C3 - Cellular Respiration (Updated 2024) PDF

C3 - Cellular Respiration I can… Explain, in general terms, how glucose is oxidized during glycolysis and the Krebs cycle to produce reducing power in the form of NADH and FADH Explain how chemiosmosis converts the reducing power of NADH and FADH to store chemical potential energy...

C3 - Cellular Respiration I can… Explain, in general terms, how glucose is oxidized during glycolysis and the Krebs cycle to produce reducing power in the form of NADH and FADH Explain how chemiosmosis converts the reducing power of NADH and FADH to store chemical potential energy in the form of ATP Describe where in the mitochondria these processes occur Distinguish between aerobic and anaerobic respiration and fermentation Summarize and explain the role of ATP in cellular metabolism Cellular Respiration Recall: Cellular respiration is the process where plants and animals break down glucose to release energy The chemical equation for cellular respiration is: C6H12O6(s) + 6 O2(g) → 6 CO2(g) + 6 H2O(l) + energy Cellular Respiration Cellular respiration takes place in the mitochondria Releases the energy of glucose molecules Glucose is oxidized to CO2 while releasing energy and water Photosynthesis & Cellular Respiration - Complementary Processes Photosynthesis Cellular Respiration Needs light energy Produces energy Needs water Produces water Produces glucose Needs glucose Occurs in the chloroplast Occurs in the mitochondria Releasing Stored Energy Cellular respiration uses glucose to synthesize ATP, a form of energy that can be used by cells It can take place either with or without oxygen: ○ Aerobic respiration: Carried out by organisms that live in oxic (oxygen containing) environments Ex. Fungi, bacteria, plants ○ Anaerobic respiration: Carried out by organisms that live in anoxic (non-oxygen containing) environments Ex. Deep ocean producers, nitrogen-fixing bacteria Fermentation: Modified form of anaerobic respiration ○ Ex. Yeast, bacteria that causes milk to sour Aerobic vs. Anaerobic Aerobic Respiration Anaerobic Respiration Requires oxygen? Yes No Energy yield High (36 ATP) Low (2 ATP) Products CO2 and H2O Animals: Lactic acid Yeast: Ethanol and CO2 Location Cytoplasm and mitochondria Cytoplasm Stages 1. Glycolysis 1. Glycolysis 2. Kreb’s Cycle 2. Fermentation 3. Electron Transport System Glucose All cells use energy from ATP molecules to to meet their energy needs ATP has a relatively low amount of energy per molecule Carbohydrates are the most usable source of energy Molecules with a higher energy content are useful because they provide: ○ Long-term storage of chemical energy ○ Bulk transportation of chemical energy Glucose: Our “blood sugar’ ○ High energy content ○ Relatively small ○ Highly soluble ○ Ideal for transportation within cells Review 1. What are the characteristics of glucose that make it well-suited as an energy supply molecule within our bodies? 2. Why is cellular respiration necessary? 3. What are the 3 stages of aerobic respiration? Aerobic Cellular Respiration Aerobic Cellular Respiration Three main stages: 1. Glycolysis 2. Prep and Kreb’s Cycle 3. Electron Transport Chain Aerobic Cellular Respiration An oxidation reaction in which a transfer of electrons occurs from high energy molecules - glucose and oxygen Most of the energy in plants, animals, and most eukaryotic (organisms with a membrane-bound nucleus) cells is produced in process Process of cellular respiration starts with glycolysis (an anaerobic reaction in cytoplasm) 1. Glycolysis Glycolysis is the first step of aerobic and anaerobic cellular respiration The main purpose of glycolysis is to split glucose into two molecules of pyruvate through a series of reactions Doesn’t require oxygen Occurs outside the mitochondria in the cytoplasm Produces 4 ATP while consuming 2 ATP - producing a net outcome of 2 ATP Produces 2 reduced NADH molecules 1. Glycolysis 1. 2 molecules of ATP are required to initiate the reactions. This causes glucose to be broken down into two molecules of G3P. 2. G3P then reduces NAD+ to NADH. NADH will later be used for the Kreb’s cycle. Reduction of NAD+ also leads to the generation of 2 molecules of ATP by each G3P (so 4 ATP produced in total, resulting in a net gain of 2 ATP throughout the entire process of glycolysis). 3. Via the process of reduction described above, G3P becomes pyruvate, a high energy three-carbon compound which is required for the next stage of cellular respiration (Kreb’s cycle). 1. Glycolysis Fate of Pyruvate There are 2 possible processes that pyruvate can proceed with, depending on the availability of oxygen: 1. IF AVAILABLE: Pyruvate is transported from cytoplasm into the mitochondria (aerobic cellular respiration) 2. IF NOT AVAILABLE: Pyruvate will proceed through fermentation process (anaerobic cellular respiration) 2. Prep Before pyruvate can enter the Krebs Cycle, it must lose one carbon atom in the form of carbon dioxide The remaining two carbon atoms then bond to a molecule called Coenzyme A (CoA) to become Acetyl Coenzyme A (acetyl CoA). This reaction also causes another molecule of NAD+ to be reduced to NADH. Acetyl CoA then enters the mitochondria to initiate the Krebs Cycle 2. Krebs Cycle (in Mitochondria) Discovered by Sir Hans Adolf Krebs (1900-1981), a German biochemist Won Nobel Prize in 1953 in Physiology or Medicine for the discovery in living organisms of the series of chemical reactions known as the tricarboxylic acid cycle, otherwise known as the Kreb’s Cycle 2. Krebs Cycle (in Mitochondria) The main purpose of the Kreb’s Cycle is to produce even more high-energy compounds (NADH & FADH2) for use in stage 3 Once acetyl CoA enters the mitochondria, it undergoes a series of reactions to generate: ○ 3 molecules of NADH from NAD+ ○ 1 molecule of ATP from ADP ○ 1 molecule of FADH2 from FAD ○ Multiply all of the above by two for an entire glucose molecule CO2 is also released as a by-product Krebs Cycle 3. Electron Transport Chain The majority of ATP is produced by the electron transport chain This takes place across the inner membrane of the mitochondria, and involves the passing of high-energy electrons (NADH & FADH 2) from carrier to carrier 3. Electron Transport Chain As electrons are passed down the chain, energy is released - this energy is used to pump hydrogen ions across the membrane from the matrix to the intermembrane space The building concentration gradient (high concentration of hydrogen in the intermembrane space, low concentration in the matrix) forces hydrogen ions through membrane-embedded protein ATP synthase, generating ATP via the reduction of ADP Oxygen is the final electron acceptor in the chain, it accepts both electrons and hydrogen ions, resulting in a molecule of water which will be released as a by-product Summary of Aerobic Cellular Respiration Aerobic cellular respiration involves 3 stages: 1. Glycolysis 2. Prep and Krebs Cycle 3. Electron Transport Chain Pyruvate oxidation occurs in the mitochondria ○ 2 NADH and 2 CO2 are formed Krebs Cycle occurs in the mitochondrial matrix ETC in the inner mitochondrial membrane transports electrons ○ Produces an electrochemical gradient Chemiosmosis: Protons (H+) move through ATP complexes embedded in membrane, free energy released, causes ATP synthesis Oxygen finally accepts electrons from the ETC No oxygen? No aerobic cellular respiration! Summary Anaerobic Respiration Anaerobic Respiration When oxygen isn’t available (anoxic conditions), the final electron acceptor is a different chemical ○ Isn’t as efficient as aerobic (produces less ATP) Organisms that live in these types of environments use inorganic chemicals - sulfate, nitrate, and CO2 as acceptors Fermentation Fermentation is a metabolic pathway to produce ATP when organisms lack oxygen ○ Pathway only produces ATP during glycolysis (less efficient aerobic respiration) Many single-celled organisms carry out fermentation 2 main types: ○ Lactate fermentation ○ Ethanol fermentation Lactate Fermentation Cells that are temporarily without oxygen carry out lactate fermentation ○ Process occurs when energy demands exceed oxygen supply - creates an oxygen deficit Cells convert pyruvate molecules formed during glycolysis to lactate/lactic acid molecule ○ Uses NADH as an energy source ○ Lactate is then started When oxygen content increases - lactate is converted to pyruvate which continues in Krebs cycle in aerobic pathway This is also the form of fermentation our muscles use when they have limited access to oxygen; the buildup of lactic acid is what causes muscle cramps Ethanol Fermentation Some organisms can function both aerobically and anaerobically When functioning anaerobically, ethanol fertilization is carried out Involves 2 steps: 1. After glycolysis produces pyruvate, pyruvate is converted into 2-carbon compound by release of CO2 2. 2-carbon molecule is then reduced by NADH to form ethanol The by-product of this form of fermentation is alcohol, this process is used to manufacture products such as wine and beer.