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Enzymes (part 2): Characteristics of enzymes

Lesson objectives<br>- investigate and explain the effects of temperature and pH on the rate of enzyme catalysed<br>reactions

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Enzymes (part 2): Characteristics of enzymes

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  1. Enzymes found at home

  2. Biological washing powders

  3. Enzyme power!

  4. Qn: How would enzymes help to clean clothes with stains on them? Qn: Can any enzyme be used in biological washing powders?

  5. *Characteristics of enzymes

  6. Some characteristics of enzymes learnt earlier…. Enzymes 1. alter the rates of reaction 2. are specific 3. are required in minute amounts

  7. Effect of temperature on enzyme action (temp. at which enzyme is most active) denaturation Note: For every increase in 10°C in temperature, the rate of reaction doubles (until the optimum temp. is reached)

  8. Why does enzyme activity increase as temperature increase? ? All particles are in constant random motion ? In a reaction, enzyme and substrate molecules move and collide with each other at random ? Increasing temperature would increase the kinetic energy supplied to the reacting molecules ? When the reacting molecules move faster, the substrate and enzyme molecules collide with each other more often ? The rate of enzyme-substrate complex formation increases ? However enzyme activity only increases till the optimum temperature

  9. Why does enzyme activity decrease at higher temperature? ? All enzymes are made of proteins ? In most proteins the chains of amino acids are coiled or folded up to give the protein a 3D shape ? The coils are held in place by weak H-bonds ? An increase in temperature increases the vibrations in the atoms of the enzyme ? At higher temperatures, the vibrations become so violent they break the bonds in the enzyme ? The protein is said to be denatured

  10. Denaturation ? Results in the loss of the enzyme’s active site ? Substrates are therefore unable to fit into the active site and no reaction will occur ? pH changes (alkali or acid) also bring about denaturation

  11. Effects of pH on enzyme action (optimum pH) (enzyme activity ↓ )

  12. Points to note on pH: Different enzymes work best in different optimum pH Extreme changes in pH causes denaturation Maximum activity at optimum pH (pH on either side causes activity to decrease) 1. 2. 3.

  13. Different enzymes = different optimum pH

  14. Reaction rate vs substrate concentration curve What do you observe?

  15. Limiting factor Definition: Any factor that directly affects the rate at which a process (e.g. chemical reaction) occurs if its quantity is changed Note: If quantity of the factor is increased, the rate of the process increases

  16. More enzyme more products formed per unit time till Y (enzyme conc. becomes the limiting factor) [substrate] ↑ ↑ ; rate of reaction ↑ ↑ till X Further ↑ enzymes (limiting factor); amt. of products formed per unit time is the same] ↑ ; no ↑ ↑ in rate [saturation of

  17. Co-enzymes ? Non-protein organic compounds ? Some enzymes require it to bind to them before they can catalyse reactions ? B complex vitamins are essential components of many co-enzymes

  18. Applying study tip (mneumonics) In pairs, list all the characteristics of enzymes and come up with a suitable mneumonics. e.g. specific = S alter reaction rate = A ….. Using first letter of the various characteristics to form a phrase…

  19. Summary (Using Mnemonics) ? Characteristics of enzymes S M R T C A p E nzyme & substrate concentrations pecific (lock and key hypothesis) inute amounts (renewable) eversible reactions emperature o-enzymes may be needed lter rates of chemical reactions (lowers activation energy) H

  20. Overview Overview Biological Molecules Water and Living Organisms Carbohydrates, Fats and Proteins Enzymes Lock & Key hypothesis Specificity Factors affecting enzyme reactions Speed up chemical Mode of Action Rxn Not chemically altered at the end Of Rxn Lowering Activation Energy pH Temperature

  21. Quiz!

  22. Quiz… 1. After observing some biological washing powders, it was noted that some brands recommend that clothes be washed at low temperatures (<45ºC). Why? Enzymes are affected by temperature. Regulating temperature ensures that the enzymes work within its temperature range to prevent denaturation.

  23. Quiz Why is it that some washing powders are able to endure higher temperatures? 2. Different enzymes used; different enzymes have different temperature range i.e. different optimum temperature as well! What purpose are higher temperatures for? 3. To remove tougher stains, e.g. oil stains

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