Chapter 7

Question 1

differentiate between first-order rate constant and a second order rate constant

Answer 1

1st order rate constant is a propotionality constance for reactions having only one reactant; it relates to to rate of reaction to concentration of sole reactant
second oder rate constant proportionalitiy constant for reactions having two reactants; it relates the rate of a reaction to concentration of both reactions

Question 2

what is a pseudo first order reaction

Answer 2

a second order reaction that appears to be first order…if the concentration of one reactant is much greater than the second reactant, the velocity will appear to be first order with respect to reactant present in lower concentration

Question 3

what is the biochemical advantage of having a Km approximately equal to the substrate concentration normally available to an enzyme?

Answer 3

at substrate concentrations near the Km, the enzyme displays significant catalysis yet is sensitive to changes in substrate concentration

Question 4

what is the defining characteristic for an enzyme catalyzing a sequential reaction? a double displacement reaction?

Answer 4

characterized by formation of a ternary complex consisting of enzyme and both substrates.
double displacement rxn always requires formation of temporarily substituted enzyme intermediate

Question 5

enzyme

Answer 5

protein catalyst

Question 6

kinetics

Answer 6

the study of reaction rates

Question 7

michaelis menten equation

Answer 7

describes kinetics of simple one-substrate reactions

Question 8

michaelis constant (km)

Answer 8

substrate concentration that yields 1/2vmacx

Question 9

lineweaver burk equation

Answer 9

double recipricol plot

Question 10

turnover number

Answer 10

k2 or kcat

Question 11

kcat/km

Answer 11

measure of enzyme efficiency

Question 12

sequencial reaction

Answer 12

ternary complex is formed

Question 13

double displacement (ping pong reaction)

Answer 13

includes substituted enzyme intermediate

Question 14

allosteric enzyme

Answer 14

responds to environmental signals

Question 15

what is feedback inhibition and why is it a useful property? (15)

Answer 15

inhibition of allosteric enzymes by end product of pathway controlled by the enzyme. feedback inhibition prevents the production of too much end product and consumption of substrates when product is not required

Question 16

an allosteric enzyme that follows the concerted mechanism has T/R ratio of 300 in the absence of substrate. suppose that a mutation reversed the ratio. how would this mutation affect the relation between the velocity of the reaction and the substrate concentration

Answer 16

the enzyme would show simple michaelis menten kinetics because its essentiall always in the R state

Question 17

differentiate between homotropic and heterotropic effectors

Answer 17

homotropic effectors are substrates of allosteric enzymes. heterotropic effectors are regulators of allosteric enzymes. homotropic account for sigmoidal nature of velocity vs substrate concentration curve. heterotropic alter midpoint of k, of curve. both work by altering T/R ratio

Question 18

ATcase is an allosteric enzyme that regulates the synthesis of UTP and CTP. it can be separated intro regulatory subunits and catalytics subunits. if isolated regulatory subunits and catalytic subunits of ATCase are mixed, the native enzyme is reconsonstituted. what is the biological significance of the observation

Answer 18

the reconstitution shows that complex quaternary structure and resulting catalytic and regulatory properties are untimately encoded in primary structure of individual components

Question 19

you have isolated a dimeric enzyme that contains two identital active sites. the binding of substrate to one active site decreases the substrate affinity of the other active site. can the concerted model account for this negative cooperativity?

Answer 19

sequential model more readily accounts for negative cooperativity than concerted model