C1.1 HL Enzyme Inhibitors
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What is an enzyme inhibitor?
A chemical that reduces or stops enzyme activity by binding to the enzyme.
What is competitive inhibition?
Inhibitor resembles substrate and competes for the active site; effect overcome by increasing substrate concentration.
What is non-competitive inhibition?
Inhibitor binds to an allosteric site, altering enzyme shape so substrate cannot bind; not overcome by more substrate.
What is feedback inhibition?
A type of allosteric inhibition where the end product binds to the first enzyme in the pathway, shutting it down when enough product accumulates.
What is allosteric regulation?
Regulation by a molecule binding to an allosteric site, changing enzyme conformation to activate or inhibit it.
What is the difference between reversible and irreversible inhibition?
Reversible inhibitors unbind; irreversible inhibitors form covalent bonds, permanently inactivating the enzyme.
Example of a competitive inhibitor in medicine.
Statins competitively inhibit HMG-CoA reductase, reducing cholesterol synthesis in the liver — safe because inhibition is reversible.
Example of an irreversible inhibitor.
Penicillin irreversibly inhibits transpeptidase, blocking bacterial cell wall synthesis.
Why does penicillin not harm human cells?
Humans lack cell walls and transpeptidase, so penicillin is selective to bacteria.
Why are heavy metals toxic?
Hg²⁺, Pb²⁺, Ag⁺ bind to –SH groups in enzyme active sites, denaturing them and halting catalysis.
How does arsenic inhibit enzymes?
Binds to –SH or phosphate groups, acting as either a competitive or non-competitive inhibitor depending on the enzyme.
What happens to the rate of reaction with competitive vs non-competitive inhibitors?
Competitive: rate can reach Vmax if substrate ↑; Non-competitive: Vmax decreases, unaffected by substrate concentration.