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Unit 3.2: Cellular Respiration Vocabulary: • Glycolysis: glyco- = sweet, sugar; lysis = break apart; process in which glucose is broken down into pyruvate, releasing energy; occurs in the cytoplasm • NAD+/NADH: a molecule that can carry energy, electrons from one part of the mitochondria to another. (NAD+ is “empty” bucket, NADH is “full”) • Anaerobic Respiration: an- = without; aero- = air; process that breaks down glucose in the absence of oxygen; also called fermentation. • Aerobic Respiration: process that breaks down glucose in the presence of oxygen. • Krebs Cycle: (also called the Citric Acid Cycle); a process in aerobic respiration that breaks down acetyl coA into CO2. 2 I. Structure of Mitochondria: A. Contains cristae: highly infolded inner membrane that increases surface area for more reactions. B. Also contains matrix: fluid that fills mitochondria 1. Like cytoplasm for the mitochondria 3 Overview of Respiration C6H12O6 + 6O2 6CO2 + 6H2O + ATP glucose + oxygen carbon dioxide + water + energy 4 C6H12O6 + 6O2 6CO2 + 6H2O + energy Cellular Respiration Glycolysis If no oxygen Anaerobic Respiration (fermentation ) If oxygen present Aerobic Respiration Kreb’s Cycle Lactic Acid Alcoholic Electron Transport Chain 5 II. Glycolysis (occurs in cytoplasm in all organisms) A. Process splits 6-carbon glucose into (2) 3-carbon pyruvate molecules B. Requires input of 2 ATP to get process started, but creates 4 ATP, so net gain of 2 ATP/glucose 1. **Inefficient for large organisms, but okay “in a pinch” 2. **Lots of energy still locked in C-C bonds of pyruvate C. NAD+ (empty bucket) collects e-’s/H+, becomes NADH (full bucket) D. So far: C6H12O6 pyruvate + ATP + NADH 6 III. Anaerobic Respiration/Fermentation • “an-” = without; “aero” = air, oxygen A. Purpose: anaerobic respiration regenerates NAD+ so it can be re-used in glycolysis 1. If NADH from glycolysis is not recycled, then respiration stops. B. Two different paths: 1. Lactic Acid fermentation 2. Alcoholic fermentation 7 B.1. Lactic Acid Fermentation: a. H from NADH and free H+ combine with pyruvate to become lactic acid (aka: lactate) 1) In cultured dairy products, bacteria break down lactose (milk sugar) into lactic acid using this NADH + H+ process: yogurt, cottage cheese 2) Your muscles go through lactic acid fermentation if there is not enough O2. Lactic acid buildup can NAD+ lead to cramping. a) When you stop exercising, lactate is turned back into pyruvate; goes into aerobic respiration b. NAD+ is “regenerated” 1) Back to cytosol for glycolysis 8 B.2. Alcoholic Fermentation Pyruvate Acetaldehyde Ethanol a. Pyruvate releases CO2, takes H+ from NADH to become ethanol (a 2-Carbon molecule) 1) Yeast use alcoholic fermentation, make CO2 that makes champagne bubbly, makes bread rise b. NAD+ is “regenerated” 1) Back to cytosol for glycolysis 9 IV. Aerobic Respiration: if O2 is present A. Krebs Cycle: occurs in mitochondrial matrix 1. 3-carbon pyruvate is converted into 2-carbon acetyl coA a. Loses 1 CO2 b. Converts NAD+ NADH 2. Acetyl coA joins with 4carbon OAA to become 6carbon citric acid. a. This is why Kreb’s is also called Citric Acid cycle. b. OAA: oxaloacetic acid 10 3. As 6-carbon Citric Acid is converted back to 4carbon OAA to continue cycle, gives off: • 2 CO2 (6-Carbon citric acid – 4-Carbon OAA = 2 CO2) 4. This conversion also transfers high-energy electrons to: • 3 NADH: now a full bucket that goes to ETC • 1 FADH2: now a full bucket that goes to ETC 11 B. Electron Transport Chain: (similar to photosynthesis) 1. NADH, FADH2 carry their stored energy/electrons to the ETC located in the membranes of the cristae • Now NAD+ and FAD are empty buckets, can return to matrix to pick up more electrons/energy 12 2. As electrons are transferred from one carrier to another, they lose energy, used to pump H+ across membrane a. Creates lots of H+ in intermembrane space, low H+ in matrix 3. Oxygen is the final electron acceptor at the end of ETC a. 4H+ + O2 2 H2O 13 C. Chemiosmosis: (similar to photosynthesis) 1. High H+ in intermembrane space, low H+ in matrix 2. H+ travel down their gradient from intermembrane space into matrix through ATP synthase • Combines ADP + P to make ATP 14 D. Energy Tally: 1. Glycolysis creates 2 ATP and 2 NADH a. Converting pyruvate to acetyl coA creates 2 more NADH 2. 3. Kreb’s Cycle creates 2 ATP, 6 NADH, and 2 FADH2 ETC converts NADH, FADH2 into ATP as follows: a. Each NADH generates 3 ATP b. Each FADH2 generates 2 ATP • • • • Glycolysis: 2 ATP; 2 NADH Conversion to acetyl coA: 2 NADH Kreb’s Cycle: 2 ATP; 6 NADH; 2 FADH2 ETC conversion 10 NADH (3 ATP per NADH) 30 ATP 2 FADH2 (2 ATP per FADH2) + 4 ATP • Total ATP per molecule glucose: 38 ATP 15 A word about the elegance of the “paradox” between photosynthesis and cellular respiration Photosynthesis: 6H2O + 6CO2 + light energy 6O2 + C6H12O6 Respiration: C6H12O6 + 6O2 6CO2 + 6H2O + energy Photosynthesis: starts with breaking apart water to release oxygen, sending electrons down the ETC (creating full buckets), sending electron carriers to the Calvin cycle to join CO2 molecules into glucose Respiration: starts with breaking apart glucose to release CO2, sending it through the Kreb’s cycle, sending electron carriers to deliver electrons down the ETC, (creating empty buckets), and combining them with oxygen to make water 16