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Chapter 5 The Working Cell
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Cool “Fires” Attract Mates and Meals
Fireflies use light to send signals to potential mates Instead of using chemical signals like most other insects
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The light comes from a set of chemical reactions
That occur in light-producing organs at the rear of the insect
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Females of some species
Produce a light pattern that attracts males of other species, which are then eaten by the female
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5.4 ATP shuttles chemical energy, drives cellular work
powers nearly all forms of cellular work
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Adenosine diphosphate Adenosine Triphosphate
energy in ATP molecule in bonds between phosphate groups Phosphate groups ATP Energy P Hydrolysis Adenine Ribose H2O Adenosine diphosphate Adenosine Triphosphate + ADP Figure 5.4A
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drives endergonic reactions by phosphorylation
Transferring P group to make molecules more reactive ATP Chemical work Mechanical work Transport work P Molecule formed Protein moved Solute transported ADP + Product Reactants Motor protein Membrane protein Solute Figure 5.4B
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Cellular work can be sustained
B/C ATP is a renewable resource that cells regenerate ATP ADP + P Energy for endergonic reactions Energy from exergonic reactions Phosphorylation Hydrolysis Figure 5.4C
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MEMBRANE STRUCTURE AND FUNCTION
5.10 Membranes organize chemical activities of cells Provide structural order for metabolism
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plasma membrane - selectively permeable
Controlling flow of substances into/out of cell Cytoplasm Outside of cell TEM 200,000 Figure 5.10
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5.11 Membrane phospholipids form a bilayer
hydrophilic head 2 hydrophobic tails main structural components of membranes CH2 CH3 CH N + O O– P C Phosphate group Symbol Hydrophilic head Hydrophobic tails Figure 5.11A
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Phospholipids form a two-layer sheet phospholipid bilayer
heads facing outward; tails facing inward Water Hydrophilic heads Hydrophobic tails Figure 5.11B
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5.12 membrane is a fluid mosaic
proteins and other molecules embedded in a phospholipid bilayer Fibers of the extracellular matrix Carbohydrate (of glycoprotein) Glycoprotein Microfilaments of cytoskeleton Phospholipid Cholesterol Proteins Plasma membrane Glycolipid Cytoplasm Figure 5.12
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5.13 Proteins make the membrane function
Many Function as enzymes Figure 5.13A
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Other membrane proteins
Function as receptors for chemical messages from other cells Messenger molecule Receptor Activated molecule Figure 5.13B
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Membrane proteins also function in transport
Moving substances across the membrane ATP Figure 5.13C
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COOL ONLINE VIDEO OF MEMBRANE TRANSPORT!
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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 Equilibrium Membrane Molecules of dye Figure 5.14A Figure 5.14B
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Small nonpolar molecules such as O2 and CO2
Diffuse easily across the phospholipid bilayer of a membrane
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5.15 Transport proteins may facilitate diffusion across membranes
Many molecules Do not diffuse freely across membranes transport proteins Provide passage across membranes: facilitated diffusion Solute molecule Transport protein Figure 5.15
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5.16 Osmosis is the diffusion of water across a membrane
Water travels from a solution of lower solute concentration to one of higher solute concentration Lower concentration of solute Higher concentration of solute Equal concentration of solute H2O Solute molecule Selectively permeable membrane Water molecule Solute molecule with cluster of water molecules Net flow of water Figure 5.16
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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 Plant cell H2O Plasma membrane (1) Normal (2) Lysed (3) Shriveled (4) Flaccid (5) Turgid (6) Shriveled (plasmolyzed) Isotonic solution Hypotonic solution Hypertonic solution Animal cell Figure 5.17
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osmoregulation The control of water balance
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5.18 Cells expend energy for active transport
Transport proteins can move solutes against a concentration gradient requires ATP Na/K PUMP animation P Protein changes shape Phosphate detaches ATP ADP Solute Transport protein Solute binding 1 Phosphorylation 2 Transport 3 Protein reversion 4 Figure 5.18
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5.19 Exocytosis and endocytosis transport large molecules
move lg molecules/particles thru membrane vesicle may fuse w/membrane and expel its contents (exocytosis) Fluid outside cell Cytoplasm Protein Vesicle Figure 5.19A
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Membranes may fold inward
Enclosing material from the outside (endocytosis) Vesicle forming Figure 5.19B
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Endocytosis can occur in 3 ways Phagocytosis Pinocytosis
Receptor-mediated endocytosis Pseudopodium of amoeba Food being ingested Phagocytosis Pinocytosis Receptor-mediated endocytosis Material bound to receptor proteins PIT Cytoplasm Plasma membrane TEM 54,000 TEM 96,500 LM 230 Figure 5.19C
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CELL OVERVIEW: DISCOVERY CLIP
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5.1 Energy is the capacity to perform work
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
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Kinetic energy is the energy of motion
Potential energy is stored energy And can be converted to kinetic energy Figure 5.1A–C
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5.2 Two laws govern energy transformations
Thermodynamics Is the study of energy transformations
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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
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Energy for cellular work
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
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5.3 Chemical reactions either store or release energy
Endergonic reactions Absorb energy and yield products rich in potential energy Potential energy of molecules Reactants Energy required Products Amount of energy required Figure 5.3A
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Exergonic reactions Release energy and yield products that contain less potential energy than their reactants Reactants Energy released Products Amount of energy released Potential energy of molecules Figure 5.3B
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Cells carry out thousands of chemical reactions
The sum of which constitutes cellular metabolism Energy coupling Uses exergonic reactions to fuel endergonic reactions
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HOW ENZYMES FUNCTION 5.5 Enzymes speed up the cell’s chemical reactions by lowering energy barriers
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For a chemical reaction to begin
Reactants must absorb some energy, called the energy of activation EA barrier Reactants Products 1 2 Enzyme Figure 5.5A
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Progress of the reaction
A protein catalyst called an enzyme Can decrease the energy of activation needed to begin a reaction Reactants EA without enzyme EA with enzyme Net change in energy Products Energy Progress of the reaction Figure 5.5B
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5.6 A specific enzyme catalyzes each cellular reaction
Enzymes have unique three-dimensional shapes That determine which chemical reactions occur in a cell
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The catalytic cycle of an enzyme
1 Enzyme available with empty active site Active site Substrate (sucrose) 2 Substrate binds to enzyme with induced fit Enzyme (sucrase) Glucose Fructose H2O 4 Products are released 3 Substrate is converted to products Figure 5.6
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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
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5.8 Enzyme inhibitors block enzyme action
Inhibitors interfere with an enzyme’s activity
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Normal binding of substrate
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 Substrate Enzyme Active site Normal binding of substrate Enzyme inhibition Noncompetitive inhibitor Competitive inhibitor Figure 5.8
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CONNECTION 5.9 Many poisons, pesticides, and drugs are enzyme inhibitors
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5.20 Faulty membranes can overload the blood with cholesterol
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 LDL particle Protein Phospholipid outer layer Cytoplasm Receptor protein Plasma membrane Vesicle Cholesterol Figure 5.20
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5.21 Chloroplasts and mitochondria make energy available for cellular work
Enzymes are central to the processes that make energy available to the cell
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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
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