Describe the mechanism of enzyme action based on
the lock-and-key hypothesis.
Answer
An
enzyme is a large globular protein with a specific three dimensional shape and
has specific region called active site containing amino acid side chains that
are complementary to the substrate. In the lock-and-key hypothesis, the shape
of substrate (key) fits into the active site of the enzyme (lock). The binding
of substrate to the enzyme causes changes in the distribution of electrons in
the chemical bonds of the substrate and causes the reactions lead to the
formation of products. This process forming an enzyme-substrate complex. The
products formed have different shape from the substrate. They therefore
released from the active site. The enzyme regenerated can be used again to bind
with another substrate.
The induced-fit hypothesis is a modified version
of lock-and-key hypothesis. When the substrate bind to the active site, it
leads to the shaping of the enzyme. The substrate was now close fit to the
enzyme. The induced-fit brings chemical groups of the active site into
positions that enhance their ability to catalyse the chemical reactions. Bonds
are broken and new bonds are formed. This makes it easier for the substrate to
changed into products thus, lowering the activation energy needed.
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