Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Energy and the Cell
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Living cells are compartmentalized by membranes Membranes are sites where chemical reactions can occur in an orderly manner Living cells process energy by means of enzyme-controlled chemical reactions ENERGY AND THE CELL
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Energy is defined as the capacity to do work All organisms require energy to stay alive Energy makes change possible Energy is the capacity to perform work
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Kinetic energyKinetic energy is energy that is actually doing work Potential energyPotential energy is stored energy
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings First law of thermodynamics Energy can be changed from one form to another –However, energy cannot be created or destroyed Two laws govern energy conversion
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Second law of thermodynamics Energy changes are not 100% efficient –Energy conversions increase disorder, or entropy –Some energy is always lost as heat
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Cells carry out thousands of chemical reactions –The sum of these reactions constitutes cellular metabolism Chemical reactions either store or release energy
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings There are two types of chemical reactions: –Endergonic reactions absorb energy and yield products rich in potential energy Reactants Potential energy of molecules Products Amount of energy INPUT
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings –Exergonic reactions release energy and yield products that contain less potential energy than their reactants Reactants Potential energy of molecules Products Amount of energy OUTPUT
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 10 Enzymes
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 11 What Are Enzymes? Proteins (Most enzymes are Proteins (tertiary and quaternary structures) CatalystAct as Catalyst to accelerates a reaction Not permanentlyNot permanently changed in the process
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 12 Enzymes catalyzeAre specific for what they will catalyze ReusableAre Reusable aseEnd in –ase-Sucrase-Lactase-Maltase
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 13 How do enzymes Work? weakening bonds which lowers activation energy Enzymes work by weakening bonds which lowers activation energy
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 14 Enzymes Free Energy Progress of the reaction Reactants Products Free energy of activation Without Enzyme With Enzyme
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 15 Enzyme-Substrate Complex substance enzyme substrate The substance (reactant) an enzyme acts on is the substrate Enzyme Substrate Joins
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 16 Active Site restricted region enzyme bindssubstrateA restricted region of an enzyme molecule which binds to the substrate. Enzyme Substrate Active Site
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 17 Induced Fit shapeA change in the shape of an enzyme’s active site InducedInduced by the substrate
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 18 What Affects Enzyme Activity? 1.Environmental Conditions 2.Enzyme Inhibitors
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Environmental Conditions 1. Extreme Temperature are the most dangerous 1. Extreme Temperature are the most dangerous - high temps denature (unfold) enzyme. - high temps may denature (unfold) the enzyme. 2.pH (most like pH near neutral) 3.Ionic concentration (salt ions)
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 20 Enzyme Inhibitors a. Competitive inhibitors: resembleenzyme’s normal substrate compete active site a. Competitive inhibitors: are chemicals that resemble an enzyme’s normal substrate and compete with it for the active site. Enzyme Competitive inhibitor Substrate
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 21 Inhibitors b. Noncompetitive inhibitors: do not enter the active site bind to another part enzyme enzymechange its shape alters the active site Inhibitors that do not enter the active site, but bind to another part of the enzyme causing the enzyme to change its shape, which in turn alters the active site. Enzyme active site altered Noncompetitive Inhibitor Substrate
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Membranes organize the chemical reactions making up metabolism Membranes organize the chemical activities of cells MEMBRANE STRUCTURE AND FUNCTION Cytoplasm
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Membranes are selectively permeable –They control the flow of substances into and out of a cell Membranes can hold teams of enzymes that function in metabolism
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Phospholipids are the main structural components of membranes They each have a hydrophilic head and two hydrophobic tails Membrane phospholipids form a bilayer Head Symbol Tails
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings In water, phospholipids form a stable bilayer Hydrophilic heads Hydrophobic tails Water –The heads face outward and the tails face inward
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Phospholipid molecules form a flexible bilayer –Cholesterol and protein molecules are embedded in it –Carbohydrates act as cell identification tags The membrane is a fluid mosaic of phospholipids and proteins
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The plasma membrane of an animal cell Fibers of the extracellular matrix Glycoprotein Carbohydrate (of glycoprotein) Microfilaments of the cytoskeleton Phospholipid Cholesterol Proteins CYTOPLASM Glycolipid
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Some membrane proteins form cell junctions Others transport substances across the membrane Proteins make the membrane a mosaic of function Transport
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Many membrane proteins are enzymes Some proteins function as receptors for chemical messages from other cells –The binding of a messenger to a receptor may trigger signal transduction Enzyme activitySignal transduction Messenger molecule Receptor Activated molecule
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings In passive transport, substances diffuse through membranes without work by the cell –They spread from areas of high concentration to areas of lower concentration Passive transport is diffusion across a membrane EQUILIBRIUM Molecule of dye Membrane EQUILIBRIUM
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings In osmosis, water travels from an area of lower solute concentration to an area of higher solute concentration Osmosis is the passive transport of water Hypotonic solution Solute molecule HYPOTONIC SOLUTION Hypertonic solution Selectively permeable membrane HYPERTONIC SOLUTION Selectively permeable membrane NET FLOW OF WATER Solute molecule with cluster of water molecules Water molecule
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Osmosis causes cells to shrink in a hypertonic solution and swell in a hypotonic solution –The control of water balance (osmoregulation) is essential for organisms Water balance between cells and their surroundings is crucial to organisms ISOTONIC SOLUTION HYPOTONIC SOLUTION HYPERTONIC SOLUTION (1) Normal (4) Flaccid (2) Lysing (5) Turgid (3) Shriveled (6) Shriveled ANIMAL CELL PLANT CELL Plasma membrane
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Small nonpolar molecules diffuse freely through the phospholipid bilayer Many other kinds of molecules pass through selective protein pores by facilitated diffusion Transport proteins facilitate diffusion across membranes Solute molecule Transport protein
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Transport proteins can move solutes across a membrane against a concentration gradient –This is called active transport –Active transport requires ATP Cells expend energy for active transport
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Active transport in two solutes across a membrane Transport protein 1 FLUID OUTSIDE CELL First solute First solute, inside cell, binds to protein Phosphorylated transport protein 2 ATP transfers phosphate to protein 3 Protein releases solute outside cell 4 Second solute binds to protein Second solute 5 Phosphate detaches from protein 6 Protein releases second solute into cell
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings To move large molecules or particles through a membrane –a vesicle may fuse with the membrane and expel its contents (exocytosis) Exocytosis and endocytosis transport large molecules FLUID OUTSIDE CELL CYTOPLASM
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings –or the membrane may fold inward, trapping material from the outside (endocytosis)
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Three kinds of endocytosis Pseudopod of amoeba Food being ingested Plasma membrane Material bound to receptor proteins PIT Cytoplasm
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Harmful levels of cholesterol can accumulate in the blood if membranes lack cholesterol receptors Connection: Faulty membranes can overload the blood with cholesterol LDL PARTICLE Phospholipid outer layer Protein Cholesterol Plasma membrane CYTOPLASM Receptor protein Vesicle
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Enzymes and membranes 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 Chloroplasts and mitochondria make energy available for cellular work
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Nearly all the chemical energy that organisms use comes ultimately from sunlight Chemicals recycle among living organisms and their environment Sunlight energy Chloroplasts, site of photosynthesis CO 2 + H 2 O Glucose + O 2 Mitochondria sites of cellular respiration (for cellular work) Heat energy