Biochemistry Exam 1: Kinetics and Regulation

first-order

reaction where velocity is directly proportional to reactant concentration

second-order

reaction that is biomolecular and its velocity is dependent on the concentration of both molecules

first assumption of the M-M model

activity is measured when [P] ~ 0 (at the beginning of the rxn); allows us to ignore P -> S reverse rxn

second assumption of the M-M model

the ES complex is a necessary intermediate for the formation of P

initial velocity (V0)

velocity under that assumptions of the M-M model

maximal velocity

the velocity when the enzyme is saturated with substrate; never achieved

dissociation constant M-M model

Kd = k-1/k1

Kd

when k1 >>> k2, KM ~ Kd

KM

Michaelis constant; the substrate concentration that produces 1/2 Vmax ; the lower this is, the greater the enzyme binding affinity; High activity and high sensitivity

M-M enzymes

enzymes that are not regulated

allosteric enzymes

regulated enzymes; regulated by non-substrate molecules and sharply responsive near KM

committed step

The first irreversible step in a metabolic pathway under physiological conditions; this step is catalyzed by an allosteric enzyme and commits the product to a particular chemical fate

feedback inhibition

A method of metabolic control in which the end product of a metabolic pathway acts as an inhibitor of an enzyme within that pathway

allostery

regulation of the activity of a protein by the binding of an effector molecule to a site other than the active site

sigmoidal

velocity vs substrate curve for allosteric enzymes are __________

quaternary

allosteric enzymes depend on changes in _________ structure

the concerted model

- multiple active sites on different polypeptide chains

- enzymes is on one of two quaternary structures: T and R

- T and R are at equilibrium

- T is more stable

- R state is more active than the T state

- substrate binds R more readily

- symmetry rule: all active sites must be in the same state (T or R)

- binding of substrate to one active site traps all sites in R state

homotropic

the concerted model is an example of ________ allosteric regulation (effects are due to substrate)

inhibitors

regulator that stabilizes the T state in allosteric enzymes

activators

regulator that stabilizes the R state in allosteric enzymes

heterotropic

disruption of the T/R equilibrium by regulators is a ________ effect in allosteric enzymes

homotropic

disruption of the T/R equilibrium by substrate is a ________ effect in allosteric enzymes

sequential model

- proposes that allosteric enzymes undergo sequential changes in structure

- "symmetry rule" is not enforced

- explains negative cooperativity