Lecture #4Date _________ Chapter 9~ A Musical Journey Through Cellular Respiration Objective: How do organisms produce energy for themselves to do work?

Principles of Energy Harvest Catabolic pathway – breaking down molecules to release energy √ Fermentation √Cellular Respiration C6H12O6 + 6O2 ---> 6CO2 + 6H2O + Energy (ATP + heat) Products of photosynthesis are the reactants of the cellular respiration

Why does ATP store energy? P O–O– O–O– O –O–O P O–O– O–O– O –O–O P O–O– O–O– O –O–O P O–O– O–O– O –O–O P O–O– O–O– O –O–O P O–O– O–O– O –O–O P O–O– O–O– O –O–O P O–O– O–O– O –O–O Each P i group more difficult to add –a lot of stored energy in each bond most stored in 3rd P i ∆G = -7.3 kcal/mole Close packing of negative P i groups I think he’s a bit unstable… don’t you?  spring-loaded instability of its P bonds makes ATP an excellent energy donor

How does ATP transfer energy? P O–O– O–O– O –O–O P O–O– O–O– O –O–O P O–O– O–O– O –O–O energy P O–O– O–O– O –O–O + Phosphorylation –when ATP does work, it transfers its 3rd P i to other molecules ATP  ADP releases energy –∆G = -7.3 kcal/mole it destabilizes the other molecule Why is 3rd phosphate like a baaad boyfriend?

Exergonic vs Endergonic Reactions What if endergonic reactions need to happen in our body? SPONTANEOUS NON-SPONTANEOUS

ATP-coupled reactions The body couples ATP hydrolysis to endergonic processes by transferring a P to another molecule The Phosphorylated molecule is less stable (more reactive) This turns an endergonic reaction to an exergonic (spontaneous) reaction

Using ATP to do work? A working muscle recycles over 10 million ATPs per second Whoa! Pass me the glucose & oxygen! Can’t store ATP  too unstable  only used in cell that produces it  only short term energy storage  carbohydrates & fats are long term energy storage ATP ADP + P work

How do we create ATP? Cellular Respiration – systematic breakdown of organic molecules (carbs, lipids, proteins, etc.) Similar to the burning of gasoline in a car

Redox reactions – relocation of electrons releases energy which is then used to synthesize ATP Oxidation-reduction OIL RIG (adding e- reduces + charge) Oxidation is e- loss; reduction is e- gain Reducing agent (oxidized):e- donor Oxidizing agent (reduced): e- acceptor

Oxidizing agent in respiration (electron carrier) NAD+ (nicotinamide adenine dinucleotide) Removes electrons from food (series of reactions) NAD+ is reduced to NADH NADH carries high energy electrons 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

Aerobic vs Anaerobic

Where does cellular respiration take place?

Intermembrane Space

Overview of cellular respiration 4 metabolic stages –Anaerobic respiration 1. Glycolysis –respiration without O 2 –in cytosol –Aerobic respiration –respiration using O 2 –in mitochondria 2. Pyruvate oxidation 3. Krebs cycle 4. Electron transport chain C 6 H 12 O 6 6O 2 6CO 2 6H 2 OATP  +++ (+ heat )

Cellular respiration Overview

Glycolysis = Sugar + Break down 1 Glucose  2 pyruvate Energy investment phase: cell uses ATP to phosphorylate fuel –Glucose  G3P Energy payoff phase: ATP is produced by substrate-level phosphorylation and NAD+ is reduced to NADH by food oxidation –G3P  Pyruvic acid Net energy yield per glucose molecule: 2 ATP plus 2 NADH; no CO2 is released; occurs aerobically or anaerobically

Energy Investment Phase ENZYMES

Energy Payoff Phase

Substrate-level phosphorylation

Oxidation of Pyruvic acid Each pyruvate is converted into acetyl CoA (begin w/ 2 pyruvate): CO2 is released; NAD+ ---> NADH; coenzyme A (from B vitamin), makes molecule very reactive ACTIVE TRANSPORT = REQUIRES 2 ATP

Kreb’s Cycle If molecular oxygen is present……. From this point, each turn 2 C atoms enter (acetyl CoA) and 2 exit (carbon dioxide) Acetyl CoA combines with Oxaloacetate to form Citric acid (why it is also called citric acid cycle) Oxaloacetate is regenerated (the “cycle”) For each pyruvate that enters: 3 NAD+ reduced to NADH; 1 FAD+ reduced to FADH2 (riboflavin, B vitamin); 1 ATP molecule Totals (2 pyruvates) = 6NADH, 2FADH2, 2 ATP’s, 4 CO2

Electron transport chain NADH and FADH2 from Glycolysis and Kreb’s are transported to the ETC Cytochromes carry electron carrier molecules (NADH & FADH2) down to oxygen Chemiosmosis: energy coupling mechanism ATP synthase: produces ATP by using the H+ gradient (proton- motive force) pumped into the inner membrane space from the electron transport chain; this enzyme harnesses the flow of H+ back into the matrix to phosphorylate ADP to ATP (oxidative phosphorylation)

Review: Cellular Respiration Glycolysis: 2 ATP (substrate-level phosphorylation) Kreb’s Cycle: 2 ATP (substrate-level phosphorylation) Electron transport & oxidative phosphorylation: 2 NADH (glycolysis) = 6ATP 2 NADH (acetyl CoA) = 6ATP 6 NADH (Kreb’s) = 18 ATP 2 FADH2 (Kreb’s) = 4 ATP 38 TOTAL ATP/glucose – 2 ATP’s used in transporting NADH from glycolysis to mitochondria Net Gain = 36 ATP’s

H+H+ H+ O2O2 + Q C 32 ATP 2 Pyruvate from cytoplasm Electron transport system ATP synthase H2O CO 2 Krebs cycle Intermembrane space Inner mitochondrial membrane 1. Electrons are harvested and carried to the transport system. 2. Electrons provide energy to pump protons across the membrane. 3. Oxygen joins with protons to form water. 2H+ NADH Acetyl-CoA FADH 2 ATP 4. Protons diffuse back in down their concentration gradient, driving the synthesis of ATP. Mitochondrial matrix 2 1 H+H+ H+H+ O2O2 H+H+ e-e- e-e- e-e- e-e-

Related metabolic processes Fermentation: alcohol~ pyruvate to ethanol (also creates CO2) – useful for bakers/brewers lactic acid~ pyruvate to lactate Both create 2 ATP’s Allow NAD+ to be recycled to glycolysis Facultative anaerobes (yeast/bacteria)