CHEM 1406 Concept Review: Lipids

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Lipids:  A family of biomolecules that have the common property of being soluble in organic solvents but not in water.  Lipids are an important feature in cell membranes and steroid hormones.

Types and Structures of Lipids

Types and Structures of Lipids.png

 

 

Fatty Acids

Fatty Acids:  A fatty acid is an organic compound that contains a carboxylic acid and a long unbranched carbon chain.  The carboxylic acid portion is hydrophilic and interacts with water, but the long hydrocarbon chain is hydrophobic and causes fatty acids as a whole to be insoluble in water.

 

 

Classification of Fatty Acids

Saturated Fatty Acids

Monounsaturated Fatty Acids

Polyunsaturated Fatty Acids

A fatty acid containing only carbon-carbon single bonds.

A fatty acid containing exactly one carbon-carbon double bond.

A fatty acid containing more than one carbon-carbon double bond.

myristic acid.png

Example: Myristic acid

Palmitoleic Acid.png

Example: Palmitoleic acid

linolenic acid.png

Example: Linolenic Acid

 

Melting Points of Fatty Acids:  Saturated fatty acids are able to be stacked together more easily due to their regular shape.  This maximizes their intermolecular attractions and causes them to have higher melting points.  However, unsaturated fatty acids almost always have their double bonds in the cis formation, giving them an irregular shape that makes it harder for them to fit closely together, causing them to have lower melting points.

 

Prostaglandins: Hormone-like substances produced in small amounts in most cells of the body.  Also called eicosanoids, these substances are formed from arachidonic acid, a polyunsaturated fatty acid with 20 carbons. These substances have powerful physiological effects ranging from increasing/decreasing blood pressure, contracting/relaxing of smooth muscle organs like the uterus, and stimulating inflammation and the sensation of pain.

Prostaglandins img.png

 

 

Waxes

Waxes: An ester of a saturated fatty acid and a long chain alcohol, each containing from 14 to 30 carbon atoms.

General Structure of Waxes:

 

Wax structure.png

Example:   

Wax example.png

 

 

Triacylglycerols

Triacylglycerols: Encountered as either fats (solids) or oils (liquids), triacylglycerols (also called triglycerides) are triesters of glycerol (a trihydroxy alcohol) and 3 fatty acid chains.

General Structure of Triacylglycerols:

Triglyceride structure.png 

 

Example:   

Triglyceride example.png

 

 

Phospholipids

Phospholipids: a family of lipids that contain a polar phosphate “head” group and one or more fatty acid tails.  This family includes both glycerophospholipids and sphingomyelins (sphingolipids), the structure of which are shown below:

General Structure of Glycerophospholipids:

Glycerophospholipids structure.png

 

General Structure of Sphingomyelins:

Sphingosine structure.png

 

 

 

Lecithins vs. Cephalins

Lecithins:

Glycerophospholipids that contain choline as the amino alcohol part of its structure.

 

Cephalins:

Glycerophospholipids that contain either ethanolamine or serine as the amino alcohol part of its structure.

Lecithin.png

 

Cephalin-1.png

 

 

Steroids

Steroids:  compounds that contain a steroid nucleus, which is a fused ring system containing three cyclohexane rings and one cyclopentane ring.  The steroid nucleus and numbering system are shown below:                                     

Steroid Nucleus Steroid Numbering System
Steroid Nucleus.png steroid numbering system.png

 

 

Cholesterol: one of the most important and abundant steroids in the body.  Among other functions, cholesterol is an important component of cell membranes, the myelin sheath, and brain and nerve tissue.  It is also an essential building block for steroid hormones.

cholesterol.png

 

 

Bile Salts: steroid-based salts that are synthesized from cholesterol in the liver.  These salts have polar and nonpolar regions similar to soaps and serve the important function of breaking down large globules of fat into smaller droplets which are more easily digested. They also help with cholesterol absorption in the intestines.

 

Lipoproteins

Lipoproteins: water-soluble complexes that are used to transport non-polar molecules to the cells that need them.  Components of lipoproteins include proteins, triacylglycerols, cholesterol, phospholipids, and cholesteryl esters.

General Lipoprotein Structure

Lipoprotein Structure.png

 

Lipoprotein Table.png

 

 

The Fluid Mosaic Model of the Cell Membrane

Fluid Mosaic Model.png

The cell membrane is a complex semipermeable bilayer composed of phospholipids, sphingolipids, various proteins, cholesterol, carbohydrates, etc. that all work together to into and out of the cell, the expelling of unwanted waste products out of the cell, and defend against unwanted invaders.