Organic CatalystsOrganic Catalysts

ISM October 1998

I have to learn all ofTHESE???

•Catalyst

•Enzyme

•Substrate

•Active site

•Enzyme-substrate complex

•Lock and Key model

•Activation energy

•Induced Fit model (IBH)

•Cofactor (IBH)

•Co-enzyme (IBH)

•Competitive inhibitors (IBH)

•Non-competitive inhibitors (IBH)

•Allosteric regulation (IBH)

•Feedback inhibition (IBH)

IBSL and IBHL

1. Define

•enzyme;

•active site;

2. Describe the “Lock and Key” model.

3. List three factors that affect enzyme activity.

4. Outline the effects of temperature and substrate concentration on enzyme activity.

5. Explain two applications of enzymes in biotechnology.

IBHL Only

6. State that metabolic pathways consist of chains and circles of enzyme catalysed reactions.

7. Describe the “Induced Fit” model.

8. Explain that enzymes lower the activation energy of the reactions they catalyse.

9. Explain the difference between competitive and non-competitive inhibition, with reference to one example of each type.

10.Explain the role of allostery with respect to feedback inhibition and the control of metabolic pathways.

Why did Ichoose IBHL?

•speed up chemical reactions without themselves being changed.

•are proteins.

•function at very small concentrations.

•are very specific.

•work best at particular levels of pH, temperature, substrate concentration, enzyme concentration…

•are necessary for metabolism.

•enable cell reactions to take place at normal temperatures.

Features of enzymes…they

I hope Ican get allthis data in here...

But wait!! There’s more...

•They are not changed in the reaction.

•They work very fast.

•They are often found in specific organelles (e.g. enzymes for respiration are in the mitochondria).

•Many need cofactors to work.

•They speed up reactions by lowering activation energy barriers.

•They can do ‘reverse reactions’.

All chemical reactions require a certain amount of energy to get them going…here chemicals AB and CD must absorb energy from their environment before they can reach the ‘transition state’ to break bonds and form new chemicals.

You mean Ihave to readGRAPHS???

The presence of enzymes specific for these chemicals lowers the amount of energy needed to run the reaction - the ‘activation energy’.

EA?? Energyof Activation?

There are two models to show how enzymes work:

So what happensif I press this??

Some enzyme model !!

These are the two models used to suggest how enzymes work:

Look! An enzyme-substrate complex!!AND an active site!

Enzymes only work best in particular environments..like a specific range of temperature..

..of course..Best at body temperature!

..and pH...

Pepsin…found in the stomach,a very acidicenvironment...

Even the amount of enzyme and substrate have an effect.

Substrate?? I guess not...

Hurry! It’s the stuffon cofactors and

coenzymes...

Cofactor: Non-protein helpers for enzymatic activity. They are necessary for the ‘enzyme’ reaction to take place. There are two types:-

1. Inorganic (e.g. Zn2+, Fe2+)

2. Organic (e.g. most vitamins)

Forward:Forward:

glucose + fructose sucroseglucose + fructose sucrose

(Enzyme used: sucrase)(Enzyme used: sucrase)

Reverse:Reverse:

sucrose glucose + fructosesucrose glucose + fructose

(Enzyme used: sucrase)(Enzyme used: sucrase)

Which reaction prevails depends mainly on the relative concentrations of reactants and products. The enzyme catalyzes the reaction in the direction of equilibrium.

The functioning of an enzyme

can be prevented by:

1. Competitive Inhibitors.

(e.g. penicillin blocks the

active site of an enzyme that

many bacteria need to make

their cell wall).

2. Non-competitive Inhibitors.

This yearswinning inhibitor..

YES! It’s a non- competitive inhibitor...

Examples of non-competitive inhibitors are:-

•the nerve gases sarin and DFP which inactivate ethanoyl (acetyl) cholinesterase, an enzyme that affects the passage of nerve impulses through neurones (nerve cells);

•the drug LisinoprilTM which lowers high blood pressure by inhibiting the enzyme ACE which manufactures angiotensin II, a hormone which causes arterioles to constrict.

3. Allosteric Regulation

Allosteric Regulation and Cooperativity.

A. Most allosteric enzymes are constructed from two or more sub-units, each having its own active site. The enzyme oscillates between two conformational shapes- one active, the other inactive. Remote from the active sites are allosteric site, specific receptors for regulators of the enzyme, which may be activators or inhibitors.

B. The opposing effects of an allosteric activator and inhibitor on the conformation of all four sub-units of an enzyme.

C. Cooperativity - one substance molecule can activate all sub-units of the enzyme by the mechanism of induced fit.

That’s it… my brain is fullnow… I need to rest!

Feedback Inhibition.

The most common type of metabolism control, and occurs when a metabolic ‘pathway’ is switched off by its end product which acts as an inhibitor of an enzyme in the pathway.

Example: Some cells use a metabolic pathway of five steps to synthesize the amino acid isoleucine from another amino acid - threonine. The end product (isoleucine) accumulates and slows down its own production as it is an allosteric inhibiitor of the enzyme that catalyzes the very first step of the pathway.

Work,work, work, work...

I wish those enzymeswould get to work!

1. Oil digesting bacteria.

2. Bacterial extraction of metal from ores.

3. Biological washing powder.

4. Meat tenderizers.

5. Making yoghurt and cheese.

IBSL and IBHL

1. Define

•enzyme;

•active ste;

2. Describe the “Lock and Key” model.

3. List three factors that affect enzyme activity.

4. Outline the effects of temperature and substrate concentration on enzyme activity.

5. Explain two applications of enzymes in biotechnology.

IBHL Only

6. State that metabolic pathways consist of chains and circles of enzyme catalysed reactions.

7. Describe the “Induced Fit” model.

8. Explain that enzymes lower the activation energy of the reactions they catalyse.

9. Explain the difference between competitive and non-competitive inhibition, with reference to one example of each type.

10.Explain the role of allostery with respect to feedback inhibition and the control of metabolic pathways.

The answersare in heresomewhere..