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. @

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

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

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 ) + +

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

One apoenzyme works with only one coenzyme or cofactor 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 Lipase

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)

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.

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

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 Maltase Amylase Starch Glucose Molecules Maltose Molecules

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

2. Induced Fit Model: @ 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. The enzyme changes shape slightly to grasp the substrate at the active site.

Characteristics of Enzyme Action: @ 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 second.

2. Enzymes enable cell reactions to take place at normal temperatures. @ enzyme activity Optimum temperature for many enzymes (about 36oC) temperature (oC) 0 10 20 30 40 50 60

At OoC, 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 55oC) enzymes are denaturated and they lose their properties. So they cannot catalyse a reaction.

3. Each enzyme works best at a certain pH. Optimum pH for pepsin enzyme activity Optimum pH for many enzymes Optimum pH for trypsin pH 0 2 4 6 8 10 12 14 The effectiveness of an enzyme depends on the pH of medium. Each enzyme works at different pH values.

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

7. Inhibitors stop or slow down the activity of enzymes. Antibiotics, 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

Inhibitors Competitive Non - Competitive 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

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

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