Enzymes What are they? Why do we need them? Name some examples ?

Enzymes

What are they?

Why do we need them?

Name some examples ?

EnzymesGlobular proteins that catalyse chemical

reactions in living organisms

EnzymesGlobular proteins that catalyse chemical reactions in living organisms

Properties

Specific

Increase rate of the reaction

Unchanged at the end of the reaction

Enzymes

Need them because...

Reactions too slow to maintain life

Can’t increase temperatures/pressure in cells (fatal)

Enzymes Are Proteins

The enzyme binds to the substrates by its active site

The active site is a pocket formed by the folding of the protein

where the substrates bind.

Enzymes Are ProteinsThe enzyme binds to the substrates by its active site

The active site is a pocket formed by the folding of the protein

where the substrates bind.

Active site

The active site involves a small number of key residues that actually bind thesubstrates

The rest of the protein structure is needed to maintain these residues in position

Lock and Key

Enzyme reactions

enzyme + substrate enzyme-substrate complex

Enzyme reactions

enzyme + substrate enzyme-substrate complex

E +S ES

Enzyme reactions

enzyme + productenzyme-substrate complex

E +PES

enzyme + substrate enzyme-substrate complex

E +S ES

How do enzymes work?

An Example

An Example

Sucrose + H2O

Glucose + Fructose

An Example

Sucrose + H2O

Glucose + Fructose

Substrates

Products

For a reaction to occur the sucroseand water would have to collide with

enough energy to break and form bonds

This is the activation energy

Sucrose + H2O Glucose + Fructose

++

Substrates Products

Energy

Progress of reaction

Energy

Progress of reaction

Substrates

Energy

Progress of reaction

Substrates Products

Energy

Progress of reaction

Substrates Products

High energy intermediate

Energy

Progress of reaction

Substrates Products

High energy intermediate

Activation energy

The minimum amount of energy needed to start the reaction,

leading to the formation of a high energy intermediate

= The Activation energy

Energy

Progress of reaction

Substrates Products

High energy intermediate

Activation energy

Enzymes reduce the height of the energy

barrier

Enzyme activity

How fast an enzyme is workingRate of Reaction

Rate of Reaction = Amount of substrate changed (or amount product formed)

in a given period of time.

Enzyme activity

Four Variables

Temperature

pH

Enzyme Concentration

Substrate Concentration

Rat

e of

Rea

ctio

n

Temperature

0 20 30 5010 40 60

40oC - denatures

5- 40oC Increase in Activity

<5oC - inactive

Effect of heat on enzyme activtyIf you heat the protein above its optimal temperature

bonds break meaning the protein loses it secondary and tertiary structure

Effect of heat on enzyme activty

Denaturing the protein

ACTIVE SITE CHANGES SHAPE SO SUBSTRATE NO LONGER FITS

Even if temperature lowered – enzyme can’t regain its correct shape

Rat

e of

Rea

ctio

n

pH

1 3 42 5 6 7 8 9

Narrow pH optima

Disrupt Ionic bonds - Structure

Effect charged residues at activesite

Rat

e of

Rea

ctio

n

Enzyme Concentration

Enzyme Concentration

Rat

e of

Rea

ctio

n

Substrate Concentration

Substrate Concentration

Active sites full- maximum turnover

What is digestion?Breaking down large, insoluble molecules into smaller, soluble molecules that can be absorbed through the wall of the small intestine

What breaks down the large molecules?Digestive enzymes made by specialised cells inside glands

Some enzymes are...

Amylase Carbohydrates

Protease Proteins

Lipase Lipids

The enzymes break down...

Carbohydrates Simple sugars

Proteins Amino acids

Lipids (fats) Fatty acids + glycerol

Digestion animation

What does bile do?

• Bile is produced in the liver and stored in the gall bladder.

• The enzymes in the small intestine need an alkaline pH to work best, so bile passes into the small intestine and neutralizes acid from the stomach.

• Bile also emulsifies fat droplets to increase their surface area

Why do you think there is acid in the stomach?

• Kills bacteria in food – protects us• Denatures proteins – makes digestion easier• Activates stomach enzymes – these only

work in acidic conditions

• Ever wondered why PEPSIN (stomach enzyme) doesn’t digest our own stomach?

• Pepsin is inactive when first made and is only activated by HCL to start digesting proteins.

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