Enzymes! (What are they good for?) Essential Questions: What is an Enzyme? How do they work? What are the properties of Enzymes? How do they maintain Homeostasis for the body?

What are Enzymes? Enzymes are proteins which act as biological catalysts. A catalyst is a substance that starts or speeds up a chemical reaction without itself being affected. It lowers the activation energy required for the reaction to take place. Their subunits are amino acids. Enzymes are used by cells to trigger and control chemical reactions. Without enzymes, several reactions in cells would never occur or happen too slowly to be useful.

Wait, What is a Chemical Reaction? It is the process of changing one set of chemicals (reactants) into another set of chemicals (products) by rearranging the atoms. Reactants’ bonds are broken and new ones are formed in the products. 2H2 + O2 → 2H2O

Wait, What is activation energy? Activation energy is the amount of energy needed to start a chemical reaction.

Ok, so How do Enzymes Work? Enzymes enable molecules called reactants to undergo a chemical reaction with specific substrates and form new substances called products. Energy can be exothermic (release heat, energy) or endothermic (require heat, energy) Enzymes speed up chemical reactions that take place in cells. They lower activation energy They catalyze specific substrates into products and leave the enzyme unchanged and ready to catalyze the next reaction.

What is a substrate? Enzymes bind to molecules called substrate(s). The(se) substrate(s) are the reactants that are catalyzed by the enzyme. Example: Typically something we ingest that needs to be broken down further for use by the body like Lactose from Cow’s milk. (Done by Lactase) Enzyme Animation: http://www.youtube.com/watch?v=V4OPO6JQLOE

Enzyme Action: Locks & Keys Enzymes provide an area where reactants can be brought together to react. The site on the enzyme where the substrates bind is called the active site. The reactants are called the substrate(s). The substrate(s) enters the active site which becomes the enzyme-substrate complex. The shape of an enzyme is so specific that generally only one enzyme will work for one substrate(s). The fit is so exact that the active site and substrates are compared to a “lock and key”. http://www.youtube.com/watch?v=V4OPO6JQLOE

Enzymes: Catch & Release After the enzyme has complexed with the substrate, the change molecule is released (called a product) to be used by the body. Each protein has a specific shape, therefore enzymes bind to substrates based on shape. the substrates are based on the complementary shape of their specific enzyme. Since only the substrate changes during the reaction, the enzyme can be reused again and again. Recall: Based upon what you know about proteins, what is it about enzymes that allows them to be so specific to only one substrate? Because of the different combination of the 20 essential amino acids, there are thousands! http://en.wikipedia.org/wiki/List_of_enzymes

Induce Fit Hypothesis Enzymes can change shape slightly to fit the substrate a little better (like a hand in glove). Induced Fit Animation: http://www.youtube.com/watch?v=ybahzSjUpB0&feature=PlayList&p=C846C10E855E64E1&index=12&playnext=2&playnext_from=PL

Enzymes can be turned on and off. Enzymes work best at specific temperatures and pH. Heating and the wrong pH can change the enzyme shape affecting the binding of the substrate to the enzyme. Recall: What is the term for heating of enzymes called? Ergo, enzymes in our body work best at 37°C (98.6°F) and at a pH between 6.5 to 7.5. Also, most cells contain proteins that turn enzymes on or off during critical stages of development. denature What other factors control this enzyme? Co factors l, r, and x

Enzyme Characteristics: Review Remember, Enzymes are catalytic proteins. 1. Speed up reaction rate but do not change the reaction. 2. Enzymes are very specific. 3. Enzymes work like locks & keys. Example: Lactose and Lactase 4. Enzymes are unchanged. 5. Enzymes are sensitive to changes in temperature and pH. 6. The suffix –ase means it is an enzyme. Example: lactase, sucrase cellulase, maltase…

Your Turn! The Effect of Catalase Question/Problem: What are the effects of pH on enzymatic reactions? Observations/Control: Watch the following clip up to 0:35. http://www.youtube.com/watch?v=bqEsvNhvN8E What initial observations can you make about the effect of this enzyme? Catalase is an enzyme that breaks down hydrogen peroxide. (H2O2 → H2O + O2) The presence of bubbling (gas) makes you know it is working. Hypothesis: What effect do you think that pH will have on the action of catalase in potatoes at pH of 4, 7 and 9? At what pH will it work the best, and which pH will it work the worst? Explain why in your response. Experiment: Watch the remainder of the clip. Take note of the anemometer reading in red. We’ll watch the clip again to make sure…freeze at 1:30.

Results and Conclusions Results: Was your hypothesis supported or rejected? Conclusions: What is catalase used for in the body? It is a digestive enzyme that occurs in plant and animal tissues to get rid of excess hydrogen peroxide (H202) Why was an anemometer used? Measures the Oxygen gas given off as the product of the enzymatic reaction of catalase. Why do you think that catalase worked best at a pH of 7? That’s the optimum condition (pH) in living things (neutral). 4. What do you think happened to the enzyme at the extremes of pH? It likely partially denatured (affected its shape) and didn’t function as well. Hydrogen peroxide is a harmful by-product of many normal metabolic processes. What do you think would happen if catalase was not functioning properly? Cells would be damaged and die, harming the organism.

Teacher notes This five-stage animation could be used as a precursor to running the experiment in the lab, or as a summary exercise.

Enzyme Animation http://www.kscience.co.uk/animations/anim_2.htm