University:
Glendale Community College
Course:
BIO160 | Introduction to Human Anatomy and Physiology
Academic year:

2020
Views:

411

Pages:

6
Author:

Ruben Owens

Section 6.1: Properties of Enzymes Key Characteristics: §Increase reaction rate by lowering Ea §Obey laws of thermodynamics – no effect on Keq values §Rate depends on DGo of activation §Occurs when colliding molecules possess a minimum amount of energy called the activation energy (Ea) §Increase rate up to 1020 §Increases forward and reverse reactions equally §Most reactions require an initial energy input §Present in low concentrations – not consumed §Controlled by regulator mechanisms §Active sites – bind transition state of reacting substrates ü Very specific catalyzing only 1 stereoisomer while others catalyze a family of similar reactions ü Negligible formation of side products Section 6.1: Properties of Enzymes Lowering activation energy §Free energy of activation (DGo‡) -amount of energy to convert 1 mol of substrate (reactant) from the ground state to the transition state §Transition state – highest energy, least stable §Free energy change (DGo) – energy released from reaction Section 6.1: Properties of Enzymes Enzyme-catalyzed reaction §Substrate, S, binds to enzyme forming ES complex §Active site: the small portion of the enzyme surface §Frequently in a cleft or crevice §Optimally orient the substrate to achieve the transition state at a lower energy § Binds by noncovalent forces §Hydrogen bonding, electrostatic attractions, van der Waals attractions §Essential amino acids in or near active site E + S ß à ES Enzymes-substrate complex Section 6.1: Properties of Enzymes Two enzymatic models §Lock-and-key model: substrate binds to portion of the enzyme with a complementary shape §Induced fit model: binding of substrate induces a conformational change in the enzyme that results in a complementary fit §Catalysis occurs in transition state §Bonds rearrange §Substrate close to atoms §Substrate in correct orientation §Non-protein components §Cofactors – ions, Mg2+ or Zn2+ §Coenzymes – complex organic molecule §Apoenzyme - protein component lacking essential cofactor §Holoenzyme – enzymes with bound cofactors 2 Modes of E-S Complex Formation Product Formation Section 6.2: Classification of Enzymes 1. Oxidoreductases oxidation-reduction reactions; oxidation state altered for 1 or more atoms; dehydrogenases, oxidases, reductases, hydroxylase, peroxidases 2. Transferases transfer molecular groups from donor molecule to acceptor molecule; transcarboxylases, transaminases 3. Hydrolases cleavage of bonds by addition of water; esterases, phosphataes 4. Lyases groups eliminated to form double bonds or added to double bonds; decarboxylases, hydratases 5. Isomerases intramolecular rearrangments; isomerases, mutases 6. Ligases bond formation between 2 substrate molecules; DNA ligase, synthetases