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Chapter 5 The working cell
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Energy and your cells Thermodynamics
First law Second law Most energy on earth arises from the sun Cycled via producers, consumers and decomposers
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Energy Exergonic Endergonic
Releases energy Endergonic Intakes energy (required energy) These reactions are coupled in “energy coupling” where exergonic reactions drive endergonic reactions
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Cellular energy Forms Energy of cells is ATP Kinetic Potential
Energy lies in covalent bonds between P groups
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ATP Drives reactions via phosphorylation
Accepts E released by reactions and delivers to reactions that require E
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ATP P groups are negatively charged and crowded together
E stored in bonds between P Released P goes to another molecule Transfer of P = phosphorylation Repulsion creates unstable bonds Broken via hydrolysis reaction
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As bonds break, E released
ATP As bonds break, E released As bonds form, E stored
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Begin a chemical reaction
Activation Energy- E to begin a reaction Energy of activation (EA) Enzymes can lower EA EA barrier Reactants Products 1 2 Enzyme
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Enzymes Molecules that catalyze reactions Substrate specific
Generally proteins Not consumed by the reaction Substrate specific Active sites where substrate binds
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Enzymes help begin chemical reactions
Enzymes that lower EA are catalysts Decrease the EA needed to begin a reaction Reactants EA without enzyme EA with enzyme Net change in energy Products Energy Progress of the reaction
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Active sites fit only specific substrates
Specificity Specific enzymes catalyze specific reactions Shape determines which chemical reaction an enzyme catalyzes Substrate Specific reactant an enzyme acts upon Active site Region of enzyme where substrate fits Active sites fit only specific substrates
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How Enzymes Catalyze Reactions
1 Enzyme available with empty active site Substrate (sucrose) Active site Substrate binds to enzyme with induced fit Enzyme (sucrase) Glucose 4 Products are released Fructose H2O 3 Substrate is converted to products Figure 5.6
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Factors Influence Enzymes
Temperature, pH, salinity Affect shape of the enzyme Optimal temperature Cofactors Non-protein “helper” Inorganic Ex: zinc, iron, copper Coenzyme Organic Ex: vitamin
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Inhibitors Interfere with an Enzyme’s Activity
Competitive inhibitor Noncompetitive inhibitor Feedback inhibition Substrate Enzyme Active site Normal binding of substrate Enzyme inhibition Noncompetitive inhibitor Competitive inhibitor
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Inhibitors Interfere with an Enzyme’s Activity
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Phospholipid bilayer Selectively permeable Imbedded proteins
Fluid mosaic of phospholipids and proteins Water Hydrophilic heads Hydrophobic tails
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Membrane Proteins Structural Cell-cell recognition Junction forming
Receptors Enzymes Signal transduction Transport
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Functions of membrane proteins
ATP Messenger molecule Receptor Activated molecule Enzymes Receptors for messages Transport of substances
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The membrane is a fluid mosaic of phospholipids and proteins
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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Mechanisms to cross Diffuse directly across plasma membrane
Restricted by size, polarity Transport proteins Act as “channels” to assist molecules in crossing the membrane Specific
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In and Out of Cells Diffusion Passive transport Concentration gradient
Equilibrium Membrane Molecules of dye
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Crossing the membrane Diffusion Speed of diffusion depends on
Movement of molecule down a concentration gradient Speed of diffusion depends on Size of molecule Temperature Strength of gradient Charge Pressure
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Plasma membrane (lipid bilayer)
Lipids Plasma membrane (lipid bilayer) Lipids, such as these yellow molecules, can dissolve in the lipid bilayer. Notice how they move down their concentration gradient -- from where they are more concentrated to where they are less concentrated. This is an example of diffusion. Diffusion is a form of passive transport -- it does not require energy from the cell.
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In and Out of Cells Facilitated diffusion
Small nonpolar molecules diffuse easily across the membrane Larger or polar molecules do not easily diffuse Transport proteins provide passage across membranes Solute molecule Transport protein
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Mechanisms to cross Facilitated diffusion
Solute diffusion driven by concentration gradient Aided by transport protein
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Fructose Plasma membrane Transport protein
Most molecules can’t cross the lipid bilayer. Here, the sugar fructose moves into intestinal cells by facilitated diffusion, moving down its concentration gradient through a transport protein. Facilitated diffusion doesn’t require energy from the cell, so it’s also a form of passive transport. Transport protein
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In and Out of Cells Osmosis Diffusion of water across a membrane
Water travels from a solution of lower solute concentration to one of higher solute concentration Solute molecule H2O Selectively permeable membrane Water molecule Solute molecule with cluster of water molecules Net flow of water
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Crossing the membrane Osmosis
Turgor- pressure a volume of fluid exerts against a barrier Osmotic pressure- amount of turgor to stop water from diffusing
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Plasma membrane Transport protein Water molecules
Water crosses the plasma membrane by facilitated diffusion or by diffusing across the lipid bilayer directly. The diffusion of water across a membrane is called osmosis. Transport protein Water molecules
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Balance Tonicity Isotonic Hypotonic Hypertonic
Relative concentration of solutes in two fluids separated by a selectively permeable membrane Isotonic Concentration of solutes are the same Hypotonic Fluid with lower concentration of solutes Hypertonic Fluid with higher concentration of solutes
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Balance Water balance between cells and their surroundings is crucial to organisms Osmosis causes cells to shrink in hypertonic solutions and swell in hypotonic solutions 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 Cells will always have a certain amount of solutes. With there is more in solution (outside of the cell) water flows out to “dilute” outside concentration. Figure 5.17
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Balance
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In and Out of Cells Active transport Requires input of energy (ATP)
Transport proteins move solutes against their concentration gradient P Protein changes shape Phosphate detaches ATP ADP Solute Transport protein Solute binding 1 Phosphorylation 2 Transport 3 Protein reversion 4
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Mechanisms to cross Active transport
Transporting molecules against their gradient Required input of energy
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Mechanisms to cross Cotransporters Active transport
Move 2 substances at the same time
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In and Out of Cells Exocytosis and endocytosis transport large molecules Exocytosis Export material from cell Endocytosis Take into cell Fluid outside cell Cytoplasm Protein Vesicle Figure 5.19A
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Types of Endocytosis Phagosytosis Pinocytosis
Cellular “eating” Pinocytosis Cellular “drinking” Receptor-mediated endocytosis Specific molecules
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Videos Enzymes Cell membrane/transport Endo/exocytosis Receptor-mediated endocytosis Active transport Passive transport
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