Page 180 - PG 101-Course notes مذكرة النظري 24-25 with spec

Medicinal plants (PG 101) Level 1 Clinical Pharmacy-PharmD

3-Mechanism of enzyme action:

1- In absence of enzymes the substrates have specific kinetic energy (not enough

to complete the biological reaction).

2- When the molecules of substrates reach a certain energy level (energy of

activation) they interact.

3- The enzymes act by decreasing such energy level.

4- Enzymes active centers carry the interacting molecules so that interacting

groups are oriented adjacent.

E (enzyme) + S (substrate) → ES → E+ P 1 + P 2 (product)

5- Two models explain the mechanism of action of enzymes:

b- induced-Fit
a- The lock and
model
key model

a- The lock and key model states that the enzyme’s active site shape is specific and

complimentary in shape to a specific substrate. If the substrate does not fit the

active site, no enzymatic reaction can occur. Just as a specific key fits a specific

lock, each substrate has a specific enzyme with a complimentary active site.

Enzyme returns from the reaction unchanged and can now react with more substrate

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