ENZYMES Topic 3.6 IB Biology Miss Werba

CARBS, LIPIDS & PROTEINS 3.5 TRANSCRIPTION & TRANSLATION TOPIC 3 - BIOCHEMISTRY 3.1 ELEMENTS & WATER 3.2 CARBS, LIPIDS & PROTEINS 3.3 DNA STRUCTURE 3.4 DNA REPLICATION 3.5 TRANSCRIPTION & TRANSLATION 3.6 ENZYMES 3.7 CELL RESPIRATION 3.8 PHOTOSYNTHESIS J WERBA – IB BIOLOGY 2

THINGS TO COVER What are enzymes & how do they work? Enzyme-substrate specificity Factors affecting enzyme activity Denaturation Use of lactase in production of lactose-free milk J WERBA – IB BIOLOGY 3

ENZYMES Command term = DEFINE Enzymes: Biological catalysts, which speed up the rate of chemical reactions without becoming a part of the products. J WERBA – IB BIOLOGY 4

ENZYMES Command term = DEFINE Enzymes are proteins with a unique shape. Without enzymes, chemical reactions would occur very slowly. Enzymes work by lowering the activation energy needed for a reaction. Many enzyme names end in –ase eg. amylase, lipase, sucrase, lactase, catalase J WERBA – IB BIOLOGY 5

ENZYMES Command term = DEFINE Active site: The region on an enzyme’s surface to which a substrate binds. J WERBA – IB BIOLOGY 6

ENZYMES Command term = DEFINE The active sites are specific: ie. enzymes are designed to “fit” the shape of their substrate This is known as the Lock and Key Model The active site is simply a groove or cleft on the surface of the enzyme J WERBA – IB BIOLOGY 7

ENZYME-SUBSTRATE SPECIFICITY Active site and substrate complement each other in terms of both shape and chemical properties (e.g. opposite charges). Binding to the active site brings the substrate into close physical proximity, creating an enzyme-substrate complex. enzyme substrate enzyme-substrate complex J WERBA – IB BIOLOGY 8

ENZYME-SUBSTRATE SPECIFICITY The enzyme catalyses the conversion of the substrate into a product (or products), creating an enzyme- product complex. As the enzyme is not consumed in the reaction, it can continue to work once the product is completed. enzyme substrate enzyme-substrate complex enzyme-product complex enzyme product J WERBA – IB BIOLOGY 9

ENZYME-SUBSTRATE SPECIFICITY An enzyme will only interact with one (or a few) specific substrates that complement its active site. This is described as the 'lock and key' model ie. a lock only opens in response to a specific key J WERBA – IB BIOLOGY 10

DENATURATION Command term = DEFINE Denaturation: changing the structure of a protein so that it can no longer carry out its function J WERBA – IB BIOLOGY 11

DENATURATION Command term = DEFINE Denaturation is usually permanent. Can be caused by high temperatures and extremes of pH. Denaturation breaks bonds holding the 3D structure of a protein together  resulting in loss of shape/function J WERBA – IB BIOLOGY 12

FACTORS AFFECTING ENZYME ACTIVITY J WERBA – IB BIOLOGY 13

FACTORS AFFECTING ENZYME ACTIVITY Temperature Low temps result in insufficient thermal energy for the activation of a reaction to be achieved Increasing the temp will increase the speed and motion of both enzyme and substrate, resulting in higher enzyme activity This is because a higher kinetic energy will result in more frequent collisions between enzyme and substrate J WERBA – IB BIOLOGY 14

FACTORS AFFECTING ENZYME ACTIVITY Temperature At an optimal temp, the rate of enzyme activity will be at its peak Higher temps will decrease enzyme stability, as the thermal energy disrupts the hydrogen bonds holding the enzyme together This causes the enzyme (particularly the active site) to lose its shape, resulting in a loss of enzyme activity (denaturation) J WERBA – IB BIOLOGY 15

FACTORS AFFECTING ENZYME ACTIVITY pH Changing the pH will alter the charge of the enzyme, which in turn will change solubility and may change the shape of the molecule Changing the shape or charge of the active site will diminish its ability to bind to the substrate, abolishing enzyme function Enzymes have an optimum pH J WERBA – IB BIOLOGY 16

FACTORS AFFECTING ENZYME ACTIVITY Substrate Concentration Increasing substrate concentration will increase enzyme activity More substrate means there is an increased chance of enzyme and substrate colliding and reacting So more products will be formed in a given time period. After a certain point, the rate of reaction will stop rising despite further increases to substrate concentration, because as the environment has become saturated with substrate and all enzymes are in use J WERBA – IB BIOLOGY 17

FACTORS AFFECTING ENZYME ACTIVITY TEMPERATURE pH SUBSTRATATE CONCENTRATION Too low Inactivated (dormant) Denatured Enzyme efficiency is high Too high Enzyme efficiency plateaus J WERBA – IB BIOLOGY 18

ENZYMES IN ACTION Production of lactose-free milk 70% of adult humans are lactose intolerant They have lost the ability to produce lactase after early childhood. Ingestion of milk will lead to excess gas production & diarrhoea. The food industry has produced lactose-free milk. Use lactase enzyme to break down lactose into glucose and galactose. Milk tastes sweeter but will not cause reaction in lactose-intolerant adults. J WERBA – IB BIOLOGY 19

ENZYMES IN ACTION Production of lactose-free milk Steps: Lactase is purified (from yeast or bacteria) Lactase is bound to an inert substance (such as alginate beads) Milk passed over immobilised enzymes becomes lactose-free J WERBA – IB BIOLOGY 20

ENZYMES IN ACTION Production of lactose-free milk Uses: Source of milk for lactose- intolerant individuals Increases the sweetness of milk, thus reducing the need for artificial sweeteners Reduces the crystallisation of ice-creams Shortens the production time for yogurts or cheese J WERBA – IB BIOLOGY 21

Sample questions Q1. The graph below shows the effect of substrate concentration on enzyme activity. What conclusion can be drawn about section X of the graph? The enzyme has started to denature and the reaction slows down. The reaction has finished and the substrate has been used up. The enzyme is saturated and is working at its maximum reaction rate. Some of the enzyme has been consumed and the reaction has reached a plateau. J WERBA – IB BIOLOGY 22

Sample questions Q2. Which of the following will cause an enzyme to permanently lose its properties? I. Hydrolysis II. Freezing to –20°C III. Dissolving it in water I only II only I and II only I and III only J WERBA – IB BIOLOGY 23

Sample questions A1. C A2. A J WERBA – IB BIOLOGY 24

Sample questions Q3. Discuss factors that affect enzyme activity. (9 marks) J WERBA – IB BIOLOGY 25

Sample questions A3. at low temperatures, rate of reaction increases as temperature increases (or vice versa); more kinetic energy / faster movement of molecules means more collisions between enzyme / active site and substrate; optimum temperature is temperature at which rate of enzyme-catalyzed reaction is fastest; at high temperatures enzymes are denatured and stop working; denatured means change of structure in enzyme / protein resulting in loss of its biological properties / no longer can carry out its function; too much kinetic energy / vibrations breaks bonds that give enzyme specific shape; optimum pH is one at which rate of enzyme-catalyzed reaction is fastest; rate of reaction reduced as increase or decrease pH (from optimum); strong acids and alkalis can denature enzymes; affect (weak, ionic, hydrogen) bonds that hold enzyme in specific shape; at low substrate concentrations, as increase concentration get increase in rate of reaction; more chance of collision between substrate and enzyme / active site; at high substrate concentration, have no change in rate as increase concentration; all active sites occupied; J WERBA – IB BIOLOGY 26