IGCSE BIOLOGY section 2.5: ENZYMES

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  • ENZYMES
    • CATALYST: the word catalyst means to speed something up. When referred to in conjunction with enzymes it means that enzymes are catalysts for chemical reactions.
      • However catalysts remain unaffected by the reaction they are involved in.
    • Are proteins that work as biological catalysts.
    • Each enzyme has an optimum temperature, around 37*C for humans, the closer to this temperature they are the better they work.
      • However if the temperature is too high or too low then the enzyme will become denatured and therefor ineffective.
    • The enzymes are also affected by pH level. Each emzyme has its own optimum pH level and if the pH level varies too much from ots optimum the enzyme will become denatured.
      • Pepsin (stomach) is an enzyme with a pH balance of pH 2.0 which is very acidic.
      • Amylase (mouth) works best at pH 7.5 which is mostly neutral (slightly basic).
    • Enzymes are folded into complex 3D shapes. The ACTIVE SITE is the part to which substrate molecules attach themselves and allow the enzyme to work as a catalyst.
      • The substrate molecules fit exactly into the active sites of specific enzymes specialised for different molecules. The substrates and enzymes react to form product(s) which are released from the enzyme allowing it to continue with a new pair of substrates.
      • Because of the way the enzymes and substrates fit together, the process is often referred to as the lock and key method. Only 1 key will fit a lock and the concept is also true of enzymes.
    • many washing powders contain enzymes that help to remove stains such as lipase and protease which can help to remove stains like fatty foods and blood.
    • Penicillium, a fungus from which penicillin is produced, makes subtstances to secrete into its surrounding to kill off disease-causing or competitive microbes.

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