CatalystsCatalystsReduces the amount of activation Reduces the amount of activation energy needed for a reaction to take energy needed for a reaction to take place.place.

A type of catalyst. Globular proteins (tertiary structure) that speed up a metabolic

reactions by lowering the activation energy needed. Name usually ends in “-ase” and also indicates the substrate it acts

on. (ex: Lipase breaks down…?) This is not always the case.

Ex. Amylase breaks down starch and Catalase breaks down hydrogen peroxide

Metabolic pathways using an enzyme can work in both the forward and reverse direction A + B C or C A + B

Very small amounts needed Reusable (are not changed or destroyed) Highly specific

(ex: catalase only works on Hydrogen peroxide))

Types of Enzymes1. Catabolic

• Enzymes that break down a molecule through hydrolysis

• Amylase breaks complex starches into simple sugars• Catalase breaks down hydrogen peroxide to water and

oxygen• More examples: Lactase breaks down lactose, Papain breaks

down papaya• Any type of digestive enzyme

2. Anabolic• Enzymes that synthesize (build) molecules through

dehydration• ATP synthase creates ATP from ADP and a phosphate• Anabolic steroids build muscle

Lactose intoleranceThe inability to metabolize lactose,

a sugar found in milk and other dairy products.

The required enzyme lactase is absent in the intestinal system.

Symptoms of lactose intolerance include loose stools, abdominal bloating and pain, flatulence, and nausea.

Activation energyActivation energy energy required to energy required to start a reaction.start a reaction.(with and without an enzyme)

• Is reaction shown endergonic or exergonic?• Do these reactions have to catabolic, anabolic, or can they be

either?

Substrate & Active site

The substrate is the substance that the enzyme is working on.

Active site –

Where the enzyme attaches

to the substrate.

Allosteric site – a separate site on an enzyme where the binding of a regulatory molecule can either inhibit or stimulate the enzymes activity

Allosteric Site (continued)

The binding of an activator to the allosteric site stabilizes the shape that has functional active sites (remember, enzymes are globular so they may have an active site on each polypeptide).

Binding of an inhibitor stabilizes the inactive form of the enzyme

Lock & Key ModelLock & Key Model

Induced Fit Model When the enzyme and substrate “lock” together, the

enzyme changes it shape slightly to fit more tightly around the substrate. Ex. Glove changing shape once hand is inserted Ex. Lock clicking when key is full inserted

Ways in which substrate can bind to enzyme

1. Hydrogen bonds

2. Van der Waals interactions

3. Ionic bonds

Types of Activators Enzymes can be “primed” to react by 2 factors.

1. Allosteric activationAs discussed earlier, the binding of an activator molecule to the allosteric

site can alter the shape of the enzyme as to make it more likely to bind to its substrate.

1. CooperativityA substrate molecule binding to one active site may stimulate the catalytic

powers of a multisubunit enzyme by affecting the other active sites

In other words, if an enzyme has 2 or more subunits, a substrate molecule causing induced fit in one subunit can trigger the same favorable shape change in all the other subunits.

Ex. Hemoglobin binding to one oxygen promotes the pickup of additional oxygen molecules (hemoglobin is not an enzyme, but the concept of cooperativity is shown here)

Cofactors and Coenzymes Cofactors – nonprotein helpers that aids enzymes in

their catalytic activity May be bound tightly to the enzyme as permanent

residents or may bind loosely and reversibly along with the substrates

Inorganic examples: zinc, iron, and copper

Organic examples: Organic cofactors are specifically called coenzymes

Most vitamins are coenzymes

Determining the reaction rate of a reaction using an enzyme Studying the rate of disappearance of the

substrate or appearance of the product. Calculating the slope on a time vs. product

formed graph Remember “Dry Mix” What does it mean when line is increasing linearly? What about when line is flat?

Enzymes are affected by 1), temperature, 2), pH, 3) concentration (of enzyme or substrate), or 4) salinity *Can be *Can be denatured denatured (change shape & (change shape & lose function)lose function)

saturation point.

The effect of concentration on reaction rate

Substrate Concentration Reaction rate increases as substrate concentration increases (b/c enzyme

works faster) Equilibrium eventually reached b/c enzyme cannot work any faster.

Enzyme Concentration Reaction rate increases as enzymes concentration increases (b/c more

enzymes present to aid in breaking down the substrate). Equilibrium eventually reached b/c all the substrate is being broken down and

adding more enzymes will not affect the reaction rate (Because those enzymes will have no substrate to break down).

Competitive InhibitorCompetitive Inhibitor Molecule competes for Molecule competes for

the “active site”the “active site” How can this kind of How can this kind of

inhibitions be inhibitions be overcome?overcome?

Noncompetitive inhibitorNoncompetitive inhibitor The presence of a noncompetitive inhibitor changes the shape of The presence of a noncompetitive inhibitor changes the shape of

the enzyme and prevents the reaction from occurring.the enzyme and prevents the reaction from occurring. Both noncompetitive inhibitors and allosteric regulators bind at a

site other than the active site to control the activity of an enzyme. They are different in that allosteric regulators are reversible

while most noncompetitive inhibitors are not. Also, allosteric regulators can be serve to excite or inhibit an enzyme while noncompetitive inhibitors only inhibit.

 

                                          

     

Inhibitors are used to control reaction rates

Beneficial examples of inhibitor usage: Negative feedback mechanism - Many enzymes work to monitor

their production because products of their reactions serve to inhibit the enzyme themselves. Ex. A + B X C

If product C inhibits enzyme X then the accumulation of product C would stop this reaction from occurring and stops the enzyme from “overworking”

Other examples: many prescription drugs work, some types of chemotherapy, some pesticides

Harmful examples of inhibitor usage: Non-prescription drugs Toxins Poisons work by inhibiting enzymes as well.