Cellular Respiration

Cellular Respiration = Glucose Oxidation

Redox Reactions

Coenzyme NAD+ is an electron carrier. NAD+ - oxidized Coenzyme NAD+ is an electron carrier NAD+ - oxidized NADH + H+ - reduced

NADH -Nicotinamide adenine dinucleotide Coenzyme found in all cells Made of 2 nucleotides

Mitochondrial structure - label

Mitochondrial structure

Cellular Respiration overview Process Starting Molecule End product Location Substrate level phosphorylation Energy shuttled to oxidative phosphorylation Glycolysis 1 glucose 2 pyruvate Cytosol 2 ATP 2 NADH (intermediate step) 2 Acetyl Co-A, 2 CO2 Matrix of mitochondria None

Substrate level phosphorylation Process Starting Molecule End product Location Substrate level phosphorylation Energy shuttled to oxidative phosphorylation Krebs cycle 2 acetyl-CoA 4 CO2 Matrix of mitochondria 2 ATP 6 NADH, 2 FADH2 Oxidative phosphorylation Electrons (carried by electron carriers) 32-34 ATP (theoretical) Inner membrane of mitochondria

Totals entering oxidative phosphorylation: 4 ATP from substrate phosphorylation 10 NADH (2 from glycolysis) 2 FADH2

NADH from glycolysis  2 ATP (need 1 to shuttle NADH into mitochondria) NADH  3 ATP FADH2  2 ATP This is theoretical yield Total energy produced = 36 – 38 ATP molecules - 2 in glycolysis, 2 in Krebs, 32-34* in Oxidative phosphorylation * 34 for plants (don’t spend an ATP to get NADH into mitochondria), 32 for animals

Glycolysis Glyco – glucose Lysis - splitting or breaking Pg. 162-163 How is glucose split?

Glycolysis summary How many reactions are required? What catalyzes each reaction? How many ATP are produced? How many net ATP are produced? What is the initial reactant? What are the final products? Where does this occur in the cell?

Glycolysis

Glycolysis summary How many reactions are required? 10 What catalyzes each reaction? Specific enzyme How many ATP are produced? 4 How many net ATP are produced? 2 What is the initial reactant? glucose What are the final products? Pyruvate, 2 ATP, 2 NADH Where does this occur in the cell? cytosol

Krebs cycle (aka citric acid cycle) What is the starting molecules for the Krebs cycle? What was the ending molecules of glycolysis?

Krebs cycle (aka citric acid cycle) What is the starting molecules for the Krebs cycle? Acetyl CoA What was the ending molecules of glycolysis? pyruvate

Pyruvate to Acetyl CoA Intermediate step: pyruvate oxidation How many reactions needed to convert pyruvate to acetyl CoA? What is “lost” in the process? What is “gained” in the process? Where does this occur?

Pyruvate to Acetyl CoA Intermediate step: pyruvate oxidation How many reactions needed to convert pyruvate to acetyl CoA? 3 What is “lost” in the process? CO2, electron to NAD+ What is “gained” in the process? NADH, Acetyl CoA Where does this occur? As pyruvate enters mitochondrion, in the mitochondrial matrix

Krebs Cycle – 1st step In first step: Oxaloacetate (4 C) + Acetyl-CoA (2 C) yields citrate (6 C) Oxaloacetate gets regenerated through Krebs cycle “-ate” – conjugate bases of the organic acids Carboxyl groups – can donate protons i.e. citrate is the conjugate base of citric acid

Krebs cycle – p. 165 How many reactions? What catalyzes these reactions? How many ATP produced? How are the ATP produced? Where does the rest of the energy harvested go?

Krebs Cycle

Krebs cycle How many reactions? 8 What catalyzes these reactions? Specific enzymes How many ATP produced? 1 per cycle (2 total) How are the ATP produced? Substrate phosphorylation Where does the rest of the energy harvested go? Electron carriers: 3 NADH, 1 FADH2 per cycle (6 NADH, 2FADH2 total)

Krebs cycle How many turns of the cycle for 1 molecule glucose? What are the initial reactants? Final products? Where does this occur?

Krebs cycle How many turns of the cycle for 1 molecule glucose? 2 – since glucose splits into 2 pyruvate What are the initial reactants? Final products? Initial: 2 Acetyl CoA, 6 NAD+, 2 FAD, 2 ADP Final: 4 CO2, 6 NADH, 2FADH2, 2 ATP Where does this occur? In the mitochondrial matrix

Substrate level phosphorylation

Substrate Level Phosphorylation As each bond of glucose is broken, energy is released: If enough energy released all at once, the energy is used to directly phosphorylate ADP to make ATP (substrate level phosphorylation)

-- If amount of energy released is small, electrons -- If amount of energy released is small, electrons are taken off as units of energy and handed to an electron shuttle, NADH NADH gathers all the electrons and passes them off to the electron transport chain , so they can make ATP through oxidative phosphorylation

Oxidative Phosphorylation: Electron Transport Chain & Chemiosmosis Electron Transport Chain – see diagram on handout Where do the electrons for the electron transport chain come from? Why are electrons transferred from carrier to carrier? Why does FADH2 enter at a different point than NADH?

Electron Transport Chain/Oxidative Phosphorylation Electron Transport Chain – see diagram on handout Where do the electrons for the electron transport chain come from? From glycolysis, intermediate, krebs Why are electrons transferred from carrier to carrier? Transferred to more electronegative carrier Why does FADH2 enter at a different point than NADH? Has higher electronegativity

What atom is the final acceptor of the electron? Why? What does it form? What is gained during this process?

What atom is the final acceptor of the electron? oxygen Why? Most electronegative What does it form? water What is gained during this process? A H+ gradient

Oxidative phosphorylation What is the purpose? What is a chemiosmotic gradient? How does this generate ATP?

Oxidative phosphorylation What is the purpose? To produce ATP from ADP What is a chemiosmotic gradient? A difference in concentration of H+ ions across a membrane (can be used to do work) How does this generate ATP? Flow of H+ ions through ATP synthase into mitochondrial matrix cause the ATP synthase to rotate- chemical energy converted to mechanical energy This drives phosphorylation of ADP into ATP (ADP + inorganic phosphate)

ATP Synthase Uses flow of hydrogen ions down gradient to form ATP from inorganic phosphate and ADP

ATP synthase video http://www.dnatube.com/video/104/ATP-synthase-structure-and-mechanism

Cellular Respiration

ATP Numbers . . . Not exact – Based on experimental data- 1 molecule glucose yields 29 ATP NADH – 2.5 ATP, FADH2 – 1.5 ATP NADH from glycolysis in cytosol – electrons get passed to NAD+ or FAD in mitochondrial matrix (which carrier makes a difference in total ATP) Also – some of the proton motive force powers mitochondrion’s uptake of pyruvate from cytosol, also transport of phosphate into mit. matrix

Cellular respiration efficiency – about 40% of energy from glucose gets stored in ATP The rest of the energy is lost as heat

Thermoregulation Reducing efficiency of cellular respiration Hibernating mammals – need to maintain body temperature Have a channel protein in inner mitochondrial membrane that allows protons to flow back down concentration gradient without generating ATP Allows for oxidation of fats to generate heat without ATP production

ATP without oxygen If oxygen is not present, etc and oxidative phosphorylation can’t occur 2 ways to produce ATP: Anaerobic respiration – prokaryotic organisms in environment without oxygen Use another final electron acceptor rather than oxygen, i.e. sulfur Fermentation

Fermentation Makes ATP through glycolysis (only 2 ATP) NADH transfers its electrons to pyruvate, so NAD+ can be used again in glycolysis Alcoholic fermentation – pyruvate converted to ethyl alcohol and CO2 Lactic acid fermentation – pyruvate converted to lactate

What about prokaryotes? Glycolysis – cytosol Krebs cycle – cytosol Electron transport chain – electron carriers in plasma membrane, gradient gets generated across plasma membrane Do not need to transport electrons (in NADH) from glycolysis into mitochondria, so can get more ATP

Evolution & Glycolysis Glycolysis is widespread among organisms Oldest fossils of bacteria 3.5 billion years old O2 in atmosphere not until 2.7 billion years ago Perhaps early cells got ATP just through glycolysis

Food Catabolism  Biosynthesis Proteins, Carbohydrates & Fats can all be used by cellular respiration to make ATP Biosynthesis Intermediates in the pathway of cell. resp. can be used to synthesize molecules for the cell.

Control of cellular respiration Phosphofructokinase – Enzyme that catalyzes 3rd step of glycolysis - commitment step for glycolysis Allosteric enzyme Inhibited by ATP, citrate Stimulated by AMP