Nutritional Biochemistry

Lecture 5: Fundamentals of Biochemistry

Lipids

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

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

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

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

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

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

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