Enzymes Flashcards
enzymes
biological catalysts that are unchanged by the reactions they catalyze and are reusable
lower the activation energy necessary for biological reactions
do NOT alter the free energy (∆G) or enthalpy (∆H) change that accompanies the reaction nor the final equilibrium position; rather they change the rate (kinetics) at which equilibrium is reached
each catalyzes a single reaction or type of reaction with high specificity
oxidoreductases
catalyze redox reactions that involve transfer of electrons
transferases
move a functional group from one molecule to another molecule
hydrolases
catalyze cleavage with the addition of water
lyases
catalyze cleavage without the addition of water and without the transfer of electrons reverse reaction (synthesis) often more important biologically
isomerases
catalyze the interconversion of isomers, including both constitutional isomers and stereoisomers
ligases
responsible for joining two large biomolecules, often of the same time
exergonic reactions
release energy, ∆G is negative
active site
site of catalysis of an enzyme
lock and key theory
explains binding to active site
hypothesizes that the enzyme and substrate are exactly complementary
induced fit model
explains binding to active site
hypothesizes that the enzyme and substrate undergo conformational changes to interact fully
cofactors/coenzymes
metal cation or small organic molecule that allows an enzyme to be active
saturation kinetics
as substrate concentration increases, the reaction rate does as well until a maximum value is reached
Michaelis-Menten plot
represents relationship between substrate concentration and reaction rate as a hyperbola
Lineweaver-Burk plot
represents relationship between substrate concentration and reaction rate as a line
cooperative enzymes
display sigmoidal curve because of the change in activity with substrate binding
feedback inhibition
regulatory mechanism whereby the catalytic activity of an enzyme is inhibited by the presence of high levels of a product later in the same pathway
reversible inhibition
characterized by the ability to replace the inhibitor with a compound of greater affinity or to remove it using mild laboratory treatment
competitive inhibition
results when the inhibitor is similar to the substrate and binds to the active site
can be overcome by adding more substrate
vmax is unchanged, Km increases
noncompetitive inhibition
results when the inhibitor binds with equal affinity to the enzyme and enzyme-substrate complex
vmax is decreased, Km is unchanged
mixed inhibition
results when the inhibitor binds with unequal affinity to the enzyme and the enzyme-substrate complex
vmax is decreased, Km is increased or decreased depending on if the inhibitor has a higher affinity for the enzyme or enzyme-substrate complex
uncompetitive inhibition
results when the inhibitor binds only with the enzyme-substrate complex
Km and vmax both decrease
irreversible inhibition
alters the enzyme in such a way that the active site is unavailable for a prolonged duration or permanently; new enzyme molecules must be synthesized for the reaction to occur again
allosteric sites
can be occupied by activators which increase either affinity or enzymatic turnover
phosphorylation/glycosylation
covalent modification with phosphate/carbohydrate
can alter the activity or selectivity of enzymes
zygomens
secreted in inactive form and are activated by cleavage
