Everything you wanted to know about ENZYMES, and more!

So – just what is an enzyme?

Questions to think about:• What type of macromolecule is it?

• What do you think it’s role is?

• Why are they important?

If you are not sure think about the following scenarios...

1. You need to light a fire, and the only tools you have are two sticks that you can rub together.

2. You need to light a fire, and the only tool you have is a match.

3. You need to light a fire, and the only tool you have is a flint (which whenstruck, creates sparks).

Things to think about...• Would all three scenarios work? • Other than type of tool used, what is the main

difference between them? • If you needed to light another fire, could you do

so (assuming other one completely went out)?

Now lets find out what anenzyme actually is – as we are doing so, decide which scenario most closely represents the role of enzymes.

What is an Enzyme?

What are they?

• Enzymes are proteins• Function is to catalyze reactions• A catalyst is a substance that speeds up the

rate of a chemical reaction by lowering the activation energy required for the reaction to begin

• Catalysts are reusable, that is they are not consumed in processes, so they can be recycled for other reactions

Why do we need enzymes?

• All reactions, energy to begin a reaction • This energy is called the Activation energy(EA)• Most chemical reactions in cells reach the

state of activation too slowly on their own• Increasing temperature, speeds up the

process, but this has draw backs in living organisms ....what might that be?

Why do we need enzymes?

• Another way – to increase rate of chemical reactions without increasing temperature is to use a catalyst

• catalysts function by lowering the activation energy of the reaction

• Almost all chemical reactions in organisms are facilitated by enzymes

• So – which scenario most closely matches the function of an enzyme?

If you are not sure think about the following scenarios...

1. You need to light a fire, and the only tools you have are two sticks that you can rub together.

2. You need to light a fire, and the only tool you have is a match.

3. You need to light a fire, and the only tool you have is a flint (which whenstruck, creates sparks).

Exergonic Reaction – a chemical reaction that releases energy

Reactions with and without a Catalyst

EA = Activation Energy

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Endergonic Reaction – chemical reaction that requires energy

Reactions with and without a Catalyst

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How does it all work?

What ways can you think of that would allow an enzyme to decrease the activation energy of a reaction?

How does it all work?

• Each enzyme contains an active site • An active site is a 3-D pocket or indentation on its

surface• It matches the shape of the substrate and is the

site on an enzyme where the substrate binds• Originally thought of as a key-and-lock model

How does it all work?• A substrate is a reactant that interacts with the

enzyme in an enzyme-catalyzed reaction• They form an enzyme-substrate complex• Enzyme-substrate complexes are highly specific

E.g. Enzymatic Hydrolysis of SucroseQ: Do you think maltose could also be a substrate for this enzyme? Why or why not?

How does it all work?

Now the thinking is:• Enzymes can adjust their shapes slightly to

accommodate a substrate• This adjustment allows the substrate to fit in the

active site, and the change in the active site of the enzyme is called induced fit

Substrate Bindinginduced-fit model - enzyme changes shape

upon substrate binding

enzyme-substrate complex

Model Comparison• Two proposed models:

– Lock-and-key model: this assumes that the active site is a perfect fit for a specific substrate (once the substrate binds there is no further modification)

Induced fit model: developed from the lock and key modelChange in shape to: bring R-groups closer to substrate

bend bonds to make them easier to break / react

reduce EA (makes transition state easier)

bring two reactants close together

provide a microenvironment for reactions

How enzymes Work• Regardless of model• Enzymes prepare substrates for reaction by:

– Changing the substrate– Its environment– Or both in some wayWith the end result being a lowering of the activation

energy of the reaction.

How enzymes Work• E.g., bring two substrates together in the correct

position for a reaction to occur

• Add or remove hydrogen ions to or from the substrate (i.e., act as an acid or base), destabilizing it and making it more likely to react

How enzymes Work• Transfer electrons to or from the substrate (i.e.,

reduces or oxidizes it), which destabilizes it and makes it morel likely to react

• Contain amino acid R groups that end up close to certain chemical bonds in the substrate, causing these bonds to stretch or bend, which makes the bonds weaker and easier to break

Steps to Enzyme Reactions

1. Substrate binds to available active site pocket.

2. Enzyme changes shape to envelope substrate(s)

3. Reaction occurs

4. Products lose affinity for the active site

5. Enzyme is set for another substrate

Whole cycle called catalytic cycle.

Enzyme Classification

• Enzymes are classified according to the type of reaction they catalyze

• E.g., hydrolases = enzymes that catalyze hydrolysis reactions

• Each enzyme has a unique name, ending in “-ase”, beginning with first part of the substrate name

• E.g., lactase (breaks down lactose)

Factors that affect enzymes

Any ideas? There are four of them. What might be the consequences?

Factors Affecting Enzyme Activity

• Temperature• pH value• Concentration of substrate• Concentration of the enzyme itself

Temperature

• As temperature rises increase in rates of reactions.....to a degree!

• Which causes the rate of enzymatic reaction to increase as well

• Every enzyme has a specific or optimal temp. where its activity is the greatest. E.g. body enzymes has optimal temp. 37.5oC

• At higher temp. intra and intermolecular bonds are broken as enzymes gain more kinetic energy, they become denatured.

pH• Each enzyme works within quite a small pH

range.• Activities are greatest at optimal pH• Changes in pH break intra- and intermolecular

bonds, changing the shape of the enzyme, and effectiveness.

Effect of Temperature and pH on Enzyme Activity

Limitations of Enzymes

• only a set number of each type of enzyme in body– reactions have a

maximum rate

Concentration of enzyme and substrate

• Rate of reaction increases with increasing substrate concentration up to a point,

• Above which any further increase in substrate concentration produces no significant change in reaction rate.

• Why? – because the active sites of the enzymes molecules at any given moment are virtually saturated with substrate.

• Enzyme/substrate complex has to dissociate before the active sites are free to accommodate more substrate

Provided that the substrate concentration is high and that temperature and pH are kept constant, the rate of reaction is proportional to the enzyme concentration.

Enzymes Regulation

Can you think of anyway enzymes can be controlled or kept in check?

Enzyme Factors

• Some enzymes require non-protein molecules to operate

Coenzymes = organic molecules that assist an enzyme

Cofactors = inorganic molecules that assist an enzyme (e.g., metal ions, iron, zinc)

Regulation of Enzyme Activity• Regulate enzyme activity through use of inhibitors

• Inhibitor = a molecule that binds to the allosteric or active site of an enzyme and causes a decrease in the activity of that enzyme

• Allosteric site = a site on an enzyme that is not the active site, where other molecules can interact with and regulate the activity of the enzyme

Regulation of Enzyme ActivityCompetitive inhibitor – binds to the same

active site as the substrate

noncompetitive inhibitor – binds to an alternate site (allosteric site) on the enzyme to keep it in an inactive form (no longer has affinity for substrate)

Q: What happens if a competitive inhibitor is present, but in a lower concentration than the substrate? In higher concentration?

Competitive Inhibition

Non-competitive Inhibition Note: If binding and reduction of enzyme is permanent, then the substance binding to the enzyme is considered a toxin

Regulation of Enzyme Activity

• Also regulate enzyme activity through use of activator molecules.– Molecules that promote the action of enzymes and

which bind to the allosteric site of an enzyme.

• The regulation of enzyme activity by activators and inhibitors binding to allosteric sites is called allosteric regulation

Allosteric Sites

Feedback Inhibitiona method for cells to regulate metabolic pathways

(i.e., maintain homeostasis)

often, products at the end of a series of a reaction will act as an allosteric inhibitor to shut the reactions down

A, B, C and D are molecules along a metabolic pathway.

E1, E2 and E3 are enzymes required for this metabolic pathway.

D is an allosteric inhibitor of E1.

Feedback Inhibition

Enzymes in Everyday Life

Use of Enzymes

• Includes industrial and commercial purposes– E.g. proteases are used in the dairy industry to

produce cheese– proteases, along with amylase, are also added to

detergents to help remove protein and carbohydrate produced stains

What you should have learned• Examine enzymatic pathways, • Focus on how they inhibit or activate reactions• Use appropriate terminology related to

biochemistry e.g. allosteric, substrate, substrate-enzyme complex, inhibition

• Describe the chemical structures and mechanisms of various enzymes

• Analyse technology applications related to enzyme activity in the food and pharmaceutical industries

Homework

• Pg. 77, Q 1, 2, 4-9

Unit 1- Quest 2 (Thurs)

• Focus – macromolecules and biochemical reactions, including enzymes (not thermodynamics)

• To be given– Multiple choice– Short answers– Application questions