Special Assignment

The Biological Effects of Alkanes.

For this discussion the class will reply back and forth on the bulletin board for each question until the instructor posts a message to go on to the next question. For example, discussion on Part 1.a should continue until the instructor notifies the class to go on to Part 1.b. Part 2 is not to be started until Part 1 is complete, etc. For each question, if others have already posted relevant comments, reply to their comments rather than simply stating your answer. If you don't follow these instructions, we may delete your message!

Background Information.

(Background information is from "Introduction to General, Organic and Biochemistry, sixth edition," by Bettelheim & March, Saunders College Publishing, 1995.)

Because they are not very chemically reactive, alkanes in general are not particularly poisonous. Gasoline, which is a mixture of alkanes, should not be swallowed because it generally contains additives, some of which can be quite harmful. Liquid alkanes can cause damage if they get into the lungs. They dissolve the lipid molecules in the cell membranes and cause pneumonia-like symptoms. For this reason, anyone who swallows liquid alkanes should not be induced to vomit them up because some might be forced into the lungs in that manner.

Liquid alkanes can also harm the skin by a similar process. Human skin is kept moist by natural body oils. Liquid alkanes dissolve these oils and cause the skin to dry out. However, mixtures of high-molecular-weight liquid alkanes, sold in drugstores under the name "mineral oil," soften and moisten skin. Petroleum jelly is a mixture of solid and liquid hydrocarbons also used to protect skin.

Part 1.

Petroleum jelly is a mixture of solid and liquid hydrocarbons.

  1. What is the range of alkane sizes (in terms of number of carbons) you would expect to be part of petroleum jelly
  2. Explain why, relative to chemical structure, petroleum jelly protects the skin from too much contact with water

    Part 2.

    A main class of compounds which make up cell membranes is the lipids. The very condensed and line-drawing structures for a typical cell membrane lipid compound are shown below.

    phospho1

    1. Identify all functional groups in this cell membrane lipid and post them on the bulletin board.
    2. Compare the structure of the cell membrane lipid to that of liquid alkanes. What are the similarities and differences?
    3. Based on the structures of cell membrane lipids and liquid alkanes, why can the liquid alkanes, such as those in gasoline, dissolve lung cell membranes?

      Finger oils (like in fingerprints) also contain lipids. The very condensed and line-drawing structures for a typical finger oil lipid are shown below.

      phospho2

    4. Identify all functional groups in this finger oil lipid and post them on the bulletin board.
    5. Compare the structure of the finger oil lipid to that of liquid alkanes. What are their similarities and differences?
    6. Based on the structure of finger oil lipids and of lipid alkanes, why can the liquid alkanes, such as those in gasoline, dissolve finger oils?
    7. Describe the similarities and differences between the cell membrane lipid structure and the finger oil lipid structure. What do you think the definition of "lipid" might be?

    Part 3.

    Are the properties which cause the effects in Parts 1 and 2 physical or chemical properties? Explain.


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    Web Author: Dr. Leon L. Combs
    Copyright 2001 by Dr. Leon L. Combs & Dr. Jennifer Powers & Dr. Vicky Bevilacqua - ALL RIGHTS RESERVED