Lipids can be categorized as either storage lipids or structural lipids. Storage lipids, like triglycerides, are used primarily to store energy and can be solid fats or liquid oils depending on their carbon chain length and saturation. Structural lipids, including phospholipids and glycolipids, provide structure for cell membranes and tissues. Phospholipids are the major structural lipid and can self-assemble into bilayers, micelles, or vesicles in water, forming the basic structure of cell membranes.

1. Nutritional Biochemistry
Lecture 5: Fundamentals of Biochemistry
Lipids

2. Lipids: Fats and Oils
• Triglycerides (triacylglycerols, TAGs, fatty acids) are
compounds that are comprised of 1 molecule of
glycerol and 3 carboxylic acids
• Depending on the length of the carbon chains of the
carboxylic acid as well as the degree of saturation or
unsaturation, triglycerides can be either solid at room
temperature (fats) or liquid at room temperature (oils)
• The three fatty acids may be identical; more often than
not, they are different from each other

9. Lipids: Waxes
• Biological waxes are esters of long-chained (C14-C36)
saturated and unsaturated fatty acids along with long-chained
(C16 to C30) alcohols
• Usually have higher melting points than triglycerides
• Unlike triglycerides (which are used for energy and
thermal protection), waxes are used primarily for
protection from water and other external chemicals

11. Storage Lipids vs. Structural Lipids
• There are two major classifications to lipids
• Storage lipids (triglycerides) are used primarily to
store energy; they are neutral
• Structural lipids provide structure for membranes and
tissues; they are negatively charged (polar)
• There are two major types of structural lipids:
phospholipids and glycolipids

12. Phospholipids
• Phospholipids can be further classified in two major
classes: glycerophospholipids and sphingolipids
• The most common glycerophospholipid is
phosphatidylcholine, which contains 2 molecules of
fatty acid + one of choline phosphate, all of which are
attached to glycerol
• This gives it a hydrophobic region (the fatty acids) and
a hydrophilic region (the choline phosphate)
• Many phospholipids together make up cell membranes

15. Sphingolipids
• Sphingolipids, which are the second largest class of
phospholipids, contain a molecule called sphingosine
instead of glycerol
• They play major roles in neural tissue, brain tissue, and
as recognition sites on the surfaces of membranes

17. Glycolipids
• Glycolipids are the other major type of polar
storage lipid
• They also contain sphingosine in the place of
glycerol; however, they also contain one fatty acid
and one molecule of a sugar
• Glycolipids also play important roles in providing
recognition sites on cell membranes

18. Micelles, Bilayer Sheets,
and Vesicles (liposomes)
• Phospholipids can form organized structures in water
solutions
• These structures can be micelles (ball-like structures),
bilayers (sandwich-like structures), or vesicles (similar
to micelles with H2O inside)
• These structures comprise cell membranes as well as
other important biological systems