Chapter 5- Enzymes. State Standard Standard 1.b.

Transcription

1 Chapter 5- Enzymes State Standard Standard 1.b. 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 Enzymes

2 Characteristics of Enzymes Enzymes Are Act as a biological catalyst - Increase the rate of a reaction without Increase the rate of a chemical reaction by lowering the amount of energy of activation needed Are not Are 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 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 Enzymes Are Specific Substrate Active site

3 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 An enzyme is specific because The active site Is a small part of the enzyme molecules that binds to the substrate Is usually a Forms temporary bonds with the substrate 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

4 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? How An Enzyme Works Induced Fit The interaction between the active site and substrate(s) causes Analogy 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

5 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. The optimal ph for most enzymes is in the range of At low ph H + ions At high ph OH - ions interfere with the enzyme s shape 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

6 3. The ph at which most enzymes activity is the greatest is A. ph 3 B. ph 5 C. ph 9 D. ph 7 Salt concentration In extremely salty solutions the salt ions interfere with some of the chemical bonds that 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) Cofactors and coenzymes Many enzymes will not work unless they are accompanied by cofactors or coenzymes Cofactor Ex: zinc, iron Coenzyme cofactor that is an organic molecule. Ex: 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

7 Inhibitors A competitive inhibitor A noncompetitive inhibitor alters an enzyme s function by changing its shape. Irreversible inhibitors form

8 Ex: certain pesticides are toxic to insects because they inhibit key enzymes in the nervous system Reversible inhibitors form Ex: penicillin, an antibiotic, inhibits an enzyme that bacteria use in making cell walls 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. Negative Feedback The product of a reaction acts as a This regulates the reaction