Enzymes Flashcards
RNA can behave like an enzyme
It is called?
Ribozyme
Number of substrate molecules converted to product per enzyme molecule per second is called?
Turnover number or Kcat
Enzyme with its non protein part is called
Holoenzyme
Enzyme without its non protein part is called?
Apoenzyme
If the non protein part is a metal ion then it’s called?
Cofactor
If the non protein part is a small organic molecule then it’s called?
Coenzyme
Coenzyme that is transiently attached to the enzyme and its form is altered when it dissociates. This coenzyme is called?
Cosubstrate
The coenzyme that is permanently attached to the enzyme and is returned to its original form is called?
Prosthetic group
NAD is an example of what coenzyme?
Cosubstrate
FAD is an example of what coenzyme?
Prosthetic group
What is Activation energy?
the difference between the energy of the substrate and the energy of the transition state.
What makes the transition state different from the substrate or product?
The bonds in the transition state are different from the bonds in the substrate or product.
How does the probability of the formation of transition state increase?
It increases due to the active site.
What does an enzyme do?
It lowers the activation energy of the substrate.
If the substrate concentration is increased then what will happen to the rate of the reaction?
The rate of reaction will increase.
What type of curve is plotted by Allosteric Enzyme? (Reaction velocity against substrate concentration)
Sigmoidal curve because the allosteric enzyme can bind to more than one substrate.
What type of curve is plotted by a typical enzyme?
Reaction velocity against substrate concentration
Hyperbolic curve. The enzyme shows Michaelis Menten kinetics.
What is the effect of temperature on an enzyme?
The rate of an enzyme-catalyzed reaction increases as the temperature is raised. Over a period of time, the enzyme will be deactivated at even moderate temperatures.
What is the effect of pH on an enzyme?
Each enzyme has an optimum pH range. Changing the pH outside of this range will slow enzyme activity. Extreme pH values can cause the enzyme to denature.
What is the optimum pH for pepsin?
2
What is the optimum pH for Trypsin?
6
What is the optimum pH for Alkaline phosphatase?
8
What is the Michaelis Menten equation?
vo = Vmax [S]/ Km + [S]
What does a higher Km mean?
it means that the enzyme has a low affinity.
What does a lower Km mean?
it means that the enzyme has a high affinity.
The rate of reaction depends on the enzyme concentration if the substrate is not limiting.
If the substrate concentration is less than Km then what happens to the rate of reaction?
The rate of reaction is then directly proportional to the substrate concentration.
First-order reaction
The rate of reaction depends on the enzyme concentration if the substrate is not limiting.
If the substrate concentration is more than Km then what happens to the rate of reaction?
The velocity is constant and equal to Vmax. It is independent of the substrate concentration.
Zero-order reaction.
What is Catalytic Efficiency?
Catalytic Efficiency= Kcat/Km
whereas Kcat is the turnover number (Vmax/[E]T) and Km is the Michaelis Menten Constant.
If the Turnover number increases then what will happen to the Catalytic Efficiency of the enzyme?
CE will increase.
If the Km increases then what will happen to the Catalytic Efficiency of the enzyme?
CE will decrease.
If the Turnover number decreases then what will happen to the Catalytic Efficiency of the enzyme?
CE will decrease.
If the Km decreases then what will happen to the Catalytic Efficiency of the enzyme?
CE will increase.
Lineweaver Burk plot is the double reciprocal of the Michaelis-Menten equation. What is LBP is used for?
It used for determining the Vmax and the Km of the reaction.
The irreversible inhibitor of ferrochelatase is known as?
Lead (Pb)
HMG-CoA reductase is inhibited by a drug. What is the name of the drug?
Statin (Reversible Inhibitor)
What is competitive inhibition?
When the inhibitor and the substrate compete for one binding site, this is called competitive inhibition.
What is noncompetitive inhibition?
The binding sites for the inhibitor and the substrate are different for each other in noncompetitive inhibition.
What happens to the Km and the Vmax of the reaction in competitive inhibition?
The Km increases and the Vmax remains unchanged
The Vmax does not change because increasing amounts of the substrate can swamp the inhibitor (present in fixed concentration).
What happens to the Km and the Vmax of the reaction in noncompetitive inhibition?
The Km is unchanged and the Vmax decreases.
Why is Km unchanged in noncompetitive inhibition?
In non-competitive inhibition, the Km does not change. This is because Km is a measure of the affinity of the enzyme for its substrate and this can only be measured by the active enzyme. The fixed amount of inactive enzyme in non-competitive inhibition does not affect the Km and the Km, therefore is unchanged.
Irreversible inhibitors bind to the enzyme by means of what kind of bond?
covalent bond
Reversible inhibitors bind to the enzyme by means of what type of bond?
Noncovalent bond
Allosteric Enzymes are regulated by molecules called effectors. There are positive and negative effectors. What do they do?
Positive Effectors which increase enzyme activity.
Negative Effectors which inhibit enzyme activity.
What are Homotropic effectors?
Substrate bind to the other site of the allosteric enzyme and it is usually a positive effector.
What are heterotropic effectors?
The effector is not a substrate, it is the product that binds to the other noncatalytic site and it mainly inhibits the enzyme activity.
