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Mechanism of enzyme mediated lowering EA
Catabolic Reaction – Enzymes increases the chance that specific bonds in a substrate will break by:
Slightly distorting substrate molecules bound to the active site which strains these bonds.
Orientating substrate at the active site such that these bonds are exposed to attack by catalytic residues.
Anabolic Reaction – Enzymes increases the chance of bond formation by:
Temporarily binding substrate molecules next to each other in the correct orientation at the active site.
Lock and Key Hypothesis
Substrate molecules has a complementary shape and charge to the active site of an enzyme. Hence, substrate molecules fits into the active site (like key into a lock) forming an enzyme-substrate complex.
At the active site:
Enzyme-substrate complex is stabilized by intermolecular ionic and weak H-bonds between the contact residues and substrate molecules.
Catalytic R-groups of amino acids at the active site are positioned to act on the bonds within the substrate molecules.
The H-bonds and ionic bonds between substrate molecule and catalytic R-groups weaken the bonds within the substrate, causing them to break.
General structure of an enzymes
The enzyme is a large globular protein with tertiary and/ or quarternery structure and has a specific configuration.
The active site of an enzymes has a precise shape and proper charge to bind to specific substrate molecules.
- Constitutes only a small portion of the enzyme and consists of catalytic and contact residues.
- Contact residues fit with substrate molecules and determine specificity of active site.
- Catalytic residues act on specific bonds within the substrate to form products.
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