Chapter 8 How Cells Release Stored Energy AKA: Cellular Respiration

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  • Chapter 8 How Cells Release Stored Energy AKA: Cellular Respiration
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  • ATP is the prime energy carrier for all cells Aerobic Respiration (with oxygen) is the main pathway for energy release from carbohydrates to ATP How do cells make ATP?
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  • All energy-releasing pathways start with glycolysis Glucose is split into two pyruvate molecules Glycolysis reactions occur in the cytoplasm
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  • Aerobic Respiration yields 36 ATP Anaerobic Respiration (without oxygen) yields 2 ATP Aerobic respiration route: C 6 H 12 O 6 + 6O 2 6CO 2 + 6H 2 O (Reverse equation to photosynthesis) Overview of Aerobic Respiration
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  • 1- Glycolysis: is the breakdown of glucose to pyruvate Small amount of ATP are generate (2 ATP) Takes place in the cytoplasm 2- Kreb Cycle: degrades pyruvate to carbon dioxide, water, ATP, H+ ions and electrons (accepted by NAD+ and FAD) Takes place in the mitochondrian Makes 2 ATP Three steps to aerobic respiration
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  • 3- Electron Transfer Phosphorylation: processes the H+ ions and electrons to generate high yields of ATP; oxygen is the final electron acceptor Takes place in the mitochondrion Yields 32 ATP (this is the real takes place) Continue
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  • 2 ATP is required to start glycosis Enzymes in the cytoplasm catalyze several steps in glucose breakdown Glucose is first phosphorylated in energy- requiring steps, then the six-carbon intermediate is split to form two molecules of PGAL (which gives a phosphate to make ATP) Enzymes remove H+ and electrons from PGAL and transfer them to NAD+ which becomes NADH (used later in the electron transfer) Glycolysis: First stage of energy- releasing pathways
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  • By substrate-level phosphorylation, four ATP are produced The end product to glycolysis is: 2 ATP (net gain) 2 pyruvates 2 NADH For each glucose moleucule degraded
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  • Continue The pyruvic acid diffuses into the inner compartment of the mitochondrion where a transition reaction occurs that serves to prepare pyruvic acid for entry into the next stage of respiration: (a) pyruvic acid acetic acid + CO 2 (a waste product of cell metabolism) + NADH + (b) acetic acid + co-enzyme A -> acetyl CoA
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  • Takes place in the inner mitochondria matrix Pyruvate enters the mitochondria and is converted to acetyl-CoA, which then joins oxaloacetate already present from a previous turn of the cycle. During each turn of the cycle, three carbon atoms enter (as pyruvate) and three leave as three carbon dioxide molecules Second Stage of the Aerobic Pathway: Kreb Cycle
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  • H+ and e- are transferred to NAD+ and FAD (coenzymes) Ten coenzymes are loaded with electrons and hydrogen Two molecules of ATP are produced by substrate-level of phosphorlyation Functions of the second stage
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  • Most of the molecules are recycled to conserve oxaloacetate for continuous processing of acetyl-CoA Carbon dioxide is produced as a by- product Continue
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  • This is where the real work is done NADH and FADH 2 give up their electrons to transfer (enzyme) system embedded in the mitochondrial inner membrane Third Stage of the Aerobic Pathway
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  • According to the chemiosmotic model, energy is released in the passage of electrons through components of the transfer series Oxygen joins with the spent electrons and H+ to yield water Electron Transfer Phosphorylation
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  • Electron transfer 32 ATP Glycolysis 2 ATP Kreb Cycle 2 ATP Total 36 ATP (per glucose molecule) Summary of the Energy Harvest Net Gain
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  • Normally, for every NADH produced within the mitochondria and processed by electrons transfer chain, three ATP are produced FADH 2 produced 2 ATP Continue
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  • NADH from the cytoplasm cannot enter mitochondrian and must transfer its electrons!! In most cells (skeletal and brain) the electrons are transferred to FAD and thus yield two ATP (for a total yield of 36) But in the liver, heart, and kidney cells, NAD+ accepts the electrons to yield three ATP because two NADH are produced per glucose, this total yield of 38 ATP Continue
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  • Cellular respiration without using oxygen (or very limited) Pyruvate from glycolysis is metabolized to produce molecules other than acetyl-CoA Example: Single Yeast Cells Anaerobic Respiration
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  • With an energy yield of only 2 ATPs Glycolysis serves the first stage (just like aerobic respiration) Fermentation Pathways
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  • Certain bacteria (as in bacteria) and muscles cells have the enzymes capable of converting pyruvate to lactate Example: Muscle Cramps No additional ATP beyond the net two from glycolysis is produced but NAD+ is regenerated Lactate Fermentation
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  • Fermentation begins with glucose degradation to pyruvate Cellular enzymes convert pyruvate to acetaldehyde, which then accepts electrons from NADH to become alcohol. Yeast are valuable in the baking industry (Carbon dioxide byproduct makes dough rise) and in alcoholic beverage production Alcoholic Fermentation
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  • Some kinds of bacteria are able to strip electrons from organic compounds and send them through a special electron transfer in their membranes to produce ATP Example: Such bacteria include those that reduce sulfate to hydrogen sulfide (foul smelling gas) and those that convert nitrate to nitrite Anaerobic Electron Transfer
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  • Excess carbohydrate intake is stored as glycogen in the liver and muscle for future use. Free glucose is used until it runs low, then glycogen reserves are tapped Alternative Energy Sources in the Human Body
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  • Excess fats (including those made from carbohydrates) are stored away in cells of adipose tissue Fats are digested into glycerol, which enters glycolysis, and fatty acids, which enter the Kreb Cycle Fatty acids have more carbon and hydrogen atoms, they degraded more slowly and yield greater amounts of ATP Energy from Fats
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  • Amino acids are released by digestion and travel in the blood After the amino group is removed, the amino acid is removed, the amino acid remanant is fed into in the Kreb Cycle Energy from Proteins
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  • Photosynthesis and cellular respiration are intimately connected Life is not some mysterious force, but a series of chemical reactions under highly integrated control. Perspective on the Molecular Unity of LIfe


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