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The Working Cell: G: Membrane Transport & H: Enzymes
The Working Cell: G: Membrane Transport & H: Enzymes Chapter 5
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Standards Unit G: Membrane Transport
I can recognize the fluid mosaic model and accurately identify and describe the function of the components. I can compare and contrast the various ways substances cross the cell membrane. I can recognize the various ways substances cross the membrane and provide examples from the human body for each. I can predict changes to a cell mass and size placed in solutions of differing concentrations I can use data to create a graph to show the relationship between concentration and mass. I can use a graph to extrapolate the concentration that is isotonic to a cell.
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MEMBRANE STRUCTURE AND FUNCTION
Crash Course: Membranes and Transport 5.10 Membranes organize the chemical activities of cells Membranes provide structural order for metabolism The plasma membrane of the cell is selectively permeable controlling the flow of substances into or out of the cell Cytoplasm Outside of cell TEM 200,000
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5.11 Membrane phospholipids form a bilayer
Figure 5.11A 5.11 Membrane phospholipids form a bilayer Phospholipids Have a hydrophilic head and two hydrophobic tails and are the main structural components of membranes Phospholipids form a two-layer sheet called a phospholipid bilayer, with the heads facing outward and the tails facing inward CH2 CH3 CH N + O O– P C Phosphate group Symbol Hydrophilic head Hydrophobic tails Water Hydrophilic heads Hydrophobic tails Figure 5.11B
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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 where the phospholipids are constantly moving and shifting (FLUID) Membrane proteins are located studded within the membrane giving it a mosaic appearance (MOSAIC) Figure 5.12 Fibers of the extracellular matrix Carbohydrate (of glycoprotein) Glycoprotein Microfilaments of cytoskeleton Phospholipid Cholesterol Proteins Plasma membrane Glycolipid Cytoplasm
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5.13 Proteins make the membrane a mosaic of functions
Many membrane proteins function as enzymes Other membrane proteins function as receptors for chemical messages from other cells Membrane proteins also function in transport moving substances across the membrane ATP Messenger molecule Receptor Activated molecule Figure 5.13A Figure 5.13B Figure 5.13C
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5.14 Passive transport is diffusion across a membrane
In passive transport, substances diffuse through membranes without work (energy) by the cell spreading from areas of high concentration to areas of low concentration Small nonpolar molecules such as O2 and CO2 diffuse easily across the phospholipid bilayer of a membrane Equilibrium Membrane Molecules of dye Figure 5.14A Figure 5.14B
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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 Solute molecule Transport protein Figure 5.15
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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 Why would water move in this direction? 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
The control of water balance is called osmoregulation Osmosis causes cells to shrink in hypertonic solutions and swell in hypotonic solutions In hypertonic solutions animals cells are shriveled and plants cells are plasmolyzed – why does this happen? In hypotonic solutions animal cells burst/lysis and plant cells are in turgid (their ideal state) – why does this happen? In isotonic solutions animal cells are normal, but plant cells are limp – why?? 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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5.18 Cells expend energy for active transport
Transport proteins can move solutes against a concentration gradient through active transport, which requires ATP 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
To move large molecules or particles through a membrane A vesicle may fuse with the 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 three 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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CONNECTION 5.20 Faulty membranes can overload the blood with cholesterol LDL – Low-density lipoproteins – receptor mediated endocytosis Harmful levels of cholesterol can accumulate in the blood if membranes lack cholesterol receptors hypercholesterolemia LDL particle Protein Phospholipid outer layer Cytoplasm Receptor protein Plasma membrane Vesicle Cholesterol Figure 5.20
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Standards Unit H: Enzymes
I can relate the function of thyroxin to metabolism. I can use words and models to show the lock and key function of enzymes. I can describe how co-enzymes and co-factors assist enzymes. I can explain how enzymes help our metabolic reactions to occur I can model/show how thyroxin production is regulated. I can relate protein structure to the denaturation of enzymes and provide examples of conditions that cause denaturation. I can represent the rate of enzyme activity graphically.
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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 The light comes from a set of chemical reactions that occur in light-producing organs at the rear of the insect 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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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 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 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 Cells carry out thousands of chemical reactions the sum of which constitutes cellular metabolism Energy coupling uses exergonic reactions to fuel endergonic reactions Reactants Energy released Products Amount of energy released Potential energy of molecules Figure 5.3B
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5.4 ATP shuttles chemical energy and drives cellular work
ATP powers nearly all forms of cellular work The energy in an ATP molecule lies in the bonds between its phosphate groups Phosphate groups ATP Energy P Hydrolysis Adenine Ribose H2O Adenosine diphosphate Adenosine Triphosphate + ADP Figure 5.4A
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ATP drives endergonic reactions by phosphorylation, transferring a phosphate 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 because ATP is a renewable resource that cells regenerate
ADP + P Energy for endergonic reactions Energy from exergonic reactions Phosphorylation Hydrolysis Figure 5.4C
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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 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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Bozeman: Enzymes
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HOW ENZYMES FUNCTION 5.5 Enzymes speed up the cell’s chemical reactions by lowering energy barriers 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 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 non-protein cofactors such as metal ions or organic molecules called coenzymes
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Normal binding of substrate
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 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 EX: Cyanide is a inhibitor in the cellular respiration reaction in the mitochondria. It causes a build-up of O2 in the blood and ultimately results in suffocation
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