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CHAPTER 5

CHAPTER 5. The Working Cell. 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

  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. SOME BASIC ENERGY CONCEPTS • Energy makes the world go around • What is energy? • Energy is defined as the capacity (or ability) to do work • Work is defined as the movement of mass through space • First and second law of thermodynamics • Energy cannot be created nor destroyed • No energy conversion is completely efficient

  5. 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

  6. Entropy • Heat is • A type of kinetic energy • A product of all energy conversions • Randomized energy • Scientists use the term “entropy” as a measure of disorder, or randomness in a system • All energy conversions increase the entropy of the universe • Time for an Estesism (or two)….YEAH!!!!!!!

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

  8. 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

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

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

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

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

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

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

  15. 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

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

  17. 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

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

  19. 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

  20. Some Key Terms • Metabolism is sum of all the chemical reactions that occur within a cell • Anabolism defines the chemical reactions that BUILD UP materials within the cell (makes polymers from monomers/require energy/typically are dehydration synthesis reactions) • Catabolism defines the chemical reactions that TEAR DOWN OR BREAK APART materials within the cell (makes monomers out of polymers/release energy/and are hydrolytic reactions requiring water)

  21. ENZYMES • Reactions would occur eventually given enough time • They would not occur often enough or quickly enough to support life without special class of proteins called ENZYMES • FOR ALL INTENTS AND PURPOSES; IF ONE DOES NOT HAVE THE ENZYME, ONE IS NOT GOING TO RUN THAT REACTION • Enzymes “usually” end in “ase”

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

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

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

  25. 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

  26. 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

  27. 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

  28. 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

  29. 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

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

  31. 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

  32. 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

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

  34. 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

  35. 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

  36. 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

  37. Osmoregulation is the control of water balance in animals

  38. 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

  39. 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

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

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

  42. 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

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

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

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

  46. 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

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

  48. The processes of natural selection and directed evolution • Both result in the production of new enzymes with new functions

  49. SUMMARY OF KEY CONCEPTS • ATP and Cellular Work Energy for cellular work Adenosine Adenosine (Phosphate transferred to other molecules) Adenosine triphosphate Adenosine diphosphate Energy from organic fuel Visual Summary 5.1

  50. Passive Transport, Osmosis, and Active Transport Requires no energy Requires energy Passive transport Osmosis Active transport Higher water concentration (hypotonic) Higher solute concentration Higher solute concentration Water Solute Solute Solute Lower water concentration (hypertonic) Lower solute concentration Lower solute concentration Visual Summary 5.2

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