Study Questions ENZYM

Study Questions

ENZYMES Answer True(T) or False (F) Which of the following statements is NOT characteristic of allosteric enzymes? a. They are often composed of subunits(T) b. Allosteric enzymes are regulated by molecules called effectors(T) c. The binding of a positi!e allosteric effector results in an increase in enzymic acti!ity (T) d. They fre"uently catalyze the slowest step in metabolic pathway(T) e. They follow #ichaelis$#enten %inetics(F)

The rate of an enzyme$catalyzed reaction can best be described as a &roportional &roportional to the substrate substrate concentrati concentration(T) on(T)  b 'eaction !elocity is proportional to enzyme enzyme concentration at all concentrations of substrate(T) c indepe independe ndent nt of enzyme enzyme conce concentr ntrati ation( on(F) F) d ero orde orderr with with respect respect to to substr substrate ate (F) (F) e ncreased ncreased in the the presence presence of a noncompetit noncompetiti!e i!e inhibit inhibitor(F) or(F) Which statement is *O''+*T? a +nzymes +nzymes are small small molecule moleculess that are heat heat stable(F stable(F) )  b +nzymes affect rates of reactions in the forward and re!erse direction(T) c +nzymes +nzymes will determine determine whether whether a reaction reaction will ta%e ta%e place(F) place(F) d +nzymes +nzymes are permanent permanently ly altered altered following following the the con!ersion con!ersion of of substrate to product(F) e +nzymes are used as therapeutic agents(T ) *ompetiti!e inhibitors are commonly used in chemotherapy because, a The inhibi inhibitors tors decrease decrease the the total total amount amount of substrate( substrate(F) F)  b The inhibitors alter the enzymes enzymes when they bind and decrease the ma-imal !elocity (.m) of the reaction(F) c The inhibit inhibitors ors resemble resemble the structur structuree of the product product and and inhibit inhibit the reaction by negati!e feedbac%(F) d The inhibit inhibitors ors do not bind the the acti!e acti!e site of of the enzyme(F enzyme(F)) e The inhibi inhibitor tor binds binds only only to the the acti!e acti!e site site and increases increases the #ichaelis constant (/m)(T) #alonate inhibits succinic dehydrogenase because it a 0inds irre!ersibly to the acti!e site(F)  b *o!alently modifies the enzyme(F)

c *helates a metal ion re"uired by the enzyme(F) d 1isplaces the FA1 coenzyme(F) e 'esembles succinate but can not react(T)

A drug which acts as a noncompetiti!e inhibitor  a increases the steady$state concentration of the +2 comple-(F) b has a structure similar to a substrate(F) c acts by remo!ing acti!e enzyme from the substrate pool(T) d is usually irre!ersible(F) e combines with allosteric sites on the enzyme(T) Which of the following is true for enzymes? a 3actate 3actate dehydrogenase dehydrogenase catalyz catalyzee o-idation o-idation and and reduction reduction processes processes (T)  b Transaminases catalyze the transfer transfer of amino group from an amino acid to alpha %etoglutaric acid(T) c *arbamoyl *arbamoyl phosphate phosphate syntheta synthetase4 se4 an enzyme enzyme catalyze catalyzess biosyntheti biosyntheticc reaction pro!iding carbamoyl phosphate by clea!age of two molecules of AT&(T) d Triose Triose isomeras isomerasee catalyzes catalyzes con!ersion con!ersion of dihydroaceto dihydroacetone ne  phosphate to 1$glyceraldehyde$5$phosphate(T) e Aldolase Aldolase catalyzes catalyzes the the clea!age clea!age of glycerald glyceraldehydes ehydes$5$phos $5$phosphate phate to fructose 64 7$phosphate(F) Notes 8ero order means that the reaction !elocity is independent of substrate concentration This is obser!ed only when the substrate concentration is much greater than /m •

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/m(#ichalies constant), is a constant4 characteristic of an enzyme and a particular substance4 and reflects the affinity of the enzyme for that substrate 2lowest step, an early committed co mmitted step in that pathway Allosteric binding sites, +nzymes are regulated by molecules called9 effectors9 also called modifiers or modulators that nonco!alently bind at site other than acti!e site +ffectors that inhibit enzyme acti!ity are termed 9negati!e effectors9 +ffectors that increased enzyme acti!ity are called9 positi!e effectors9