Chapter 4 - Enzymes Flashcards
hydrolase
hydrolyzes chemical bonds (ex. ATPase, proteases)
isomerase
rearranges bonds within a molecule to form an isomer
ligase
forms a chemical bond (ex. DNA ligase)
lyase
breaks chemical bonds by means other than oxidation or hydrolysis
kinase
transfers a phosphate group to a molecule from a high energy carrier, such as ATP
oxidoreductase
runs redox reactions
polymerase
polymerization (ex. addition of nucelotides to the leading strand of DNA)
phosphatase
removes a phosphate group from a molecule
protease
hydrolyzes peptide bonds
reaction coupling
one very favorable reaction is used to drive an unfavorable reaction
free energy changes are ____
additive
active site
region in an enzyme’s three dimensional structure that is directly involved in catalysis
enzymes are usually ____ shaped
globular/spherical
substrates
reactants in an enzyme-catalyzed reaction
active site model
substrate and active site are perfectly complementary
induced fit model
substrate and active site differ slightly in structure and that the binding of the subtrate induces a conformational change in the enzyme
recognition pocket
pocket in the enzyme’s structure which attracts certain residues on substrate polypeptides
enzymes that act on hydrophobic substrates have ___ amino acids in their active sites
hydrophobic
both ____ and ____ play critical roles in enzymatic function
temperature and pH
cofactors
metal ions or small molecules required for activity in many enzymes (ex. vitamins)
coenzyme
organic cofactors that often bind to the substrate during the catalyzed reaction
4 types of enzyme activity regulation
1) covalent modification
2) proteolytic cleavage
3) association with other polypeptides
4) allosteric regulation
covalent modification
phosphorylation through covalent bonds that either activate or inactivate the enzyme (ex. hydroxyl group on serine)
proteolytic cleavage
inactive forms of enzymes (zymogens) become activated by cleavage by a protease
association with other polypeptides
association with other polypeptides that affect enzyme activity
constitutive activity
continuous rapid catalysis
allosteric regulation
binding of small molecules to particular sites on an enzyme that are distinct from the active site; alters conformation which can increase or decrease catalysis
allosteric regulation is usually ___ and ___
noncovalent; reversible
feedfoward stimulation
stimulation of an enzyme by its substrate
enzymes can act as ___ because they can regulate flow of substrates into products
valves
enzyme kinetics
study of rate of formation of products from substrates in the presence of an enzyme
reaction rate
amount of product formed per unit time in mol/s
reaction rate depends on concentration of ___ and ___
substrate; enzyme
if we double amount of substrate then the reaction rate ___
doubles
point of saturation
adding more substrate will not increase reaction rate at all; denoted as Vmax
Km
substrate concentration at which the reaction velocity is half its maxium
if enzyme-substrate pair has a low Km then ___
enzyme has high affinity for that particular substrate
positive cooperativity
binding of a substrate to one subunit increase affinity for rest of the subunits; binding occurs at active sites
sigmoidal curve results from ____
positive cooperative binding
4 types of inhibition of enzyme activity
1) competitive
2) noncompetitive
3) uncompetitive
4) mixed-type
competitive inhibition
- molecules compete with subtrate for binding at active site
- can be overcome by excess substrate
- does not affect Vmax
noncompetitive inhibition
- bind at an allosteric site
- cannot be overcome by excess substrate
- lowers Vmax; doesn’t affect Km
uncompetitive inhibition
- inhibitor can only bind to enzyme-substrate complex
- binds to allosteric sites; lowers Vmax
- decreases Km
mixed-type inhibition
- inhibitor can bind to either free enzyme or enzyme-substrate complex
- if enzyme has greater affinity for the inhibitor in its free form, Km increases
- if enzyme has greater affinity for the inhibitor in its complex form, Km decreases
- lowers Vmax
lineweaver-burk plot
- slope is Km/Vmax
- y-intercept is 1/Vmax
- x-intercept is -1/Km
when there is increasing concentrations of a competitive inhibitor then the lines will intersect along the ___
y-axis
when there is an increase in concentration of non-competitive inhibitor the lines will intersect on the ___
x-axis
