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Activation Energy … is the amount of energy needed to start reaction In order to speed up reaction, catalysts are used Enzymes are catalysts in cells.

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Presentation on theme: "Activation Energy … is the amount of energy needed to start reaction In order to speed up reaction, catalysts are used Enzymes are catalysts in cells."— Presentation transcript:

1 Activation Energy … is the amount of energy needed to start reaction In order to speed up reaction, catalysts are used Enzymes are catalysts in

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3 protein active site non-protein part holo enzyme (active enzyme) apoenzyme Cofactor - inorganic - ex: zinc, iron, potassium, copper Coenzyme - organic - ex: vitamins, NAD, FAD, NADP + Non-protein part can be a cofactor or a coenzyme. It is the part which makes an enzyme

4 Enzymes… Are made up of proteins Simple Enzymes: only made up of proteins. Complex Enzymes: are made up of proteins + non protein part

5 Structure of Enzymes… Two major parts: Protein part: Apoenzyme : made up of protein. not catalyze the reaction by itself has to interact with non protein part Non- protein part : Coenzyme: made up of organic molecules (vitamins) Cofactor: made up of inorganic molecules (K, Ca ) ++

6 Structure of Enzymes… Substrate:The molecule which enzyme acts on Active site: Specific region on the enzyme that substrate binds Lock and key Enzyme –Substrate Complex

7 Enzymes are not changed or used up The same enzyme works for the forward and reverse of the reactions Lipid +H2O 3 Fatty Acids +Glycerol One apoenzyme works with only one coenzyme or cofactor Lipase

8 Properties of Enzymes Specificity: Enzymes work with only one type of substrate Final molecule of the reaction is product Not used up, destroyed at the end of reaction Can be used over and over until destroyed by other factors (heat)

9 Properties of Enzymes… Reversibility Catalyze reactions for forward and reverse directions Not determine direction Ratio of equilibrium Only digestive enzymes catalyze reaction in one way Naming According to molecules they act : -ase Exp: Lipase, Amylase or Pepsin, Tripsin According to type of reaction catalizing.

10 Properties of Enzymes… The exact point of effect Surface of area Wider surface Greater rate of reaction Speed Speed up reaction Without enzyme breaking down takes more time

11 Properties of Enzymes… Work in Teams the product of one reaction catalyzed The substrate for another enzyme Place of synthesis Apoenzyme part is protein, so synthesized in ribosomes just like proteins Gene destroyed Enzyme not synthesized Cell dies Starch Amylase Maltase Maltose Molecules Glucose Molecules

12 There are two models that provide explanation to enzyme action: 1.Lock and Key Model: The substrate(s) fits exactly into the active site of the enzyme.Lock and Key Model: The substrate(s) fits exactly into the active site of the enzyme. E + S E – S E + P EnzymeSubstrate Enzyme-substrate complex (temporary) Enzyme

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14 IIn this model, the enzyme has no rigid shape. Instead the enzyme changes shape slightly as the substrate enters the active site. Once it has changed shape, the enzyme fits tightly around the substrate. As the enzyme embraces the substrate it can weaken the chemical bonds in the substrate, which helps the reaction to proceed. TThe enzyme changes shape slightly to grasp the substrate at the active site. 2. Induced Fit

15 Characteristics of Enzyme Action: 1.Small amounts of an enzyme can cause the reaction of large quantities of substrate.Small amounts of an enzyme can cause the reaction of large quantities of substrate. - The time needed for an enzyme-substrate complex to form and a reaction to occur is very short. - A simple enzyme molecule can catalyze thousands of substrate reactions in a

16 2. Enzymes enable cell reactions to take place at normal temperatures Optimum temperature for many enzymes (about 36 o C) temperature ( o C) enzyme

17  At O o C, enzymes do not function although their structure is not changed (they are not denaturated).  The temperature at which an enzyme is most effective is called the optimum temperature of an enzyme. At their optimum temperature values enzymes work best.  At higher temperatures (like 55 o C) enzymes are denaturated and they lose their properties. So they cannot catalyse a reaction.

18 3. Each enzyme works best at a certain pH enzyme activity pH Optimum pH for pepsin Optimum pH for many enzymes Optimum pH for trypsin The effectiveness of an enzyme depends on the pH of medium. Each enzyme works at different pH values.

19 5. Some enzymes need substances called activators in order to function. Activators are coenzymes or cofactors. 6. Some enzymes function inside the cell, others act outside of the cell. Ex: pepsin

20 7. Inhibitors stop or slow down the activity of enzymes. InhibitorsAntibiotics, pesticides, herbicides, heavy metal ions (Pb +2, Hg +2, Ag +2 ), CO, snake and scorpion poisons, CN, Cu They slow down or stop the activity of enzymes

21 Inhibitors Non - CompetitiveCompetitive Those inhibitors compete with the normal substrate in attachment to the active site They have an influence on the protein part of the enzyme apart from the active site

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23 Enzyme activity Concentration of inhibitor or activator enzyme + activator enzyme enzyme + inhibitor

24 8. Amount of water affects the enzyme activity. If a medium contains less than 15% water, then the enzyme activity stops. 9. Substrate surface rate of reaction surface area Enzyme action begins from the substrate surface. Therefore, increasing surface area of substrate increases the rate of recation until a maximum rate is reached.


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