Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings PowerPoint Lectures for Biology: Concepts and Connections, Fifth Edition – Campbell, Reece, Taylor, and Simon Lectures by Chris Romero Chapter 5 The Working Cell

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings ENERGY AND THE CELL 5.1 Energy is the capacity to perform work Energy is defined as the capacity to do work Life depends on the fact that energy can be converted from one form to another – Kinetic energy is the energy of motion Heat and light are forms of kinetic energy

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Potential energy is stored energy that is dependent on an object's location or structure – The most important potential energy for living things is the chemical energy stored in molecules – Potential energy can be converted to kinetic energy Animation: Energy Concepts Animation: Energy Concepts

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 5.2 Two laws govern energy transformations Thermodynamics is the study of energy transformations The First Law of Thermodynamics – Energy can be changed from one form to another but cannot be created or destroyed The Second Law of Thermodynamics – Energy transformations increase disorder, or entropy, and some energy is lost as heat

LE 5-2b Heat Glucose Oxygen Chemical reactions ATP Energy for cellular work Carbon dioxide Water

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 5.3 Chemical reactions either store or release energy Endergonic reactions – Require an input of energy from the surroundings – Yield products rich in potential energy – Example: photosynthesis

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LE 5-3a Reactants Products Amount of energy required Potential energy of molecules Energy required

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Exergonic reactions – Release energy – Yield products that contain less potential energy than their reactants – Examples: cellular respiration, burning

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

LE 5-3b Energy released Potential energy of molecules Reactants Products Amount of energy released

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Cells carry out thousands of chemical reactions, which constitute cellular metabolism Energy coupling uses energy released from exergonic reactions to drive endergonic reactions

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 5.4 ATP shuttles chemical energy and drives cellular work ATP (adenosine triphosphate) powers nearly all forms of cellular work ATP is composed of one adenine, one ribose, and three negatively charged phosphates The energy in an ATP molecule lies in the bonds between its phosphate groups

LE 5-4a AdenosineTriphosphate Phosphate group PPP H2OH2O Hydrolysis ATP ADP Ribose Adenine Adenosine diphosphate PPP Energy 

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings ATP powers cellular work through coupled reactions – The bonds connecting the phosphate groups are broken by hydrolysis, an exergonic reaction – Hydrolysis is coupled to an endergonic reaction through phosphorylation A phosphate group is transferred from ATP to another molecule

LE 5-4b ATP Chemical work Mechanical workTransport work P P P P P P P ADP  Reactants Product Molecule formed Protein moved Solute transported Motor protein Membrane protein Solute

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Cellular work can be sustained, because ATP is a renewable resource that cells regenerate – The ATP cycle involves continual phosphorylation and hydrolysis

LE 5-4c Energy from exergonic reactions ATP ADP  P Energy for endergonic reactions Hydrolysis Phosphoylation

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings HOW ENZYMES FUNCTION 5.5 Enzymes speed up the cell's chemical reactions by lowering energy barriers Energy of activation – Amount of energy that must be input before an exergonic reaction will proceed (the energy barrier)

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Enzymes – Proteins that function as biological catalysts Increase the rate of a reaction without themselves being changed – An enzyme can decrease the energy of activation needed to begin a reaction

LE 5-5b Reactants Net change in energy E A without enzyme Products Progress of the reaction Energy E A with enzyme

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 5.6 A specific enzyme catalyzes each cellular reaction Each enzyme has a unique three-dimensional shape that determines which chemical reaction it catalyzes – Substrate: a specific reactant that an enzyme acts on – Active site: A pocket on the enzyme surface that the substrate fits into

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings – Induced fit: The way the active site changes shape to "embrace" the substrate A single enzyme may act on thousands or millions of substrate molecules per second Animation: How Enzymes Work Animation: How Enzymes Work

LE 5-6 Enzyme available with empty active site Active site Glucose Fructose Products are released Enzyme (sucrase) Substrate (sucrose) H2OH2O Substrate is converted to products Substrate binds to enzyme with induced fit

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 5.7 The cellular environment affects enzyme activity Physical factors influence enzyme activity – Temperature, salt concentration, pH Some enzymes require nonprotein cofactors – Metal ions, organic molecules called coenzymes

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 5.8 Enzyme inhibitors block enzyme action Inhibitors interfere with an enzyme's activity – 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 – In feedback inhibition, enzyme activity is blocked by a product of the reaction catalyzed by the enzyme

LE 5-8 Substrate Enzyme Active site Normal binding of substrate Competitive inhibitor Noncompetitive inhibitor Enzyme inhibition

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings CONNECTION 5.9 Many poisons, pesticides, and drugs are enzyme inhibitors Cyanide inhibits an enzyme involved with ATP production during cellular respiration Some pesticides irreversibly inhibit an enzyme crucial for insect muscle function Many antibiotics inhibit enzymes essential for disease-causing bacteria Ibuprofen and aspirin inhibit enzymes involved in inducing pain

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings MEMBRANE STRUCTURE AND FUNCTION 5.10 Membranes organize the chemical activities of cells Membranes provide structural order for metabolism – Form most of the cell's organelles – Compartmentalize chemical reactions The plasma membrane forms a boundary between a living cell and its surroundings – Exhibits selective permeability – Controls traffic of molecules in and out

LE 5-10 Outside of cell Cytoplasm

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 5.11 Membrane phospholipids form a bilayer Phospholipids are the main structural components of membranes – Two nonpolar hydrophobic fatty acid "tails" – One phosphate group attached to the hydrophilic glycerol "head"

LE 5-11a Hydrophilic head Phosphate group Symbol Hydrophobic tails

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings In membranes, phospholipids form a bilayer – Two-layer sheet – Phospholipid heads facing outward and tails facing inward – Selectively permeable Polar lipid-soluble molecules pass through Nonpolar molecules not soluble in lipids do not pass through

LE 5-11b Hydrophilic heads Hydrophobic tails Water

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 5.12 The membrane is a fluid mosaic of phospholipids and proteins A membrane is a mosaic – Proteins and other molecules are embedded in a framework of phospholipids A membrane is fluid – Most protein and phospholipid molecules can move laterally Membrane glycoproteins and glycolipids function in cell identification

LE 5-12 Extracellular matrix Glycoprotein Carbohydrate Plasma membrane Microfilaments of cytoskeleton Phospholipid Cholesterol Proteins Cytoplasm Glycolipid

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 5.13 Proteins make the membrane a mosaic of function Proteins perform most membrane functions – Identification tags – Junctions between adjacent cells – Enzymes – Receptors of chemical messages from other cells (signal transduction) – Transporters of substances across the membrane

LE 5-13a Enzyme activity

LE 5-13b Messenger molecule Receptor Activated molecule Signal transduction

LE 5-13c Transport ATP

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Animation: Membrane Selectivity Animation: Membrane Selectivity

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 5.14 Passive transport is diffusion across a membrane Diffusion is the tendency for particles to spread out evenly in an available space – From an area of high concentration to an area of low concentration Passive transport across membranes occurs when a molecule diffuses down a concentration gradient Small nonpolar molecules such as O 2 and CO 2 diffuse easily across the phospholipid bilayer of a membrane

LE 5-14a Molecules of dye Membrane Equilibrium

LE 5-14b Equilibrium

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Animation: Diffusion Animation: Diffusion

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 5.15 Transport proteins may facilitate diffusion across membranes In facilitated diffusion – Transport proteins that span the membrane bilayer help substances diffuse down a concentration gradient To transport the substance, a transport protein may – Provide a pore for passage – Bind the substance, change shape, and then release the substance

LE 5-15 Solute molecule Transport protein

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 5.16 Osmosis is the diffusion of water across a membrane In osmosis water, molecules diffuse across a selectively permeable membrane – From an area of low solute concentration – To an area of high solute concentration – Until the solution is equally concentrated on both sides of the membrane The direction of movement is determined by the difference in total solute concentration – Not by the nature of the solutes Animation: Osmosis Animation: Osmosis

LE 5-16 Water molecule Selectively permeable membrane Solute molecule H2OH2O Lower concentration of solute Higher concentration of solute Equal concentration of solute Solute molecule with cluster of water molecules Net flow of water

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 5.17 Water balance between cells and their surroundings is crucial to organisms Osmoregulation is the control of water balance Tonicity is the tendency of a cell to lose or gain water in solution – Isotonic solution: solute concentration is the same in the cell and in the solution No osmosis occurs Animal cell volume remains constant; plant cell becomes flaccid

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings – Hypotonic solution: solute concentration is greater in the cell than in the solution Cell gains water through osmosis Animal cell lyses; plant cell becomes turgid – Hypertonic solution: solute concentration is lower in the cell than in the solution Cell loses water through osmosis Animal cell shrivels; plant cell plasmolyzes

LE 5-17 Isotonic solution Hypotonic solution Hypertonic solution H2OH2O H2OH2O (1) Normal (2) Lysed H2OH2O H2OH2O H2OH2O H2OH2O Animal cell Plant cell (4) Flaccid(5) Turgid(6) Shriveled (plasmolyzed) (3) Shriveled Plasma membrane H2OH2O H2OH2O

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Video: Plasmolysis Video: Plasmolysis Video: Turgid Elodea Video: Turgid Elodea

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 5.18 Cells expend energy for active transport Active transport requires energy to move solutes against a concentration gradient – ATP supplies the energy – Transport proteins move solute molecules across the membrane Animation: Active Transport Animation: Active Transport

LE 5-18 Transport protein Solute ATP P ADP Protein changes shape P Solute bindingPhosphorylation Transport Protein reversion Phosphate detaches P

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 5.19 Exocytosis and endocytosis transport large molecules To move large molecules or particles through a cell membrane – A vesicle may fuse with the membrane and expel its contents outside the cell (exocytosis) – Membranes may fold inward, enclosing material from the outside (endocytosis)

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 5.19 Exocytosis and endocytosis transport large molecules To move large molecules or particles through a cell membrane – A vesicle may fuse with the membrane and expel its contents outside the cell (exocytosis) – Membranes may fold inward, enclosing material from the outside (endocytosis)

LE 5-19a Vesicle Fluid outside cell Protein Cytoplasm

LE 5-19b Vesicle forming

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Endocytosis can occur in three ways – Phagocytosis ("cell eating") – Pinocytosis ("cell drinking") – Receptor-mediated endocytosis

LE 5-19c Pseudopodium of amoeba Phagocytosis Plasma membrane Food being ingested Material bound to receptor proteins PIT Cytoplasm Receptor-mediated endocytosis TEM 54,000  TEM 96,500  LM 230  Pinocytosis

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Animation: Receptor-Mediated Endocytosis Animation: Receptor-Mediated Endocytosis Animation: Exocytosis and Endocytosis Introduction Animation: Exocytosis and Endocytosis Introduction Animation: Exocytosis Animation: Exocytosis Animation: Pinocytosis Animation: Pinocytosis Animation: Phagocytosis Animation: Phagocytosis

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings CONNECTION 5.20 Faulty membranes can overload the blood with cholesterol Cholesterol is carried in the blood by low- density lipoprotein (LDL) particles Normally, body cells take up LDLs by receptor- mediated endocytosis Harmful levels of cholesterol can accumulate in the blood if membranes lack cholesterol receptors – People with hypercholesterolemia have more than twice the normal level of blood cholesterol

LE 5-20 Phospholipid outer layer LDL particle Cholesterol Protein Plasma membrane Receptor protein Vesicle Cytoplasm