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05 Lecture Ppt

  1. 1. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chapter 5 Dynamic Activities of Cells
  2. 2. Living Things Transform Energy
  3. 3. 5.1 Energy makes things happen <ul><li>Energy - the capacity to do work </li></ul><ul><ul><li>Chemical energy present in organic molecules and is the direct source of energy for living things </li></ul></ul><ul><ul><li>Potential energy is stored energy </li></ul></ul><ul><ul><li>Kinetic energy is energy in action </li></ul></ul><ul><li>Calorie - the amount of energy to raise the temperature of 1 g of water by 1° Celsius </li></ul>
  4. 4. Figure 5.1 Potential energy versus kinetic energy
  5. 5. 5.2 Two laws apply to energy and its use <ul><li>1 st law of thermodynamics—the law of conservation of energy </li></ul><ul><ul><li>Energy cannot be created or destroyed, but it can be changed from one form to another </li></ul></ul><ul><li>2 nd law of thermodynamics </li></ul><ul><ul><li>Energy cannot be changed from one form to another without a loss of usable energy </li></ul></ul><ul><ul><ul><li>Entropy - disorder increases because it is difficult to use heat to perform more work </li></ul></ul></ul>
  6. 6. Figure 5.2 Flow of energy from the sun to an animal that eats a plant
  7. 7. 5.3 Cellular work is powered by ATP <ul><li>ATP (Adenosine TriPhosphate) - the energy currency of cells </li></ul><ul><ul><li>Cells use ATP to perform nearly all activities </li></ul></ul><ul><li>Exergonic reactions </li></ul><ul><ul><li>Energy exits the reaction </li></ul></ul><ul><li>Endergonic reactions </li></ul><ul><ul><li>Energy enters the reaction </li></ul></ul>
  8. 8. Figure 5.3A The ATP cycle
  9. 9. 5.4 ATP breakdown is coupled to energy-requiring reactions <ul><li>Coupled reactions occur in the same place, at the same time </li></ul><ul><ul><li>energy-releasing (exergonic) reaction drives an energy-requiring (endergonic) reaction </li></ul></ul>
  10. 10. Figure 5.4 Muscle contraction occurs when it is coupled to ATP breakdown
  11. 11. Enzymes Speed Chemical Reactions
  12. 12. 5.5 Enzymes speed reactions by lowering activation barriers <ul><li>Enzyme - usually a protein molecule that functions as an organic catalyst to speed a chemical reaction without itself being affected by the reaction </li></ul><ul><ul><li>Enzymes lower energy of activation (E a ) </li></ul></ul>
  13. 13. Figure 5.5 The energy of activation (E a ) is lower when an enzyme is involved
  14. 14. 5.6 An enzyme’s active site is where the reaction takes place <ul><li>Each enzyme is specific to its reaction </li></ul><ul><li>Substrate(s) – reactants in an enzymatic reaction </li></ul><ul><ul><li>Substrates combine with an enzyme, forming an enzyme-substrate complex </li></ul></ul><ul><li>The enzyme’s active site , binds with the substrate(s) </li></ul><ul><ul><li>Induced fit model the enzyme is induced to undergo a slight alteration to achieve optimum fit with the substrate </li></ul></ul>
  15. 15. Figure 5.6 Enzymatic action
  16. 16. 5.7 Enzyme speed is affected by local conditions <ul><li>Substrate Concentration </li></ul><ul><ul><li>More substrate means more chance encounters between substrate molecules and the enzyme </li></ul></ul><ul><li>Temperature </li></ul><ul><ul><li>warmer temperatures cause more effective encounters between enzyme and substrate </li></ul></ul><ul><li>pH </li></ul><ul><ul><li>A change in pH can change the enzyme’s shape and disrupt normal interactions </li></ul></ul><ul><li>Cofactors </li></ul><ul><ul><li>The presence of molecules like coenzymes or vitamins allow enzymes to be active </li></ul></ul>
  17. 17. Figure 5.7A The effect of temperature on the rate of an enzymatic reaction
  18. 18. 5.8 Enzymes can be inhibited noncompetitively and competitively <ul><li>Metabolic pathway - series of linked reactions </li></ul><ul><li>Enzyme inhibition occurs when a molecule (the inhibitor) binds to an enzyme and decreases its activity </li></ul><ul><li>Noncompetitive inhibition – inhibitor binds to the enzyme at a location other than the active site </li></ul><ul><li>Competitive inhibition – inhibitor and the substrate compete for the same active site </li></ul>
  19. 19. Figure 5.8 Metabolic pathways and noncompetitive inhibition. In the pathway, A–E are substrates, E 1 –E 5 are enzymes, and F is the end product of the pathway.
  20. 20. APPLYING THE CONCEPTS—HOW BIOLOGY IMPACTS OUR LIVES 5.9 Enzyme inhibitors can spell death <ul><li>Cyanide can be fatal because it binds to a mitochondrial enzyme necessary for the production of ATP </li></ul><ul><li>Sarin is a chemical that inhibits an enzyme at neuromuscular junctions, where nerves stimulate muscles </li></ul>
  21. 21. The Plasma Membrane Has Many and Various Functions
  22. 22. 5.10 The plasma membrane is a phospholipid bilayer with embedded proteins <ul><li>Plasma membrane is a fluid phospholipid bilayer </li></ul><ul><ul><li>Polar head of a phospholipid is hydrophilic, while the nonpolar tails are hydrophobic </li></ul></ul><ul><li>Fluid-mosaic model – proteins embedded in the membrane form a mosaic within the phospholipid bilayer </li></ul><ul><ul><li>Cholesterol molecules are steroids that lend support to the membrane </li></ul></ul><ul><ul><li>Glycolipids and glycoproteins – lipids and proteins carrying carbohydrate chains </li></ul></ul>
  23. 23. Figure 5.10 Fluid-mosaic model of plasma membrane structure
  24. 24. 5.11 Proteins in the plasma membrane have numerous functions <ul><li>Channel proteins have channels that let molecules to move across the membrane </li></ul><ul><li>Carrier proteins combine with a molecule to help it move across the membrane </li></ul><ul><ul><li>Differentially permeable - only certain substances can pass through </li></ul></ul><ul><li>Receptor proteins have a binding site for a specific molecule </li></ul><ul><li>Enzymatic proteins carry out metabolic reactions </li></ul><ul><li>Junction proteins form various types of junctions between cells </li></ul>
  25. 25. Figure 5.11 Functions of plasma membrane proteins
  26. 26. APPLYING THE CONCEPTS—HOW BIOLOGY IMPACTS OUR LIVES 5.12 Malfunctioning plasma membrane proteins can cause human diseases <ul><li>Diabetes Type 2 - insulin binds to receptor protein, but the number of carriers sent to the plasma is not enough </li></ul><ul><ul><li>Too much glucose in the blood, which spills over into the urine </li></ul></ul><ul><li>Color Blindness – Usually three types of photopigment proteins in plasma membrane within photoreceptor cells </li></ul><ul><ul><li>Some people lack of functional red or green photopigment </li></ul></ul><ul><li>Cystic Fibrosis (CF) - Usually, chloride ions pass easily through a plasma membrane channel protein </li></ul><ul><ul><li>When not regulated, a thick mucus appears in the lungs and pancreas damaging the lungs and contributing to an early death </li></ul></ul>
  27. 27. <ul><li>Figure 5.12 Cystic fibrosis is due to a defective CF gene and defective CF channel proteins </li></ul>
  28. 28. The Plasma Membrane Regulates the Passage of Molecules Into and Out of Cells
  29. 29. 5.13 Simple diffusion across a membrane requires no energy <ul><li>Simple diffusion – molecules move down concentration gradient until equilibrium is achieved and they are distributed equally </li></ul><ul><li>Dissolved gases can diffuse readily through the phospholipid bilayer </li></ul><ul><ul><li>How oxygen enters and carbon dioxide exits cells </li></ul></ul><ul><ul><li>How oxygen enters blood, and carbon dioxide leaves the blood from air sacs in the lungs </li></ul></ul>
  30. 30. Figure 5.13 Some molecules can simply diffuse across a membrane
  31. 31. 5.14 Facilitated diffusion requires a carrier protein but no energy <ul><li>Facilitated diffusion – certain molecules cross membranes by combining with a carrier protein </li></ul><ul><ul><li>The carrier proteins are thought to be specific. </li></ul></ul><ul><li>Figure 5.14 During facilitated diffusion, a carrier protein assists solute movement across the membrane </li></ul>
  32. 32. 5.15 Osmosis can affect the size and shape of cells <ul><li>Osmosis - diffusion of water across a differentially permeable membrane due to concentration differences </li></ul><ul><ul><li>Solution contains both a solute and a solvent </li></ul></ul><ul><ul><ul><li>Solvents dissolve solutes </li></ul></ul></ul>
  33. 33. Figure 5.15A During osmosis, net movement of water is toward greater solute concentration
  34. 34. How Osmosis Affects the Size and Shape of Cells <ul><li>Isotonic solutions ( iso, same as) - concentration of water is the same on both sides of the membrane </li></ul><ul><li>Hypotonic solution ( hypo , less than) - </li></ul><ul><li>Outside the cell, the concentration of solute is less, and the concentration of water is greater, than inside the cell </li></ul><ul><li>hypertonic solution ( hyper , more than) - Outside the cell, the concentration of solute is more, and the concentration of water is less, than inside the cell </li></ul>
  35. 35. Figure 5.15B Osmosis in animal and plant cells
  36. 36. 5.16 Active transport requires a carrier protein and energy <ul><li>Active transport , molecules or ions move through the plasma membrane, accumulating on one side of the cell </li></ul><ul><ul><li>Movement of molecules against their concentration gradients requires both a carrier protein and ATP </li></ul></ul><ul><li>Sodium-potassium pump undergoes a change in shape when it combines with ATP allowing it to combine alternately with sodium ions and potassium ions </li></ul>
  37. 37. Figure 5.16 During active transport, a substance moves contrary to its concentration gradient
  38. 38. 5.17 Bulk transport involves the use of vesicles <ul><li>Bulk transport occurs when fluid or particles are brought into or out of a cell by vacuole formation, called endocytosis or by evagination, called exocytosis </li></ul><ul><ul><li>Phagocytosis occurs when the material taken in is large </li></ul></ul><ul><ul><li>Pinocytosis occurs when vesicles form around a liquid or around very small particles </li></ul></ul><ul><ul><li>Receptor-mediated endocytosis - receptors for particular substances are found at one location in the plasma membrane </li></ul></ul>
  39. 39. Figure 5.17 Bulk transport into the cell is by endocytosis
  40. 40. Connecting the Concepts: Chapter 5 <ul><li>Energy is the ability to do work, to bring about change, and to make things happen </li></ul><ul><li>A cell is dynamic because it carries out enzymatic reactions </li></ul><ul><li>Exchanges across the plasma membrane allow the cell to continue to perform its usual reactions </li></ul><ul><ul><li>Few reactions occur without enzymes, which are proteins, because they lower the energy of activation with their substrate </li></ul></ul><ul><li>ATP, the universal energy “currency” of life, get energy-requiring (endergonic) reactions going </li></ul><ul><li>The plasma membrane is called the gatekeeper of the cell because its numerous proteins allow only certain substances to enter or exit </li></ul>