Chapter 5 The Working Cell Power Point Lectures

Chapter 5 The Working Cell Power. Point Lectures for Campbell Biology: Concepts & Connections, Seventh Edition Reece, Taylor, Simon, and Dickey © 2012 Pearson Education, Inc. Lecture by Edward J. Zalisko

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. © 2012 Pearson Education, Inc.

Figure 5. 0_1 Chapter 5: Big Ideas Cellular respiration Membrane Structure and Function How Enzymes Function Energy and the Cell

Figure 5. 0_2

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. © 2012 Pearson Education, Inc.

MEMBRANE STRUCTURE AND FUNCTION © 2012 Pearson Education, Inc.

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. © 2012 Pearson Education, Inc.

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. © 2012 Pearson Education, Inc.

Figure 5. 1 CYTOPLASM Enzymatic activity Fibers of extracellular matrix (ECM) Phospholipid Cholesterol Cell-cell recognition Receptor Signaling molecule Transport Attachment to the cytoskeleton and extracellular matrix (ECM) Signal transduction ATP Intercellular junctions Microfilaments of cytoskeleton Glycoprotein CYTOPLASM

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. © 2012 Pearson Education, Inc.

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 Animation: Overview of Cell Signaling © 2012 Pearson Education, Inc.

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. © 2012 Pearson Education, Inc.

Figure 5. 2 Water-filled bubble made of phospholipids

Figure 5. 2 Q Water

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. © 2012 Pearson Education, Inc.

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 © 2012 Pearson Education, Inc.

Figure 5. 3 A Molecules of dye Membrane Pores Net diffusion Equilibrium

Figure 5. 3 B Net diffusion Equilibrium

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 © 2012 Pearson Education, Inc.

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. © 2012 Pearson Education, Inc.

Figure 5. 4 Lower Higher concentration of solute Solute molecule Equal concentrations of solute H 2 O Selectively permeable membrane Water molecule Solute molecule with cluster of water molecules Osmosis

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. © 2012 Pearson Education, Inc.

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 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. © 2012 Pearson Education, Inc.

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. © 2012 Pearson Education, Inc.

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. © 2012 Pearson Education, Inc. Video: Chlamydomonas Video: Plasmolysis Video: Paramecium Vacuole Video: Turgid Elodea

Figure 5. 5 Hypotonic solution H 2 O Isotonic solution Hypertonic solution H 2 O Animal cell Normal Lysed Plasma membrane H 2 O Shriveled H 2 O Plant cell Turgid (normal) Flaccid Shriveled (plasmolyzed)

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. © 2012 Pearson Education, Inc.

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. © 2012 Pearson Education, Inc.

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. © 2012 Pearson Education, Inc.

Figure 5. 6 Solute molecule Transport protein

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. © 2012 Pearson Education, Inc.

Figure 5. 7

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 © 2012 Pearson Education, Inc.

Figure 5. 8_s 1 Transport protein Solute 1 Solute binding

Figure 5. 8_s 2 Transport protein Solute 1 Solute binding P ADP Phosphate attaching ATP 2

Figure 5. 8_s 3 Transport protein Solute 1 Solute binding 2 P ATP ADP Phosphate attaching P Protein changes shape. 3 Transport

Figure 5. 8_s 4 Transport protein Solute 1 Solute binding 2 P ATP ADP Phosphate attaching P Protein changes shape. 3 Transport Phosphate P detaches. 4 Protein reversion

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. © 2012 Pearson Education, Inc.

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 © 2012 Pearson Education, Inc.

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 Receptor Plasma membrane Coated vesicle Coated pit Specific molecule Coated pit Material bound to receptor proteins

Figure 5. 9_1 Phagocytosis EXTRACELLULAR FLUID Pseudopodium CYTOPLASM “Food” or other particle Food vacuole Food being ingested

Figure 5. 9_2 Pinocytosis Plasma membrane Vesicle Plasma membrane

Figure 5. 9_3 Receptor-mediated endocytosis Coat protein Plasma membrane Coated vesicle Receptor Coated pit Specific molecule Coated pit Material bound to receptor proteins

Figure 5. 9_4 Food being ingested

Figure 5. 9_5 Plasma membrane

Figure 5. 9_6 Plasma membrane Coated pit Material bound to receptor proteins

ENERGY AND THE CELL © 2012 Pearson Education, Inc.

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. © 2012 Pearson Education, Inc.

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. © 2012 Pearson Education, Inc.

Figure 5. 10 Energy conversion Fuel Waste products Heat energy Carbon dioxide Gasoline Combustion Kinetic energy of movement Water Oxygen Energy conversion in a car Heat energy Glucose Oxygen Cellular respiration ATP Energy for cellular work Energy conversion in a cell Carbon dioxide Water

Figure 5. 10_1 Energy conversion Fuel Waste products Heat energy Carbon dioxide Gasoline Combustion Kinetic energy of movement Water Oxygen Energy conversion in a car

Figure 5. 10_2 Fuel Energy conversion Waste products Heat energy Glucose Oxygen Cellular respiration ATP Energy for cellular work Energy conversion in a cell Carbon dioxide Water

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. © 2012 Pearson Education, Inc.

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 © 2012 Pearson Education, Inc.

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. © 2012 Pearson Education, Inc.

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. © 2012 Pearson Education, Inc.

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. © 2012 Pearson Education, Inc.

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). © 2012 Pearson Education, Inc.

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. © 2012 Pearson Education, Inc.

Potential energy of molecules Figure 5. 11 A Reactants Amount of energy released Energy Products

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. © 2012 Pearson Education, Inc.

Potential energy of molecules Figure 5. 11 B Products Energy Reactants Amount of energy required

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. © 2012 Pearson Education, Inc.

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. © 2012 Pearson Education, Inc.

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. © 2012 Pearson Education, Inc.

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. © 2012 Pearson Education, Inc.

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. © 2012 Pearson Education, Inc.

Figure 5. 12 A_s 1 ATP: Adenosine Triphosphate Phosphate group Adenine Ribose P P P

Figure 5. 12 A_s 2 ATP: Adenosine Triphosphate Phosphate group P P Adenine P Ribose Hydrolysis P ADP: H 2 O P Adenosine Diphosphate P Energy

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. © 2012 Pearson Education, Inc.

Figure 5. 12 B Chemical work Mechanical work Transport work ATP ATP Solute P Motor protein P P Reactants Membrane protein P Product Molecule formed ADP P Protein filament moved ADP P Solute transported ADP P

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. © 2012 Pearson Education, Inc.

Figure 5. 12 C ATP Energy from exergonic reactions ADP P Energy for endergonic reactions

HOW ENZYMES FUNCTION © 2012 Pearson Education, Inc.

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 (EA). © 2012 Pearson Education, Inc.

5. 13 Enzymes speed up the cell’s chemical reactions by lowering energy barriers § We can think of EA § 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. © 2012 Pearson Education, Inc.

Figure 5. 13 A Activation energy barrier Enzyme Activation energy barrier reduced by enzyme Reactant Energy Reactant Products Without enzyme Products With enzyme

Figure 5. 13 A_1 Activation energy barrier Energy Reactant Products Without enzyme

Figure 5. 13 A_2 Enzyme Activation energy barrier reduced by enzyme Energy Reactant Products With enzyme

Figure 5. 13 Q Energy a b Reactants c Products Progress of the reaction

5. 13 Enzymes speed up the cell’s chemical reactions by lowering energy barriers § Enzymes § function as biological catalysts by lowering the EA 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 © 2012 Pearson Education, Inc.

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. © 2012 Pearson Education, Inc.

5. 14 A specific enzyme catalyzes each cellular reaction § The following figure illustrates the catalytic cycle of an enzyme. © 2012 Pearson Education, Inc.

Figure 5. 14_s 1 1 Enzyme available with empty active site Active site Enzyme (sucrase)

Figure 5. 14_s 2 1 Enzyme available with empty active site Active site Substrate (sucrose) 2 Enzyme (sucrase) Substrate binds to enzyme with induced fit

Figure 5. 14_s 3 1 Enzyme available with empty active site Active site Substrate (sucrose) 2 Substrate binds to enzyme with induced fit Enzyme (sucrase) H 2 O 3 Substrate is converted to products

Figure 5. 14_s 4 1 Enzyme available with empty active site Active site Substrate (sucrose) 2 Glucose Substrate binds to enzyme with induced fit Enzyme (sucrase) Fructose H 2 O 4 Products are released 3 Substrate is converted to products

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 p. H for most enzymes is near neutrality. © 2012 Pearson Education, Inc.

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. © 2012 Pearson Education, Inc.

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. © 2012 Pearson Education, Inc.

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. © 2012 Pearson Education, Inc.

Figure 5. 15 A Substrate Active site Enzyme Allosteric site Normal binding of substrate Competitive inhibitor Noncompetitive inhibitor Enzyme inhibition

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. © 2012 Pearson Education, Inc.

Figure 5. 15 B Feedback inhibition Enzyme 1 B A Starting molecule Enzyme 2 Reaction 1 Reaction 2 Enzyme 3 C D Reaction 3 Product

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. © 2012 Pearson Education, Inc.

Figure 5. 16

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. © 2012 Pearson Education, Inc.

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. © 2012 Pearson Education, Inc.

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. © 2012 Pearson Education, Inc.

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. © 2012 Pearson Education, Inc.

Figure 5. UN 01 Passive transport (requires no energy) Diffusion Facilitated diffusion HIgher solute concentration Active transport (requires energy) Osmosis HIgher free water concentration HIgher solute concentration Solute Water Lower solute concentration Lower free water concentration ATP Lower solute concentration

Figure 5. UN 02 ATP cycle Energy from exergonic reactions ATP ADP P Energy for endergonic reactions

Figure 5. UN 03 Molecules cross cell membranes by by passive transport may be (a) moving down moving against requires ATP (b) uses diffusion of (c) (d) uses of polar molecules and ions (e)

Figure 5. UN 04 c. b. a. d. f. e.

Table 5. UN 05

Rate of reaction Figure 5. UN 06 0 1 2 3 4 p. H 5 6 7 8 9 10