Question

enzyme activity is often influenced by the presence of other substances. some of these may enhance an enzymes activity (cofactors), while others may reduce it (enzyme inhibitors). enzyme inhibitors may be of two kinds: reversible and irreversible. reversible inhibitors are used to control enzyme activity. there is often an interaction between the substrate or end - product and the enzyme controlling the reaction. buildup of the end - product or a lack of substrate may serve to deactivate the enzyme. this deactivation may take the form of competitive (competes for the active site) or non - competitive inhibition. while non - competitive inhibitors have the effect of slowing down the rate of reaction, allosteric inhibitors block the active site altogether and prevent its functioning.

1. describe the general role of cofactors in enzyme activity.
2. heavy metals can be very toxic to life forms.

(a) name four heavy metals that are toxic to humans:
(b) explain in general terms why these heavy metals are toxic:

1. there are many enzyme inhibitors that are not heavy metals (e.g., those found in some pesticides).

(a) name a common poison that is an enzyme inhibitor, but not a heavy metal:
(b) try to find out how this poison interferes with enzyme function. briefly describe its effect on a named enzyme:

1. explain the difference between competitive and non - competitive inhibition:
2. explain how allosteric inhibitors differ from other non - competitive inhibitors:

Explanation:

1. Cofactors are non - protein substances that assist enzymes in their catalytic activity. They can be metal ions or small organic molecules and are often required for an enzyme to function properly.
2. (a) Four toxic heavy metals to humans are cadmium (Cd), lead (Pb), mercury (Hg), and arsenic (As). (b) These heavy metals are toxic because they bind tightly and permanently to the active sites of enzymes, destroying their catalytic properties.
3. (a) Cyanide is a common poison that is an enzyme inhibitor but not a heavy metal. (b) Cyanide binds to the cytochrome c oxidase enzyme in the electron - transport chain, preventing the transfer of electrons and thus inhibiting cellular respiration.
4. Competitive inhibition occurs when the inhibitor molecule has a similar structure to the substrate and competes with the substrate for the active site of the enzyme. Non - competitive inhibition occurs when the inhibitor binds to a site other than the active site (an allosteric site), causing a conformational change in the enzyme that reduces its activity, and the substrate can still bind to the active site but the reaction rate is decreased.
5. Allosteric inhibitors bind to an allosteric site on the enzyme, causing a conformational change that blocks the active site altogether and prevents the enzyme from functioning. Other non - competitive inhibitors slow down the rate of reaction by binding to an allosteric site and changing the enzyme's shape in a way that makes it less efficient, but they do not completely block the active site like allosteric inhibitors.

Answer:

1. Cofactors assist enzymes in catalytic activity, often required for proper function.
2. (a) Cadmium (Cd), lead (Pb), mercury (Hg), arsenic (As). (b) Bind tightly and permanently to enzyme active sites, destroying catalytic properties.
3. (a) Cyanide. (b) Binds to cytochrome c oxidase in electron - transport chain, inhibiting cellular respiration.
4. Competitive: Inhibitor competes with substrate for active site. Non - competitive: Inhibitor binds to allosteric site, changes enzyme shape, reduces activity while substrate can still bind to active site.
5. Allosteric inhibitors completely block the active site by binding to an allosteric site; other non - competitive inhibitors just slow down the reaction rate by changing enzyme shape without completely blocking the active site.