Types of Lipids

Lipids

• Lipids are very diverse
• Insoluble in water, but soluble in organic solvents
• Can be divided into three main biological groups:

1. Storage Lipids (Triacylglycerols)
2. Structural Lipids (Phospholipids, Sphingolipids, Glycolipids, Sterols)
3. Signaling Lipids (Eicosanoids, Steroids)

Fatty Acids

• Building blocks for many different kinds of lipids
• Contain a carboxylic acid group, a carbon chain (2 - 22 carbons long), and an additional methyl group at the end
• Can be saturated (only single bonds) or unsaturated (at least one double bond)
• A double bond holds a cis conformation resulting in a kink in the chain
• Saturated Fatty acids have been linked to heart problems
• Trans-fatty acids are linked to cardiovascular disease
• Can be linked together via ester bonds or remain individual as "Free Fatty Acids"

• Structural: [# C] : [# of Double Bonds]( ∆ position of double bond)
• i.e. for an fatty acid with 18 carbons (no double bonds): 18:0
• i.e. for the same fatty acid with two double bonds: 18:2 ( ∆ 6,8)
• Systematic (saturated): n-number of carbons-anoic acid
• i.e. for an fatty acid with 18 carbons: n-Octadecanoic acid
• Systematic (unsaturated): cis-position of carbon-enoic acid
• i.e. for the same fatty acid with a single double bond: cis-6-octadecenoic acid
• i.e. for the same fatty acid with two double bonds: cis-6,8-octadecadienoic acid

• The longer the carbon chain, the higher the melting point of the fatty acid
• The more double bonds, the lower the melting point

Triacylglycerols (TAGs)

• Energy reserves of the cell
• Made up of three fatty acids joined by glycerol
• Found in fat cells (adipocyte cells)
• Can be found as simple or mixed

• Fats are varying compositions of simple and mixed TAGs
• TAG composition dictates melting temperature

Glycerophospholipids

• A structural membrane lipid
• One of the most abundant lipids in cellular membranes
• Has four components:

1. Fatty acids
2. Glycerol backbone
3. Phosphate
4. Head group

• Can be neutral (net neutral charge) or anionic (net negative charge)

Sphingolipids

• The second most abundant membrane lipid
• Structure is built off of sphingosine (an unsaturated 18-carbon amino alcohol)
• They play a role in signal transduction and cell recognition

• Sphingolipids are broken down in the lysosomes through hydrolytic enzymes (Glucosidase)
• Defects in these lipids or their metabolic processes often yield neurological disorders
• Gaucher disease

Cholesterol

• The third most common lipid in cellular membranes
• The most common steroid in mammals (can be synthesized, but not broken down)
• Modulates membrane fluidity (the more of this rigid steroid, the less fluid)
• Increases membrane packing and reduces the permeability of the membrane

phospholipases hydrolyze ester bonds in glycerophospholipids converting them to fatty acids

• Circulate through the blood to targeted tissues and relay messages
• Cholesterol is the base for all animal steroids

• Phospholipids contribute to signaling through local chemical signals
• phospholipases hydrolyze ester bonds in glycerophospholipids converting them to fatty acids
• Several different phospholipases are present and they each break different bonds along the glycerol/carbon chain
• These cleaved signaling molecules are precursors of eicosanoids
• Eicosanoid signaling pathways are involved in inflammation, heat, pain, smooth muscle contraction, pregnancy and so on