Biology Reference
In-Depth Information
CHAPTER
4
Memb
rane Lipids: Fatty
Acids
OUTLINE
A. What are Lipids?
43
Monoenoic Fatty Acids 50
Polyenoic Fatty Acids 50
Omega Designation 51
Most Abundant Membrane Fatty Acids 53
Trans Fatty Acids 53
Branched Chain (Isoprenoid) Fatty Acids 54
Unusual Fatty Acids
B. Why are there so Many Different
Lipids?
44
Lipid Functions
44
C. Lipid Classification Systems
45
55
D. Fatty Acids
46
Chain Length
47
Summary
55
Saturated Fatty Acids
47
References
55
Double Bonds
48
Fatty Acid Nomenclature
49
A. WHAT ARE LIPIDS?
The term 'lipid' is derived from the Greek word 'lipos' for fat. Lipids are therefore by
definition insoluble in water but soluble in non-polar organic solvents. Water insolubility
is conferred by lipid molecular structure, having large regions of their surface composed
of hydrocarbons with very few polar groups. A subset of lipids, those of interest in
membrane studies, are structurally schizophrenic, containing segments that are polar
and so prefer dissolution into water, and more extensive regions that are totally non-polar
and which would avoid water at all costs. These lipids are referred to as 'amphipathic',
containing both hydrophobic and hydrophilic moieties (Figure 3.7), and are the focus of
this topic.
