U3 AOS1 Topic 6: Enzyme Introduction and Model

Enzymes are proteins which catalyze biochemical reactions. Biochemical reactions involve cellular respiration, detoxification in liver and DNA replication. These reactions need energy called as activation energy to start the process. Enzymes speed up the biochemical reactions by lowering this activation energy. The reactants of biochemical reaction facilitated by enzymes are called as substrates. Enzyme binds to the substrate and coverts the substrate into product. Enzyme remains unchanged and leaves the reaction to participate in further reactions.

Structure of Enzyme:          

Enzyme being a protein is made up of amino acids. The three dimensional structure of enzyme includes alpha helices and beta sheets both of which are secondary structures of protein. Enzyme has active site on which a specific substrate can bind.

Features of Enzyme:

Enzymes are reusable. As enzymes are not used up in the reaction and leave a reaction unchanged, they can be used up again in further reactions.

Enzymes are specific. They can bind to a specific substrate only and therefore catalyze only one chemical reaction.

Enzymes can catalyze reversible reactions. Same enzyme can catalyze both forward and reverse reactions. For example, if enzyme is use to build up large molecules it can break those large molecules into smaller ones.

Enzymes only speed up the reactions. Biochemical reactions can occur naturally but takes time therefore enzymes are used to speed up these reactions.

Enzymes have active site on which specific substrate can fit in.

Enzymes are proteins in nature made up of amino acids.

Enzymes are organic catalysts which can speed up only biochemical reactions. Some inorganic catalysts such as metal ions can also speed up various reactions but are not considered as enzymes.

Enzymes can catalyze each step of an entire biochemical pathway.

Each enzyme has a specific name but all names ends with suffix “-ase”.

Name of Enzyme is written above the arrow in a chemical equation.

 

Binding site of substrate is complementary in shape to the active site of enzyme. When substrate binds to active site there is conformational change in active site so that the substrate can fit in.

Lock and key model vs Induced fit model:

Lock and key model shows that substrate binds perfectly to active site of enzyme as a key can fit into a lock.

Whereas, induced fit model shows that whenever a substrate encounters an active site of enzyme there is conformational change in active site and substrate so that both can fit perfectly into each other.