Topic Biomolecule (Enzyme) Essay - Main Points!

Q) How does inhibitors affect enzyme activity ?

Main points
Key idea:	Basic effect of all enzyme inhibitors
· Decrease enz activity, hence rate of enz-catalyzed rx
Key idea:	Competitive inhibitors
· Structure:  inhibitor has a similar shape as substrate · Mode of action : binds reversibly to active site (AS) of enz, compete w substrate for AS · Details : effect of inhibition can be overcome by increasing substrate conc · which increases chance of successful collision b/w substrates & enz over inhibitors to enz · At high substrate conc, rate of rx can reach same max velocity (Vmax) as non-inhibited rx · Km for rx is increased b/c inhibitor lowers affinity of enz active site for substrate
Key idea:	Non-competitive inhibitors
· Structure:  does not have a similar shape as substrate · Mode of action: binds reversibly or irreversibly to inhibitor site but not at AS of enz · E.g. allosteric inhibition · Details : inhibitor binds to allosteric site, induces a change in specific shape of AS · Substrates unable to bind to AS to form enz-substrate complexes · Inhibitor cannot be overcome by increasing substrate concentration. · Inhibitor decreases Vmax of rx but does not affect Km of rx
Key idea:	End product inhibition or feedback inhibition
· What : Inhibits enz that catalyze rx at beginning of pathway, stops further syn of itself when sufficient amount is made · Mode of action: Accumulation of end product of metabolic pathway, acts as an allosteric inhibitor
Comments: (i) Visualize the answer with the aid of a labelled diagram. (ii) Verbalize the answer + write down the main points w/o referring to the answer (use abbreviations) (iii) Read again within the next 24h & once more within 72h (do not spend more than 10min) (iv) Km value is the concentration of the substrate at half the maximum velocity of the enzyme-catalyzed reaction. The larger the 1/ Km value, the higher the affinity of the enzyme for the substrate (v) The shape of the graph of an enzyme exhibiting allosteric inhibition is a sigmoidal shaped curve. (vi) In addition to allosteric inhibition, there are enzymes which are regulated by allosteric activator. When the activator binds to the allosteric site, it induces the change of the shape of active site such that substrate can now bind to it to form enzyme substrate complex.