Biochem 305 Exam 2 Study Guide

Biochem 305 Exam 2 Study Guide - 1 Biochem 305 Exam 2 Study...

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Fi g. 6. 1 Biochem 305 Exam 2 Study Guide Mechanisms of Enzyme Regulation 1. Describe the various ways that enzymes can be regulated by covalent modification. a. covalent modification – the reversible (can be) attachment or modification of a functional group to/on a protein or enzyme via a covalent bond i. phosphorylation/dephosphorylation – addition or removal of a phosphate group from an enzyme 1. depending on the enzyme: a. phosphorylation can activate or deactivate the enzyme b. dephosphorylation can inactivate or activate the enzyme c. often found in signaling cascades 2. oxidation-reduction a. redox reactions involve cysteine disulfides & changes in enzyme conformations b. common with photosynthetic enzymes 2. proenzymes & zymogens a. proenzyme – inactive enzyme precursor (polypeptide) that must be proteolytically cleaved or hydrolyzed in order to become active i. zymogen – subset of proenzyme 1. digestive proenzyme 3. Describe (and exemplify) what is meant by “rational drug design” and its applications. a. biologically active compounds are specifically designed or chosen to work with a particular drug target b. example: HIV i. HIV virus is a complex encapsulated RNA virus that causes AIDS in humans ii. the capsule contains all information for the production of more viral particles iii. translation forms a large polypeptide with many domains the encapsulated protease cleaves the polypeptide into the various components required to make more virus particles iv. HIV protease is an “ aspartate ” protease v. viral protease – key protein (it is the target of the drugs) 1. by attacking the protease, you can prevent the protein from getting cut vi. designer HIV protease inhibitors – competitive (suicide) inhibitors 1. invirase, crixivan, viracept, naorvir 4. Describe the general characteristics of allosteric enzymes. a. substance (inhibitor or activator) binds to a site OTHER than the active site b. sigmoidal curve c. most allosteric enzymes are multisubunit enzymes with multiple substrate and effector binding sites d. example: phosphofructokinase i. inhibitors: 1. ATP 2. citrate 3. PEP ii. activators: 1. AMP 2. ADP 3. fructose-2,6-P 2
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22 2 5. Explain how and why cofactors, pH, and temperature affect or regulate enzyme activities. a. availability of co-factors i. metal ions ii. co-enzymes b. changes in pH i. change the ionization state of active site groups ii. change the ionization state of substrates iii. precipitate proteins iv. examples: 1. pepsin – by stomach lining into stomach 2. chemotrypsin – by pancreas into small intestine c. changes in temperature i. speed up/slow down the rate of a reaction (via kinetic energy changes) ii. high temperature can denature & precipitate proteins iii. examples of optimum temperature 1. animal/human: 3 C 7 7 2. plant: 25-4 C 0 7 d. substrate concentration i. increasing substrate concentration will increase the rate of enzyme activity until a certain point, at which it will plateau off Structure of DNA 1. Identify all the common purines and pyrimidines 2. Identify and/or describe the
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