Enzyme Activity and Inhibition Notes

Enzymes are highly selective in the reactions they catalyze; each enzyme promotes a specific chemical reaction.
The molecule that an enzyme acts on is called the substrate.
Enzymes illustrate the close link between structure and function: each enzyme has a unique three‑dimensional shape that determines which reaction is promoted.
The active site is a region with a shape and chemistry that fit the substrate; it is typically a pocket or groove on the enzyme surface.
Substrate docking into the active site can cause the active site to change shape slightly to embrace the substrate and catalyze the reaction.
This interaction is called induced fit: the entry of the substrate induces a conformational change that tightens the fit between substrate and active site.
Analogy: handshake — as hands touch, they adjust shape slightly to make a better fit.
After the products are released, the enzyme can accept another substrate molecule. Enzymes can function repeatedly (catalyze multiple rounds).

The active site’s shape and chemistry determine which substrate can bind.
Induced fit means the enzyme is not a rigid lock; it adapts to snugly accommodate the substrate during catalysis.
The concept highlights how minor structural adjustments can significantly influence catalytic efficiency.

Figure 5.9 (from the transcript) traces the action of lactase, an enzyme that breaks down the disaccharide lactose (the substrate).
Lactase is underproduced or defective in lactose‑intolerant individuals.
Many enzymes are named for their substrates, with an “-ase” ending (e.g., lactase).

Enzyme inhibitors are molecules that bind to an enzyme and disrupt its function, thereby slowing or stopping a metabolic reaction (Figure 5.10 from the transcript).
Competitive inhibitors (substrate imposters) bind to the active site, blocking substrate access (analogy: you can’t shake a person’s hand if someone else puts a banana in it!).
Noncompetitive inhibitors bind to a site remote from the active site; binding changes the enzyme’s shape and reduces activity.
The binding of an inhibitor can be reversible in many cases.
Feedback inhibition (a form of reversible inhibition) occurs when a product inhibits an enzyme required for its own production, preventing wasteful overproduction.

Many beneficial drugs work by inhibiting enzymes.
- Penicillin blocks the active site of an enzyme involved in bacterial cell-wall synthesis.
- Ibuprofen inhibits an enzyme involved in transmitting pain signals.
- Many cancer drugs inhibit enzymes that promote cell division.
Toxins and poisons also act as enzyme inhibitors.
- Nerve gases irreversibly bind to the active site of a vital enzyme involved in transmitting nerve impulses, leading to rapid paralysis and death.
- Many pesticides are toxic insects because they inhibit the same nerve‑related enzyme.

Understanding enzyme inhibition underpins drug design, treatment of diseases, and management of pain and cancer therapies.
Inhibitors can be used therapeutically (e.g., antibiotics, analgesics, anticancer drugs) but can also be dangerous (toxins, nerve agents).
Ethical and practical implications include safety, regulation, and the potential for misuse of enzyme inhibitors in chemical warfare or pest control.

Substrate: the molecule acted upon by an enzyme.
Active site: the region of the enzyme where the substrate binds.
Induced fit: the conformational change in the enzyme upon substrate binding that improves the fit and promotes catalysis.
-ase ending: common naming convention for enzymes based on their substrate or reaction.

The transcript does not provide explicit numerical values, measurements, or equations.
No specific mathematical formulas are given in the provided content.