Module 7 Intro

Module 7—The Digestive and Respiratory Systems

Watch and Listen

 

What’s in This Food?

 

Three macromolecules (carbohydrates, proteins, and lipids) that you have studied in this lesson have different tests that reveal their presence in various foods. The standard tests for them are outlined in the video "What’s in This Food?"

 

 

 

Self-Check

 

SC 1. After you have watched the video, complete the summary table that follows. You may use the information in “Investigation 6.A: Testing for Macromolecules” on page 212 of your textbook to help complete this question. Note that there is more than one test for lipids. Save this chart in your course folder for future reference.

 

Testing for Macromolecules

Test Name	Molecule Indicated	Negative Test	Positive Test
Benedict’s test
iodine
Biuret
translucence
Sudan IV

 

 

Read

 

Enzymes are specific types of proteins that help regulate the many different chemical reactions that occur in your body. Enzymes lower the activation energy required to catalyze reactions. Otherwise, the energy required would be too large and these reactions could cause damage to your body’s cells. You may want to read pages 214 to 216 in the textbook before watching the following animations.

 

Watch and Listen

 

Enzyme function can be simply described as the speeding up of a chemical reaction due to the interaction of an enzyme’s active site with a specific substrate molecule or molecules. Watch the following animation How Enzymes Work. As you watch, notice how the active site of the enzyme changes shape slightly as the enzyme performs its function. This is sometimes known as the induced–fit model of enzyme activity. At one time, scientists described this enzyme activity as the lock and key model where the active site fits the substrate molecule(s) perfectly and doesn’t change shape during the reaction. The induced-fit model is the more accepted model today.

 

For example, the enzyme sucrase only binds to the substrate molecule of sucrose.

 

Now combine your prior knowledge of catabolic reactions with enzyme function by watching a second animation Enzyme Action and the Hydrolysis of Sucrose. This animation illustrates a practical example of an enzyme-catalyzed reaction in the human body. Remember that hydrolysis is the decomposition of a compound by a reaction with water. The hydrolysis of sucrose into its components of glucose and fructose is controlled by the enzyme sucrase, which is found in the human digestive tract. Note how the enzyme never actually becomes part of the reactants or products of the reaction. The enzyme can be used over and over.

 

Self-Check

SC 2. What are three ways an enzyme will no longer function?

 

 

Watch and Listen

 

One factor that affects enzyme action is inhibition. This next animation illustrates how the end products of a series of enzymatic reactions will inhibit enzyme activity in a negative feedback loop. Feedback inhibition ensures that the body doesn’t needlessly produce more products of the biochemical pathway than are needed.

 

An analogy is driving down the highway: You should be maintaining the speed limit. If you are going too fast, you slow down. If you are going too slowly, you speed up. Your speed is the product; your car is the enzyme. Gasoline and air are your substrates. You are translating your knowledge of your vehicle's speed into feedback inhibition. The rate at which your car acts upon gasoline and air determines your product (speed).

 

If you have not already read pages 214 to 216 of your textbook, you should do so now.

 

Biology 20 © 2008 Alberta Education