Chapter 5- Enzymes

State Standard

Standard 1.b. – Enzymes are proteins that catalyze biochemical reactions without altering the reaction equilibrium and the activities of enzymes depend on the temperature, ionic conditions, and the pH of the surroundings

* http://www.youtube.com/watch?v=AFbPHlhI13g&safety_mode=true&persist_safety_mode=1&safe=active

Enzymes Speed Up Chemical Reactions

• Most of the essential chemical reactions in cells must occur quickly and precisely for the cell to survive

• For a chemical reaction to begin, reactants must absorb some energy

- This energy is called the energy of activation (EA)http://www.sumanasinc.com/webcontent/animations/content/enzymes/enzymes.html

Enzymes Speed Up Chemical Reactions

Enzymes decrease the energy of activation

EA with enzyme

Figure 5.5B

Reactants

Products

EA without

enzyme

Net change in energy

Enzymes Speed Up Chemical Reactions

http://www.ryancshaw.com/Files/micro/Animations/Enzyme-Substrate/micro_enzyme-substrate.swf

Characteristics of Enzymes

Enzymes • Are proteins• Act as a biological catalyst

- Increase the rate of a reaction without being changed into a different molecule

• Increase the rate of a chemical reaction by lowering the amount of energy of activation needed

• Are not changed or used up in the chemical reaction• Are specific• http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__

how_enzymes_work.html

Lecture Review

1. Which of the following can be used to start (initiate) a chemical reaction?A. Addition of ATPB. Heat and addition of ATPC. EnzymesD. HeatE. Heat and enzymes

2. True or False? Enzymes raise the activation energy to break the bonds of reactant molecules.3. Most of a cell’s enzymes areA. LipidsB. ProteinsC. Amino acidsD. Nucleic acids

Lecture Review

4. The amount of energy that reactants need to start a chemical reaction is the _______.5. When an enzyme catalyzes (speeds up) a chemical reactionA. It acts as a reactantB. It acts as a productC. It raises the activation energy of a reactionD. It lowers the activation energy of a reaction

Enzymes Are Specific

Substrate – the substance the enzyme acts on, the reactant in a chemical reaction

Active site – the part of the enzyme molecule that binds to a substrate

SubstratesActivesite

Product

SubstrateEnzymeComplex

Enzymes Are Specific

Enzymes are specific• It takes many different

kinds of enzymes to catalyze all the reactions of the cell

• They have a unique 3D shape

• The active site of an enzyme recognizes only the substrate(s) of the reaction it catalyzes

Enzymes Are Specific

• An enzyme is specific because the active site fits only the substrate(s) of the chemical reaction it catalyzes

• http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_enzymes_work.html

The active site• Is a small part of the

enzyme molecules that binds to the substrate

• Is usually a pocket or groove on the surface of the enzyme

• Forms temporary bonds with the substrate

Active site

Substrate

Lecture Review

1. Which of the following is not true of enzymes?A. Are proteinsB. Act as a biological catalystC. Supplies energy to start a chemical reactionD. Is specificE. Lowers the energy of activation

2. An enzyme is specific, this meansA. It has a certain amino acid sequenceB. It is found only in a certain placeC. It speeds up a particular reactionD. It occurs in only one type of cell

Lecture Review

3. Enzyme(s)A. Function depends on its 3D shapeB. Are not specificC. Are used up in chemical reactionsD. All of the above

4. Why can a single enzyme molecule act on thousands or millions of substrate molecules per second?5. What is the relationship between the active site and the substrate?

How An Enzyme Works

Enzyme available with empty active site

Substrate bonds to active site with induced fit

Substrate is converted to products

Products are released

The enzyme is unchanged and can repeat the process

How An Enzyme Works

Induced Fit• The interaction between the active site and

substrate(s) causes the enzyme to change slightly so the active site fits the substrate better

• Analogy – baseball and glove• http://www.uic.edu/classes/bios/bios100/lectures/enzymes02.html

Lecture Review

In your own words explain how an enzyme works. Include the following:

substrate enzymeactive site Energy of activationproduct Rate of reactioninduced fit

Factors that Affect Enzyme Activity

• Enzyme activity is influenced by- temperature- salt concentration- pH

http://usmanscience.com/12bio/enzyme/enzyme_animations.htm

Factors that Affect Enzyme Activity

Temperature

As temperature increases therate of contact between the substrate and active site increases

The optimum temperature occurs when the rate ofContact between the active site and substrate is greatest. In humans this is between 35-40oC

Higher temperatures denaturethe enzyme altering the shape of the active site

Lecture Review

1. Why does heating interfere with the activity of an enzyme?A. It kills the enzyme.B. It changes the enzyme’s shape.C. It decreases the energy of the substrate molecules.D. It causes the enzyme to break up.E. It decreases the chance that the enzymes will meet a substrate molecule.

Factors That Affect Enzyme Activity

The optimal pH for most enzymes is in the range of pH 6-8

At low pH H+ ions interfere with bonds that maintain the enzyme’s shape

At high pH OH- ions interfere with the enzyme’s shape

If additional Acid is added…

Lecture Review

2. Low pH and extremely salty conditions affect enzyme activity because

A. They cause the structure of the enzyme to change.B. The salt and hydrogen ions compete with the substrate for the active site.C. The salt and hydrogen ions are irreversible inhibitors.D. They reduce the number of collisions between the enzyme and substrate

Lecture Review

3. The pH at which most enzymes’ activity is the greatest is

A. pH 3B. pH 5C. pH 9D. pH 7

Factors that Affect Enzyme Function

Salt concentration• In extremely salty solutions the salt ions

interfere with some of the chemical bonds that maintain the enzyme’s shape and the enzyme is denatured.

Na+ Na+

Na+

Cl-Cl-

Cl-

Lecture Review

Food rots when microbes break down food molecules. Food preservation methods interfere with the enzyme activity of microbes and prevent them from surviving.

4. Explain how each of the following would interfere with enzyme activity -pickling (soaking in acetic acid)

-salting-canning (heating)

Factors that Affect Enzyme Function

Cofactors and coenzymes• Many enzymes will not

work unless they are accompanied by cofactors or coenzymes

• Cofactor – nonprotein helper. Ex: zinc, iron

• Coenzyme – cofactor that is an organic molecule. Ex: many vitamins

• http://highered.mcgraw-hill.com/sites/0070960526/student_view0/chapter6/animations.html

Lecture Review

5. Some enzymes involved in hydrolysis cannot function without the help of sodium ions. Sodium in this case functions asA. A substrateB. A cofactorC. An active siteD. A noncompetitive inhibitorE. A coenzyme

Factors that Affect Enzyme Function

Inhibitors

• A competitive inhibitor takes the place of a substrate in the active site and prevents the substrate from binding to the active site

http://www.wiley.com/college/pratt/0471393878/student/animations/enzyme_inhibition/

Factors that Affect Enzyme Activity

A noncompetitive inhibitor alters an enzyme’s function by changing its shape. The active site can no longer bind to the substrate.

http://highered.mcgraw-hill.com/sites/0072943696/student_view0/chapter2/animation__feedback_inhibition_of_biochemical_pathways.html

Factors that Affect Enzyme ActivityJUST ADDED- not in Outline!!!Feedback regulation to maintain

homeostasis The product of the reaction catalyzed by

an enzyme acts as a reversible inhibitor and regulates the reaction… this is called negative feedback

Ex: enzymes involved in the breakdown of sugars to provide the ENERGY to recycle ADP +P back to ATP are inhibited by ATP…prevents cells from “burning” more sugar than needed!

D=ATPA=sugar

Factors that Affect Enzyme Function

Irreversible inhibitors form covalent bonds between the enzyme and the inhibitor

Ex: certain pesticides are toxic to insects because they inhibit key enzymes in the nervous system

http://www.wiley.com/college/pratt/0471393878/student/animations/enzyme_inhibition/

• Reversible inhibitors form weak bonds between the inhibitor and the active site

• Ex: penicillin, an antibiotic, inhibits an enzyme that bacteria use in making cell walls

Lecture Review

A farm worker accidentally was splashed with a powerful insecticide. A few minutes later, he went into convulsion, stopped breathing, and died. The insecticide was a competitive inhibitor of an enzyme important in the function of the nervous system.

6. Describe the relationship between the structure of the enzyme, the structure of its substrate, and the structure of the insecticide.

Factors that Affect Enzyme Function

Negative Feedback• The product of a

reaction acts as a reversible inhibitor of the enzyme that catalyzes the reaction

• This regulates the reaction