Download Enzyme Webquest

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Biology
Enzyme Investigation Webquest
Enzymes
As in all organisms, enzymes are critical for chemical reactions in humans. One reaction produces
melanin, which gives skin a dark color. Melanin helps protect skin cells from ultraviolet radiation—the
greater the exposure to ultraviolet radiation, the greater the production of melanin. Melanin is made
from the amino acid tyrosine by an enzyme called tyrosinase. Without tyrosinase the reaction cannot
take place, which causes a condition called albinism.
Problem
What happens if an enzyme is missing or defective?
Instructions
Research the effect of one of the following enzyme deficiencies:
• phenylketonuria • galactosemia • lactose intolerance
For the enzyme deficiency that you have selected:
1. Identify the enzyme involved and its function.
2. Examine how a person's health is affected by this enzyme deficiency.
3. Find out how the deficiency is diagnosed.
4. Describe the effects of not treating the deficiency.
5. How common is this condition in humans?
Teacher Notes
Time 45 minutes
Teacher Preparation
Student Difficulty
Post-Lab Discussion Remind students that most metabolic processes consist of several reactions. Ask,
What happens if one enzyme in a pathway is missing or defective? The entire pathway is shut down. The
products in the reaction before the blocked reaction will accumulate. These accumulated products may
be toxic.
ANSWERS
Phenylketonuria (PKU): This condition results when the enzyme phenylalanine hydroxylase cannot be
produced by the body. This enzyme is needed to change phenylalanine into tyrosine. If the condition is
left untreated, phenylalanine builds up in the blood, causing rashes, seizures, and severe mental
retardation. In most states newborn babies are given a blood test to screen for PKU. Treatment includes
a diet that almost excludes phenylalanine.
Galactosemia: This condition results when the enzyme needed to break down the simple sugar
galactose is absent. Galactose is a sugar found in milk. Symptoms in untreated newborn babies that are
being fed milk include vomiting, jaundice, poor weight gain, and convulsions. If left untreated, liver and
brain damage will occur. A diagnosis is made through blood and urine tests. Treatment includes a
lifelong restriction of milk and milk products from the diet.
Lactose intolerance: This condition results when the body cannot produce the enzyme lactase, which
breaks down the sugar lactose. Symptoms include diarrhea, gas, and abdominal cramps after consuming
dairy products. Treatment includes avoiding dairy products and substituting other sources of calcium.