It’s time for new material!Section 2.4

Chemical reactions and Enzymes

We need to understand some details about

enzymes that are NOTin you book…so pay

ATTENTION!

Enzymes• Enzymes are proteins

that act as biological catalysts

• They lower the activation energy of a specific chemical reaction

• Lowering the activation energy has a profound effect on how rapidly the reaction is completed

In order to understand enzyme activity, we need to also understand the

energy transformations that

occur during a chemical reaction

What do you know about… • Energy?

• The first law of thermodynamics?

• The second law of thermodynamics?

• Endergonic & Exergonic Reactions?

• Enzymes

Let’s Review….

What is energy?• Etymology: Gk, energia

• the capacity to do work or to perform vigorous activity. Energy may occur in the form of heat, light, movement, sound, or radiation.

• Human energy is usually expressed as muscle contractions and heat production, made possible by the metabolism of food that originally acquired the energy from sunlight. Chemical energy is that released as a result of a chemical reaction, as in the metabolism of food.

Energy is..

• The capacity to perform work• Kinetic Energy: actually doing work• Thermal (Heat) Energy: energy associated

with movement of molecules• Potential Energy: capacity to perform work• Chemical Energy: a form of potential energy

related to the structural arrangement of atoms or molecules. Chemical energy can be transformed into other types of energy during a chemical reaction

ThermodynamicsThermodynamics is the field of physics that

deals with energy transformation – from heat to other forms

• 1st law of Thermodynamics: The principle of conservation of energy

• 2nd law of Thermodynamics: Energy conversions reduce the order of the universe (aka: increase disorder [entropy]).

The First Law of Thermodynamics

Energy is neither created nor destroyed (but it can be

transferred from one part of the universe to another…)

The Second Law of Thermodynamics

‘Energy spontaneously disperses from being localised to being dispersed, provided it is not hindered from doing so’

Some real life examples of the Second Law

• A rock falls if you pick it up then let it go• A frying pan will cool down if you take it off

the stove• Ice cubes melt in a warm room• High pressure air escapes from a puncture

until pressure is equalised

So how does this apply to chemical reactions?

• During a chemical reaction, one set of chemicals is transformed into another

• Both mass and energy are conserved during a chemical reaction (1st Law of Thermodynamics)

• Chemical reactions always involve energy transfer

• Chemical reactions always involve changes in chemical bonds

Chemical reactions are classified as exergonic or endergonic (I)

Chemical reactions can be endergonic or exergonic

Chemical reactions are classified as exergonic or endergonic (I)

Enzymes activity

Chemical Reactions

EndergonicRequires a net input of

energy (from elsewhere).

Energy is absorbed by the chemical products

Will not occur spontaneously

Chemical Reactions

ExergonicA reaction that

releases energy.Occurs

spontaneously

Enzymes

Lower the activation energy of a reaction

Enzymes Lower Activation Energy

What is the cellular energy source?

ATP – adenosine triphosphate• Powers nearly all forms of cellular work• It is a nucleotide

How does ATP work?

• ATP works by energy coupling• Energy Coupling is the use of an

exergonic process to drive an endergonic process

• Bonds between phosphate groups are broken and energy is released (exergonic)

• Called dephosphorylation

What are enzymes?• Enzymes are typically

proteins

• Enzymes are specific

• Enzymes act as catalysts to speed up the rate of reaction of a biological process

• Enzymes are not used up by the reaction they catalyse

Enzymes are essential to all forms of life…

Enzymes: Vocabulary Check

• Catalyst: A substance that speeds up a chemical reaction without itself being changed

• Enzyme: A biological catalyst that is usually a protein

• Substrate: The reactant(s) upon which an enzyme has its action

• Product: A substance that results from a chemical reaction

Enzyme-Substrate Interaction

Factors affecting Enzymes

• Substrate concentration• Enzyme availability• pH• Temperature• Inhibitors

© 2007 Paul Billiet ODWS

Factors which affect enzyme activity 1: Temperature

From: GCSE Bitesize:26.08.12 http://www.bbc.co.uk/schools/gcsebitesize/science/add_ocr_pre_2011/homeostasis/importancerev4.shtml

The effect of temperature

Temperature / °C

Enzyme activity

0 10 20 30 40 50

Q10 Denaturation

© 2007 Paul Billiet ODWS

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 are fully denatured at 70°C© 2007 Paul Billiet ODWS

Factors which affect enzyme activity 2: pH

From: GCSE Bitesize:26.08.12http://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa_pre_2011/enzymes/enzymes1.shtml

The effect of pH Optimum pH values

Enzyme activity Trypsin

Pepsin

pH1 3 5 7 9 11

© 2007 Paul Billiet ODWS

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 its substrate molecules will occur

• This change in ionisation will affect the binding of the substrate with the active site due to shape change.

© 2007 Paul Billiet ODWS

Factors which affect enzyme activity 3: Substrate and enzyme concentration

From: http://www.skinnersbiology.co.uk/enzyme.htmAugust 26th 2012

Complete this sentence…

The _____________ (more/less) enzyme, the faster the product is made.

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 Vmax will change too.

Reaction velocity

Substrate concentration

Vmax

© 2007 Paul Billiet ODWS

Enzyme action can be blocked by:

• 1. Inhibition (many drugs work through enzyme inhibition)

• 2. Denaturation -

Enzyme Inhibition

What does ‘enzyme denaturation’ mean?

Denaturation is a change in the shape of an enzyme which prevents it from fulfilling its function.

Enzymes (and other proteins) can be denatured by heat, pH changes, or certain chemicals

NB: Denaturation is not the same as ‘killing’ – proteins and enzymes are not living things, so can’t be killed!

What does ‘enzyme denaturation’ mean?