Describe three ways in which enzyme activitylevels in a cell can be regulated. I

Question

Describe three ways in which enzyme activitylevels in a cell can be regulated. Include at least one example inwhich the substrate itself is involved in regulation, and at leastone in which a non-substrate molecule is involved. For asubstrate/enzyme interaction, describe the induced fit model ofenzyme activity. For a non-substrate/enzyme interaction, describehow the enzyme itself is affected by that interaction. Finally,explain how negative feedback is often used to maintain metaboliccontrol of enzymatic pathways.

Explanation / Answer

The key and lock idea is too simple, sometimesthe fit is not perfect between enzyme and substrate. A theorycalled the induced-fit theory retains the key–lock idea butpostulates in addition that the substrate must do more than simplyfit into shape of an active site. Rather, the theory states, thebinding of the substrate to the enzyme must cause a change in theenzyme that results in the proper alignment of the catalytic groupson its surface. This is one way a substrate is involved inregulation.

Another possible scenario is“noncompetitive inhibition” in which a compoundinhibits the reaction of an enzyme but does not prevent the bindingof the substrate. In this case, the inhibitor compoundbinds the enzyme at a placewhich is too far away from thesubstrate to react. The site at which the inhibitor binds to theenzyme is not the active site and is called allostericsite. This is one way a NONSUBSTRATEis involved.

Enzyme flexibility is extremely importantbecause it provides a mechanism for regulating enzymaticactivity. If an enzyme produces toomuch of one substance it may act as an inhibitor for the enzyme atthe beginning of the pathway that produces it, causing productionof the substance to slow down or stop .

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