Chapter 8 p

 Metabolism: sum of all chemical rxns in the body  Metabolic Pathway: series of rxns catalyzed by specific enzymes  Catabolic Pathways: energy-releasing Usually by breaking down large molecules i.e.: cellular respiration  Anabolic Pathways: energy-consuming Usually by building macromolecules i.e.: protein synthesis

 Energy: the capacity to cause change or rearrange a collection of matter  A) Kinetic Energy: energy of motion  i.e. leg muscles pushing bicycle pedals  Heat/Thermal Energy: kinetic energy of atomic movement  B) Potential Energy: stored energy  i.e. water built up behind a dam  Chemical Energy: potential energy stored in molecules When broken down, gets released

On the platform, the diver has more potential energy. Diving converts potential energy to kinetic energy. Climbing up converts kinetic energy of muscle movement to potential energy. In the water, the diver has less potential energy.

 The study of energy transformations  Based on open systems, or organisms that transfer energy between self & surroundings  1 st Law of Thermodynamics: Energy can be transferred and transformed but can not be created nor destroyed  “Principle of Conservation”  Energy is converted from 1 form to another as it passes through open systems  i.e.: chemical energy in food kinetic energy for muscle contraction

 2 nd Law of Thermodynamics: Every energy transfer or transformation increases the entropy of the universe  Entropy: measure of randomness or disorder Every time energy is transformed, some of it is converted to heat & escapes to the surroundings If a process increases entropy, it will occur spontaneously (w/o energy input)

Chemical energy Heat CO 2 First law of thermodynamicsSecond law of thermodynamics H2OH2O

 ΔG = G final state – G initial state  Final state has less free energy, then it is more stable  Systems will always try to move to more stable state  Chemical rxns at equilibrium are at their most stable state (ΔG is lowest)  Can’t do any more work

 Exergonic Rxns: net release of free energy  ΔG is negative; rxns are spontaneous  Value of ΔG = amount of work that can be performed  Endergonic Rxns: absorb free energy  ΔG is positive; rxns are NOT spontaneous  Value of ΔG = amount of energy required to drive the reaction

 Living cells never exist at equilibrium  Are “Open Systems”  There is a constant flow of materials into & out of a cell  The products of 1 rxn may become the reactants of another rxn; wastes are expelled from the cell

 Energy Coupling: the use of exergonic rxns to drive endergonic ones, using ATP  i.e.: beating of cilia, pumping substances across membranes, synthesizing polymers  Adenosine Triphospahte (ATP): ribose (sugar), adenine (nitrogenous base), 3 phosphate groups  To release energy, one PO 4 is removed by hydrolysis Each PO 4 is neg. charged & close together ΔG = -7.3 kcal/mol  This rxn may be coupled to endergonic ones to help them proceed

 When ATP hydrolysis is coupled to another rxn, the removed PO 4 is transferred to a reactant of an endergonic rxn  “Phosphorylated” reactant is less stable & thus more likely to react  To regenerate ATP (replace the PO 4 ), use energy from exergonic rxns  i.e. cellular respiration

Chapter 8 p

 Some rxns, although spontaneous, occur so slowly they can not be detected  Catalyst: a chemical compound that speeds up a rxn w/o being consumed  Enzyme: A protein catalyst Named for the rxn/substrate catalyzed Usually end in “-ase”

 All chemical rxns involve breaking & forming bonds  Starting molecules must contort to unstable position; requires energy  Activation Energy (E A ): energy required to start a rxn/contort the reactants  Often comes in form of heat from surroundings (speeds up molecules, collide more often)  Transition State: point at which reactants absorb enough energy so bonds begin to break & form (“peak” of rxn)

 Instead of heat, living cells use enzyme catalysts to overcome E A  Heat denatures proteins & would speed up all rxns  Enzymes decrease E A, lowering amount needed to reach transition state  Substrate: reactant the enzyme acts upon  Very specific (I enzyme/substrate)  Forms Enzyme-Substrate Complex w/ active site of enzyme  Active Site: region of enzyme to which substrate binds  Formed by few amino acids w/in the protein  Induced Fit: brings substrate & enzyme in perfect position to maximize catalysis

 Substrates are held in place by weak interactions  Hydrogen bonds, ionic bonds  Active Site & R-groups of amino acids decrease E A by:  A) Holding substrate in proper position  B) Contorting substrate into transition-state conformation  C) Providing microenvironment (pH, salinity, etc)  D) Participating in rxn Side chain of enzyme aa may briefly bond to substrate  Rate often depends on:  1) Amount of Substrate Saturated Rxn: when all enzyme molecules are being used  2) Amount of Enzyme If rxn is saturated, can increase rate of reaction

 Temperature: up to a point, an increase in temp will increase enzyme activity  If too high, bonds are broken & protein will denature  Each enzyme has its own “optimal temp”  pH: most enzymes work best at a pH of 6-8  If too acidic/basic protein will denature  Some enzymes are designed to work in extreme pH conditions  Cofactor: a non-protein “helper” bound to an enzyme (i.e. zinc, iron, copper)  Performs a variety of functions  Coenzyme: an organic cofactor (i.e.vitamins)

 Inhibitor: selectively inhibits the action of a specific enzyme  If binds covalently, may be irreversible  Competitive Inhibitor: resembles substrate & blocks it from entering active site  Can be overcome by increasing substrate concentration  Noncompetitive Inhibitor: binds to enzyme, causing it to change shape  Substrate no longer fits in active site  Can be overcome by increasing enzyme concentration

 Enzyme activity has to be constantly and specifically regulated  Allosteric Regulation: activity at one site of a protein can alter the activity at another site (i.e. the active site)  Enzymes are composed of 2+ polypeptides, each with its own active site  Enzymes are constantly switching from “active” to “inactive” states  Allosteric Activation: uses an “activator” to hold the complex into the active state  Allosteric Inhibition: Uses an “inhibitor” to hold the complex into the inactive state  The allosteric molecule will affect each active site on the enzyme

 When a pathway is shut off b/c the end product binds to and inhibits an enzyme  Prevents the cell from wasting resources  Is a type of allosteric inhibition