VIEWS: 4 PAGES: 8 POSTED ON: 11/17/2011
The Working Cell ch 5 HOW CELLS USE ENERGY, ENZYMES and MEMBRANES Fire flies Glow: light energy attract mates attract prey Luciferase + ATP + Oxygen converts Luciferin into a chemical that emits energy. Enzymes control a cells chemical reactions by reducing the energy needed [activation energy EA] for a reaction to occur. SO FIREFLIES NEED ENERGY AND ENZYMES TO PRODUCE LIGHT. Energy capacity to do work Kinetic (motion) heat (molecular movement) light (powers photosynthesis Potential (position) chemical energy (arrangement of nuclei and electrons) ex. sugar E Transformations ------------> sugar protein nucleic acids lipids kinetic to potential --OR-- potential to kinetic Laws of Thermodynamics 1) 1st law _________E-transferred or transformed (but not created or destroyed) nd 2) 2 law __________E transfer or transformation makes universe more disordered (raises entropy) closed system--isolated from surrounding open system--E transferred between system and surroundings evolution of complex life forms from simple forms does not violate the second law. E taken from surroundings( raises entropy of universe) ex. *maintain highly ordered structure by raising entropy of environment *take in complex high energy molecules as food--extract energy (create, maintain order) *return to the environment simpler low energy molecules (CO + H O) and heat 2 2 Free Energy (Delta G) + ---------> + E -- Delta G + E -----------> +Delta G exergonic--products have less free energy than reactants endergonic--products have more free energy than reactants ATP and Cellular Work ATP--immediate source of energy mechanical work chromosome movement, mitosis/meiosis transport work chemical work Structure of ATP O- O- O- I I I adenine ribose --P--O~~~P--O~~~P--O-- II II II O O O unstable bonds H O + ATP ---------> ADP + P - G 7.3 K/cal / mol 2 How ATP Works ATP is hydrolyzed, the phosphate group is transferred to another molecule WHICH BECOMES MORE REACTIVE A--P---P---P A---P---P Glu + NH --------> Gln 3 Glu + ATP ---------> Glu-- + ADP Glu-- + NH ---------> Gln + P Making new ATP ADP + + E ---------> ATP from cell respiration) ATP used and regenerated continually by cells 7 10 molecules / sec / cell --------> --------> I I ENERGY I I -Delta G Delta G= 7.3 K/cal / mol + 7.3 K/cal / mol ATP and Cellular Work ATP--immediate source of energy mechanical work chromosome movement, mitosis/meiosis transport work chemical work Structure of ATP O- O- O- I I I adenine ribose --P--O~~~P--O~~~P--O-- II II II O O O unstable bonds H O + ATP ---------> ADP + P - G 7.3 K/cal / mol 2 Enzymes free E change indicates a reaction that is spontaneous from one that is not --Delta G spontaneous reactions may be too s l o w enzymes speed up and control rates catalyst--accelerates reaction without being permanently changed in the process, and can therefore be used over and over Enzymes---lower activation energy usually proteins very specific I I Transition state I Free I Energy I reactants I I --Delta G I products I__________________________________________________ progress of reaction------------------> Free I Transition state Energy I I products I I +Delta G I I I reactants I__________________________________________________ progress of reaction-------------------> Specificity of Enzymes substrate-the substance an enzyme acts on Enzyme + Substrate --------> Enzyme substrate complex----------> Product + Enzyme Active Site place on the enzyme where the substrate fits *pocket or groove *changes shape with contact by substrates *determines enzyme specificity induced fit-change in shape of active site induced by substrate [old “lock and key hypothesis”] Catalytic Cycle of Enzymes Step 1) substrate binds to active site H-bonds, ionic bonds Step 2) induced fit of active site around substrate side chains of a few A.A. catalyze conversion of substrate ----> product Step 3) product departs active site Lowering activation E / Speeding up reaction rate 1) active site properly aligns reactants so they may react (two or more reactants) 2) induced fit may distort the substrates’ chemical bonds; therefore, less E needed to form / break bonds 3) active site produces a micro environment conductive to a particular reaction (A.A. side chains) initial substrate concentration partly determines rate of reaction higher concentration--faster reaction (up to a limit) temp may affect the speed of a reaction if the substrate concentration is high enough enzyme is saturated (all sites filled) saturated--speed depends upon individual enzyme unsaturated--slower Factors affecting enzyme activity 1) enzymes have optimal conditions *Temperature greatest number of collisions without denaturing enzyme (35-40 most humans) 37 C 40 C 45 C *pH optimal pH for most enzymes is 6-8 (some exist for extremes--pepsin in stomach pH 2) pH 7 pH 3 2) Ionic concentration ions can interfere with ionic bonds within the enzyme (most enzymes can’t tolerate high salt) I I I I I I I I I I I I I I I I I I I I I I I I I_______________ _I I___ _____________I 2) Cofactors non-protein molecules required by many enzymes complete active site some inorganic Zn, Fe, Cu some organic--coenzymes (most vitamins) + -----------> vitamin C unable to catalyze able to catalyze 3) Inhibitors chemicals that selectively inhibit enzyme activity irreversible--inhibitor attaches with covalent bonds reversible--inhibitor attaches with weak bonds competitive inhibitors--chemicals that resemble the enzyme’s normal substrate, therefore compare for the active site *block active site *if reversible, can be overcome by a raise in substrate concentration antifreeze / ethanol non-competitive inhibitors--inhibitor does not enter active site, binds to another location *causes enzyme to change shape---active site altered <--active site (correct) <--active site (damaged) I I inhibitor DDT / many antibiotics penicillin--cell wall of bacteria selective activation substrates (won’t fit) substrates fit—reaction occurs selective inhibition and activation essential mechanisms for metabolic control Allosteric Regulation allosteric--specific receptor other than active site *two or more peptide chains *2 conformations active / inactive bind an activator--locks enzyme in the active shape active sites activator <=====> active inactive inhibitor concentrations of activators and inhibitors can control enzyme activity ex. ATP /ADP presence of ADP changes enzyme to ATP SYNTHESIS activity presence of ATP changes enzyme to inactivate further ATP SYNTHESIS cooperativity--substrate locks enzyme in active shape Control of Metabolism metabolism regulated by controlling enzyme activity feedback inhibition end product inhibits an enzyme within a pathway enzyme 1 2 3 4 5 threonine---> A ---> B ---> C ---> D---> isoleucine (end product--allosteric inhibitor of enzyme) /\ ______________________I prevents the cell from wasting chemical resources Multi-enzyme complex enzymes assembled for steps of a metabolic pathway within or along cell structures fixed on a membrane, dissolved within an organelle high salt Membrane Structure artificial membranes fluid mosaic model phospholipid bilayer embedded proteins some drift, some tethered unsaturated fatty acids and embedded cholesterol enhance fluidity proteins determine membrane function surface carbohydrates cell--cell recognition sorting cells into tissues bonded to protein / lipids membrane protein functions transport (ATP) enzymes cell-cell adhesion Traffic of small molecules selective permeability non-polar + O lipid 2 permeability small polar--H O, CO 2 2 large polar-glucose ions Na+, H+ transport proteins integral proteins, specific, receptor site avoids contact with lipid bilayer tunnels, physical movement anti port 2 solutes opposite direction Na+ Ca++ symport--2 solutes same time, same direction uniport single solute 1. diffusion and passive transport *concentration gradient *net movement *diffusion--movement down a concentration gradient random molecular motion, no ATP energy required *passive transport diffusion across a membrane 2. osmosis *diffusion-H O---across selectively permeable membrane 2 hyperosmotic solution hypoosomotic selectively permeable membrane solution osmotic pressure--amount of (energy) force needs to prevent H O movement 2 H O-------> until equilibrium reached water balance maintaining correct solute / H O concentrations 2 3. facilitated diffusion proteins help solutes cross a cell membrane transport proteins specific saturation possible inhibited by similar solutes do not catalyze reactions facilitated diffusion 4. active transport energy requiting against concentration gradient maintains strong gradients Na+, K+, Mg+, Ca+, Cl- sodium potassium pump _____________________________________ ion transport anions and cations unequally distributed across plasma membrane; voltages across the membrane membrane potential measured voltage range-50mv to -200mv (inside--compared to outside cell) this difference represents potential E ____________________________________ cotransport ATP powered pump transports one solute indirectly drives transport of two solutes against concentration gradient Transport of LARGE molecules exocytosis endocytosis
"CH 5 The working cell "