Enzymes ppt

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Slide 1

ENZYMES

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What Is A Catalyst? A catalyst is a substance that affects the speed of a chemical reaction, but is itself unchanged at the end of the reaction. Usually allows reaction to be carried out At a lower temperature faster Not denatured by high temperatures and changes in pH

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What is An Enzyme? Enzymes are proteins which function as biological catalysts. They alter the rate of chemical reaction but is itself unchanged at the end of the reaction. Without enzymes, complex apparatus and higher temperature needed to break down carbohydrates, fats, proteins High temperatures and extreme changes in pH break bonds within proteins and cause change in shape – denaturation.

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Functions of Enzymes Almost every reaction taking place in living cells is dependent on enzymes. photosynthesis cellular respiration growth and repair (protein synthesis) digestion Produced only when needed

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The stone rolls down and breaks into tiny pieces (products are formed). The energy needed to start a chemical reaction is called activation energy. 20 March 2012 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. 5 Activation Energy Imagine a chemical reaction as the process of rolling a huge stone (reactant) up a hill so that it rolls down and breaks into tiny pieces (products). 1 Activation energy is the energy needed to roll the stone up the hill. 2 Once over the hill, the rest of the reaction occurs. 3 4 5

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Activation energy is an amount of energy needed to start a chemical reaction. An enzyme lowers the activation energy of a reaction Activation Energy Activation Energy

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Enzymes in Plants

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What do Enzymes Do? A substrate is the substance acted upon by the enzyme The products are the end result of the reaction

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What do Enzymes Do? The active site - part of the enzyme that substrate binds to (this is due to the physical configuration caused by hydrogen bonding within the protein molecule)

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Digestive Enzymes Needed to convert large molecules into simpler smaller substances which are Soluble in water Small enough to diffuse through cell surface membrane

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Digestive Enzymes

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inside the cell outside the cell Large molecules such as starch and protein molecules cannot pass through the cell surface membrane. starch molecule protein molecule 20 March 2012 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. 12 cell surface membrane pore on cell surface membrane Digestive Enzymes

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starch molecule protein molecule action of digestive enzymes protease amylase 20 March 2012 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. 13 Digestive Enzymes maltose molecules polypeptide molecules

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20 March 2012 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. 14 Digestive Enzymes maltose molecules polypeptide molecules action of digestive enzymes protease maltase amino acid molecules glucose molecules

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inside the cell outside the cell inside the cell 20 March 2012 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. 15 Small molecules such as glucose and amino acid molecules pass through the cell surface membrane. glucose molecules (from digestion of starch) amino acid molecules (from digestion of proteins) Digestive Enzymes

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Characteristics of Enzymes Speed up chemical reactions By lowering the activation energy needed to start the reaction 20 March 2012 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. 16

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Characteristics of Enzymes Speed up chemical reactions Required in minute amounts Remain unchanged at the end of reactions Can be used over and over again A small amount of enzymes can catalyse a large number of reactions 20 March 2012 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. 17

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Characteristics of Enzymes Speed up chemical reactions Highly specific in their actions Each chemical reaction is catalysed by a unique enzyme. Specific due to their three-dimensional shapes E.g. lock and key hypothesis 20 March 2012 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. 18 Required in minute amounts

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Characteristics of Enzymes Speed up chemical reactions Affected by temperature Enzymes have an optimum temperature at which the enzymes are most active. Enzyme activity increases as temperature rises, but decreases at high temperatures due to denaturation. 19 Required in minute amounts Highly specific in their actions

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Characteristics of Enzymes Speed up chemical reactions Affected by temperature Affected by pH Some enzymes work best in slightly acidic solutions e.g. pepsin and rennin in the stomach, others require slightly alkaline solutions. Extreme changes in the pH of the solutions denature the enzymes. 20 March 2012 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. 20 Required in minute amounts Highly specific in their actions

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Characteristics of Enzymes Speed up chemical reactions Affected by temperature Affected by pH Some catalyse reversible reactions Reversible reactions can proceed in the forward or backward direction Some enzymes catalyse both reactions until equilibrium is reached. 20 March 2012 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. 21 Required in minute amounts Highly specific in their actions

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Characteristics of Enzymes Speed up chemical reactions Affected by temperature Affected by pH Some catalyse reversible reactions Some require coenzymes for activity Coenzymes are non-protein organic compounds that are essential for enzyme activity. Some enzymes require coenzymes to be bound to them before they can catalyse reactions. 20 March 2012 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. 22 Required in minute amounts Highly specific in their actions

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The Lock and Key Hypothesis To open a lock we need the correct key Many different keys are available, but only one key fits the keyhole and is able to open the lock Enzymes are very highly specific in their action If incompatible, they cannot bind together to form an enzyme-substrate complex No catalytic reaction.

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active sites A B AB enzyme molecule (the ‘lock’) enzyme-substrate complex substrate molecules ( A and B) can fit into the active sites enzyme molecule is free to take part in another reaction a new substance (product) AB leaves the active sites 20 March 2012 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. 24 reactions take place at the active sites to convert the substrate molecule(s) into product molecule(s). Lock and Key Hypothesis

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Temperature Rate of reaction (enzyme activity) 0 K (optimum temperature) D At point D, the enzyme has lost its ability to catalyse the reaction. 25 An enzyme is less active at very low temperatures 1 As the temperature rises, enzyme activity increases as indicated by the increase in the rate of reaction it catalyses. Usually the enzyme is twice as active for every 10°C rise in temperature until the optimum temperature is reached. 2 The optimum temperature is reached. Enzyme is most active. 3 Beyond the optimum temperature, enzyme activity decreases. 4 5 Effect of Temperature on the Rate of Reaction

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Effect of pH on Enzyme Action Every enzyme has an optimum pH at which its activity is greatest Beyond this narrow and highly specific pH range, the enzyme will not only be inactivated, but may be denatured When enzyme activity = 0 , enzyme completely denatured

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Enzymes in Industry What do bread and beer have in common? Both make use of the the enzymes present in yeast. Beverages like wine and beer are brewed by alcoholic fermentation. The respiration of yeast provides gas bubbles, used as a rising agent in baking bread.

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Enzymes in Everyday Life Enzyme action speeds up the reactions that cause food to spoil and cut fruits to turn brown Because these enzymes have an optimum pH near to room temperature, we can slow down these processes by storing fresh food in refrigerators. Understanding enzyme reactions and knowing the properties of enzymes can be very useful. Another solution is to change the pH of the medium, for example adding lemon juice which makes it acidic

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Enzymes and Technology Treatment of sewage Cleaning up toxic oil spills Biological detergents that remove stains by digesting them

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