Enzyme Function and Models
Enzymes work by providing an alternative pathway for reactions with lower activation energy. They're highly specific - each enzyme only works with particular substrates that fit into their active site.
There are two main models explaining how this works. The lock and key model suggests the active site has a perfectly complementary shape to the substrate, like a key fitting a lock. However, the induced fit model is more accurate - here, the active site moulds around the substrate when it binds, creating the perfect fit needed for the reaction.
Once the enzyme-substrate complex forms, the products are created and released. Since the products have different shapes, they don't fit the active site anymore and detach, leaving the enzyme ready for the next reaction.
Quick Tip: Remember that enzymes aren't used up in reactions - they can be recycled over and over again!
Factors Affecting Enzyme Activity
Temperature has a major impact on enzyme function. As temperature increases, enzyme activity increases up to the optimum temperature where the enzyme works most efficiently. Beyond this point, the enzyme denatures - its shape changes permanently and it stops working.
Enzyme concentration affects reaction rates too. More enzymes mean more active sites available for substrates to bind to, increasing reaction speed. However, there's a limit - once all substrates are occupied, adding more enzymes won't help.
Similarly, substrate concentration increases reaction rates until you reach saturation point. After this, enzyme concentration becomes the limiting factor, and adding more substrate makes no difference.
Coenzymes are organic helper molecules (often vitamins) that don't bind permanently but help substrates attach to enzymes. Activators are inorganic metal ions that temporarily bind to enzymes, altering their active sites to make reactions more feasible.
Enzyme Inhibition
Inhibitors are substances that slow down or stop enzyme reactions, and they come in several types. Irreversible inhibitors like heavy metal ions (mercury, silver) permanently damage the enzyme structure by breaking disulphide bonds, changing the active site shape forever.
Reversible inhibitors bind temporarily through weak bonds and can be removed. Competitive inhibitors have similar shapes to the substrate and compete for the same active site - they slow the reaction but don't change the final amount of product.
Non-competitive inhibitors bind to a different site called the allosteric site, changing the active site's shape so substrates can't bind properly. Unlike competitive inhibition, increasing substrate concentration won't overcome this type of inhibition.
Exam Tip: Remember that competitive inhibition can be overcome by adding more substrate, but non-competitive inhibition cannot!
