Problem 1

As you and a friend sit together enjoying your breakfast of Fruit Loops one morning, your friend glances at the cereal box and says “What is this unsaturated, saturated fat thing? Isn’t fat just fat?”.   Draw a diagram that you could use to explain the molecular difference between saturated and unsaturated fat to your friend. Label your diagram so that it clearly shows what is different about these two types of fat molecules.

Problem 2

Draw a diagram that represents the molecular structure of a phospholipid.  Be sure to show any part of the molecule that might be charged. Describe 2 ways in which the molecular structures of phospholipids and triglycerides are similar, and two ways in which they are different.

Problem 3

A chemist synthesizes a new phospholipid that has fatty acid tails which are 18 carbons long.  The chemist drops hundreds of these molecules into water.  Draw a diagram that shows how these molecules will spontaneously organize themselves.   Label which regions are hydrophobic and which regions are hydrophilic.

In 1975, the following paper was published:  

Goldman,S.S. 1975.  Cold resistance of the brain during hibernation.  III.  Evidence of a lipid adaptation.  American Journal of Physiology  228: 834-838.

For the experiment described in this paper, the researchers used two types of hamsters – one group of hamsters was kept in a warm (22 degrees C) laboratory room (Warm-adapted hamsters), the other group of hamsters was put into a cold (5-7 degrees C) laboratory room to induce hibernation (Hibernating hamsters).  After being kept in each environment for a length of time, brain cells were extracted from all hamsters and the phospholipids found in the cell membranes were analyzed.  The phospholipids were found to have fatty acid tails of vary lengths (range from 14 to 18 carbons) and to be a mixture of saturated and unsaturated tails.

The table below shows the percent of each type of fatty acid tail found in each type of hamster.  The first column in the table shows the length of the fatty acid and the number of double-bonds in the fatty acid.  For example the fatty acid “14:0” would be a fatty acid that was 14 carbons long and had 0 double-bonds.  The second and third columns show the percent of phospholipid fatty acids that were of this type.  For example, in warm-adapted hamsters, 15.2 % of the phospholipid fatty acids were 14 carbons long and had no double-bonds (14:0 type), and in hibernating hamsters 10.3 % of the phospholipid fatty acids were 14 carbons long and had no double-bonds (14:0 type).

Problem 4

Draw a bar graph that shows the percent of phospholipids that were saturated in each group of hamsters and the percent of phospholipids that were unsaturated in each group of hamsters.

Problem 5

Based on what we learned in class about how cell membranes adapt to cold temperatures, are these the results that you would have expected?  Why?