Chapter 5 The working cell

Cellular energy Forms – Kinetic – Potential Energy of cells is ATP – Energy lies in covalent bonds between P groups

Energy Exergonic – Releases energy Endergonic – Intakes energy (required energy) These reactions are coupled in “energy coupling” where exergonic reactions drive endergonic reactions

ATP Chemical work Mechanical work Transport work P P P P P P P Molecule formedProtein moved Solute transported ADP + Product Reactants Motor protein Membrane protein Solute + ATP Drives reactions via phosphorylation – Transfer of a phosphate group to make molecules more reactive Figure 5.4B

ATP P groups are negatively charged and crowded together – Repulsion creates unstable bonds – Broken via hydrolysis reaction – As bonds break, 1 P leaves and ATP becomes ADP & energy is released Released P goes to another molecule – Transfer of P = phosphorylation

Begin a chemical reaction Reactants must absorb some energy – Energy of activation (E A ) – Enzymes can lower E A E A barrier Reactants Products 12 Enzyme

Enzymes help begin chemical reactions Enzymes that lower E A are catalysts – Decrease the E A needed to begin a reaction Reactants E A without enzyme E A with enzyme Net change in energy Products Energy Progress of the reaction

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

Figure 5.6 Enzyme (sucrase) Glucose Fructose Active site Substrate (sucrose) H2OH2O 1 Enzyme available with empty active site Substrate binds to enzyme with induced fit 4 Products are released 3 Substrate is converted to products How Enzymes Catalyze Reactions

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

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

Phospholipid bilayer Selectively permeable Imbedded proteins – Fluid mosaic of phospholipids and proteins Water Hydrophilic heads Hydrophobic tails

Membrane Proteins Structural Cell-cell recognition Junction forming Receptors Enzymes Signal transduction Transport

Functions of membrane proteins Messenger molecule Receptor Activated molecule ATP EnzymesReceptors for messagesTransport of substances

The membrane is a fluid mosaic of phospholipids and proteins Figure 5.12 Fibers of the extracellular matrix Carbohydrate (of glycoprotein) Glycoprotein Microfilaments of cytoskeleton Phospholipid Cholesterol Proteins Plasma membrane Glycolipid Cytoplasm

In and Out of Cells Diffusion Passive transport – Concentration gradient EquilibriumMembraneMolecules of dye Equilibrium

Plasma membrane (lipid bilayer) Lipids

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

Plasma membrane Fructose Transport protein

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 Selectively permeable membrane H2OH2O Solute molecule Water molecule Net flow of water Solute molecule with cluster of water molecules

Plasma membrane Transport protein Water molecules

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 Figure 5.17 Plant cell H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O Plasma membrane (1) Normal (2) Lysed (3) Shriveled (4) Flaccid (5) Turgid (6) Shriveled (plasmolyzed) Isotonic solution Hypotonic solution Hypertonic solution Animal cell

P P P Protein changes shape Phosphate detaches ATP ADP Solute Transport protein Solute binding1Phosphorylation2 Transport 3 Protein reversion4 In and Out of Cells Cells expend energy for active transport – Transport proteins can move solutes against concentration gradient Figure 5.18

Fluid outside cell Cytoplasm Protein Vesicle In and Out of Cells Exocytosis and endocytosis transport large molecules – Exocytosis Export material from cell – Endocytosis Take into cell Figure 5.19A

Types of Endocytosis Phagosytosis – Cellular “eating” Pinocytosis – Cellular “drinking” Receptor-mediated endocytosis – Specific molecules

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