2.5 & 8.1 EnzymesIB Biology HL 1Mrs. PetersFall 2014

2.5 Enzymes• All enzymes are proteins with characteristic three

dimensional shape• Found in all living cells• Thousands of enzymes are produced by cells

2.5 Enzymes• Shape determines the function of the enzyme• Enzymes will work until shape is changed and can’t

function any longer

2.5 U1. EnzymesThe Parts of the Enzyme-Substrate Complex

Enzyme: globular protein that conducts specific reaction

Substrate: substances the enzyme converts into a product

2.5 U1. EnzymesThe Parts of the Enzyme-Substrate Complex

Active site: site on the enzyme where the substrate attaches

• Shape and chemical properties of the active site and the substrate must match each other

2.5 U1. Enzymes• The active site fits a specific substrate.• Substrate bonds to the active site and are converted

into a product, then product released

2.5 U1. EnzymesDraw the enzyme-substrate complex, yellow only!

2.5 U1 Enzyme SpecificityEnzyme Specificity: each enzyme fits only 1 substrate.

2.5 U1 Enzyme SpecificityLock and Key Model

• Enzyme is like the lock, substrate is like the key…only one key fits the lock

2.5 U1 Enzyme SpecificityInduced 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

8.1 U2. Enzymes

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

8.1 U2. Enzymes

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

8.1 U2. Enzymes

DRAW THIS DIAGRAM!

8.1 U2. Activation Energy

• Activation Energy: the input of energy required for any reaction to start

8.1 U2. 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.

2.5 U2. Enzyme Activity

• Most reactions take place in solution, dissolved substances in water

• Each particle moves separately

• Direction of the movement is random and constantly changes

2.5 U2. Enzyme Activity

• Substrates are smaller and move faster than enzymes.

• Substrates collide with enzymes

• When the collision is correctly aligned, substrate will attach to the active site.

2.5 U2. Enzyme Activity

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

2. Enzyme completes the reaction, converting substrate to product

2.5 U2. Enzyme Activity

3. Product leaves the active site

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

8.1 U1 Enzymes & Metabolic Pathways

Metabolism• Huge range of chemical reactions that take place in

living cells• Most chemical changes happen in a sequence of small

steps which form a metabolic pathway

8.1 U1 Enzymes & Metabolic Pathways

Metabolic Pathways• A chain or cycle of reactions• Several enzymes are used to complete a pathway• The product of each enzyme is the substrate for the

next enzyme until the final product is produced.

8.1 U1 Enzymes & Metabolic Pathways

• Metabolic Pathways• Draw this diagram

2.5 U3. 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

2.5 U3. Enzyme Activity and Substrate Concentration

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

2.5 U3. Enzyme Activity and Substrate ConcentrationReaction Rate:• When substrate concentration is increased, more collisions are possible, reaction rate increases

DRAW THIS DIAGRAM!

2.5 U3. Enzyme Activity and Substrate ConcentrationReaction Rate:• As active sites fill with substrate, the rate of reaction increases, increasing the amount of product produced

DRAW THIS DIAGRAM!

2.5 U3. Enzyme Activity and Substrate ConcentrationReaction Rate:• 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!

2.5 U3. Enzyme Activity and pH• Enzyme activity affected by pH• All enzymes have an

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

Draw this diagram!

2.5 U3. Enzyme Activity and pH• Enzyme activity affected by pH• pH range for enzyme

activity is relatively small, won’t work outside that range

• reaction will increase to a point before being disrupted

Draw this diagram!

2.5 U3. Enzyme Activity and pH• Enzyme activity affected by pH• changes in environmental

pH will cause denaturation

Draw this diagram!

2.5 U3. 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

Draw this diagram!

2.5 U3. Enzyme Activity and Temp.• Enzyme activity affected by temperature• Significant increased

temperature causes denaturation

• Enzyme won’t function after denaturation

Draw this diagram!

2.5 U4 Denaturation

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

2.5 U4 Denaturation

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

2.5 U4 Denaturation

Denatured Enzymes:•The active site is altered in some way and the substrate can not bind •If substrate binds, the reaction does not occur•usually become insoluable

8.1 U3 Enzyme Inhibitors

• Inhibitors: molecules which selectively disrupt the action of enzymes

• Two types: competitive and non-competitive

8.1 U3 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

8.1 U3 Enzyme InhibitorsInhibitor Types

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

8.1 U3. 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 allosteric 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

8.1 U4 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

8.1 A1 End Product Inhibition Example

Pathway converting amino acid threonine to isoleucine•Start with threonine (substrate 1) and threonine deaminase (enzyme 1)•5 enzyme reactions later isoleucine is produced (end product)

8.1 A1 End Product Inhibition Example

• As Isoleucine concentration builds, it binds to the allosteric site of the first enzyme (threonine deaminase) in the pathway

• Isoleucine acts as a non-competitive inhibitor

8.1 S1. Inhibition Graphs

• Must be able to identify different types of inhibition from graphs.

Substrate concentration

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8.1 S1. Inhibition Graphs

• Competitive is slightly lower than normal

• Non-competitive is significantly lower than normal

Substrate concentration

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2.5 U5. Immobilized Enzymes - History

• 1897 Hans and Eduard Buchner used an extract of yeast, which contained no yeast cells, to convert sucrose to alcohol

• This provided additional evidence against the theory of vitalism

• Enzymes can be used outside the cell

2.5 U5. Immobilized Enzymes

• Over 500 enzymes are used for commercial uses

2.5 U5. Immobilized Enzymes

• Enzymes are usually immobilized, (attached to another material)• Attached to glass• Trapped in a gel• Bonded together to

form aggregates

2.5 U5. Immobilized Enzymes Advantages:•Enzyme is easily separated from product, stopping the reaction at the ideal time•Enzymes can be recycled, saving costs (enzyme use is expensive)

2.5 U5. Immobilized Enzymes Advantages:•Increases stability of enzyme to changes in temp and pH•Substrate exposed to higher conc. of enzymes, speeding up reaction rate

2.5 A1. Production of Lactose-free milkLactose is the sugar in milkCan be converted into glucose and galactose by the lactase enzyme.

Lactase is extracted from Kluveromyces lactis, a yeast that grows naturally in milk.

Biotech companies culture the yeast, extract and purify the lactase for sale to food manufacturers.

2.5 A1. Production of Lactose-free milkAdvantages of Lactose-free milk•Lactose intolerant people can drink milk to get its benefits without the trouble of digesting lactose•Galactose and glucose are sweeter than lactose, less sugar needs to be added to foods that contain milk

2.5 A1. Production of Lactose-free milkAdvantages of Lactose-free milk•Lactose crystallizes during ice cream production creating a gritty texture, glucose and galactose are more soluble creating a smooth texture•Bacteria ferment glucose and galactose more quickly producing yogurt and cottage cheese more quickly

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.