ENZYMES A protein with catalytic properties due to its power of specific activation IB Topics 3.6 & 7.6 Material on this power point adapted from Paul Billiet ODWSODWS

Chemical reactions  Chemical reactions need an initial input of energy = THE ACTIVATION ENERGY  During this part of the reaction the molecules are said to be in a transition state.

Reaction pathway

How Enzymes Affect Reaction Rates Enzymes affect the rates of reactions by lowering the amount of energy of activation required for the reactions to begin. Therefore processes can occur in living systems at lower temperatures or energy levels than it would require for these same reactions to occur without the enzymes present.

How Enzymes Affect Reaction Rates C 6 H  6CO 2 + 6H ENERGY Above is the formula for the complete combustion of glucose. This reaction can be carried out in a laboratory at several hundred degrees Celsius. The same reaction occurs during the process of cellular respiration in living cells. In humans at a temperature of 37 o Celsius. What makes the difference? ENZYMES!

Enzyme structure  Enzymes are proteins  They have a globular shape  A complex 3-D structure Human pancreatic amylase © Dr. Anjuman BegumDr. Anjuman Begum

Enzyme defined:  Enzyme (C)- a globular protein which acts to catalyze a chemical reaction  Active site (A)- the region on the surface of an enzyme to which substrates bind.  Substrate/s (B)- the substance that an enzyme acts on- the reactant/s

How Enzymes Bind to Substrates  There are two proposed methods by which enzymes bind to their substrate molecules: a. Lock and Key Model b. Induced-Fit Model

The Lock and Key Model  Enzymes are very specific to certain substrates, like a lock is to a certain key.  1 enzyme for every substrate  This explains enzyme specificity  This explains the loss of activity when enzymes denature

The Lock and Key Model Enzyme may be used again Enzyme- substrate complex E S P E E P Reaction coordinate

The Induced Fit Hypothesis  Some proteins can change their shape (conformation)  When a substrate combines with an enzyme, it induces a change in the enzyme’s conformation  The active site is then moulded into a precise conformation  Making the chemical environment suitable for the reaction  The bonds of the substrate are stretched to make the reaction easier (lowers activation energy)

The Induced Fit Hypothesis  This explains the enzymes that can react with a range of substrates of similar types Hexokinase (a) without (b) with glucose substrate

Factors That Affect Enzymes:  substrate concentration  pH  temperature  inhibitors

Substrate concentration: Non-enzymic reactions  The increase in velocity is proportional to the substrate concentration Reaction velocity Substrate concentration © 2007 Paul Billiet ODWSODWS

Substrate concentration: Enzymic reactions  Faster reaction but it reaches a saturation point when all the enzyme molecules are occupied.  If you alter the concentration of the enzyme then V max will change too. Reaction velocity Substrate concentration V max

The effect of pH  Extreme pH levels will produce denaturation (the structure of the enzyme is changed)  The active site is distorted and the substrate molecules will no longer fit in it  At pH values slightly different from the enzyme’s optimum value, small changes in the charges of the enzyme and it’s substrate molecules will occur  This change in ionization will affect the binding of the substrate with the active site.

The effect of pH Optimum pH values Enzyme activity Trypsin Pepsin pH

The effect of temperature  For most enzymes the optimum temperature is about 30°C  Many are a lot lower, cold water fish will die at 30°C because their enzymes denature  A few bacteria have enzymes that can withstand very high temperatures up to 100°C  Most enzymes however are fully denatured at 70°C

The effect of temperature  Optimum temperature is at crest. Temperature / °C Enzyme activity Denaturation

Inhibitors  Inhibitors are chemicals that reduce the rate of enzymic reactions.  They are usually specific and they work at low concentrations.  They block the enzyme but they do not usually destroy it.  Many drugs and poisons are inhibitors of enzymes in the nervous system.

Enzymes and Lactose

Enzymes have been used in biotechnology for millennia

Enzymes are useful  They are catalysts so they make reactions easier. This increases productivity and yield.  As catalysts they are not consumed by the reaction. They may be used over and over again.  Enzymes show specificity to the reaction they control.  Enzymes are sensitive to their environment so they can be controlled by adjusting the temperature, the pH or the substrate concentration

Example: Lactase  Lactase is used to remove the sugar lactose from milk and other dairy products The Reaction: Substrate: Lactose Lactose + H 2 OGlucose + Galactose This is a hydrolysis reaction  -galactosidase

Lactose Intolerance  Some people are intolerant of lactose in milk; they cannot digest it  The lactose remains in the digestive system and is fermented by bacteria.  The result is nausea, cramps, bloating, gas, and diarrhea occurring within 4h of consuming milk products.  The treatment includes taking a tablet of lactase enzyme with a meal.  The lactase digests the lactose in the food.  A special lactose-free diet may be necessary

Source of the enzyme:  Lactase enzyme (  -galactosidase) is extracted from fungi such as Aspergillus oryzae

Biotechnology Connection: Pectinase  Pectinase- used in fruit juice production. Pectin keeps plant cells together. When crushing fruit for fruit juice, adding pectinase helps get a further yield of juice, as more will separate from the pulp.

Other examples in Biotech  Protease- breaks down proteins  amino acids, used in baby food production to make baby foods easier to digest.  Enzymes in detergent- used to break down organic molecules (proteins and fats) into smaller pieces, so that the detergent can work more efficiently.