Exam 2: Chp 13 Flashcards
What are enzymes?
Proteins specialized to catalyze metabolic reactions by changing kinetics
What is catalytic power?
The ratio of enzyme-catalyze rate to uncatalyzed rate
What is specificity of a molecule?
it is selective for substrate, product, or type of reaction
What is regulation of enzymes?
the rate controlled to meet cellular requirements
On what two levels is regulation performed?
production/genetic level and binding interaction by inhibitors or activators
What type of reactions do oxidoreductase enzymes catalyze?
redox reactions
What type of reactions do transferase enzymes catalyze?
transfer functional groups
What type of reactions do hydrolase enzymes catalyze?
hydrolysis
What type of reactions do lyase enzymes catalyze?
bond cleavage not via redox or hydrolysis
What type of reactions do isomerase enzymes catalyze?
isomerization
What type of reactions do ligase enzymes catalyze?
bond formation with the help of ATP
What type of reactions do translocate enzymes catalyze?
molecule or ion movement across a membrane
What is an enzyme cofactor? Examples?
An inorganic component that allows chemistry AAs cannot perform alone; metal ions, Na+, Ca+
What is a coenzyme/prosthetic group?
A small organic fragment covalently or non-covalently associated with an enzyme
What is an holoenzyme?
A complex of protein and cofactor or coenzyme
What is an apoenzyme?
A protein without its specific cofactor or coenzyme; typically inactice
How does temperature affect reaction rate?
Reaction rate increases as temperature does
How do catalysts affect reaction rate?
Stabilizes the transition state which lowers activation energy, speeding up the reaction
What is the lock and key model?
The substrate molecular structure is complementary to the enzyme structure which create specificity
What is the induced fit model?
As the substrate binds the active site and substrate change confirmation and become complimentary
Why is the induced fit model beneficial?
Explains catalytic activity and specificity
Where does the energy for confirmation changes during substrate and enzyme binding come from?
Formation of stabilizing non-covalent interactions between enzyme and substrate
What is Vmax?
The maximum reaction rate of an enzyme-substrate complex
When does Vmax occur?
when all enzyme is occupied by substrate
What is steady state assumption kinetics?
Assume ES is constant in E+ S → ES → E + P is nonreversible
What is Km and what does is measure?
It is 1/2 of Vmax and is a measure of binding affinity between substrate and enzyme
What is Kcat?
A measure of catalytic efficiency
What does a low Km mean?
Strong binding affinity
What does a high Kcat mean?
High catalytic efficiency
What is the x-intercept of a Lineweaver-Burke plot equal to?
-1/km
What is the slope of a Lineweaver-Burke plot equal to?
Km/Vmax
What is the y-intercept of Lineweaver Burke plot equal to?
1/Vmax
What are two factors that influence enzyme kinematics?
pH and temperature
How does pH influence enzyme kinetics?
Enzymes have a standard distribution surrounding their optimal pH because pH influences their protonation, thus overall structure
How does temperature influence enzyme kinetics?
Most enzyme activity increases rate up to 50-60°C then denature
What are enzyme inhibitors?
Small molecules that bind to the enzyme and either slow or completely inhibit the catalytic process
What are the two general kinds of inhibitors?
Reversible and Irreversible
Why are reversible inhibitors able to be removed?
They bind via non-covalent interactions
What are the four kinds of reversible inhibitors?
Competitive, Noncompetitive uncompetitive, and mixed
How does a competitive inhibitor interact with the enzyme and substrate?
Competes with substrate to bind to active site
How does concentration affect competitve inhibition?
Binding favors that in higher concentration
How does a competitive inhibitor affect the y-intercept of a Lineweaver-Burke plot of an enzyme?
Vmax stays the same because it assumes high substrate concentration → y-intercept does not change
How does a competitive inhibitor affect the x-intercept of a Lineweaver-Burke plot of an enzyme?
Km increases because more substrate is needed to reach Vmax → x-intercept decrease
How does a noncompetitive inhibitor interact with an enzyme and its substrate?
The inhibitor binds to a site distinct from the active site and does not affect substrate binding, but prevents catalytic activity
How does a non-competitive inhibitor affect the y-intercept of a Lineweaver-Burke plot of an enzyme?
Vmax decreases because no turnover → y-intercept increases
How does a non-competitive inhibitor affect the x-intercept of a Lineweaver-Burke plot of an enzyme?
Km stays the same because substrate binding is unaffected→ x-intercept remains unchanged
How does a uncompetitive inhibitor interact with an enzyme and its substrate?
Inhibitor binds to the enzyme-substrate complex and inhibits catalytic activity
How does a uncompetitive inhibitor affect the y-intercept of a Lineweaver-Burke plot of an enzyme?
Vmax decreases because substrate cannot compete with inhibitor → y-intercept increases
How does a uncompetitive inhibitor affect the x-intercept of a Lineweaver-Burke plot of an enzyme?
Km decreases because more inhibitor complex shifts the equilibrium → x-intercept increases
How does a mixed inhibitor interact with an enzyme and its substrate?
inhibitor binding to the enzyme makes it harder for substrate to bind
What are two kinds of mixed inhibition?
1) inhibitor favors binding E on its own
2) inhibitor favors binding to enzyme substrate complex
In mixed inhibition where lone enzyme is favored, how is the y-intercept of a Lineweaver-Burke plot of an enzyme affected?
Vmax stays the same → y-intercept stays the same
In mixed inhibition where lone enzyme is favored, how is the x-intercept of a Lineweaver-Burke plot of an enzyme affected?
Km increases because more substrate is needed to reach Vmax → x-intercept decreased
In mixed inhibition where enzyme-substrate complex is favored, how is the y-intercept of a Lineweaver-Burke plot of an enzyme affected?
Vmax is decreased → y-intercept increased
In mixed inhibition where enzyme-substrate complex is favored, how is the x-intercept of a Lineweaver-Burke plot of an enzyme affected?
Km is decreased → x-intercept is increased
How does an irreversible inhibitor affect Vmax and Km?
Km remains the same and Vmax is decreased
Why can irreversible inhibitors not be removed?
They follow the enzyme catalytic process but form covalent intermediate
What is the chemical function of penicillin?
prevents crosslinking of peptidoglycan in bacterial cell walls by inhibiting transpeptidase
How and why does penicillin inhibit transpeptidase?
Mimics D-Ala-D-Ala pattern of normal substrate that irreversibly binds to serine
