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Why does a Phospholipid have an unsaturated fatty acid tail?

  • #1

Homework Statement


Hi guys. In the biochemistry chapter, the book shows the structure of a phospholipid (picture attached) with a PO4 3- group and 2 fatty acid chains attached to a glycerol molecule. However, one of the fatty acid chains has a C=C bond while the other is fully saturated. I’m wondering what’s the reason for this.

Homework Equations




The Attempt at a Solution


I looked through the section and it doesn’t give an explanation for it. I also searched it up but I couldn’t find what I was looking for, and the images online had similar structures as well.
Thanks for help.
 

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Answers and Replies

  • #2
Borek
Mentor
28,353
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I doubt there is a "reason", looks like just an example made to show several important properties of such molecules.
 
  • #3
I doubt there is a "reason", looks like just an example made to show several important properties of such molecules.
Okay thank you. That is what I thought.
So that means there’s variation in the fatty acid chains? And does that affect the phospholipid in any way (if the chains are linear or not)?
 
  • #4
TeethWhitener
Science Advisor
Gold Member
1,678
990
Yes and yes. cis-unsaturated fatty acids pack less efficiently than trans-unsaturated and saturated fatty acids. A higher proportion of cis-acids causes the phospholipid membrane to behave more as a fluid, whereas a higher proportion of saturated/trans-unsaturated acids acts to stiffen the phospholipid membrane. The balance of these affects the membrane's mechanical properties as well as the transport of various species across the membrane. Here's a relevant wiki page:
https://en.wikipedia.org/wiki/Lipid_bilayer_phase_behavior
 

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