1.12 - Enzymes

1.12 Enzymes

• Activation Energy (EA) – the energy required for a chemical reaction to occur

ENZYMES are “Specialized Proteins”

• ENZYMES are proteins that increase the rate at which chemical reactions occur (biological catalysts)

• Enzymes allow chemical reactions to occur faster without increasing things like body temperature (which would damage tissues)

Enzyme Function has an OPTIMUM TEMPERATURE

A temperature at which enzyme activity is highest

Enzyme Names• Enzyme names nearly always end in “-ase”• The beginning of an enzyme’s name suggests

the substrate that it acts on

Examples:*Sucrase: breaks down sucrose*Peroxidase: breaks down hydrogen peroxide

into water (H2O) and oxygen gas (O2)

There are 2 types of enzymes:• Anabolic Enzyme – puts substrates together• Catabolic Enzyme – breaks down substrates

Anna built the blocks up and the cat knocked them down

SHAPE DETERMINES FUNCTION• SUBSTRATE: a substance that an enzyme acts

upon (an enzyme bonds a substrate together or breaks it apart)

• ACTIVE SITE: a location on an enzyme where a substrate binds• The shape of the enzyme and its active site are

important because the substrate fits into the active site

• Each enzyme has an active site specific to a substrate (like a lock and its key!)

Induced Fit Model describes an enzyme as a dynamic protein molecule that slightly changes shape to better accommodate the substrate

“The Lock & Key Model” of Enzymes

Substrate and enzyme must fit together perfectly, like a lock and key (in order for the enzyme to break down the substrate)

Enzyme Function in Human Digestion

Enzymes are very important for speeding up chemical reactions in our digestive system

Examples:Amylase breaks down starchPepsin breaks down proteins into smaller peptidesLactase breaks down lactose into glucose and galactoseLipases break down fats

Factors That Affect Enzyme Function• An enzyme’s ability to function depends largely on its

shape (and environment) – remember, enzymes are just specialized proteins

• Extreme changes in temperature or pH can change the shape of the enzyme (protein)

• How well (how fast) an enzyme can work is affected by:1) Temperature

2) pH3) Concentration of Enzyme4) Concentration of Substrate

The OPTIMUM TEMPERATURE and OPTIMUM pH are the temperature or pH values at which the enzyme works the best (the fastest)

• Optimal temperature for humans is normal body temperature (37C)

• Optimal pH for humans is neutral (pH = 7.0)

1. Temperature• Low temperatures make most enzymes work

slowly• Very high temperatures (>60 C) break bonds

and change the shape of the active site, making the enzyme completely dysfunctional

2. pH• High or low pH conditions also change the

shape of the active site, making the enzyme dysfunctional

• The optimum pH for enzyme activity in humans is normal body pH (7) (with some exceptions, such as those enzymes which function in the stomach)

3. High Concentration of Substrate• If there is more to break down (substrate

molecules are increased) then the rate of reaction will increase… BUT only to a certain point

• There is only so much enzyme that can be used to break down available substrates

4. High Concentration of Enzyme• If there is more enzyme then the rate of

reaction will increase… BUT only to a certain point

• If there isn’t very much substrate, the extra enzymes do not have to ‘work’

Enzyme Inhibition

Competitive inhibitors – substances that compete with the substrate for an enzyme’s active site• These substances are often similar in shape to the

enzyme’s substrate and are able to enter the active site and block the substrate from binding

Non-competitive inhibitors – substances that bind to a site on an enzyme other than the active site, changing the enzyme’s shape to the point where it loses its “affinity” (or ability) for the substrate and the substrate can no longer bind

Allosteric RegulationCells control enzyme activity in 2 ways:

1. By restricting the production of a particular enzyme

2. By inhibiting the action of an enzyme that has already been produced

Industrial Uses of Enzymes

1. Brewing, Baking, and Winemaking• Enzymes produced by yeast cells catalyze the

conversion of glucose into ethanol and CO2

• In baked goods, the ethanol made by yeast evaporates and the CO2 makes bubbles that give breads and cakes their spongy texture

2. Converting starch, wheat, and barley into glucose

• Completed by certain bacteria and moulds3. Cleaning• Some detergent companies add different amylases,

proteases, and lipases to help remove tough carbohydrate, protein, and fat stains

• Enzymes allow stains to be removed with lower temperatures and less agitation

TextbookComplete page 55 #1-4