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Chapter 6 - Ground Rules of Metabolism Ground Chapter 6...

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Unformatted text preview: Ground Rules of Metabolism Ground Chapter 6 What is energy? What Capacity to do work Types of energy Potential energy Kinetic energy Kinetic Kinetic Potential Potential Conversion of potential energy to kinetic energy and back again… kinetic Chemical Energy being Converted First Law of Thermodynamics: Conservation of Energy Conservation The total amount of energy in the universe remains constant Energy can undergo conversions from one form to another, but it cannot be created or destroyed Ultimately, all ends up as thermal energy (heat) One­Way Flow of Energy: Kinetic Energy (photons) to Chemical Energy During Photosynthesis Sunlight Energy in 12H2O WATER + 6CO2 6O2 CARBON DIOXIDE OXYGEN REACTANTS + C6H12O6 GLUCOSE + 6H2O WATER PRODUCTS The sun is life’s primary energy source Photoautotrophs trap energy from the sun and convert it into chemical bond energy (in glucose) Fig ure 2 .8 P a g e 2 5 One way flow of energy – remember it all ends up as heat? remember Second Law of Thermodynamics: Tendency Toward Maximum Entropy Tendency Entropy: Measure of degree of disorder, or randomness in a system High Entropy High Low Entropy – an investment of energy!!! energy!!! Entropy Entropy The world of life can exist despite the flow toward maximum entropy only because it is resupplied with energy from the sun Endergonic Reaction Endergonic Reaction needs an input of energy and products have more potential/chemical energy than the reactants did Exergonic Reaction Exergonic Reaction released energy, so products have less energy than the reactants did Figure 6.6a Page 101 Energy Releasing Reactions ATP Forms Energy Requiring Reactions Cellular Work Structure of ATP Structure nucleotide base (adenine) three phosphate groups sugar (ribose) Figure 6.6b Page 101 Catabolic and Anabolic Pathways Pathways large energy-rich molecules DEGRADATIVE PATHWAYS (CATABOLIC) ADP + Pi ATP energy-poor products BIOSYNTHETIC PATHWAYS (ANABOLIC) simple organic compounds Participants in Metabolic Pathways Metabolic Reactants Energy Carriers Intermediates Enzymes Products Cofactors (nonprotein or ion) Activation Energy Activation For a reaction to occur, an energy barrier must be surmounted Enzymes make the energy barrier smaller Figure 6.12a Page 105 starting substance activation energy without enzyme activation energy with enzyme energy released by the reaction products Catalase Catalase Four purple heme (iron­containing) groups Action of Catalase ONE degrades 40x106 H2O2 molecules per second! histidine hydrogen peroxide heme group Histidine and the heme group are both part of the catalase enzyme active site. Heme is a cofactor that is a prosthetic group. It is bonded to catalase. Stepped Art Figure 6.14 Page 107 Factors Influencing Enzyme Activity Factors Coenzymes (organic cofactor) and cofactors Allosteric regulators Temperature pH Salt concentration Cofactors and Coenzymes Cofactors Coenzymes are organic, cofactors are not Both are vital to the proper functioning of the enzyme (or they wouldn’t be called cofactors and coenzymes) Heme is the cofactor that is essential to have present in the active site of catalase. (Why?) Magnesium is a cofactor in chlorophyll Allosteric Activation Allosteric allosteric activator vacant allosteric binding site enzyme active site active site cannot bind substrate active site altered, can bind substrate Figure 6.15a Page 108 allosteric inhibitor allosteric binding site vacant; active site can bind substrate active site altered, can’t bind substrate Allosteric Inhibition Inhibition Figure 6.15b Page 108 Inhibition Feedback Inhibition Feedback Think of the feedback inhibition that occurs when a two­year old touches a hot stove! The signal (the pain) caused an inhibition of the activity (touching the stove). In cells, the signal may be the final product of the pathway, itself. enzyme 2 enzyme 1 SUBSTRATE Figure 6.16 Page 108 enzyme 3 enzyme 4 enzyme 5 A cellular change, caused by a specific activity, shuts down the activity that brought it about END PRODUCT (tryptophan) Effect of Temperature Effect Small increase in temperature increases molecular collisions, reaction rates High temperature disrupts bonds and destroys the shape of active sites 104oF 140oF Figure 6.17b Page 109 Figure 6.17c Page 109 Effect of pH: 3 different enzymes Effect Depends on the enzyme (stomach vs. blood vs small intestine?) Salinity and Enzyme Activity Salinity Higher than usual salt concentrations will disrupt the activity of an enzyme The excess ions will interfere with the bonds that are maintaining the enzyme’s conformation Which Way Will a Reaction Run? Reaction Nearly all chemical reactions are reversible Direction reaction runs depends upon – Energy content of participants – Reactant­to­product ratio Chemical Equilibrium Chemical (Really this will be the case when the energy content of the reactants (Really and products are similar. What would occur if, say, the yellow compounds needed a big investment of energy to make???) compounds RELATIVE CONCENTRATION OF REACTANT RELATIVE CONCENTRATION OF PRODUCT HIGHLY SPONTANEOUS EQUILIBRIUM HIGHLY SPONTANEOUS Figure 6.9 Page 103 Chemical Equilibrium Chemical Energy in the reactants equals that in the products Product and reactant molecules usually differ in energy content Therefore, at equilibrium, the amount of reactant almost never equals the amount of product But, at equilibrium the rate of the forward reaction equals the rate of the reverse Chemical Equilibrium – the concentrations of the compounds settle at levels where the system is most stable system A Reversible Reaction Glucose-1-phosphate Figure 6.10 Page 103 Glucose-6-phosphate A high concentration of glucose­1­phosphate has the reaction run forward. A high concentration of glucose­6­phosphate has the reaction run in reverse. The forward and reverse reactions run at the same rate when the ratio of glucose­1­phosphate to glucose­6­ phosphate is 19:1. ...
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