Chapter 5: Enzymes

Enzymes are Biological Catalysts What are enzymes? Biological catalysts made up of protein which alter rate of chemical reaction without themselves being chemically changed at the end of reactions Catalysts : Substance that increase rate of reaction without being used up.

Enzymes are Biological Catalysts Enzymes are made up of protein Denatures (enzyme loses it shape and function) if exposed to high temperature or extreme changes in pH Speeds up reaction without the need to increase temperature.

Mode of actions of enzymes Breaking down of fats Heat at high temperature Using enzymes Body cannot withstand high temperatures Energy is required to start breaking down fats – activation energy Enzymes lower activation energy > Required to start chemical reaction.

Enzymes-catalysed Reactions Digestion Process whereby large insoluble food substances are broken down into small soluble molecules Carbohydrates  Monosaccharides Protein  Amino Acids Fats  Fatty Acids + Glycerol

Enzymes-catalysed Reactions 2. Synthesis of complex substances from simpler ones. Synthesis of proteins Synthesis of glycogen for storage in the body Synthesis of fats

Enzymes-catalysed Reactions 3. Oxidation of Glucose Release of Energy to do work Involves a series of enzyme catalysed reactions 4. Breakdown of toxic materials Hydrogen peroxide to water and oxygen catalysed by catalase. Enzymes catalyse almost all reactions in body. There are many different types of enzymes and each is specific and will be produced only when required.

Classifying Enzyme According to chemical reaction they catalyse Usually ends up with –ase Example: Breaking down of starch = amylase Breaking down of Protein = Protease Breaking down of Lipids/Fats = Lipase Enzyme combine with molecules it acts upon (substrate) to form an enzyme-substrate complex. Enzyme controlled reaction can be either Anabolic : building up larger molecules Catabolic: breaking down large molecules into smaller molecule

Characteristics of Enzymes Speeds up rate of chemical reactions Required in minute amount (small) – (itself not breakdown) Specific (Lock & Key hypothesis)

Lock & Key Hypothesis Substrate which the enzyme acts on is called substrate Example: Breaking down of starch, amylase is the enzyme and starch is substrate. End-product = Maltose Enzyme molecules are usually larger than substrate Small part of enzyme, called active site comes into contact with substrate Enzyme (lock) and substrate(key) Enzyme(lock) Substrate (Key) Product Amylase Starch Maltose Lipase Lipid Fatty acids + glycerol Protease Protein Amino acids

Active site Enzyme substrate complex amylase starch 2 maltose units amylase

Enzyme are affected by temperature Enzyme and substrate in constant motion Increase temperature results in increased kinetic energy Molecules move faster Rate of enzyme colliding with substrate is higher Rate of enzyme-substrate complex formed higher Only up to an optimum temperature Low temperature = enzymes are inactive

Enzyme are affected by temperature Around 37 ℃ in mammals Too high a temperature will result in protein being denatured Active sites change shape and activity gradually decline Different enzymes can withstand different temperature range Most enzymes will be completely denatured above 60 ℃ Molecules move slower and rate of collision lower

Q: How does temperature affect Enzyme activity What happens at low temperature? Enzyme are inactive at low temperature What happens as temperature increase? As temperature increase, enzymes gain more kinetic energy causing them to move faster. When they move faster, chances of colliding into a substrate is higher. Hence, rate of forming enzyme-substrate complex is higher. Rate of reaction increases What happens at optimum temperature? At optimum temperature, enzyme are most active What happens above optimum temperature? Enzymes loses active sites, denatured.

Enzymes are affected by temperature: Activeness of enzymes 0 ℃ 50 ℃ 100 ℃

Enzyme are affected by pH Enzyme usually work efficiently within a narrow pH range. Some enzymes works best in slightly acidic conditions (pepsin and rennin) while others in slightly alkaline conditions. Extreme pH will result in denaturation of enzymes Low High Temperature Inactive Denatured pH value denatured

Enzymes are affected by pH: Activeness of enzymes pH 1 pH 7 pH 14

Enzyme are affected by Enzyme concentration Increase enzyme concentration, increased rate of reaction Temperature and pH are at optimum values Substrate level must be high.

Enzyme are affected by substrate concentration Concentration of enzyme remains the same Increased substrate concentration doesn’t necessarily increase rate of reaction Active sites become saturated, therefore could not work any faster

For example, you are making burgers with buns and the number of patties you have is limited. Buns = Substrate, Patties = Rate of reaction 5 No. of patties (Rate of Reaction) 4 3 2 1 Number of buns (substrate) 2 4 6 8 10

Enzyme are affected by substrate concentration How do you know that substance is not enough? When I increase number of substance, I can produce more burgers (Also: When I increase number of that substance, there is an increase of rate of reaction)

Limiting Factors Any factor that directly affects the rate of reaction if its quantity is changed Value of this factor has to be increased in order to increase rate of reaction

D C A B Reversible Reactions Most reactions in living cells are reversible. Enzyme can catalyse reversible reactions Usually not allowed as products formed are used up or transported away. REACTANTS    PRODUCTS D C B A PRODUCTS     REACTANTS