Chapter 16.6 & 16.7 Enzymes & Enzyme Actions

SWBAT: Describe how enzymes function as catalysts and give their namesDescribe the role of an enzyme in an enzyme-catalyzed reaction

Introduction to Enzymes

Biological catalyst which speed up biological reactions by lowering the activation energy required for them to take place

Mostly made up of proteinsMot used up or

chemically change at the end of the biological reaction

What is an enzyme?

Introduction to Enzymes

Can be used again and againProduced only when neededCatalyse reversible reactionsE + S ES EP E + P

E = enzyme S = substrate P = product

How enzymes work?

Classification of Enzymes

Oxidoreductoases (Oxidation – Reduction)Transferases (Transfer groups of atoms)Hydrolases (Hydrolysis)

Carbohydrases, Proteases, Lipases

Lyases (Add/Remove atoms to/from a double bond)

Isomerases (Rearrange atoms)Ligases (Combine molecules using ATP)

Enzyme Action

Enzymes are globular proteinsUnique 3-D shape that binds to a small

group of reacting molecules called substrates

Active Site

Area where the enzyme binds the substrate and catalyzes the reaction

The active site of a particular enzyme fits the shape of only a few types of substrates

Active SiteSubstrate

Enzyme-Catalysed Reactions

Anabolic reactions Synthesis is simpler substances into complex

substances Amino Acids Polypeptides Proteins

Catabolic reactions Breakdown of complex substance into more

simple substances Hydrogen peroxide Oxygen + Water 2 H2O2 O2 + 2 H2O

Characteristics of Enzymes

Speed up chemical reactionsSmall amount needed to catalyse a

reaction because enzymes can be used again and again

The shapes of the active sites make enzymes highly specific, meaning they can only interact with 1 type of substrate to form an enzyme-substrate complex

“Lock and Key” Hypothesis

The active site of an enzyme molecule = lock; substrate molecule that the enzyme acts on = key

When the enzyme and substrate molecules are bound together, they form an enzyme-substrate complex

“Lock and Key” Hypothesis (cont.)

Substrate molecule is subsequently converted into products

Product molecules leave the active siteEnzyme molecule is free to bind with more

substrate molecules

“Induced Fit” Model

Enzyme molecule can undergo adjustments at its active site

Binds more tightly with substrate moleculeFacilitates binding at active site and

speeds up rate of chemical reaction

Chapter 16.8 Factors Affecting Enzyme

Activity

SWBAT: Describe the effect of temperature, pH, concentration of substrate and inhibitors on enzyme activity

Factors Which Affect Enzyme Activity

TemperaturepH Concentrations of substrates in enzymatic

reactions

Temperature

Optimum temperature (37°C) – the temperature at which an enzyme is most active (can catalyze the most number of reactions per second)

Rise in temperature (until optimum) Increase in enzyme activity Kinetic energy of particles increases Increases chance of substrate molecules fitting into the

active sites of enzyme molecules More rapid formation of enzyme-substrate complexes Increase in formation of products

Temperature (cont.)

When temperature exceeds optimum temperature of enzyme activity, it starts to fall rapidly

H-H bonds in enzymes break, leading to the denaturation of enzymes

Unique 3-D structure lostDenaturation is

irreversible

pH

Optimum pH (~7.4) = maximum activityMost enzymes lose their abilities to

catalyse reactions at pH 3 and pH 11Extreme changes in pH of a solution will

denature the enzyme, just like temperature

pH (cont.)

Slight changes in pH is enough to change the electrostatic charges of the active site of enzyme and substrate

Electrostatic repulsion occurs

Inhibits the formation of enzyme-substrate complex

Substrate & Enzyme Concentrations

Substrate concentration increases rate of reaction increases

Saturation of enzyme molecules (all being made use of in reaction)

Reaction cannot take place Increase in enzyme concentration will increase

the rate of reaction again

Animation

Animation comparing Enzymes Substrates Inhibitors Temperature pH

Link to animation

Enzyme Inhibitor

Competitive Inhibition

Non-Competitive Inhibition