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2/29/2016 Metabolism • Consists of ALL OF THE chemical reactions that take place in a cell Bio 105: Cellular Metabolism Lecture 6 Reading: Chapter 3 (Pages 56 – 62) Metabolism Cellular Metabolism • Glycolysis Summary • 2 kinds – https://www.youtube.com/watch?v=8Kn6B VGqKd8 – Aerobic cellular respiration – Anaerobic fermentation Summary of Cellular Respiration Aerobic Cellular Respiration Electrons transferred by NADH Blood vessel Glucose Cytoplasm Electrons transferred by NADH – Sugar CO2 and H2O – Requires Oxygen Electrons transferred by NADH and FADH2 Plasma membrane Carrier protein Citric Acid Cycle Transition Reaction Glycolysis glucose pyruvate • Cells take in sugar (glucose) • Produces energy Electron Transport Chain – ATP Oxygen Mitochondrion Extracellular fluid +2 ATP +2 ATP +32 ATP 36 ATP C6H12O6 + 6O2 → 6CO2 +6H2O + Energy Figure 3.27 1 2/29/2016 Aerobic Cellular Respiration • 4 steps – Glycolysis – Transition Reaction – Citric Acid Cycle (Krebs Cycle) – Electron Transport Chain NADH and FADH2 are important carriers of electrons Cellular Respiration - Glycolysis Glycolysis Glycolysis (in cytoplasm) • Phase 1: Glycolysis – Occurs in cytoplasm – Splits 1 glucose 2 pyruvate molecules – Net Gain: 2 ATP and 2 NADH – Does not require oxygen Cytoplasm During the first steps, two molecules of ATP are consumed in preparing glucose for splitting. Glucose During the remaining steps, four molecules of ATP are produced. 2 ATP Energyinvestment phase 2 ADP 4 ADP 4 ATP The two molecules of pyruvate then diffuse from the cytoplasm into the inner compartment of the mitochondrion, where they pass through a few preparatory steps (the transition reaction) before entering the citric acid cycle. 2 NAD+ 2 NADH 2 Pyruvate Glucose 2 ATP + 2 NADH + 2 pyruvate Energyyielding phase Two molecules of nicotine adenine dinucleotide (NADH), a carrier of high-energy electrons, also are produced. Figure 3.23 2 2/29/2016 Glycolysis Rap • https://www.youtube.com/watch?v=EfGl znwfu9U In Cytosol Cellular Respiration - Transition Reaction Cellular Respiration – Transition Reaction • Start with • Phase 2: Transition Reaction – 2 pyruvate (3 carbon molecule) – 2 Coenzyme A – Occurs in mitochondria – Coenzyme A combines with pyruvate – CO2 is removed from each pyruvate – Forms: 2 acetyl CoA molecules – Net Gain: 2 NADH • End with – 2 CO2 – 2 NADH – 2 Acetyl CoA (2 carbon molecule) Cellular Respiration – Citric Acid Cycle Transition Reaction (in mitochondrion) Transition Reaction • Phase 3: Citric Acid Cycle Pyruvate (from glycolysis) – Occurs in mitochondria – Acetyl CoA enters – Releases 2 ATP, 2 FADH2 and 6 NADH, 4 CO2 molecules – Net Gain: 2 ATP, 2 FADH2 and 6 NADH – Requires Oxygen One carbon (in the form of CO2) is removed from pyruvate. A molecule of NADH is formed when NAD+ gains two electrons and one proton. CO2 NAD+ Coenzyme A NADH (electron passes to electron transport chain) CoA Acetyl CoA The two-carbon molecule, called an acetyl group, binds to coenzyme A (CoA), forming acetyl CoA, which enters the citric acid cycle. • Does not use it Citric Acid Cycle Figure 3.24 3 2/29/2016 Cellular Respiration – Citric Acid Cycle • AKA Krebs Cycle • Start with Citric Acid Cycle Citric Acid Cycle (in mitochondrion) The citric acid cycle also yields several molecules of FADH2 and NADH, carriers of high-energy electrons that enter the electron transport chain. – 2 Acetyl CoA Acetyl CoA, the two-carbon compound formed during the transition reaction, enters the citric acid cycle. Acetyl CoA CoA CoA Oxaloacetate Citrate • End with NADH CO2 leaves cycle NAD+ – 4 CO2 – 2 ATP – 6 NADH and 2 FADH2 NAD+ Citric Acid Cycle Malate NADH FADH2 ADP + Pi ATP FAD -Ketoglutarate Succinate CO2 leaves cycle NAD+ The citric acid cycle yields One ATP from each acetyl CoA that enters the cycle, for a net gain of two ATP. NADH Figure 3.25 • https://www.youtube.com/watch?v=JPCs 5pn7UNI • Remember there are 2 acetyl CoA molecules for each 1 glucose that entered glycolysis Cellular Respiration – Electron Transport Chain • NADH and FADH2 are important carriers of electrons – Donate electrons to ETC – Oxygen accepts electrons at the end of the chain • Produces ATP using ATP synthase protein molecule • Produces 32 ATP!! Cellular Respiration – Electron Transport Chain • Phase 4: Electron Transport Chain – Electrons of FADH2 and NADH are transferred from one protein to another – Transferred until they reach oxygen – Net Gain: 32 ATP – Requires oxygen Electron Transport Chain Electron Transport Chain (inner membrane of mitochondrion) The molecules of NADH and FADH2 produced by earlier phases of cellular respiration pass their electrons to a series of protein molecules embedded in the inner membrane of the mitochondrion. High NADH NAD+ As the electrons are transferred from one protein to the next, energy is released and used to make ATP. 2e– Potential energy Cellular Respiration – Citric Acid Cycle FADH2 Membrane proteins 2e– FAD 2e– 2e– Eventually, the electrons are passed to oxygen, which combines with two hydrogens to form water. 2e– Low Energy released is used for synthesis of ATP H2O 1 2 H+ + 2 O2 Figure 3.26 4 2/29/2016 Electron Transport Chain • ATP is made through a series of steps 1) In the mitochondria, NADH and FADH2 donate electrons to the ETC 2) Oxygen is the final electron acceptor 3) ETC uses the energy from electrons to transport H+ against the concentration gradient • Transporting them from the lumen of the mitochondria to the intermembrane space Electron Transport Chain Electron Transport Chain • ATP is made, cont’d… 4) ATP Synthase transports the H+ back to the lumen of the mitochondria 5) H+ falling through the ATP synthase provides the energy for the ATP synthase to catalyze the reaction • ADP + P ATP Cellular Respiration Summary • Electron Transport Chain – https://www.youtube.com/watch?v=xbJ0nbzt5 Kw • ATP Synthase – https://www.youtube.com/watch?v=3y1dO4n NaKY&ebc=ANyPxKpaQgOjhUhrwCJplTqYfxSJulZdtyt3Zrb7PwYb20zc rYe4lJbfCVr6SETniI6Ft21DgQOb0wQXzI3CXdnqwCOUeMRw 5 2/29/2016 Cellular Respiration Summary • 1 molecule glucose 36 ATP • Oxygen – Used by the electron transport chain – Accepts electrons from the ETC • CO2 – Produced by the transition reaction – Produced by the Citric Acid Cycle (Krebs) Cellular Respiration - Summary • Glycolysis – Starts the process – Takes in glucose – Produces 2 ATP • Transition Reaction – Produces CO2 and NADH • Citric Acid Cycle – Produces 2 ATP – Produces lots of NADH and FADH2 – Produces CO2. Cellular Respiration Summary Complex Carbohydrates must first be broken down into glucose before entering glycolysis • Electron Transport Chain – Takes electrons from NADH and FADH2 – Uses electrons to produce ATP • ATP synthase molecule Fats and proteins enter the process at different steps – Requires oxygen • 1 glucose 36 ATP Oxygen • Cellular respiration requires O2 – Aerobic cellular respiration • What if an organism, including humans, need energy without using oxygen? Anaerobic Fermentation • Breakdown of glucose without oxygen • Occurs in cytoplasm • Very inefficient – Net gain: 2 ATP – Glycolysys 6 2/29/2016 Fermentation in Animals • 2 pyruvic acid + 2 NADH 2 lactate + 2 NAD+ • End Result: – Lactate – 2 ATP – NAD+ is regenerated Review Questions • What is the starting molecule of glycolysis? • Which stage(s) produces CO2? • Which stage uses O2? • Which stage produces the most NADH? • Which stage produces the most ATP? Important Concepts • What are the 4 steps of aerobic cellular respiration? – What happens in each step? – What are the starting molecules? – What comes out of each step? – Where in the cell does each step occur? – How many ATP and NADH/FADH2 are produced in each step? Important Concepts • What is cellular respiration? • What is anaerobic fermentation? • What are the differences between cellular respiration and anaerobic fermentation? Important Concepts • Describe in detail how ATP is made using the electron transport chain (ETC) • What is the role of ATP synthase, H+, O2, NADH and FADH2 and the electron transport chain in ATP production? • Know the overall picture of cellular respiration (summary slides) 7 2/29/2016 Important Concepts • What is the role of oxygen in cellular respiration? • What steps produce carbon dioxide? • What is anaerobic fermentation? – What steps are involved? – What end products are produced in humans? – Is oxygen required? – When is it used? Definitions • • • • Aerobic cellular respiration Anaerobic fermentation ATP synthase Metabolism The End Image From: https://maddieknits.wordpress.com/category/randomness/ 8