ENZYMES

S P E E D I N G U P C H E M I C A L R E AC T I O N S

TEKS

9C: Students will…

identify and investigate the role of enzymes

WHAT ARE ENZYMES?

• Enzymes are proteins (what is their monomer?)

• These proteins are used by the cell to speed up and

regulate chemical reactions

• Enzymes can also be called catalysts

• They remain unchanged by the reaction

HOW DO ENZYMES WORK?

• Enzymes lower the activation energy of a reaction

–Activation energy = the minimum amount of energy

needed for a chemical reaction to occur

• They do this by adding some of their own energy to the

reaction

• If there were no enzymes, many reactions would require

higher temperatures to occur

PLEASE NOTE

• Enzymes do NOT increase how much product is

made (just how quickly and easily it is made)

• Enzymes do NOT get used up in the reaction

(therefore, they can continue to catalyze reactions over

and over again)

HOW DO ENZYMES WORK?

ENZYME STRUCTURE

• Enzymes are proteins with a 3-dimentional shape caused by the folding of the protein

• The specific shape of the enzyme determines which substrate it works with

– Substrate = substances acted on by enzymes

• Most enzymes end with -ase

– Lipase acts of lipids

– Maltase acts on maltose

– Protease acts on proteins

– Lactase acts on lactose

All enzymes end

with –ase….so if I

say “Studentase”

what type of

enzyme is this?

ACTIVE SITE

• The substrate is temporarily bound to its enzyme at the

active site

• Only substrates that are the same size and shape as the

active site can bind to an enzyme (specificity)

• The enzyme may change shape slightly to accommodate the

substrate (induced fit)

– Induced fit helps substrates react to form product(s)

ACTIVE SITE

TWO JOBS

• Enzymes can break down substrates into their

component parts (what is this called? Example?)

OR

• Enzymes can put multiple substrates together into

one larger molecule (what is this called? Example?)

CHAINS

• Enzymes often work as a series of reactions that turn

substrates into products

• If one step in the chain doesn’t work, the product cannot

be made

DENATURE

• If enzyme #4 in the image above stopped functioning

correctly, what would happen?

– Would the green substrate be turned into the orange substrate?

– Would the orange substrate be turned into the yellow substrate?

– Would the yellow substrate be turned into the purple substrate?

– Would the purple substrate be turned into the blue substrate?

– Would the blue substrate be turned into the red substrate?

• Which substrate would you have the most of?

DENATURE

• Enzymes work within a narrow range of environmental

factors

– Temperature, pH, and concentration must be correct if an

enzyme is to function properly

• If the environment is not conducive to enzyme activity, the

enzyme may fall apart. This distorts the shape of the active

site, which means the substrate cannot attach to the enzyme,

and the enzyme cannot do its job

• If the enzyme comes apart and its active site no longer has the

correct shape, it is said to be “denatured”

FACTORS AFFECTING ACTIVITY

• Temperature

–The temperature where the enzyme functions most

effectively is called the optimal temperature

– If the temperature is lowered too much, enzyme activity

will slow down and eventually stop

– If the temperature is raised too far above the optimal

temperature, the enzyme will become denatured and stop

functioning

FACTORS AFFECTING ACTIVITY

• Temperature

FACTORS AFFECTING ACTIVITY

• Temperature

1. What is the optimal temperature

for enzyme A? _________

2. What is the optimal temperature

for enzyme B? _________

3. Knowing that room temperature is approximately 22°

Celsius, which enzyme would work best? _________

FACTORS AFFECTING ACTIVITY

• pH

–pH tells you how acidic (or basic) a solution is

–pH is a measure of the number/concentration of hydrogen

ions in solution [H+]

• pH = 7 is neutral and occurs when [H+] = [OH-]

• pH lower than 7 is acidic and occurs when [H+] > [OH-]

• pH higher than 7 is basic and occurs when [H+] < [OH-]

– If the pH is lowered or raised outside optimal, the

enzyme will denature & stop functioning

FACTORS AFFECTING ACTIVITY

• pH

FACTORS AFFECTING ACTIVITY

• pH

FACTORS AFFECTING ACTIVITY

• pH

1. What is the optimal pH for

the enzyme found in your

stomach? ________

2. What is the optimal pH for

the enzyme found in your intestines? ________

3. What organic substances are both of these enzymes

digesting? ___________

Gastric Protease

Intestinal Protease

FACTORS AFFECTING ACTIVITY

• Concentration

–Concentration = amount of enzyme and/or substrate

present

–The larger the concentration of the enzyme, the faster

the rate of the reaction (up to a point)

–Saturation point is the point at which no more substance

can be absorbed/worked on

FACTORS AFFECTING ACTIVITY

• Concentration

FACTORS AFFECTING ACTIVITY

• Rate of the reaction depending on the concentration of

the substrate (with or without enzymes)

INHIBITION

• Enzyme inhibitor: a molecule that binds to an enzyme and decreases its activity

(2 types)

– Competitive: the inhibitor is competing with the substrate for access to the active site

– Non-competitive: the inhibitor binds to the enzyme at the allosteric site (which is

different than the active site). This binding changes the shape of the active site,

making it impossible for the substrate to bind

INHIBITION