Enzymes Flashcards
Enzymes catalyze reactions by….
increasing chemical reaction rate, reducing free energy needed for reaction to occur, increasing the probability of reaction occurrence
Are enzymes bidirectional or unidirectional?
Both
Cofactors
Inorganic ions, play a role in stabilizing structures (?)
Cu, Mg, Zn, Fe
What is a holoenzyme?
Complete catalytically active enzy,e with coenzymes and cofactors bound
What are the six types of enzymes? (slide 4)
oxidoreductases, transferases, hydrolases, lyases, isomerases, ligases,
Define Oxidoreductases
.
Define Transferases
.
Define hydrolases
.
Define lyases
.
Define Isomerases
.
Define Ligases
.
How does the structure of the enzyme relate to its substrate’s structure?
the enzyme matches the substrate’s transition state structure (enzyme is complementary to transition state)
What are the four activation barriers that enzymes overcome?
entropy of molecules in a solution, solvation shell, substrate conformation, and substrate orientations
Define kinetics
the rate at which enzymes create products
kinetics allow:
- identification of mechanism
- rate limiting steps of product formation
- identification of inhibitors
Define velocity
the primary measure of reaction rate
- initial velocity (Vo)
- maximum velocity (Vmax)
Define Km (slide 9/10)
the concentration at which the Vo is half of the Vmax
or the substrate concentration at which the enzyme is functioning at half capacity (?)
Define Km (slide 9/10)
the concentration at which the Vo is half of the Vmax
or the substrate concentration at which the enzyme is functioning at half capacity (?)
What affects velocity
enzyme, substrate, cofactors, coenzymes, enzyme modifications, pH, temperature
How do drugs/inhibitors relate to Km?
drugs want to move it to the left (reach half max sooner/enzyme is more efficient at becoming active)
if you move it to the right (….)
How do drugs/inhibitors relate to Vmax?
you can move the Vmax to increase or decrease ….?
What are the two classes of inhibitors?
Irreversible and reversible inhibitors
Irreversible inhibitors
inhibitor covalently binds to enzyme –> preventing fx and leading to degradation
-suicide
(permanent, bind enzyme and need to be replaced)
Reversible inhibitors
inhibitor binds the enzyme or substrate to temporarily affect catalysis
- competitve
- mixed
- uncompetitive
- noncompetitive
what are the four types of reversible inhibitors
competitive, uncompetitive, mixed, noncompetitive
competitive inhibition
inhibitor competes with substrate
Km moves to the right, but no change in Vmax
—preventing substrate from binding/would need to increase amount of substrate to make up for this
uncompetitive inhibition
inhibitor binds the ES (enzyme-substrate) complex, but not the enzyme alone
Reduces Vmax, Km moves left
—total amount of product that can be produced is impaired (prevention of conversion from substrate to product)
mixed inhibition
inhibitor binds enzyme alone or ES complex
-affects substrate binding and enzyme
Reduces Vmax, Km moves right
—prevents substrate binding and prevents substrate to product
noncompetitive inhibition
- inhibitor binds the enzyme or ES complex
- slows or stops enzymatic process, substrate binding not affected
Reduces Vmax, no change in Km
—inhibitor just prevents substrate to product
Allosteric regulation
Allosteric Enzymes:
- enzyme conformation is changed by effector binding
- this can alter catalytic fx (stimulate/inhibit)
- do not follow Michaelis-Menten Kinetics
- complex protein structures
What are the types of allosteric/covalent modifications?
phosphorylation, acetylation, methylation, ubiquitination, and myristoylation
What is homotropic regulation
the substrate itself regulates enzyme fx
regulation occurs at separate site from substrate binding
what is heterotropic regulation
non-substrate molecules regulate enzyme fx
regulation occurs at separate site from substrate binding
