09 May 2021

5.1. Enzymes

Many chemical reactions in living things are helped along by enzymes. Enzymes are proteins that function as biological catalysts.

A catalyst = a substance that increases the rate of a chemical reaction and is not changed and not used up by the reaction.

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Enzymes and reactions

Most enzyme names end in –ase, e.g. lipase, protease.

Enzymes make sure that reactions take place at a necessary speed to sustain life. Without enzymes, those reactions would still take place, but at too slow of a speed for organisms to survive.

Enzymes can build up or break down molecules.

Enzyme specificity
Each enzyme is specific to (can only take care of) a chemical reaction. It has high specificity.
The shape of the active site is complementary to its substrate. i.e.: Amylase and protease have different shapes of active sites. Protease cannot break down starch due to shape differences and the substrate won't fit in the enzyme's active site.

During a reaction:
  • enzymes and substrates have a temporary bond, creating the enzyme-substrate complex
  • the product(s) is released
  • the enzyme molecule is free to combine with a different substrate molecule

Factors affecting enzyme
A) Temperature
  • enzymes work slow at low temperatures. 
  • as temperature increases --> more kinetic energy --> higher rate of collisions
  • until reaches optimum temperature 
    • 37 °C in humans
  • beyond the optimum temperature --> enzyme molecules start to permanently lose shape --> deforms active site --> enzyme is denatured; substrate no longer fits into the enzyme's active site
    • most enzymes stop working beyond 60 °C

B) pH
  • enzymes work best at the optimum pH
  • at lower or higher pH, they're less effective
  • at extreme pH, they're denatured (active site changes shape permanently, substrate can no longer fit in)

Different enzymes have vastly different pH levels at which they work at. You're not required to know this specifically for the syllabus, but it can give you a good idea about the diversity of enzymes.

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