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The specific action of an enzyme with a single substrate can be explained using a Lock and Key analogy first postulated in 1894 by Emil Fischer. In this analogy, the lock is the enzyme and the key is the substrate. Only the correctly sized key (substrate) fits into the key hole (active site) of the lock (enzyme).


Lock and Key Hypothesis. In order to explain why enzymes have such a high level of specificity, Emil Fischer in 1894 suggested that both a substrate and an enzyme have specific geometric shapes that fit exactly into each other. This idea of both substrates and enzymes having a natural geometric fit has been called the lock and key hypothesis.


The lock-and-key model refers to the way in which a substrate binds to an enzyme's active site. Similar to how a key has to be the correct one for a lock, no reaction takes place if an incorrect substrate tries to bind. The active site of an enzyme is a specific region that receives the substrate.


Enzymes are biological catalysts which speed up reactions. They are specific for their substrate. The lock and key hypothesis models this. Enzymes are denatured at extremes of temperature and pH.


"Lock and key" model. To explain the observed specificity of enzymes, in 1894 Emil Fischer proposed that both the enzyme and the substrate possess specific complementary geometric shapes that fit exactly into one another. This is often referred to as "the lock and key" model.: 8.3.2 This early model explains enzyme specificity, but fails to explain the stabilization of the tran...


The enzyme sites work like the keyhole in a lock. Like the lock on a door, only certain keys will fit in the keyholes, and perhaps only one key will open the lock. Put the wrong key into the keyhole, and you can prevent the correct key from unlocking the door.


In the lock and key mechanism, the binding pockets for the substrates exist in full form in the free enzyme. The substrates readily bind and the reaction is driven because the active site has better complementarity to the transition state of the reaction than to the substrates at the ground state.


LOCK & KEY THEORY Enzymes (e.g. globular proteins) are biological catalysts which speed up chemical reactions without being use dup in the process. They are vital b/c otherwise reactions would be too slow and the body can’t meet demands => cells die. Each enzyme only catalyses one reaction/c only a specific shaped […]