Active Site and models of the Enzyme MCQ - Practice Questions with Answers

How Enzymes Work - Active Sites and Models

Active Sites:

• Enzymes bind the specific substrates on regions called active sites to form enzyme-substrate complexes.
• By binding substrates, enzymes stabilize the energy of the transition state, which in turn stimulates the breakage of old bonds and formation of new bonds.
• At a constant concentration of enzyme, the enzyme activity will continue to rise up until a certain maximal value. 
• This maximal value represents the condition in which all the active sites are filled with the appropriate substrate.
• The active site is a specific region on enzymes that binds to the substrate.
• The active site is a three-dimensional crack in the enzyme that contains the catalytic groups which catalyse the actual reaction.
• As enzymes are proteins, the active sites have a combination of unique amino acid residue.
• Each residue has a different property.
• These properties provide specific environment suited to bind to a very specific chemical substrate.
• Active sites stabilize the transition state.
• Active sites make up only a small component of the overall enzyme. The remaining portion of the enzymes acts to create and support the active site by bringing residues together.

Models:

• The active site and the substrate bind via non-covalent bonds.
• In order for these bonds to be functional, the distance between the active sites and substrate should be minimal.
• It implies that the substrate must fit in the active sites. 

1. Lock and Key Model:  It was put forward by Emil Fischer in 1894. It suggests that the substrate fit into active site like a key fits into the lock, all because of exact complementary shapes.
    
2. Induced Fit Model:  It is modification of lock and key hypothesis which was proposed by Koshland in 1959. It suggests that the shape of the active site becomes complementary to the substrate when the substrate binds to the active site.