ENZYMESENZYMES

Enduring UnderstandingEnduring Understanding

All biological systems need catalysts to alter speed of chemical reactions in the system.

Organic catalysts are proteins, therefore they are affected by extremes of temperature and pH changes.

CatalystsCatalysts

Chemicals that speed up chemical reactions

Not changed at end of reaction

Why do we need catalysts in biological systems?Why do we need catalysts in biological systems?

Without them the chemical reactions vital to life could not take place quickly enough.

Eg. digestion, respiration

Biological MoleculesBiological Molecules

T H E M E O N E : P R I N C I P L E S O F B I O L O G Y

3.2 Enzymes

Enzymes and Activation Energy

• Biological catalysts made up of tertiary proteins.

• Produced by living cells (organic)

• Speed up chemical reactions

• Not changed at end of chemical reaction

• Specific in their reaction

3.2 EnzymesEnzymes

Structure of enzymesStructure of enzymes

Polypeptides (chains of amino acids) are folded around each other to form a roughly spherical structure.

Results in 3-dimensional shape.

The shape is maintained by hydrogen bonds.

Folding gives rise to active site (place at which enzyme reaction takes place)

ACTIVE SITEACTIVE SITE

Pockets or clefts on enzyme surface Shape is complementary to substrate,

therefore specific This is where the enzyme substrate

reaction actually occurs. High temperature results in loss or

alteration of active site, ie. denatured

TYPES OF ENZYMESTYPES OF ENZYMES IntracellularThese are both made and have their action

inside cells. Eg. photosynthetic enzymes inside chloroplasts

ExtracellularThese are made inside the cells but have their

action outside the cell.Eg. digestive enzymes in the human gut,

enzymes released by fungi and bacteria (decomposers)

Naming enzymesNaming enzymes

Based on what it reacts with (substrate) Add -ase to endingEg. enzyme lactase – reacts with

substrate lactose, a sugar

enzyme salivary amylase reacts with substrate starch

ExampleExample

Hydrolytic / digestive enzymes

- chemically breaks down larger molecules in the presence of water.

Eg. amylase, lipase, proteases,

HOW ENZYMES WORKHOW ENZYMES WORK

enzyme

substrate

http://www.bbc.co.uk/education/asguru/biology/02biologicalmolecules/01proteins/11enzymes/index.shtml

Click on the link below

STEPS IN ENZYME REACTIONSTEPS IN ENZYME REACTION

Substrate molecule fits into complementary active site

Enzyme-substrate complex formed. Reaction takes place

Substrate leaves active site. Enzyme is ready for another reaction

NB: A small quantity of enzyme can bring about a large amt of reaction.

For an enzyme to work, it must ....For an enzyme to work, it must ....

1. Come into physical contact with its substrate

2. Have an active site which fits the substrate

Any factor that influence the rate at which an enzyme works do so by affecting one or both of the above conditions.

Effect of temperature on enzyme catalysed reaction. (Pg 68, txtbook)

Effect of temperature on enzyme catalysed reaction. (Pg 68, txtbook)

At low temperature, the enzyme is less active. Why? Recall kinetic theory + condition 1.

As temp. increases, enzyme activity increases. At optimum temperature, enzyme is most active. Beyond optimum temperature, the enzyme begins to

denature, ie. The weak bonds within the enzyme start to break down, the enzyme begins to lose its 3-D structure and active site. Therefore, rate of reaction declines.

At very high temperature, reaction stops. Enzyme is completely denatured, irreversible structural change into a simple chain of protein.

Enzymes are proteins, so .....Enzymes are proteins, so .....

Sensitive to temperature Sensitive to pH changes.

Effect of Substrate ConcentrationEffect of Substrate Concentration

At low substrate concentrations, the active sites of enzyme molecules are not all occupied. So reaction is fast. WHY??

As substrate concentration increases, more and more of the active sites are being occupied for reaction. Further increase in substrate concentration will not increase speed of reaction. WHY??

Enzyme concentrationEnzyme concentration

When there are excess substrate molecules, the speed of reaction is directly proportional to enzyme concentration.

A student who had seen a cook place slices of fresh pineapple on top of meat before cooking it, decided to carry out some experiments using fresh pineapple juice.A milk agar was prepared by mixing fat-free milk and warm water with agar powder. It was then poured into a sterilised petri dish and allowed to cool. After it had set, five holes were made in the milk agar. Each hole was filled with a different substance, as shown in Fig. 1.1

The petri dish was then kept at 400C for 2 hours. The results obtained are shown in Fig. 1.2.

Explain the results obtained for each of the holes 1-5.

THE ENDTHE END