules into cellular respiration Glycolysis accepts a wide range of carbohydrates Proteins must be digested to amino acids; amino groups can feed glycolysis or the citric acid cycle Fats are digested to glycerol (used in glycolysis) and fatty acids (used in generating acetyl CoA) An oxidized gram of fat produces more than twice as much ATP as an oxidized gram of carbohydrate Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Citric acid cycle Oxidative phosphorylation Fig. 9-20 Proteins Carbohydrates Fats Amino acids Sugars Glycerol Fatty acids Glycolysis Glucose Glyceraldehyde-3- P NH3 Pyruvate Acetyl CoA Figure 9.20 The catabolism of various molecules from food Citric acid cycle Oxidative phosphorylation

Regulation of Cellular Respiration via Feedback Mechanisms Feedback inhibition is the most common mechanism for control If ATP concentration begins to drop, respiration speeds up; when there is plenty of ATP, respiration slows down Control of catabolism is based mainly on regulating the activity of enzymes at strategic points in the catabolic pathway Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Figure 9.21 The control of cellular respiration Glucose AMP Glycolysis Fructose-6-phosphate Stimulates + Phosphofructokinase – – Fructose-1,6-bisphosphate Inhibits Inhibits Pyruvate ATP Citrate Acetyl CoA Figure 9.21 The control of cellular respiration Citric acid cycle Oxidative phosphorylation