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Lesson # 18

Lesson # 18. Metabolism and Energetic 1. Chapter 25. Objectives:. 1- Define energetics and metabolism, and explain why cells must synthesize new organic components.

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Lesson # 18

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  1. Lesson # 18 Metabolism and Energetic 1 Chapter 25 Objectives: • 1- Define energetics and metabolism, and explain why cells must synthesize new organic components. • 2- Describe the basic steps in glycolysis, the citric acid cycle, and the electron transport system, and summarize the energy yields of glycolysis and cellular respiration.

  2. ENERGY An Introduction to Metabolism and Energetics Metabolism: All the chemical reactions of the body. 1- Catabolism 1- Periodic breakdown and replacement of the organic compounds of a cells. 2- Anabolism 2- Grow and cell division. 3- Special processes: secretion, contraction, propagation of action potentials. Metabolism • The breakdown of organic substrates to obtain energy. 1- Catabolism: Reactants (Glucose) Products (Carbon Dioxide) CO2 CO2 More energy Less energy CO2 CO2 CO2 CO2 Decomposition Reaction

  3. Catabolism proceeds in a series of steps • Most energy production takes place in mitochondria. Cellular Respiration • To carry out the energy production reactions cells need a supply of chemicals: Glucose + O2 • Body Chemicals 1- Oxygen Heat (60%) 2- Water (40%) • Nutrients • Organic compounds 1- Carbohydrates + CO2 + H2O 2- Fats (lipids) • Locomotion • Contraction • Intracellular transport • Cytokinesis • Endocytosis • Exocytosis 3- Proteins 4- Vitamins 5- Mineral ions

  4. Nutrient Pool Digestion • Organic Compounds • Organic Molecules CYTOPLASM Anaerobic catabolism in the cytosol releases small amounts of ATP that are significant only under unusual conditions. Anaerobic catabolism • Proteins • Lipids • Carbohydrates • Amino acids • Fatty acids • Simple sugars 2 ATP per glucose molecule Aerobic Metabolism (in the mitochondria) ATP expenses • ATP • ATP • Locomotion • Contraction • Intracellular transport • Cytokinesis • Endocytosis • Exocytosis • 40% • HEAT • 60% 34 ATP per glucose molecule

  5. ENERGY 2- Anabolism: • It is the synthesis of new organic molecules. Product (Protein) Reactants (aminoacids) Less energy More energy Synthetic Reaction Anabolism is an “uphill” process that involves the formation of new chemical bonds. Cells synthesize new organic compounds for four basic reasons: 1- To carry out structural maintenance and repair because most structures in the cell are temporary. Their removal and replacement is part of the process called metabolic turnover. 2- To support growth. 3- To produce secretions. 4- To store nutrient reserves (glycogen and triglycerides) .

  6. Anabolism is driven by the energy that catabolism releases, so endergonic and exergonic reactions, anabolism and catabolism, are coupled. • Maintenance and repairs • Growth • Secretion • Stored nutrient reserves • Nutrient Pool ANABOLISM Digestion • Organic Compounds • Organic Molecules CYTOPLASM • Results of Anabolism CATABOLISM Anaerobic catabolism in the cytosol releases small amounts of ATP that are significant only under unusual conditions. Anaerobic catabolism • Proteins • Lipids • Carbohydrates • Amino acids • Fatty acids • Simple sugars 2 ATP per glucose molecule Aerobic Metabolism (in the mitochondria) ATP expenses • ATP • ATP • Locomotion • Contraction • Intracellular transport • Cytokinesis • Endocytosis • Exocytosis • 40% • HEAT • 60% 36 ATP per glucose molecule

  7. co co co co co co Glycogen 2 2 2 2 2 2 Energy Energy Anabolism is driven by the energy that catabolism releases, so endergonic and exergonic reactions, anabolism and catabolism, are coupled. Catabolism Anabolism Endergonic Exergonic ATP Endergonic Exergonic

  8. e- Structural, functional, and storage components Triglycerides Glycogen Proteins Organic compounds that can be absorbed by cells are distributed to cells throughout the body by the bloodstream. Nutrient pool Amino acids Fatty acids Glucose Beta-oxidation Glycolysis Three-carbon chains Two-carbon chains • ATP • ATP MITOCHONDRIA Catabolic pathway Citric acid cycle Electron transport system • O2 Coenzymes (NADH) Anabolic pathway • H2O Cellular Respiration • CO2

  9. ATP + 6 H O 2 6 CO 2 Most cells generate ATP by breaking down glucose: 36 Glucose + o 6 Break down operation (Catabolism) 2 This reaction has two steps: 1- Glycolysis It takes place in the cytosol, does not require oxygen (anaerobic) and yields 2 ATP per molecule of glucose. 2- Cellular respiration It takes place inside the mitochondria, requires oxygen (aerobic) and yields 34 ATP per molecule of glucose.

  10. - - - - e e e e Electrons Fall Down the Energy Hill to drive the Uphill Production of ATP Energy Hill Energy Energy Energy

  11. - - - - e e e e + NAD NADH Reduction-Oxidation Reaction or Redox Reaction REDOX REACTION oxidized REDOX REACTION reduced oxidized Coenzyme (electron carrier) reduced REDOX REACTION The reduced molecule gains electrons and, therefore, gains energy. The oxidized molecule looses electrons and, therefore, looses energy.

  12. 1 - - - - e e e e 2 Pyruvic acid ATP E N E R G Y NAD P + ADP Glycolysis High level of energy GLUCOSE H H Glycolysis Lower level of energy + NAD 2 Coenzyme (electron carrier)

  13. Glycolysis Glucose INTERSTITIAL FLUID CYTOSOL Steps in Glycolysis Glucose-6-phosphate As soon as a glucose molecule enters the cytosol, a phosphate group is attached to the molecule. Fructose-1,6-bisphosphate A second phosphate group is attached. Together, steps 1 and 2 cost the cell 2 ATP. Dihydroxyacetone phosphate Glyceraldehyde 3-phosphate The six-carbon chain is split into two three-carbon molecules, each of which then follows the rest of this pathway. From mitochondria To mitochondria Another phosphate group is attached to each molecule, and NADH is generated from NAD. Energy Summary Energy Summary 1,3-Bisphosphoglycerate Steps 1 & 2: 2 Steps 1 & 2: +2 -2 +2 +2 ATP ATP ATP ATP Step 5: 2 One ATP molecule is formed for each molecule processed. 3-Phosphoglycerate Step 7: 2 Steps 5: The atoms in each molecule are rearranged, releasing a molecule of water. 2 NET GAIN: Steps 7: Phosphoenolpyruvate A second ATP molecule is formed for each molecule processed. Step 7 produces 2 ATP molecules NET GAIN: Pyruvate To mitochondria

  14. Citric Acid Cycle 2 3 1 - - - - e e e e 2 Pyruvic acid ATP ATP ATP ATP E N E R G Y NAD P + ADP Electron Transport System Mitochondrial ATP Production High level of energy GLUCOSE 36 32 2 H H Glycolysis Lower level of energy 2 Electron carrier

  15. Pyruvate Acetyl-CoA

  16. The Citric Acid Cycle The function of the citric acid is to remove hydrogen atoms (and electrons) from organic molecules and to transfer them to coenzymes (NADH and FADH2). X 2 Three-carbon chains Pyruvate Coenzyme A The coenzymes NADH and FADH2 remove hydrogen atoms and electrons from the substrate molecule and carry them to the Electron Transport System. Two-carbon chains Acetyl-CoA Coenzyme A Oxaloacetic acid Citric acid 6-carbon 4-carbon CITRIC ACID CYCLE ELECTRON TRANSPORT SYSTEM 5-carbon 4-carbon (via GTP)

  17. The Electron Transport System Substrate-H2 Substrate-H2 Steps in Oxidative Phosphorylation A coenzyme strips 2 hydrogen atoms from a substrate molecule. NADH and FADH2 deliver hydrogen atoms to coenzymes embedded in the inner membrane of a mitochondrion. Coenzyme Q releases hydrogen ions and passes electrons to cytochrome b. Cytochrome b Electrons are passed along the Electron Transport System, losing energy in a series of small steps. Cytochrome c Cytochrome a Oxygen accepts the low- energy electrons, and with hydrogen ions, forms water. Cytochrome a3 The Electron Transport System or Respiratory Chain is a sequence of proteins called cytochromes. It is the site where oxidative phosphorylation takes place. Oxidative phosphorylation is the generation of ATP within the mitochondria in a reaction sequence that requires coenzymes and consumes oxygen.

  18. ENERGY The basis of oxidative phosphorylation is the formation of water: 2H2 + O2 2 H2O2 Hydrogen is a good, clean fuel, producing only water as a by-product. Unfortunately it produces so much energy that it can get out of control, resulting in an explosion. This powerful reaction proceeds in a series of small, enzymatically controlled steps. Under these controlled conditions, energy can be captured safely, and ATP generated. Oxidative phosphorylation produces more than 90% of the ATP used by body cells.

  19. The Electron Transport System CYTOSOL Outer membrane Hydrogen ion channel Intermembrane space Inner membrane ATP synthase Reduced substrate molecule Oxidized substrate molecule MITOCHONDRIAL MATRIX The locations of the coenzymes and the electron transport system. Notice the sites where hydrogen ions are pumped into the intermembrane space, providing the concentration gradient essential to the generation of ATP. The red line indicates the path taken by the electrons.

  20. Glycolysis (anaerobic): produced during enzymatic reactions in the cytosol used to initiate glycolysis net gain to cell The Electron Transport System and Citric Acid Cycle (Aerobic): from NADH produced in glycolysis from NADH generated in citric acid cycle Energy Summary 2 - 2 24 36 4 4 4 2 from FADH2 generated in citric acid cycle ATP ATP ATP ATP ATP ATP ATP ATP via GTP produced during enzymatic reactions net gain to cell from complete catabolism of one glucose molecule

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