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CHAPTER 5

CHAPTER 5. The Working Cell Figures 5.1 – 5.3. A handful of peanuts contains enough energy to boil a quart of water. It takes about 10 million ATP molecules per second to power an active muscle cell. About 75% of the energy generated by a car’s engine is lost as heat.

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CHAPTER 5

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  1. CHAPTER 5 The Working Cell Figures 5.1 – 5.3

  2. A handful of peanuts contains enough energy to boil a quart of water • It takes about 10 million ATP molecules per second to power an active muscle cell

  3. About 75% of the energy generated by a car’s engine is lost as heat • You’d have to run about 14 miles to burn the calories from a pepperoni pizza

  4. BIOLOGY AND SOCIETY:STONEWASHING WITHOUT THE STONES • The sturdy cotton fabric denim has been worn because of its toughness and appeal • Stonewashing jeans with pumice stone can damage the fabric • Recently the enzyme cellulase has been used to achieve better results Figure 5.1

  5. SOME BASIC ENERGY CONCEPTS • Energy makes the world go around • What is energy?

  6. Conservation of Energy • Energy is defined as the capacity to perform work

  7. Kinetic energy is the energy of motion • Potential energy is stored energy 2 High potential energy 1 Conversion of kinetic energy to potential energy 3 Conversion of potential energy to kinetic energy 4 Low potential energy Figure 5.2

  8. Energy can be changed from one form to another • However, it cannot be created or destroyed • This is the conservation of energy principle

  9. Entropy • Heat is • A type of kinetic energy • A product of all energy conversions • Randomized energy

  10. Scientists use the term entropy as a measure of disorder, or randomness • All energy conversions increase the entropy of the universe

  11. Chemical Energy • Chemical energy • Is a form of potential energy • Is found in food, gasoline, and other fuels

  12. Living cells and automobile engines use the same basic process to make chemical energy do work Waste products poor in chemical energy Fuel rich in chemical energy Heat energy Carbon dioxide Gasoline Combustion Kinetic energy of movement Oxygen Water (a) Energy conversion in a car Figure 5.3a

  13. Heat energy Cellular respiration Carbon dioxide Food Oxygen Water Energy for cellular work (b) Energy conversion in a cell Figure 5.3b

  14. Cellular respiration • Is the energy-releasing chemical breakdown of fuel molecules • Provides energy for the cell to do work

  15. Food Calories • A calorie is the amount of energy that raises the temperature of 1 gram of water by 1 degree Celsius

  16. The kilocalorie is • 1,000 calories • The unit used to measure the energy in food Figure 5.4a

  17. The energy of calories in food is burned off by many activities Figure 5.4b

  18. ATP AND CELLULAR WORK • The chemical energy of organic molecules is released in cellular respiration to make ATP in the mitochondria

  19. The Structure of ATP • ATP (adenosine triphosphate) • Consists of adenosine plus a tail of three phosphate groups • Is broken down to ADP, accompanied by the release of energy Energy Adenosine Adenosine Phosphate transferred to other molecules Figure 5.5

  20. Phosphate Transfer • ATP can energize other molecules by transferring phosphate groups • This energy can be used to drive cellular work

  21. Motor protein Protein moved (a) Mechanical work Transport protein Solute Solute transported (b) Transport work ATP Reactants Product made (c) Chemical work Figure 5.6

  22. The ATP Cycle • Cellular work spends ATP • ATP is recycled from ADP and phosphate through cellular respiration

  23. ATP functions in what is called energy coupling, or the ATP cycle Cellular respiration: chemical energy harvested from fuel molecules Energy for cellular work Figure 5.7

  24. ENZYMES • Metabolism is defined as the many chemical reactions that occur in organisms • Few metabolic reactions occur without the assistance of enzymes

  25. Activation Energy • Activation energy • Is the energy that activates the reactants • Triggers a chemical reaction

  26. Enzymes • Lower the activation energy for chemical reactions Activation energy barrier Enzyme Reactants Products (a) Without enzyme (b) With enzyme Figure 5.8

  27. Induced Fit • Each enzyme is very selective • It catalyzes specific reactions

  28. Each enzyme recognizes a specific substrate • The active site fits to the substrate, and the enzyme changes shape slightly • This interaction is called induced fit

  29. Enzymes can function over and over again • This is a key characteristic of enzymes Substrate (sucrose) Enzyme available with empty active site 1 2 Substrate binds to enzyme Active site Enzyme (sucrase) Fructose Glucose Substrate is converted to products 4 3 Product are released Figure 5.9

  30. Enzyme Inhibitors • Enzyme inhibitors • Can inhibit a metabolic reaction • Bind to the active site, as substrate impostors Inhibitor Substrate Substrate Active site Active site Enzyme Enzyme (b) Enzyme inhibition by a substrate imposter (a) Normal enzyme action Figure 5.10a, b

  31. Other inhibitors • Bind at a remote site, changing the enzyme’s shape • In some cases, this is called feedback regulation Substrate Active site Inhibitor Enzyme (c) Enzyme inhibition by a molecule that causes the active site to change shape Figure 5.10c

  32. MEMBRANE TRANSPORT • Working cells must control the flow of materials • This is the primary function of the plasma membrane • Transport proteins also help with this task

  33. Passive Transport: Diffusion Across Membranes • Molecules contain heat energy • They vibrate and wander randomly

  34. Diffusion is one result of the movement of molecules • Molecules tend to spread into the available space • Diffusion is passive transport; no energy is needed

  35. Molecules of dye Membrane Equilibrium (a) Passive transport of one type of molecule Equilibrium (b) Passive transport of two types of molecules Figure 5.11

  36. Another type of passive transport is facilitated diffusion, the transport of some substances by specific transport proteins that act as selective corridors

  37. Osmosis and Water Balance in Cells • Osmosis is the passive transport of water across a selectively permeable membrane Hypotonic solution Hypertonic solution Isotonic solutions Sugar molecule (solute) Selectively permeable membrane Osmosis (net movement of water) Figure 5.12

  38. A hypertonic solution • Has a higher concentration of solute • A hypotonic solution • Has a lower concentration of solute • An isotonic solution • Has an equal concentration of solute

  39. Water Balance in Animal Cells • The survival of a cell depends on its ability to balance water uptake and loss Animal cell Normal Lysing Shriveled Plasma membrane Plant cell Shriveled Flaccid (wilts) Turgid Figure 5.13 (a) Isotonic solution (b) Hypotonic solution (c) Hypertonic solution

  40. Osmoregulation is the control of water balance in animals

  41. Water Balance in Plant Cells • Water balance in plant cells is different • They have rigid cell walls • They are at the mercy of the environment Figure 5.14

  42. Active Transport: the Pumping of Molecules Across Membranes • Active transport requires energy to move molecules across a membrane Lower solute concentration Solute Higher solute concentration Figure 5.15

  43. Exocytosis and Endocytosis: Traffic of Large Molecules • Exocytosis • Secretes substances outside of the cell Outside cell Plasma membrane Cytoplasm (a) Exocytosis Figure 5.16a

  44. Endocytosis • Takes material into the cell (b) Endocytosis Figure 5.16b

  45. In phagocytosis (“cellular eating”) a cell engulfs a particle and packages it within a food vacuole • In pinocytosis (“cellular drinking”) a cell “gulps” droplets of fluid by forming tiny vesicles Pseudopod of amoeba Food being ingested Figure 5.17

  46. Receptor-mediated endocytosis • Is triggered by the binding of external molecules to membrane proteins

  47. The Role of Membranes in Cell Signaling LDL particle Phospholipid coat Protein Receptor protein Cholesterol Plasma membrane Cholesterol processed Liver cell Figure 5.18

  48. Cellular communication • Begins with the reception of an extracellular signal • The signal transduction pathway • Consists of proteins and other molecules that relay the signal

  49. Inside cell Outside cell Reception Response Transduction Receptor protein Hydrolysis of glycogen releases glucose for energy Signal transduction pathway Epinephrine (adrenaline) from adrenal glands Plasma membrane Figure 5.19

  50. EVOLUTION CONNECTION:EVOLVING ENZYMES • Organisms use many different enzymes • Scientists compare enzymes from different organisms • Comparisons show similarities between organisms

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