Biological Science 101 General Biology

Transcription

1 Lecture Seven: Cellular Respiration Ch. 9, Pgs Figs 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.

2 - 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

3 - 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

4 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%)

5 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.

6 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.

7 - 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.

8 - 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.

9 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