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

Enzymes Speed Up Chemical Reactions http://www.ryancshaw.com/Files/micro/Animations/Enzyme-Substrate/micro_enzyme-substrate.swf EA without enzyme EA with enzyme Reactants Net change in energy Products Figure 5.5B

Characteristics of 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 ATP B. Heat and addition of ATP C. Enzymes D. Heat E. 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 are A. Lipids B. Proteins C. Amino acids D. Nucleic acids B False

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 reaction A. It acts as a reactant B. It acts as a product C. It raises the activation energy of a reaction D. It lowers the activation energy of a reaction 4. Energy of Activation 5. D.

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 Substrate Active site

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 The active site 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 Substrate Active site

Lecture Review 1. Which of the following is not true of enzymes? A. Are proteins B. Act as a biological catalyst C. Supplies energy to start a chemical reaction D. Is specific E. Lowers the energy of activation 2. An enzyme is specific, this means A. It has a certain amino acid sequence B. It is found only in a certain place C. It speeds up a particular reaction D. It occurs in only one type of cell C

Lecture Review 3. Enzyme(s) A. Function depends on its 3D shape B. Are not specific C. Are used up in chemical reactions D. 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? 3. A 4. Because at the end of assisting one reaction, the enzyme returns to its original shape so it can bind to the next substrate 5. Substrate (what goes into the chemical reaction) binds to the enzyme’s active site (a small grove or pocket where the substrate fits like a lock and key)

How An Enzyme Works Enzyme available with empty active site Substrate bonds to active site with induced fit The enzyme is unchanged and can repeat the process Products are released Substrate is converted to products

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 enzyme active site product induced 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 The optimum temperature occurs when the rate of Contact between the active site and substrate is greatest. In humans this is between 35-40oC Higher temperatures denature the enzyme altering the shape of the active site As temperature increases the rate of contact between the substrate and active site increases

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. 1.B

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 2.A

Lecture Review 3. The pH at which most enzymes’ activity is the greatest is A. pH 3 B. pH 5 C. pH 9 D. pH 7 3. D

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+ 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 as A. A substrate B. A cofactor C. An active site D. A noncompetitive inhibitor E. A coenzyme 5. B

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.google.com/search?q=enzyme+competitive+inhibitor+animations&rls=com.microsoft:en-us:IE-Address&ie=UTF-8&oe=UTF-8&sourceid=ie7&rlz=1I7ADFA_enUS426

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 Activity JUST 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! A=sugar D=ATP

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