Chapter 9: Cellular Respiration 9-1 Chemical Pathways

Chemical Energy and Food Cellular respiration happens slowly and in many steps. If all the energy was release in one step . . . Most would be lost as light and heat! Cellular respiration breaks down glucose molecules and banks their energy in ATP

Chemical Energy and Food PHOTOSYNTHESIS ___________ + _________ + ___________ →_______________ + __________ 6 CO2 6 H2O C6H12O6 6O2 CELLULAR RESPIRATION C6H12O6 6 CO2 _____________ + _________ →________ + __________ + __________ 6O2 6 H2O The two equations are exact opposites!

Chemical Energy and Food Amount of heat it takes to raise 1 gram of water 1o Celsius = calorie Unit for measuring energy in food = Calorie 1 Calorie = 1,000 calories

Overview of Cellular Respiration Occurs in three main stages Stage 1: Glycolysis Occurs in the cytoplasm Breaks down glucose into pyruvate, producing a small amount of ATP Stage 2: The citric acid cycle (Krebs cycle) Takes place in the mitochondria Completes breakdown of glucose, produces a small amount of ATP Provides third stage of cell respiration with electrons Stage 1 Stage 2 Stage 3

Overview of Cellular Respiration Stage 3: Oxidative phosphorylation (ETC) Occurs in the mitochondria Uses the energy released by “falling” electrons to pump H+ across a membrane Harnesses the energy of the H+ gradient through chemiosmosis, producing ATP Stage 3

Understanding Oxidation and Reduction Oxidation is the loss of electrons; electrons are removed from hydrogen atoms contained in glucose. Reduction is the gain of electrons; oxygen atoms accept hydrogen and electrons forming water H2O. Remember OIL RIG (oxidation is loss, reduction is gain)

Electron Carriers (enzymes) Involved NAD+ (Nicotinamide adenine dinucleotide) Accepts H+ to become NADH FAD (Flavin adenine dinucleotide) Accepts 2H+ to become FADH2

Overview of Cellular Respiration NADH FADH2 GLYCOLYSIS Glucose Pyruvate CITRIC ACID CYCLE OXIDATIVE PHOSPHORYLATION (Electron Transport and Chemiosmosis) Substrate-level phosphorylation Oxidative phosphorylation Mitochondrion and High-energy electrons carried by NADH ATP CO2 Cytoplasm Stage 1 Stage 3 Stage 2 Krebs

(Glykos = sweet, Lysis = split apart) 9.2 Glycolysis (Glykos = sweet, Lysis = split apart) The first step in cellular respiration = Glycolysis Happens in the CYTOPLASM outside the mitochondria Does not require oxygen, BUT it needs some energy to get it started. What molecule is going to supply the energy? ATP

____________________ + _______________ Glycolysis ________ ↓ ___________ → → _____________ ____________________ + _______________ GLUCOSE 2 PYRUVIC ACID ATP ATP ATP ATP NADH NADH PUT IN 2 ATP and GET BACK 4 ATP Net gain of 2 ATP and 2 NADH

Glycolysis Produces pyruvic acid (pyruvate – a 3 carbon compound) Cell needs to invest some energy to get a higher return (2 ATP gained) Occurs quickly, in miliseconds to respond to increased energy demand

9-2 The Krebs Cycle and Electron Transport

Mitochondria Structure Has a double membrane, with an intermembrane space between the two layers. Cristae are folds of the inner membrane The matrix is the innermost compartment, which is filled with a gel-like fluid. Krebs Cycle occurs in the matrix of the mitochondria.

The Krebs Cycle Pyruvic acid enters the mitochondria matrix Pyruvic acid is converted into an intermediate 2 carbon molecule called Acetyl-CoA before entering the Krebs Cycle. The Krebs cycle breaks down carbon compounds into carbon dioxide (waste), ATP, NADH, and FADH2

The Krebs Cycle Carbon dioxide is lost to the atmosphere as waste ATP can be used directly to supply energy for the cell High energy electron carriers move into the ELECTRON TRANSPORT CHAIN

Electron Transport Chain Enzymes (protein complexes) for the electron transport chain are located on the inner mitochondrial membrane. Several complexes are called cytochromes. Virtual Cell ETC Animation

Electron Transport Chain Electrons from NADH and FADH2 travel down the electron transport chain, between protein complexes to oxygen (final electron acceptor), which picks up H+ to form water Energy released by the redox reactions is used to pump H+ into the space between the mitochondrial membranes H2O NAD+ NADH ATP H+ Controlled release of energy for synthesis of ATP Electron transport chain 2 O2 2e + 1

Chemiosmosis In chemiosmosis, the H+ diffuses back through the inner membrane through ATP synthase complexes. Driving the synthesis of ATP Intermembrane space Inner mitochondrial membrane Mitochondrial matrix Protein complex Electron flow Electron carrier NADH NAD+ FADH2 FAD H2O ATP ADP ATP synthase H+ + P O2 Electron Transport Chain Chemiosmosis . OXIDATIVE PHOSPHORYLATION + 2 1 2

Fermentation Pyruvic acid moves to the next step If there is no oxygen = anaerobic If there is oxygen = aerobic

Fermentation Fermentation – process by which cells release energy in the absence of oxygen Two types of fermentation: Alcoholic Fermentation Lactic Acid Fermentation

Alcoholic Fermentation _______ +_____ →__________ + ______ + _____ PYRUVIC ACID ALCOHOL CO2 NAD+ Happens when yeast makes bread dough rise, CO2 bubbles make air spaces in bread. (Alcohol evaporates during cooking) Happens when: Yeast make beer Bacteria make wine

Lactic Acid Fermentation _______ +_____ →______________ + ________ PYRUVIC ACID LACTIC ACID NAD+ Happens in muscles during exercise when body can’t get oxygen to tissues fast enough. Lactic acid builds up in muscles causing soreness. Bacteria use lactic acid fermentation to make: yogurt, cheese, sour cream, pickles, sauerkraut, kimchi

The Totals Cellular Respiration (aerobic: with oxygen) 1 glucose → 36 ATP Fermentation (anaerobic: without oxygen) 1 glucose → 2 ATP

Respiration Questions List the reactants and products of respiration List the three steps (stages) involved in respiration Name two electron carriers involved What step produces the most ATP

Respiration Questions In your group: See if you can write the chemical equation for respiration (inputs and outputs) What is the organelle in cells that is “releasing” energy during respiration? What primary molecule is energy being “released” from? How is the sun indirectly involved in respiration?

Fermentation Questions List two types of fermentation List the reactants for both types of fermentation List the products for fermentation used to brew beer List the products for fermentation used to make yogurt What important molecule cycles back from fermentation to keep glycolysis going? What process starts fermentation?

Krebs Cycle 1.___________ 2.___________ 3.________ 7.________ 4.________ 6.________ 5.________

Electron Transport Chain (ETC) Intermembrane space Inner mitochondrial membrane Mitochondrial matrix Protein complex Electron flow Electron carrier NADH NAD+ FADH2 FAD H2O ATP ADP ATP synthase H+ + P O2 Electron Transport Chain Chemiosmosis . OXIDATIVE PHOSPHORYLATION + 2 1 2