Chapter 5

1. Chapter 5 0 The Working Cell

2. Cool “Fires” Attract Mates and Meals • Fireflies use light to send signals to potential mates • Instead of using chemical signals like most other insects

3. The light comes from a set of chemical reactions • That occur in light-producing organs at the rear of the insect

4. Females of some species • Produce a light pattern that attracts males of other species, which are then eaten by the female

5. ENERGY AND THE CELL • 5.1 Energy is the capacity to perform work • All organisms require energy • Which is defined as the capacity to do work

6. Kinetic energy is the energy of motion • Potential energy is stored energy • And can be converted to kinetic energy Figure 5.1A–C

7. 5.2 Two laws govern energy transformations • Thermodynamics • Is the study of energy transformations

8. The First Law of Thermodynamics • According to the first law of thermodynamics • Energy can be changed from one form to another • Energy cannot be created or destroyed Figure 5.2A

9. The Second Law of Thermodynamics • The second law of thermodynamics • States that energy transformations increase disorder or entropy, and some energy is lost as heat Heat Chemical reactions Carbon dioxide + Glucose + ATP ATP water Oxygen Energy for cellular work Figure 5.2B

10. Products Amount of energyrequired Energy required Potential energy of molecules Reactants • 5.3 Chemical reactions either store or release energy • Endergonic reactions • Absorb energy and yield products rich in potential energy Figure 5.3A

11. Reactants Amount of energyreleased Energy released Potential energy of molecules Products • Exergonic reactions • Release energy and yield products that contain less potential energy than their reactants Figure 5.3B

12. Cells carry out thousands of chemical reactions • The sum of which constitutes cellular metabolism • Energy coupling • Uses exergonic reactions to fuel endergonic reactions

13. 5.4 ATP shuttles chemical energy and drives cellular work • ATP powers nearly all forms of cellular work

14. Phosphategroups Adenosine diphosphate Adenosine Triphosphate H2O + P Energy P P P P P + Hydrolysis Adenine Ribose ATP ADP • The energy in an ATP molecule • Lies in the bonds between its phosphate groups Figure 5.4A

15. ATP Mechanical work Chemical work Transport work Membraneprotein Solute + P Motorprotein P Reactants P P P Product P Molecule formed Protein moved Solute transported + ADP P • ATP drives endergonic reactions by phosphorylation • Transferring a phosphate group to make molecules more reactive 0 0 Figure 5.4B

16. ATP Phosphorylation Hydrolysis Energy fromexergonicreactions Energy forendergonicreactions ADP + P • Cellular work can be sustained • Because ATP is a renewable resource that cells regenerate Figure 5.4C

17. HOW ENZYMES FUNCTION • 5.5 Enzymes speed up the cell’s chemical reactions by lowering energy barriers

18. EA barrier Enzyme Reactants Products 1 2 • For a chemical reaction to begin • Reactants must absorb some energy, called the energy of activation Figure 5.5A

19. EA withoutenzyme EA withenzyme Reactants Net changein energy Energy Products Progress of the reaction • A protein catalyst called an enzyme • Can decrease the energy of activation needed to begin a reaction Figure 5.5B

20. 5.6 A specific enzyme catalyzes each cellular reaction • Enzymes have unique three-dimensional shapes • That determine which chemical reactions occur in a cell

21. 1 Enzyme availablewith empty activesite Substrate binds to enzyme with induced fit 2 4 Products arereleased 3 Substrate is converted to products • The catalytic cycle of an enzyme Active site Substrate(sucrose) Enzyme(sucrase) Glucose Fructose H2O Figure 5.6

22. 5.7 The cellular environment affects enzyme activity • Temperature, salt concentration, and pH influence enzyme activity • Some enzymes require nonprotein cofactors • Such as metal ions or organic molecules called coenzymes

23. 5.8 Enzyme inhibitors block enzyme action • Inhibitors interfere with an enzyme’s activity

24. Active site Substrate Enzyme Normal binding of substrate Competitiveinhibitor Noncompetitiveinhibitor Enzyme inhibition • A competitive inhibitor • Takes the place of a substrate in the active site • A noncompetitive inhibitor • Alters an enzyme’s function by changing its shape Figure 5.8

25. CONNECTION • 5.9 Many poisons, pesticides, and drugs are enzyme inhibitors

26. MEMBRANE STRUCTURE AND FUNCTION • 5.10 Membranes organize the chemical activities of cells • Membranes • Provide structural order for metabolism

27. Outside of cell Cytoplasm TEM 200,000  • The plasma membrane of the cell is selectively permeable • Controlling the flow of substances into or out of the cell Figure 5.10

28. CH3 Hydrophilic head + N CH2 CH3 CH3 CH2 Phosphategroup O P O– O O CH CH2 CH2 O O O O C C CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 Symbol CH CH2 CH CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH3 CH3 Hydrophobic tails • 5.11 Membrane phospholipids form a bilayer • Phospholipids • Have a hydrophilic head and two hydrophobic tails • Are the main structural components of membranes Figure 5.11A

29. Water Hydrophilicheads Hydrophobictails Water • Phospholipids form a two-layer sheet • Called a phospholipid bilayer, with the heads facing outward and the tails facing inward Figure 5.11B

30. Fibers of the extracellular matrix Carbohydrate(of glycoprotein) Glycoprotein Glycolipid Plasmamembrane Phospholipid Proteins Cholesterol Microfilamentsof cytoskeleton Cytoplasm • 5.12 The membrane is a fluid mosaic of phospholipids and proteins • A membrane is a fluid mosaic • With proteins and other molecules embedded in a phospholipid bilayer Figure 5.12

31. 5.13 Proteins make the membrane a mosaic of function • Many membrane proteins • Function as enzymes Figure 5.13A

32. Messenger molecule Receptor Activatedmolecule • Other membrane proteins • Function as receptors for chemical messages from other cells Figure 5.13B

33. ATP • Membrane proteins also function in transport • Moving substances across the membrane Figure 5.13C

34. Molecules of dye Membrane Equilibrium Equilibrium • 5.14 Passive transport is diffusion across a membrane • In passive transport, substances diffuse through membranes without work by the cell • Spreading from areas of high concentration to areas of low concentration Figure 5.14A Figure 5.14B

35. Small nonpolar molecules such as O2 and CO2 • Diffuse easily across the phospholipid bilayer of a membrane

36. Solutemolecule Transportprotein • 5.15 Transport proteins may facilitate diffusion across membranes • Many kinds of molecules • Do not diffuse freely across membranes • For these molecules, transport proteins • Provide passage across membranes through a process called facilitated diffusion Figure 5.15

37. Equalconcentrationof solute Higherconcentrationof solute Lowerconcentrationof solute H2O Solutemolecule Selectivelypermeablemembrane Watermolecule Solute molecule with cluster of water molecules Net flow of water • 5.16 Osmosis is the diffusion of water across a membrane • In osmosis • Water travels from a solution of lower solute concentration to one of higher solute concentration Figure 5.16

38. Hypertonic solution Hypotonic solution Isotonic solution H2O H2O H2O H2O Animalcell (3) Shriveled (2) Lysed (1) Normal Plasmamembrane H2O H2O H2O H2O Plantcell (6) Shriveled (plasmolyzed) (5) Turgid (4) Flaccid • 5.17 Water balance between cells and their surroundings is crucial to organisms • Osmosis causes cells to shrink in hypertonic solutions • And swell in hypotonic solutions • In isotonic solutions • Animal cells are normal, but plant cells are limp Figure 5.17

39. The control of water balance • Is called osmoregulation

40. Transportprotein P P P Phosphatedetaches Proteinchanges shape ATP Solute ADP Transport 1 Solute binding 2 Phosphorylation 3 4 Protein reversion • 5.18 Cells expend energy for active transport • Transport proteins can move solutes against a concentration gradient • Through active transport, which requires ATP Figure 5.18

41. Fluid outside cell Vesicle Protein Cytoplasm • 5.19 Exocytosis and endocytosis transport large molecules • To move large molecules or particles through a membrane • A vesicle may fuse with the membrane and expel its contents (exocytosis) Figure 5.19A

42. Vesicle forming • Membranes may fold inward • Enclosing material from the outside (endocytosis) Figure 5.19B

43. Plasma membrane Food being ingested Pseudopodium of amoeba Material bound to receptor proteins PIT TEM 96,500  TEM 54,000 Cytoplasm LM 230 Phagocytosis Receptor-mediated endocytosis Pinocytosis • Endocytosis can occur in three ways • Phagocytosis • Pinocytosis • Receptor-mediated endocytosis Figure 5.19C

44. Phospholipid outer layer LDL particle Vesicle Cholesterol Protein Plasmamembrane Receptorprotein Cytoplasm CONNECTION • 5.20 Faulty membranes can overload the blood with cholesterol • Harmful levels of cholesterol • Can accumulate in the blood if membranes lack cholesterol receptors Figure 5.20

45. 5.21 Chloroplasts and mitochondria make energy available for cellular work • Enzymes are central to the processes that make energy available to the cell

46. Chloroplasts carry out photosynthesis • Using solar energy to produce glucose and oxygen from carbon dioxide and water • Mitochondria consume oxygen in cellular respiration • Using the energy stored in glucose to make ATP