<![CDATA[Enzyme-Controlled Reactions]]> Purpose

In this investigation you will determine the effects of substrate concentration and pH on the initial 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. In normal individuals who eat lactose, their digestive system produces the enzyme lactase which breaks down the sugar lactose into two monosaccharides – 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 sufficiently in their digestive tract. This leads to the discomfort associated with lactose intolerance such as cramps, bloating, gas,and diarrhea.



Objectives:

  • Determine the effect of lactose concentration on the initial rate of a lactase-catalyzed reaction.


  • Determine the effect of pH on the initial rate of a lactase-catalyzed reaction.



Procedure

1. Click the monitor to watch a video about enzyme action.



2. Click Information to read about enzymes and lactose.




3. To conduct the experiment, adjust the pH level of the test tube by clicking the up and down arrows, then add lactose to each of the test tubes that already contain a lactase solution. Click and drag a piece of weighing paper with the powdered lactose to a test tube. Note: Assume that the enzyme concentration in each test tube is constant.



4. 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 is the initial reaction rate of this enzyme-catalyzed reaction.



5. Click the Data Table button to record the data in the Data Table.



6. Click the Reset button. Repeat the experiment using different amounts of lactose at a constant pH value. Or, use one lactose at five different pH levels. Record your results in the Data Table. When all the data have been collected and recorded, within the Data Table, click the Graph button to see a graph of the results.



After you have performed the experiment, click the Journal button and answer the Analysis questions.

]]> Describe the relationship between substrate concentration and the initial reaction rate of an enzyme-catalyzed reaction. Is this a linear relationship? What happens to the initial reaction rate as substrate concentration increases?

]]> What is the maximum initial reaction rate for the lactase enzyme at pH 7?

]]> Explain why the maximum initial reaction rate cannot be reached at low lactose concentrations.

]]> What does your data indicate about the optimum pH level for this lactase-catalyzed reaction?

]]> Enzymes function most efficiently at the temperature of a typical cell, which is 37 degrees Celsius. Increases or decreases in temperature can significantly lower the reaction rate. What does this suggest about the importance of temperature-regulating mechanisms in organisms? Explain.

]]> People with a lactose intolerance are able to take products such as Lactaid that contain the lactase enzyme with their meals. These products can be taken in pill form. Considering the fact that the pill form of the enzyme would have to travel through the person's stomach, what special consideration would the producer of this product need to be concerned about?

]]> Velvet Ant
Scientific Name: Dasymutilla occidentalis
Habitat: deserts, semi-arid environments
Range: throughout US and Canada
Observations: The Velvet Ant is actually a wasp. "Velvet Ant" is the common name for any of a family of wasps whose appearance is similar to that of large furry ants. The wasps live primarily in deserts and hot, semiarid environments. There are thousands of species of Velvet Ants throughout the world, including nearly 500 species in North America alone. All Velvet Ants in North America are parasites. They invade the nest of bees and other wasps, then lay their eggs in the host's cocoon. As adults, the ants feed on green shrubs, cacti, and other available plants.

Whirligig Beetle
Family: Gyrinus sp.
Habitat: Tropical environments, freshwater lakes, ponds
Range: North American and African continents
Observations: Whirligig beetles received their name from their tendency to move rapidly in small circles on the surface of the water. This apparent dance - or gig - is just one of the distinctive characteristics that the beetles display. Others include its compound eyes, that allow it to see both under the water and above the water simultaneously, and its antennae, which allow it to sense wavelets on the surface of the water, thereby providing information regarding potential food sources and obstacles. The Whirligig can remain under the water for a long period of time. It is able to do this by trapping a bubble of air under its body before it submerges.]]> How do substrate concentration and pH affect the rate of an enzyme-controlled reaction?



To sustain the processes of life, a typical cell carries out thousands of biochemical reactions each second. Many of these reactions require the help of enzymes. Enzymes are proteins that speed up the rate of chemical reactions. Many important processes in the body involve the work of enzymes, including the digestion of nutrients such as carbohydrates, proteins and fats.



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 themselves in the reaction. Enzymes enable molecules to undergo chemical changes, forming new substances called products. Substrates are molecules that are acted upon by enzymes. For instance, amylase, an enzyme found in saliva, helps break down complex starch molecules (substrates) into smaller sugar molecules (products). In other biochemical reactions, substrates require assistance of specific enzymes to form new 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. However, researchers believe that the fit between enzyme and substrate need not be exact. Enzymes are viewed as flexible keys that can shape and conform to the shape of the substrate.

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