Empowering Teachers Through Modeling
Membrane Fatty Acid Composition Data Analysis
Fatty acid nomenclature:
18:2n-9
18:2ω6
 Number in red indicates
number of carbons in fatty
acid chain.
 Number in blue indicates the
number of double bonds
between the carbons in the
fatty acid chain.
 Value in purple indicates
location of last double bond
– counting DOWN from the
last carbon in the carboxylic
acid (which is the largest
numbered carbon). Both of
the fatty acid names above
describe the fatty acid drawn
in figure C below.
 Value in green (omega value)
counts from the lowest
numbered carbon (noncarboxylic acid end) and
indicates the first carbon
that has a double bond.
Note that there is always one single-bonded carbon between double-bonded carbons, so if you know
the first or last carbon atom that is double-bonded, and the number of double bonds, you can easily
draw the structures.
Image from https://www.nature.com/scitable/content/a-quick-introduction-to-fatty-acids-14461944
Standard
nomenclature
Omega
nomenclature
Homeostasis – homeo (the same) + stasis (standing) – standing the same, or keeping things in
equilibrium
Fish are poikilotherms (poikilo = varied; therm = heat), meaning that their body temperature varies with
the temperature of the environment. Often we say they are “cold-blooded”. Since we’ve just explored
the structure of membranes, let’s explore fish membrane homeostasis at various water temperatures. Is
it more important for fish to maintain the same membrane structure or the same membrane function?
Let’s explore some data: Juvenile rainbow trout of both sexes were anesthetized and blood sampled
when fish were summer acclimatized. Half the trout were subjected to cold acclimation (6°C) and
samples drawn over a period of 41 days. Some of the trout were marked and blood samples collected in
summer (22°C) and winter (8°C). Fatty acid analysis of plasma phospholipids was completed and data is
below.
From: Cossins, A.R., and Prosser, C.L. (1978). Evolutionary adaptation of membranes to temperature.
Proc. Natl. Acad. Sci. 75, 2040–2043.
Here are some questions to guide you through interpreting the information in the table. You don’t need
to write your answers, but you and your partner should be able to explain what you discover to each
other:
 In general, how are the fatty acids organized in the fatty acid column based on length?
 In general, how are the fatty acids organized in the fatty acid column based on degree of
saturation (number of double bonds)?
 What is the difference in how the fish were treated between winter and cold-acclimated fish?
 The figure legend describes some statistical analyses that were done to determine whether
differences in measurements could have been due to random variation in samples, or whether
the differences are statistically significant. The statistical analysis results in a “P” value (think
probability) that measures the likelihood that the variation between the samples is due to
chance variations or real differences. The higher the P value, the more likely that random
variations have an affect. A P value of 0.05 is the cut-off that is used to indicate statistically
significant differences. P=0.05 means that there is a 5% chance that differences are due to
random variation. P values less than 0.05 indicate that there are statistically significant
differences in the data.
 What is the likelihood that two measurements, with a P value of 0.01, are due to random
variations? (List as a percentage.) Is this statistically significant?
 Focus on the data that are statistically significant as you study the table. (How do you know
which data are statistically significant?)
 Is there much difference between the fatty acid composition in cold-aclimated vs. winter fish?
After analysing the data, complete the generalized statements about warm- vs. cold-adapted fatty acid
composition in rainbow trout:
As the temperature decreases, the length of fatty acids ______________.
As the temperature decreases, the number of double bonded carbons in the fatty acids ____________.
Thinking beyond the data:
Saturated fats are typically from animal sources. Think chicken skin, butter, ham fat.
Unsaturated fats are typically from plant sources. Think vegetable oil, olive oil, salad dressing.
What happens to a vinegar and oil based salad dressing when you refrigerate it?
Discuss with your partner why it would be beneficial to rainbow trout to change the composition of their
membrane lipids in cold water. After your discussion, write your explanation here. Include in your
explanation whether homeostasis in this instance is related more to structure or to function.
Now it’s your turn!
Below are two additional data tables, taken from Cossins, A.R., and Prosser, C.L. (1978). Evolutionary
adaptation of membranes to temperature. Proc. Natl. Acad. Sci. 75, 2040–2043.
After briefly examining the data, you will work with a partner to develop an activity for your classroom
similar to activity you just completed.
Here are some thoughts to guide your activity development:
 How do these data build upon the activity you’ve just completed?
 What is different about these data?
 What is the key question that will guide the exploration of the data and engage your students?
 What information needs to be explained to guide your students through data interpretation?
 What questions will guide your students to think about the data and draw conclusions?
 How can you apply this information to something your students already know or expand their
knowledge about everyday life?