Virtual Lab: Enzyme Controlled Reactions



NAME _____________________________ Date ______ Group ______ Block _______

Honors Biology

Virtual Lab: Enzymes and Reactions

For the processes of life (such as breathing and digestion) the body carries out thousands of biochemical reactions every second. Many of these reactions require the help of enzymes. Enzymes are proteins that speed up the rate of chemical reactions.

Enzymes are organic catalysts. A catalyst is a chemical that controls the rate of a reaction, but is itself not used up in the process. Reactions that are accelerated due to the presence of enzymes are known as enzyme-catalyzed reactions.

Enzymes are proteins that accelerate chemical reactions but do not change in the reaction. Enzymes help molecules to undergo chemical changes, to form new substances called products. The substrate is the substance that the enzyme acts upon.

For example, amylase, an enzyme found in saliva, helps break down complex starch molecules (substrates) into smaller sugar molecules (products).

Each substrate fits into an area of the enzyme called the active site. This fitting together is often compared to a lock-and-key mechanism. Enzymes speed up the rates of reactions by bringing the molecules together in the correct orientation and by lowering the activation energy required to start the reaction.

Purpose: In this investigation you will determine the effects of substrate concentration and pH on the rate of a reaction. We will examine the enzyme lactase to investigate how these factors affect the rate of an enzyme-catalyzed reaction.

Millions of people suffer from an enzyme related condition called lactose intolerance. Lactose is a disaccharide that is commonly referred to as dairy sugar or lactose. In normal individuals who drink milk, their digestive system produces lactase which breaks down the sugar lactose in to two monosacharides—glucose and galactose which can be used by the body. In a person with a lactose intolerance, there is not enough of the lactase enzyme produced to break down the substrate lactose. When this individual eats lactose, it cannot be broken down in their digestive tract. This leads to discomfort, cramps, bloating and diarrhea.

1. Go to my Biology website and open the Virtual Enzyme Lab. This is located in the links section. Or type the following :

2. Watch the video about enzyme action by clicking on the pic of the monitor.

3. Follow the instructions on the next page to complete the virtual lab.

4. Answer the questions on the Lab Worksheet. TYPE or use Blue or Black ink with COMPLETE SENTENCES.

Problem: How does the amount of lactose (substrate concentration) and pH affect the rate of the breakdown of lactose?

Hypothesis:

If there is a higher concentration of lactose then______________________________________

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If the pH is higher then _________________________________________________________

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Experiment:

1. Each test tube already contains the lactase enzyme.

2. To conduct the experiment, adjust the pH levels of the test tubes by clicking the up and down arrows then add lactose to each of the test tubes. Click and Drag a piece of weighing paper with the powdered lactose to a test tube.

3. Click the computer monitor to see the digital counter table that displays the number of glucose and galactose molecules formed during the first minute in each of the five test tubes. This tells you the rate of the reaction—if _____________________ molecules are formed, then the reaction is going ________________________.

4. Record your data in Table 1 below AND in the virtual data table within the website.

5. Click the Reset button. Repeat the experiment using different amounts of lactose at a constant pH value. Or, use on lactose at five different pH levels. Record your results in the Data Table. You will run several trials because you must test each lactose sample at all pH levels: 3,5,7,9, and 11.

6. When all the data has been collected (on both your paper and on the sim) click the Graph button to see a graph of the results. PRINT your graph and attach.

7. CREATE PROPERLY FORMATTED TITLES FOR BOTH THE DATA TABLE BELOW AND THE PRINTED GRAPH.

Table 1: Record your data on the number of product molecules formed per minute obtained from the virtual lab.

# Product Molecules/minute at:

|Amount of Substrate |pH 3 |pH 5 |pH 7 |pH 9 |pH 11 |

|(Lactose) | | | | | |

|0.5 g | | | | | |

|g | | | | | |

|g | | | | | |

|g | | | | | |

|8.0 g | | | | | |

1. If you haven’t done so already, click the “graph” button on the virtual data table. In the graph you created:

a. What is represented by the green line?

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b. What is the best pH for lactase enzyme activity?

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2. What substrate amount was required to achieve the maximum reaction rate? ________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

3. At what pH level did the maximum reaction rate occur? How many molecules per minute were produced? ________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

4. Why was there no increase in the reaction rate with 8 g of substrate as compared to 4 g of substrate? Hint: think about the lock and key analogy. ________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

5. What would you need to add to see an increase in the reaction rate with 8.0 g. of substrate? ________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

6. Which of the following would interfere most with the ability of an enzyme to catalyze a reaction? Examine your data to answer this!

a. Reduced amount of substrate available (number of grams of substrate)

b. Reduced concentration of product available (# of molecules/min produces)

c. Increased amount of substrate available (number of grams of substrate)

d. A change in the pH

7. Which of the following statements is accurate in describing the activity of the lactase enzyme?

a. Lactase can function equally effectively at many different pH levels

b. The shape of lactase does not change during the reaction

c. Lactase is converted to glucose and galactose by the reaction

d. One lactase enzyme can catalyze many reactions

8. Consider only the trials you conducted with 0.5 g. of lactose.

a. What is the independent variable?____________________________

b. What is the dependent variable?_____________________________

9. The maximum rate of this reaction is 350 molecules product/minute. List two changes you could make in the experimental conditions or variables that would increase this reaction rate. Explain why each change you listed will increase the reaction rate.

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10. When an enzyme catalyzes a reaction:

a. Substrate(s) bind in the active site

b. Products bind in the active site

c. The shape of the enzyme remains unchanged

d. The enzyme is consumed by the reaction

11. Feedback mechanisms regulate the rate of enzyme activity, effectively “turning off” an enzyme in a reversible way until more product is needed. Which of the following would be most effective as a feedback mechanism?

a. Reduced concentration of product

b. Increased concentration of substrate

c. A change in pH

d. Temporary binding of a non-substrate molecule in the active site

12. Which of the following does NOT apply to an enzyme:

a. Catalyst

b. Inorganic

c. Protein

d. All of the above apply to an enzyme

13. Look up and write in the following definitions as they apply to chemical reactions:

a. Catabolic

b. Anabolic

c. Endergonic

d. Exergonic

14. Is the action of the enzyme illustrated in the video:

a. Anabolic or catabolic?

b. Endergonic or exergonic?

15. Endergonic or exergonic? Is the action of lactase:

a. Anabolic or catabolic?

b. Endergonic or exergonic?

16. Why is enzyme activity similar to, but not exactly like, a “Lock” and “Key”?

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