ENZYMESIB Biology HL 1Mrs. PetersFall 2013

3.6.1 Enzymes• All enzymes are proteins with characteristic three

dimensional shape• Shape determines the function of the enzyme• Work until shape is changed and can’t function any

longer

3.6.1 Enzymes• Biological catalysts that lower the activation energy of a reaction which speeds up the rate of a reaction such as digestion or respiration.

• Enzymes reduce the amount of energy required to make the reaction take place; lower the activation energy• DRAW THIS DIAGRAM!

7.6.3 Activation Energy

• For any reaction to start it usually requires the input of energy (Activation Energy)

• Enzymes function to lower the activation energy of a specific reaction • The amount of energy

required to start the reaction is reduced because the enzyme is doing the reaction.

3.6.1 Enzymes• The Parts of the Enzyme-Substrate Complex

• Enzyme: protein that conducts specific reactions• Substrate: what it reacts with to produce a product• Active site: where the substrate binds to the enzyme• DRAW THE YELLOW MODEL, LABEL PARTS

3.6.2 EnzymesEnzyme Specificity: each enzyme fits only 1 substrate.

• Lock and Key Model• Enzyme is like the lock,

substrate is like the key…only one key fits the lock

• Induced Fit• A substrate enters the active

site, inducing the enzyme to change its shape slightly, so the active site fits the substrate more snuggly• Ex: like a clasping handshake

7.6.1 EnzymesEnzyme Cycle

1. Substrate attaches to enzyme active site by weak bonds (hydrogen and ionic)

2. Enzyme completes the reaction, converting substrate to product

3. Product leaves the active site

4. Enzyme takes up the next substrate in the active site, repeating cycle.

7.6.1 Enzymes & Metabolic Pathways

• Metabolic Pathways• Several enzymes are used to complete a reaction• The product of each enzyme is the substrate for the

next enzyme until the final product is produced.• Draw this diagram!

3.6.3 Enzyme Activity and Substrate Concentration

• Enzyme activity is directly affected by substrate concentration• Amount of substrate present at the time of the reaction

• Enzymes can only make as much product as there is substrate available

• Enzymes will continue to work until all substrate is used up• Adding additional substrate will produce more product

3.6.3 Enzyme Activity and Substrate ConcentrationReaction Rate:• As active sites fill with substrate, the rate of reaction increases, increasing the amount of product produced

• When all active sites are full and there are no more available sites, the reaction will continue at a stable rate producing products DRAW THIS DIAGRAM!

3.6.3 Enzyme Activity and pH• Enzyme activity affected by pH• All enzymes have an

optimum pH at which most active (work the most efficiently)

• pH range for enzyme activity is relatively small, won’t work outside that range

• reaction will increase to a point before being disrupted

• changes in environmental pH will cause denaturation

Draw this diagram!

3.6.3 Enzyme Activity and Temp.• Enzyme activity affected by temperature• All enzymes have an

optimum temperature at which most active

• If temperature increases, reaction will increase to a point before being disrupted

• Significant increased temperature causes denaturation

• Enzyme won’t function after denaturation

Draw this diagram!

3.6.4 Denaturation

• Denaturation is a structural change in a protein that results in the loss (usually permanently) of its biological properties.

• Enzymes can be denatured by changes in temperature and pH. • Original environment is changed in some way• Placed in environments that are outside their optimum range• Temperature usually has to be hotter than it’s optimum range, if it

is colder, the enzyme will work slowly or not at all, but won’t be effected permanently

Enzyme Activity

• Cofactors: small molecules that bind with enzymes, necessary for function

• Inhibitors: molecules which selectively disrupt the action of enzymes

7.6.4 Enzyme InhibitorsInhibitor Types• Competitive: a molecule similar in shape to the substrate that competes with substrate for active site, blocks substrate from attaching to the active site, temporarily shutting down the enzyme

7.6.4 Enzyme InhibitorsInhibitor Types

• Non-competitive: a molecule that binds to a location separate from active site, changing shape of enzyme, blocking the substrate from attaching to the active site, temporarily shutting down the enzyme

7.6.4 Enzyme Inhibitors Comparison

Competitive• Structurally similar to the

substrate molecule• Occupies and blocks the

active site, lowering the rate of the reaction

• If inhibitor concentration is low, increasing the substrate concentration will reduce the inhibition

Noncompetitive• Structurally unlike the

substrate molecule• Binds to a site away from

the active site, changing the shape of the active site, lowering the rate of the reaction

• If inhibitor concentration is low, increasing the amount of substrate has no effect, enzyme stays inhibited

7.6.4 Enzyme Inhibitors Comparison

Competitive Exs:• Penicillin blocks the active

site of bacteria enzyme• Oxygen: competes with CO2

for the active site of ribulose bisphoste carboxylase (RuBP) in photosynthesis

• Disulfiram: competes with acetaldehyde in the liver

Noncompetitive Exs:• Cyanide and carbon

monoxide will block cytochrome oxidase in respiration, leading to death

• Oxalic and citric acid inhibit blood clotting by forming complexes with calcium ions (a cofactor for enzymes)

7.6.5 Enzyme Inhibition

• End-Product Inhibition: the end product of a metabolic pathway reaction acts as an inhibitor of an enzyme earlier in the pathway (usually the first enzyme) causing the pathway to stop producing product

7.6.5 Enzymes and Allostery• Allosteric Enzymes: a series of the same enzyme bonded

together • Allosteric Regulation: molecules bind to an allosteric site

(non-active site) to either inhibit or activate enzyme activity• Activators: molecules that activate, or turn on the allosteric enzyme by

attaching to the allosteric site• Inhibitors: molecules that will shut off, or inhibit the allosteric enzyme

by attaching to the allosteric site, changing the shape of the active site

3.6.5 Enzyme Uses• Example #1 (KNOW THIS EXAMPLE)

• Lactase in the production of lactose-free milk• Lactase breaks down lactose into glucose and galactose, uses

the hydrolysis reaction• Lactose-free milk is made so people who are lactose intolerant

can still receive the nutrition of milk without indigestion.

• Other Examples• Enzymes are used in digestion

• Amylase, pepsin, trypsin• Many enzymes are used in Biotechnology to cut DNA or

add nucleotides together to create new DNA copies (***we will cover this later during the DNA and Biotech units)

Enzyme Practice Questions

With a partner, write the answer first without notes!• Explain how competitive and non-competitive

inhibition can include allostery.• Explain how the concentration of substrate and

competitive inhibitors can effect enzyme reactions.

• Describe how lock and key and induced fit explain enzyme specificity.

Now, go back and use your notes, a new color writing utensil, and Mrs. Peters to fill in more information for each answer.

Enzymes

• Cooperactivity: resembles allosteric activation• One substrate binding to an active site opens all other

active sites of the enzyme, if multiple subunits together form the enzyme