Enzymology II Flashcards
Always fit each other
Lock and key model
Fit only at binding
Induced fit
The active site of the enzyme is not a rigid structure that the substrate fit precisely. T/F
T. It is flexible.
Catalytic step of Michael’s menten theory
ES to EP
Rate limiting step of Michael menten theory.
Step 2: fate of ES
A quantitative description of kinetics of enzyme-catalyzed
reactions.
Michael menten equation
In a typical enzyme catalyzed reaction, reactants and products are hundreds and thousands times greater than the number of enzyme. T/F
T
[S] 1/2 Vmax
Km
Michael menten saturation curve
Hyperbolic or rectangular hyperbola
The Michael menten saturation curve is used for non-allosteric enzymes. T/F
T
S < Km. What order?
1st order
Rate is dependent on substrate concentration.
S < Km and S = km
S = km. What order?
1st order
50% of the enzymes are bound a substrate.
S = Km
Only a portion of the enzyme is ES
S < km
100% of the enzymes is saturated
S > km
S > km. What order.
Zero order. NOT Dependent on substrate concentration.
Once the Vmax has been reached, the velocity will no longer increase. T/F
T. It will decrease because at this point the 2nd and 3rd structures have been desaturated.
Half of the active sites of the enzyme is filled up.
Km
“Signature” of an enzyme
Km
There is an inverse measure of the affinity of an enzyme for a substrate. T/F
T
If there is high km, _______ affinity. Why?
Low. Need more substrate for it to reach km and to be saturated.
If there is low km, ________ affinity. Why?
High. Only a small amount of substrate is needed to reach vmax. Faster saturation.
A more precise way to measure Vmax and Km of an enzyme.
LINEWEAVER-BURKE DOUBLE RECIPROCAL PLOT
Pharmaceutical compounds (drugs) function as inhibitors of specific enzymes. T/F
T
2 types of inhibition
Reversible
Irreversible
Inhibitor that is NOT covalently bound to the enzyme and can dissociate at any moment.
Reversible
Competitive inhibition is under what type of inhibition.
Reversible
Inhibitor compete with the substrate at the binding site.
Competitive inhibitor
In competitive inhibitor, substrate and inhibitor can bind at the same time. T/F
False. It CANNOT bind at the same time. Isa lang pwede.
No product will be formed if an inhibitor binds with the enzyme. T/F
T
According to the lineweaver-Burke plot, the Vmax of competitive inhibition is:
A. Increased
B. Decreased
C. Unchanged
C
According to the lineweaver-Burke plot, the Km of competitive inhibition is:
A. Increased
B. Decreased
C. Unchanged
A
According to the lineweaver-Burke plot, the Vmax of non-competitive inhibition is:
A. Increased
B. Decreased
C. Unchanged
B
According to the lineweaver-Burke plot, the Km of non-competitive inhibition is:
A. Increased
B. Decreased
C. Unchanged
C
According to the lineweaver-Burke plot, the Vmax of uncompetitive inhibition is:
A. Increased
B. Decreased
C. Unchanged
B
According to the lineweaver-Burke plot, the Km of competitive inhibition is:
A. Increased
B. Decreased
C. Unchanged
B
Examples of drugs of competitive inhibition.
Malonate
Lovastatin
Drug that inhibits HMG-CoA reductase that is active as a rate-limiting enzyme in cholesterol synthesase.
Lovastatin
Examples of drugs of irreversible inhibition
Diisopropylphosphofluoridate (DIPF)
Penicillin
Aspirin is an example of what time of inhibition.
Suicide inhibition
Inhibitor that permanently and irreversibly inactivates or incapacitates the enzyme while forming a COVALENT BOND with protein enzyme.
Irreversible
3 types of irreversible inhibition
Noncompetitive inhibition
Uncompetitive inhibition
Suicide inhibition
Inhibits the enzyme-serine complex that is crucial to the release of choline and acetate.
DIPF
Penicillin inhibits what enzyme that is essential in bacterial cell wall.
Glycopeptide transpeptodase
Inhibitor binds to allosteric binding site of the enzyme.
Non competitive
Substrate binding to active site is unaltered.
Non competitive inhibition
Inhibitor binds only to ES complex.
How can non competitive inhibition be overcomed?
Synthesis of new enzyme
How can uncompetitive inhibition be overcomed?
Synthesis of new enzyme
Drug: Captopril
Enzyme: Anguotensin - converting enzyme (ACE)
Disease:?
Hypertension
Drug: Digoxin
Enzyme: ?
Disease: cardiac problem
Na+ k+ - ATPase pump
Drug: lipitor & atorvastatin
Enzyme:
Disease: hypercholesterolemia
HMG-CoA reductase
Drug:
Enzyme: xanthin oxidase
Disease: gout
Allopurinol
Drug: sildenafil (viagra)
Enzyme: ?
Disease: erectile disfunction
Phosphodiesterase
Drug:
Enzyme: protease
Disease: AIDS
Agenerase
Atorvastatin and lipitor is what type of drug.
Statins
Inhibits phosphodiesterase and converts cGMP to GMP.
Viagra
Allosteric enzyme exhibit what type of curve?
Sigmoid curve
Substrate: hyperbolic curve
Allosteric enzyme: _______
Sigmoid curve on a REACTION VELOCITY.
Allosteric enzymes is usually the slowest step in the reaction, catalyze irreversible reactions. T/F
T
Allosteric enzyme causes conformational change via protein enzyme bulk. T/F
T
” negative feedback” or “end product inhibition”
Feedback inhibition
Prevents the accumulation of intermediate products that can lead to harmful effects to the metabolism
Feedback inhibition
Examples of feedback inhibitions
Succinyl CoA
Cholesterol
Feedback inhibitor of krebs cycle
Succinyl CoA
Feedback inhibitor of HMG-CoA reductase
Cholesterol
Allosteric modification is the conformational change of the enzyme as allosteric enzymes bind to active site. T/F
T
2 types of allosteric modification
Positive/stimulatory
Negative/inhibitory
Allosterically active PFK 1 = ______ glycolysis rate
Increases
Allosterically inhibit PFK 1 = ________ glycolysis rate
Decrease
Additional or removal of a group by cleaving covalent bond to the enzyme protein.
Covalent modification
Active when phosphorylated ; inactive when dephosphorylated
Anabolic/biosynthetic enzyme
Active when dephosphorylated ; inactive when phosphorylated
Catabolic/degradative enzymes
PFK is an anabolic enzyme in the synthesis of ATP via glycolysis. T/F
Pyruvate dehydrogenase is catabolic or anabolic?
Catabolic
Inactive precursors of enzymes
Zymogen
Cleavage of zymogen results to activation or inactivation?
Activation
Example of zymogen activation
Blood coagulation
Increase in the rate of enzyme synthesis
Induction
Enzyme concentration is independent of inducers
Constitutive enzymes
Enzymes concentration that is dependent of inducers
Inducible enzymes
Feedback inhibitors are actually the products. T/F
T. Such as succinyl coa and cholesterol
Low molecular weight substances that decrease enzyme synthesis
Repressors
Factors that affect enzyme activity
Tempt
pH
Cofactor
Substrate concentration.
Velocity before optimum temperature is reached increases. T/F
T
Velocity after optimal tempt increases still. T/F
F. It decreases as enzymes are desaturated at very high temperature, more than 37 degrees.
A 10 degrees rise in temperature increases the activity of the enzyme by _____
50 - 100%
Optimum tempt of for human enzymes
37 degrees
Is thermal denaturation reversible or irreversible?
Irreversible
Optimal pH for enzyme activity
5-9
Before optimum pH is reached, velocity increases. T/F
T
Why does velocity increase as an enzyme reaches an optimal pH.
Due to ionization of functional group of Amino acids
After the optimum pH is reached, velocity decreases. T/F
T
Why does velocity of the enzyme decrease after it reaches optimal pH?
Deprotonation of amino terminal group
Cofactors increase the rate of enzyme-catalyzed rxn. T/f
T
When the Vmax is reached, any increase in substrate will not change the velocity of the reaction. T/F
T. Reaction Velocity decreases after Vmax is met.
Why is there a decreased reaction Velocity after Vmax is met?
Excess substrate present accumulates and blocks or impedes ES complex formation
How does Atorvastatin® as a competitive inhibitor of
HMG CoA reductase decrease cholesterol synthesis?
a. Binds to the active site of the enzyme
b. Binds to the allosteric site of the enzyme
c. Promotes the inactivation of the enzyme
d. Increases the Km of the enzyme
A
Which among the following do not occur during Competitive Enzyme Inhibition?
a. Vmax Unchanged
b. Substrate and Inhibitor bind at the same time
c. KmIncrease
d. Cross 1/Vmax of Lineweaver-Burke Plot
B
Which among the following inhibitors are reversible?
a. Lovastatin
b. Penicillin
c. Aspirin
A
The Michaelis-Menten constant Km represents which of the following?
a. Dissociation constant of the ES complex
b. [Substrate] at Vmax
c. [Substrate] at Vmax/2
d. Vmax at highest [substrate]
C
- What happens when enzymes are heated to very high temperatures?
a. Velocity increase in velocity due to denaturation.
b. They function more efficiently
c. Velocity decreases in velocity due to denaturation.
d. Rate of the reaction increases.
C
The primary role of a cofactor is:
a. To slow the reaction down
b. Assist enzymes in turning substrates into products
c. Modify the function of the enzyme
d. Increase the activation energy
B
Which of the ff is TRUE about the characteristics/attributes of HMG CoA reductase as a rate-limiting enzyme?
a. Activity is not affected by number of allosteric molecules
b. Catalyzes the first irreversible step of a metabolic pathway
c. Catalyzes the slowest reaction in a multi-step pathway
d. Favors a highly spontaneous and irreversible reaction
C
Which regulatory mechanism affects HMG CoA reductase activity in a patient with hypercholesterolemia?
a. Allosteric (Non Covalent modification)
b. Feedback inhibition
c. Induction or Repression of enzyme synthesis
d. Reversible covalent modification
e. Zymogen activation
B
Which of the following are components of the active site of the HMG CoA reductase, EXCEPT?
a. Allosteric effectors
b. Amino acids in the active site
c. Coenzymes
d. Prosthetic groups
A
Choose the CORRECT enzyme classification: chemical reaction catalyzed pair for HMG CoA reductase
a. Isomerase : transfer of PO4 group from ATP to an acceptor
b. Kinase : transfer of functional group within the same molecule
c. Lyase: condensation of two substrates in the presence of ATP
d. Oxidoreductase : transfer of an H to an acceptor molecule
D
Denaturation is an effect of which factor affecting the activity of HMG CoA reductase?
a. Cofactor
b. pH
c. Substrate concentration
d. Temperature
D
- HMG CoA reductase accelerates a chemical reaction in the biologic system via: *
a. Changing the concentration of the reactants and products.
b. Changing the equilibrium constant of the reaction.
c. Inducing a conformational change in the substrate.
d. Lowering the energy of activation of the reaction.
D
