1. Which of the following is not true for substrate collision theory?
a) Both enzyme and substrate stumble upon each other
b) Both enzyme and substrate provide good molecular orbital interactions
c) Specificity of the substrate binding site
d) Both enzyme and substrate should be flexible in forming transition states
Explanation: Specificity of the substrate binding site comes into picture when dealing with active site. The following is essential for forming transition state by substrate collision theory:
* Stumble upon each other through proper diffusion limited collision.
* Good molecular orbital interactions by enduring the changes in the medium.
* Overwhelm the vander waals repulsive forces that happen commonly between them.
* Flexibility in forming transition states through proper interactions.
2. The disruption of interactions between substrate and solvent is referred to as __________
a) desolvation
b) molecular orbital steering
c) protonation
d) deprotonation
Explanation: The removal and addition of protons [H+] is referred to as deprotonation and protonation respectively. Molecular orbital steering explains that the active residues should guide the groups in the substrate for catalysis to occur. Desolvation refers to disruption of interactions between substrate and interaction. This may be achieved by multiple non-covalent interactions between hydrophobic active site group and the substrate.
3. Which of the following is not explained by molecular orbital steering?
a) The juxtaposition of the side chain groups of amino-acid and the reactive groups of the substrate is not sufficient for proper catalysis
b) Overwhelm the vander waals repulsive forces that happen commonly between them
c) The active residues should guide the groups in the substrate for exact interaction by thermal vibration due to elevated temperature
d) Thermal vibration create motion in the active site amino acid side chain that direct reactive groups in the substrate to interact
Explanation: Overwhelm the vander waals repulsive forces that happen commonly between them is not explained by molecular orbital steering. It is a part of substrate collision theory. Molecular orbital steering explains the following:
* The juxtaposition of the side chain groups of amino-acid and the reactive groups of the substrate is not sufficient for proper catalysis.
* The active residues should guide the groups in the substrate for exact interaction by thermal vibration due to elevated temperature.
* Thermal vibration create motion in the active site amino acid side chain that direct reactive groups in the substrate to interact.
4. If the catalysis involves participation of small organic molecules, cofactors, and amino-acid side chains from the enzyme is termed as ____________
a) specific acid base catalysis
b) general acid base catalysis
c) substrate collision theory
d) lock and key model
Explanation: If the catalysis involves participation of small organic molecules, co-factors and amino-acids side chains from the enzyme is referred to as general acid-base catalysis. If the catalysis involves water molecules for proton donation or acceptance, the catalysis is referred to as general acid-base catalysis. Lock and key model is proposed by Emil Fischer in 1958. Substrate collision theory deals with binding between enzyme and substrate molecule.
5. ________________ involves substrates forming transient covalent bond with the residues present in the active site
a) Covalent catalysis
b) Specific acid-base catalysis
c) General acid-base catalysis
d) Lock and key model
Explanation: Catalysis which involves substrates forming transient covalent bond with the residues present in the active site is referred to as covalent catalysis. If the catalysis involves participation of small organic molecules, co-factors and amino-acids side chains from the enzyme is referred to as general acid-base catalysis. If the catalysis involves water molecules for proton donation or acceptance, the catalysis is referred to as general acid-base catalysis. Lock and key model proposes that as a key fits into a lock same way, substrate fits into the enzyme.
6. The covalent catalysis is aided by one of the following method?
a) General acid-base catalysis
b) Specific acid-base catalysis
c) Nucleophilic catalysis
d) Substrate collision theory
Explanation: Covalent catalysis involves substrates forming transient covalent bond with the residues present in the active site. The covalent catalysis is aided by nucleophilic and electrophilic catalysis. In most of the enzymatic reaction protons are involved. General and specific acid-base catalysis are types of acid-base catalysis. Substrate collision theory says about the binding between substrate and enzyme.
7. Which is the first step involved in chymotrypsin mediated peptide bond hydrolysis?
a) Acylation
b) Specific acid-base catalysis
c) General acid-base catalysis
d) Deacylation
Explanation: Chymotrypsin reaction with its substrates takes place in 2 stages, an initial burst phase at the beginning of the reaction and steady state phase following MM kinetics. The mode of action is explained in 2 steps:
* Acylation of substrate to form an acyl-enzyme intermediate.
* Deacylation in order to return the enzyme to its original state.
Hence the first step is acylation.
8. Which of this is not true for the active site of an enzyme?
a) Active site is constituted by 3 to 4 amino-acids in a big protein structure
b) Active site is mainly constituted by non-polar amino acids for catalysis to take place
c) Water is generally included in the site
d) Active site is a cleft formed by different amino-acids from different positions in an enzyme molecule
Explanation: Active site has the following features:
* It is a cleft formed by different amino-acids from different positions in an enzyme molecule.
* It is constituted by 3 to 4 amino-acids in a big protein structure.
* It is mainly constituted by non-polar amino-acids for catalysis to take place. Sometime polar may also be present. Water is excluded from the site unless it’s a reactant.
* The ES complex is a must to form products. So, appropriate substrate binding site is essential for any enzyme.
* The specificity of substrate binding is mediated by spatial arrangement of atoms in an enzyme’s substrate binding site as well as substrate.
Therefore, water is generally included in the site is not true for active site.
9. Daniel Koshland proposed a model for enzyme’s reaction mechanism in 1958 which is termed as __________
a) Induced fit model
b) Lock and key model
c) Henri kinetic model
d) Miachelis Menten kinetic model
Explanation: Henri and Michalis Menten kinetic model was proposed in 1903 and 1913 respectively. The main difference is that Miachelis and Menten did a strong experimental work to prove that enzyme substrate catalyzed reaction will possess a hyperbolic curve. Daniel Koshland proposed induced fit model. Whereas, Emil Fischer proposed lock and key model.
10. In lock and key model, the enzyme catalyzed reaction may produce an adverse reaction.
a) True
b) False
Explanation: The lock and key model represents that as a key fits into a lock, the substrate in the same way binds to active site of the enzyme producing required products. In this model, the catalytic site is freely accessible. Thus any other compound can also interact with the active site and produce an adverse reaction. Hence the statement.