Chapter 5. The Working Cell. PowerPoint Lectures for Campbell Biology: Concepts & Connections, Seventh Edition Reece, Taylor, Simon, and Dickey

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1 Chapter 5 The Working Cell PowerPoint Lectures for Campbell Biology: Concepts & Connections, Seventh Edition Reece, Taylor, Simon, and Dickey Lecture by Edward J. Zalisko

2 Lesson Plans Flipped Classroom HW Day 1Notes outline section , review notes, watch examples, do problems in packet HW Day 2 Notes , Review notes, watch examples, do problems in packet HW Day 3 Notes finish chapter, Review notes, watch examples, do problems in packet

3 Introduction Some organisms use energy-converting reactions to produce light in a process called bioluminescence. Many marine invertebrates and fishes use bioluminescence to hide themselves from predators. Scientists estimate that 90% of deep-sea marine life produces bioluminescence. The light is produced from chemical reactions that convert chemical energy into visible light.

4 Figure 5.0_1 Chapter 5: Big Ideas Cellular respiration Membrane Structure and Function Energy and the Cell How Enzymes Function

5 Figure 5.0_2

6 Introduction Bioluminescence is an example of the multitude of energy conversions that a cell can perform. Many of a cell s reactions take place in organelles and use enzymes embedded in the membranes of these organelles. This chapter addresses how working cells use membranes, energy, and enzymes.

7 MEMBRANE STRUCTURE AND FUNCTION

8 5.1 Membranes are fluid mosaics of lipids and proteins with many functions Membranes are composed of a bilayer of phospholipids with embedded and attached proteins, in a structure biologists call a fluid mosaic.

9 5.1 Membranes are fluid mosaics of lipids and proteins with many functions Many phospholipids are made from unsaturated fatty acids that have kinks in their tails. These kinks prevent phospholipids from packing tightly together, keeping them in liquid form. In animal cell membranes, cholesterol helps stabilize membranes at warmer temperatures and keep the membrane fluid at lower temperatures.

10 Figure 5.1 Fibers of extracellular matrix (ECM) Enzymatic activity Phospholipid Cholesterol CYTOPLASM Cell-cell recognition Receptor Signaling molecule Transport ATP Intercellular junctions Glycoprotein Attachment to the cytoskeleton and extracellular matrix (ECM) Signal transduction Microfilaments of cytoskeleton CYTOPLASM

11 5.1 Membranes are fluid mosaics of lipids and proteins with many functions Membrane proteins perform many functions. 1. Some proteins help maintain cell shape and coordinate changes inside and outside the cell through their attachment to the cytoskeleton and extracellular matrix. 2. Some proteins function as receptors for chemical messengers from other cells. 3. Some membrane proteins function as enzymes.

12 5.1 Membranes are fluid mosaics of lipids and proteins with many functions 4. Some membrane glycoproteins are involved in cell-cell recognition. 5. Membrane proteins may participate in the intercellular junctions that attach adjacent cells to each other. 6. Membranes may exhibit selective permeability, allowing some substances to cross more easily than others. Animation: Signal Transduction Pathways

13 5.2 EVOLUTION CONNECTION: Membranes form spontaneously, a critical step in the origin of life Phospholipids, the key ingredient of biological membranes, spontaneously self-assemble into simple membranes. The formation of membrane-enclosed collections of molecules was a critical step in the evolution of the first cells.

14 Figure 5.2 Water-filled bubble made of phospholipids

15 Figure 5.2Q Water Water

16 5.3 Passive transport is diffusion across a membrane with no energy investment Diffusion is the tendency of particles to spread out evenly in an available space. Particles move from an area of more concentrated particles to an area where they are less concentrated. This means that particles diffuse down their concentration gradient. Eventually, the particles reach equilibrium where the concentration of particles is the same throughout.

17 5.3 Passive transport is diffusion across a membrane with no energy investment Diffusion across a cell membrane does not require energy, so it is called passive transport. The concentration gradient itself represents potential energy for diffusion. Animation: Diffusion Animation: Membrane Selectivity

18 Figure 5.3A Molecules of dye Membrane Pores Net diffusion Net diffusion Equilibrium

19 Figure 5.3B Net diffusion Net diffusion Net diffusion Net diffusion Equilibrium Equilibrium

20 5.4 Osmosis is the diffusion of water across a membrane One of the most important substances that crosses membranes is water. The diffusion of water across a selectively permeable membrane is called osmosis. Animation: Osmosis

21 5.4 Osmosis is the diffusion of water across a membrane If a membrane permeable to water but not a solute separates two solutions with different concentrations of solute, water will cross the membrane, moving down its own concentration gradient, until the solute concentration on both sides is equal.

22 Figure 5.4 Lower concentration of solute Higher concentration of solute Equal concentrations of solute Solute molecule H 2 O Selectively permeable membrane Water molecule Solute molecule with cluster of water molecules Osmosis

23 5.5 Water balance between cells and their surroundings is crucial to organisms Tonicity is a term that describes the ability of a solution to cause a cell to gain or lose water. Tonicity mostly depends on the concentration of a solute on both sides of the membrane.

24 5.5 Water balance between cells and their surroundings is crucial to organisms How will animal cells be affected when placed into solutions of various tonicities? When an animal cell is placed into an isotonic solution, the concentration of solute is the same on both sides of a membrane, and the cell volume will not change, a hypotonic solution, the solute concentration is lower outside the cell, water molecules move into the cell, and the cell will expand and may burst, or a hypertonic solution, the solute concentration is higher outside the cell, water molecules move out of the cell, and the cell will shrink.

25 5.5 Water balance between cells and their surroundings is crucial to organisms For an animal cell to survive in a hypotonic or hypertonic environment, it must engage in osmoregulation, the control of water balance.

26 5.5 Water balance between cells and their surroundings is crucial to organisms The cell walls of plant cells, prokaryotes, and fungi make water balance issues somewhat different. The cell wall of a plant cell exerts pressure that prevents the cell from taking in too much water and bursting when placed in a hypotonic environment. But in a hypertonic environment, plant and animal cells both shrivel. Video: Chlamydomonas Video: Plasmolysis Video: Paramecium Vacuole Video: Turgid Elodea

27 Figure 5.5 Hypotonic solution Isotonic solution Hypertonic solution H 2 O H 2 O H 2 O H 2 O Animal cell Lysed Normal Shriveled H 2 O H 2 O Plasma H 2 O membrane Plant cell Turgid (normal) Flaccid Shriveled (plasmolyzed)

28 5.6 Transport proteins can facilitate diffusion across membranes Hydrophobic substances easily diffuse across a cell membrane. However, polar or charged substances do not easily cross cell membranes and, instead, move across membranes with the help of specific transport proteins in a process called facilitated diffusion, which does not require energy and relies on the concentration gradient.

29 5.6 Transport proteins can facilitate diffusion across membranes Some proteins function by becoming a hydrophilic tunnel for passage of ions or other molecules. Other proteins bind their passenger, change shape, and release their passenger on the other side. In both of these situations, the protein is specific for the substrate, which can be sugars, amino acids, ions, and even water.

30 5.6 Transport proteins can facilitate diffusion across membranes Because water is polar, its diffusion through a membrane s hydrophobic interior is relatively slow. The very rapid diffusion of water into and out of certain cells is made possible by a protein channel called an aquaporin.

31 Figure 5.6 Solute molecule Transport protein

32 5.7 SCIENTIFIC DISCOVERY: Research on another membrane protein led to the discovery of aquaporins Dr. Peter Agre received the 2003 Nobel Prize in chemistry for his discovery of aquaporins. His research on the Rh protein used in blood typing led to this discovery.

33 Figure 5.7

34 5.8 Cells expend energy in the active transport of a solute In active transport, a cell must expend energy to move a solute against its concentration gradient. The following figures show the four main stages of active transport. Animation: Active Transport

35 Figure 5.8_s1 Transport protein 1 Solute Solute binding

36 Figure 5.8_s2 Transport protein 1 Solute Solute binding 2 ATP P ADP Phosphate attaching

37 Figure 5.8_s3 Transport protein Solute Solute binding ATP P ADP Phosphate attaching Protein P changes shape. Transport

38 Figure 5.8_s4 Transport protein 1 Solute Solute binding 2 ATP P ADP Phosphate attaching Protein P changes shape. 3 Transport Phosphate detaches. 4 Protein reversion P

39 5.9 Exocytosis and endocytosis transport large molecules across membranes A cell uses two mechanisms to move large molecules across membranes. Exocytosis is used to export bulky molecules, such as proteins or polysaccharides. Endocytosis is used to import substances useful to the livelihood of the cell. In both cases, material to be transported is packaged within a vesicle that fuses with the membrane.

40 5.9 Exocytosis and endocytosis transport large molecules across membranes There are three kinds of endocytosis. 1. Phagocytosis is the engulfment of a particle by wrapping cell membrane around it, forming a vacuole. 2. Pinocytosis is the same thing except that fluids are taken into small vesicles. 3. Receptor-mediated endocytosis uses receptors in a receptor-coated pit to interact with a specific protein, initiating the formation of a vesicle. Animation: Exocytosis and Endocytosis Introduction Animation: Exocytosis Animation: Pinocytosis Animation: Phagocytosis Animation: Receptor-Mediated Endocytosis

41 Figure 5.9 Phagocytosis EXTRACELLULAR FLUID Pseudopodium CYTOPLASM Food being ingested Food or other particle Food vacuole Pinocytosis Plasma membrane Vesicle Receptor-mediated endocytosis Coat protein Plasma membrane Receptor Coated vesicle Coated pit Specific molecule Coated pit Material bound to receptor proteins

42 Figure 5.9_1 Phagocytosis EXTRACELLULAR FLUID Pseudopodium CYTOPLASM Food being ingested Food or other particle Food vacuole

43 Figure 5.9_2 Pinocytosis Plasma membrane Vesicle Plasma membrane

44 Figure 5.9_3 Receptor-mediated endocytosis Coat protein Plasma membrane Receptor Coated vesicle Coated pit Specific molecule Coated pit Material bound to receptor proteins

45 Figure 5.9_4 Food being ingested

46 Figure 5.9_5 Plasma membrane

47 Figure 5.9_6 Plasma membrane Coated pit Material bound to receptor proteins

48 ENERGY AND THE CELL

49 5.10 Cells transform energy as they perform work Cells are small units, a chemical factory, housing thousands of chemical reactions. Cells use these chemical reactions for cell maintenance, manufacture of cellular parts, and cell replication.

50 5.10 Cells transform energy as they perform work Energy is the capacity to cause change or to perform work. There are two kinds of energy. 1. Kinetic energy is the energy of motion. 2. Potential energy is energy that matter possesses as a result of its location or structure.

51 Figure 5.10 Fuel Energy conversion Waste products Heat energy Gasoline Oxygen Combustion Kinetic energy of movement Energy conversion in a car Carbon dioxide Water Heat energy Glucose Cellular respiration ATP ATP Carbon dioxide Oxygen Energy for cellular work Water Energy conversion in a cell

52 Figure 5.10_1 Fuel Energy conversion Waste products Heat energy Gasoline Oxygen Combustion Kinetic energy of movement Energy conversion in a car Carbon dioxide Water

53 Figure 5.10_2 Fuel Energy conversion Waste products Heat energy Glucose Cellular respiration ATP ATP Carbon dioxide Oxygen Energy for cellular work Water Energy conversion in a cell

54 5.10 Cells transform energy as they perform work Heat, or thermal energy, is a type of kinetic energy associated with the random movement of atoms or molecules. Light is also a type of kinetic energy, and can be harnessed to power photosynthesis.

55 5.10 Cells transform energy as they perform work Chemical energy is the potential energy available for release in a chemical reaction. It is the most important type of energy for living organisms to power the work of the cell. Animation: Energy Concepts

56 5.10 Cells transform energy as they perform work Thermodynamics is the study of energy transformations that occur in a collection of matter. Scientists use the word system for the matter under study and surroundings for the rest of the universe.

57 5.10 Cells transform energy as they perform work Two laws govern energy transformations in organisms. According to the first law of thermodynamics, energy in the universe is constant, and second law of thermodynamics, energy conversions increase the disorder of the universe. Entropy is the measure of disorder, or randomness.

58 5.10 Cells transform energy as they perform work Cells use oxygen in reactions that release energy from fuel molecules. In cellular respiration, the chemical energy stored in organic molecules is converted to a form that the cell can use to perform work.

59 5.11 Chemical reactions either release or store energy Chemical reactions either release energy (exergonic reactions) or require an input of energy and store energy (endergonic reactions).

60 5.11 Chemical reactions either release or store energy Exergonic reactions release energy. These reactions release the energy in covalent bonds of the reactants. Burning wood releases the energy in glucose as heat and light. Cellular respiration involves many steps, releases energy slowly, and uses some of the released energy to produce ATP.

61 Figure 5.11A Potential energy of molecules Reactants Energy Products Amount of energy released

62 5.11 Chemical reactions either release or store energy An endergonic reaction requires an input of energy and yields products rich in potential energy. Endergonic reactions begin with reactant molecules that contain relatively little potential energy but end with products that contain more chemical energy.

63 Figure 5.11B Potential energy of molecules Products Reactants Energy Amount of energy required

64 5.11 Chemical reactions either release or store energy Photosynthesis is a type of endergonic process. Energy-poor reactants, carbon dioxide, and water are used. Energy is absorbed from sunlight. Energy-rich sugar molecules are produced.

65 5.11 Chemical reactions either release or store energy A living organism carries out thousands of endergonic and exergonic chemical reactions. The total of an organism s chemical reactions is called metabolism. A metabolic pathway is a series of chemical reactions that either builds a complex molecule or breaks down a complex molecule into simpler compounds.

66 5.11 Chemical reactions either release or store energy Energy coupling uses the energy released from exergonic reactions to drive essential endergonic reactions, usually using the energy stored in ATP molecules.

67 5.12 ATP drives cellular work by coupling exergonic and endergonic reactions ATP, adenosine triphosphate, powers nearly all forms of cellular work. ATP consists of the nitrogenous base adenine, the five-carbon sugar ribose, and three phosphate groups.

68 5.12 ATP drives cellular work by coupling exergonic and endergonic reactions Hydrolysis of ATP releases energy by transferring its third phosphate from ATP to some other molecule in a process called phosphorylation. Most cellular work depends on ATP energizing molecules by phosphorylating them.

69 Figure 5.12A_s1 ATP: Adenosine Triphosphate Phosphate group Adenine Ribose P P P

70 Figure 5.12A_s2 ATP: Adenosine Triphosphate Phosphate group Adenine Ribose Hydrolysis P P P H 2 O P P P Energy ADP: Adenosine Diphosphate

71 5.12 ATP drives cellular work by coupling exergonic and endergonic reactions There are three main types of cellular work: 1. chemical, 2. mechanical, and 3. transport. ATP drives all three of these types of work.

72 Figure 5.12B Chemical work Mechanical work Transport work ATP ATP ATP Solute P Reactants Motor protein P P Membrane protein P P Product P Molecule formed Protein filament moved Solute transported ADP ADP ADP P P P

73 5.12 ATP drives cellular work by coupling exergonic and endergonic reactions ATP is a renewable source of energy for the cell. In the ATP cycle, energy released in an exergonic reaction, such as the breakdown of glucose,is used in an endergonic reaction to generate ATP.

74 Figure 5.12C ATP Energy from exergonic reactions ADP P Energy for endergonic reactions

75 HOW ENZYMES FUNCTION

76 5.13 Enzymes speed up the cell s chemical reactions by lowering energy barriers Although biological molecules possess much potential energy, it is not released spontaneously. An energy barrier must be overcome before a chemical reaction can begin. This energy is called the activation energy (E A ).

77 5.13 Enzymes speed up the cell s chemical reactions by lowering energy barriers We can think of E A as the amount of energy needed for a reactant molecule to move uphill to a higher energy but an unstable state so that the downhill part of the reaction can begin. One way to speed up a reaction is to add heat, which agitates atoms so that bonds break more easily and reactions can proceed but could kill a cell.

78 Figure 5.13A Energy Energy Activation energy barrier Enzyme Reactant Reactant Activation energy barrier reduced by enzyme Without enzyme Products With enzyme Products

79 Figure 5.13A_1 Energy Activation energy barrier Reactant Products Without enzyme

80 Figure 5.13A_2 Energy Enzyme Reactant Activation energy barrier reduced by enzyme Products With enzyme

81 Figure 5.13Q Energy a Reactants b c Progress of the reaction Products

82 5.13 Enzymes speed up the cell s chemical reactions by lowering energy barriers Enzymes function as biological catalysts by lowering the E A needed for a reaction to begin, increase the rate of a reaction without being consumed by the reaction, and are usually proteins, although some RNA molecules can function as enzymes. Animation: How Enzymes Work

83 5.14 A specific enzyme catalyzes each cellular reaction An enzyme is very selective in the reaction it catalyzes and has a shape that determines the enzyme s specificity. The specific reactant that an enzyme acts on is called the enzyme s substrate. A substrate fits into a region of the enzyme called the active site. Enzymes are specific because their active site fits only specific substrate molecules.

84 5.14 A specific enzyme catalyzes each cellular reaction The following figure illustrates the catalytic cycle of an enzyme.

85 Figure 5.14_s1 1 Enzyme available with empty active site Active site Enzyme (sucrase)

86 Figure 5.14_s2 1 Enzyme available with empty active site Active site Substrate (sucrose) Enzyme (sucrase) 2 Substrate binds to enzyme with induced fit

87 Figure 5.14_s3 1 Enzyme available with empty active site Active site Substrate (sucrose) Enzyme (sucrase) 2 Substrate binds to enzyme with induced fit H 2 O 3 Substrate is converted to products

88 Figure 5.14_s4 1 Enzyme available with empty active site Active site Substrate (sucrose) Glucose Enzyme (sucrase) 2 Substrate binds to enzyme with induced fit Fructose H 2 O 4 Products are released 3 Substrate is converted to products

89 5.14 A specific enzyme catalyzes each cellular reaction For every enzyme, there are optimal conditions under which it is most effective. Temperature affects molecular motion. An enzyme s optimal temperature produces the highest rate of contact between the reactants and the enzyme s active site. Most human enzymes work best at 35 40ºC. The optimal ph for most enzymes is near neutrality.

90 5.14 A specific enzyme catalyzes each cellular reaction Many enzymes require nonprotein helpers called cofactors, which bind to the active site and function in catalysis. Some cofactors are inorganic, such as zinc, iron, or copper. If a cofactor is an organic molecule, such as most vitamins, it is called a coenzyme.

91 5.15 Enzyme inhibitors can regulate enzyme activity in a cell A chemical that interferes with an enzyme s activity is called an inhibitor. Competitive inhibitors block substrates from entering the active site and reduce an enzyme s productivity.

92 5.15 Enzyme inhibitors can regulate enzyme activity in a cell Noncompetitive inhibitors bind to the enzyme somewhere other than the active site, change the shape of the active site, and prevent the substrate from binding.

93 Figure 5.15A Substrate Active site Enzyme Allosteric site Normal binding of substrate Competitive inhibitor Noncompetitive inhibitor Enzyme inhibition

94 5.15 Enzyme inhibitors can regulate enzyme activity in a cell Enzyme inhibitors are important in regulating cell metabolism. In some reactions, the product may act as an inhibitor of one of the enzymes in the pathway that produced it. This is called feedback inhibition.

95 Figure 5.15B Feedback inhibition Enzyme 1 Enzyme 2 Enzyme 3 A B C D Reaction 1 Reaction 2 Reaction 3 Starting Product molecule

96 5.16 CONNECTION: Many drugs, pesticides, and poisons are enzyme inhibitors Many beneficial drugs act as enzyme inhibitors, including Ibuprofen, inhibiting the production of prostaglandins, some blood pressure medicines, some antidepressants, many antibiotics, and protease inhibitors used to fight HIV. Enzyme inhibitors have also been developed as pesticides and deadly poisons for chemical warfare.

97 Figure 5.16

98 You should now be able to 1. Describe the fluid mosaic structure of cell membranes. 2. Describe the diverse functions of membrane proteins. 3. Relate the structure of phospholipid molecules to the structure and properties of cell membranes. 4. Define diffusion and describe the process of passive transport.

99 You should now be able to 5. Explain how osmosis can be defined as the diffusion of water across a membrane. 6. Distinguish between hypertonic, hypotonic, and isotonic solutions. 7. Explain how transport proteins facilitate diffusion. 8. Distinguish between exocytosis, endocytosis, phagocytosis, pinocytosis, and receptor-mediated endocytosis.

100 You should now be able to 9. Define and compare kinetic energy, potential energy, chemical energy, and heat. 10. Define the two laws of thermodynamics and explain how they relate to biological systems. 11. Define and compare endergonic and exergonic reactions. 12. Explain how cells use cellular respiration and energy coupling to survive.

101 You should now be able to 13. Explain how ATP functions as an energy shuttle. 14. Explain how enzymes speed up chemical reactions. 15. Explain how competitive and noncompetitive inhibitors alter an enzyme s activity. 16. Explain how certain drugs, pesticides, and poisons can affect enzymes.

102 Figure 5.UN01 Diffusion Passive transport (requires no energy) Facilitated diffusion HIgher solute concentration Osmosis HIgher free water concentration Active transport (requires energy) HIgher solute concentration Solute Lower solute concentration Water Lower free water concentration ATP Lower solute concentration

103 Figure 5.UN02 ATP cycle ATP Energy from exergonic reactions ADP P Energy for endergonic reactions

104 Figure 5.UN03 Molecules cross cell membranes by by passive transport (a) may be moving down moving against requires (b) ATP uses diffusion (d) uses (e) of of (c) polar molecules and ions

105 Figure 5.UN04 b. c. a. d. f. e.

106 Table 5.UN05

107 Figure 5.UN06 Rate of reaction ph