Lecture Seven: Cellular Respiration Ch. 9, Pgs. 163-181 Figs. 9.2-9.20 Biological Science 101 General Biology Cellular Respiration: - A series of processes that is involved in converting food to energy (ATP) - Breakdowns food (Catabolism) - Aerobic process (O2) - Involves enzymes. - Conversion of food to energy One glucose molecule -> 38 Molecules of ATP Three Phases: 1) Glycolysis (sugar splitting) Takes place in the cytoplasm. Glucose (6-C) -> -> -> (10 Steps) -> Pyruvate + (3-C) 2H2O 2) Citric Acid Cycle Pyruvate (3-C) -> Acetyl CO-A (2-C) -> -> -> (8 Steps) -> CO2 3) Electron transport (Oxidative Phosphorylation) - ATP is produced.
- Energy Input: 2ATP -> 2ADP (Endergonic) - Energy Output: 4ATP (Exergonic) 2NADH 2 Pyruvate - Net Output: 2ATP (Energy Molecule) 2NADH (Energy Molecule) 2 Pyruvate Citric Acid cycle
- Energy Output: 3NAD -> 3NADH (x2 for Pyruvate [2X]) 1FAD -> 1 FADH (x2 for Pyruvate [2X]) 1 ADP -> 1 ATP (x2 for Pyruvate [2X]) Electron transport chain Electron Transport: - Mitochondria inner membrane (cristae). - Electrons transferred step-by-step from NADH, FADH -> O2 (acceptor) Electron Loss -> Oxidized Electron Accept -> Reduced Chemiosmosis - Energy in the form of electrons is converted into ATP. - Enzyme involved is called ATP-Synthase. - Hydrogen ions (H+) accumulate outside the membrane, causing a differential charge is created (Proton-Motive-Force) Proton-Motive-Force -> Drives the ATP-Synthase
Net yield of energy (ATP) Energy Production: Food -> Source of -> Glycolysis: -> Electrons -> Electron (Glucose) Electrons (2 ATP, 2 NADH) Transport Acetyl CoA: (2 NADH) Citric Acid: (6NADH, 2 FADH, 2 ATP) 10 NADH = 3 ATP 2 FADH = 2 ATP 4 ATP 30 ATP + 4 ATP + 4 ATP = 39 ATP (+/- 10%)
Efficiency: 1 Glucose -> 686 kcal/mole 1 ATP -> 7.3 kcal/mole Efficiency in Respiration: 7.3 x 38 ATP = 686 kcal (40% Efficiency, 60% lost as heat ) E.g. Car -> Gasoline -> 25% Efficiency. * Background Reading: Laboratory Week 4 Handout.
Review Questions: 1. What is the role of ATP in the cell? Why is it considered a "high-energy" molecule? Energy captured -> ATP (Adenosine triphosphate) ATP drives transport and mechanical work. - ATP hydrolyses causes changes in shapes and binding affinities of proteins - ATP transports chemical energy within cells for metabolism. - It is produced by photophosphorylation and cellular respiration and used by enzymes and structural proteins in many cellular processes, including biosynthetic reactions, motility, and cell division. It is considered to be a high-energy molecule because it aids in intracellular energy transfer. 2. What does NAD+ do in the cell? Another energy molecule: NAD + (Nicotinamide Adenine Dinucleotide) NAD + aids Oxidation -- Electrons --> Reduction - High-energy foods Fats Carbohydrates 3. What is an enzyme? What does it do in the cell? Enzymes: - Involved in catabolism. - Food broken down. - Energy released. - Catalytic proteins that speed up the rate of a reaction, without altering the end products or change the reaction. For chemical reactions to start, they require initial energy (activation energy), usually heat energy. - Enzymes reduces the activation energy required. 4. Describe 4 features that show how enzymes function. 1) Substrate Specific - Sucrase -> Sucrose - Sucrose binds to an active site on the enzyme. - Form enzyme + substrate complex.
- Products released (glucose + fructose) - Reaction occurs at 1000 x per second. 2) Affected by Environment (Sensitive) - Temperatures can affect enzymes ability to function. - Each enzyme has its own optimal temperature. - ph can also affect enzymes. - Each enzyme has its own optimal ph. 3) Requires Cofactors or Co-enzymes - Assist with the catalytic activity. E.g. Zn, Cu, Co-enzyme A, Vitamins (function as cofactors or co-enzymes) 4) Activity of Enzymes are affected by Chemicals - This may cause enzymes to stop. - It can be reversible or irreversible: 5. Give 3 methods through which the cell can regulate enzyme activity. Enzyme regulation - Has to be regulated in the cell: a) Allosteric Sites: - Sites in the enzyme that are regulators of activity receptors. - Regulates activity up or down. b) Feedback Inhibition: - The accumulation of product causes the enzyme to switch off (temporary shutdown). Switch off -> Binding to Allosteric Sites. c) Co-operativity: - Interaction between allosteric sites. - One active site is needed to become activated. 6. What is the difference between a competitive inhibitor and a noncompetitive inhibitor of enzyme activity? a) Competitive Inhibition: - Chemical inhibitor. - Competes for active site. - Reaction stop. - Reversible. b) Non-competitive Inhibition: - Chemical molecule binds to enzyme.
- Alters active site. - Enzyme nonfunctional. - Irreversible. E.g. Pesticides, Antibiotics, Poisons (Nerve gas), DDT Review Questions 1. What are the locations in the cell where glycolysis, the Citric Acid cycle, and electron transport take place? Glycolysis: Takes place in the cytoplasm. The Citric Acid Cycle: The matrix of the mitochondrion. Electron Transport: Mitochondria inner membrane (cristae). 2. At what step during glycolysis is NADH produced? When Glyceraldehyde 3-phosphate (3-C) turns into 1-3-bisphoglycerate. 3. What is the total yield of energy-containing molecules produced from glycolysis? - Energy Input: 2ATP -> 2ADP (Endergonic) - Energy Output: 4ATP (Exergonic) 2NADH 2 Pyruvate - Net Output: 2ATP (Energy Molecule) 2NADH (Energy Molecule) 2 Pyruvate 10 NADH = 3 ATP 2 FADH = 2 ATP 4 ATP 30 ATP + 4 ATP + 4 ATP = 39 ATP (+/- 10%) 4. In what form does pyruvate enter into the Citric Acid cycle? Pyruvate enters the Citric Acid cycle in the form on an enzyme.
5. At what step in the Citric Acid cycle is FADH produced? Citric Acid cycle produces FADH when succinate turns into Fumarate. 6. What is the total yield of energy-containing molecules produced from the Citric Acid cycle? - Energy Output: 3NAD -> 3NADH (x2 for Pyruvate [2X]) 1FAD -> 1 FADH (x2 for Pyruvate [2X]) 1 ADP -> 1 ATP (x2 for Pyruvate [2X]) 7. What is meant by the term "chemiosmosis"? Chemiosmosis: - Energy in the form of electrons is converted into ATP. - Enzyme involved is called ATP-Synthase. - Hydrogen ions (H+) accumulate outside the membrane, causing a differential charge is created (Proton-Motive-Force) Proton-Motive-Force -> Drives the ATP-Synthase