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What Is a Lipid Molecule?
Organic Chemistry of Fats, Phospholipids, Waxes & Steroids
CLASS NOTES from Science Prof Online
Organic molecules are compounds that contain carbon-hydrogen bonds and are found in living things.The major classes of organic molecule are carbohydrates, proteins, lipids and nucleic acids.
Lipids
Lipids are molecules that are hydrophobic (insoluble in water) because the non-polar covalent bonds linking carbon and hydrogen aren’t attracted to the polar bonds of water. The four major categories of lipids include fats, phospholipids, waxes and steroids.
Article Summary: What are the different kinds of lipids? What is the difference between saturated and unsaturated fats? Read on and discover.
What Is a Lipid?
Unsaturated fats (oils):These fats are mostly derived from plant sources. There are double bonds between some of the carbons in the hydrocarbon tails, causing the tails to bend or “kink.” These kinks in the hydrocarbon tails prevent the tails from packing closely together. This is why unsaturated fats are liquid at room temperature.
Phospholipids
Phospholipids have a hydrophobic, “water hating,” hydrocarbon tails and hydrophilic, "water loving" phosphate groups on the end, so they are soluble in both water and oil.
Our cell membranes are made mostly of phospholipids arranged in a double layer with the tails from both layers facing inward and the heads facing outward, called the lipid bilayer.
Waxes
These lipids are esters of alcohol, insoluble in water and difficult to hydrolyze, or break down. Wax forms protective and waterproof layers on some plants, bacteria, animal fur and integuments of insects.
Steroids
Cholesterol is a type of steroid, with a central core consisting of four fused rings, a characteristic shared by all steroids. Our bodies make about 2g of cholesterol per day, about 85% of blood cholesterol, while only about 15% comes from dietary sources.
Cholesterol is precursor to our sex hormones and Vitamin D. Our cell membranes contain a lot of cholesterol which helps to keep the membrane flexible and fluid even when our cells are exposed to cooler temperatures.
Sources and Helpful Organic Chemistry Resources
- Bauman, R. (2005) Microbiology
- Park Talaro, K. (2008) Foundations in Microbiology
- Biomolecules - The Lipids animated interactive tutorial from Wisc-Online.com
- Organic Chemistry Lecture Main Page from the Virtual Cell Biology Classroom
- Intro to Lipids interactive animations from Dept of Biological Sciences, Carnegie Mellon
- The Digestion and Absorption of Fats animated tutorial and quiz from WH Freeman
- Macromolecules: Proteins, Nucleic Acids, Carbohydrates & Lipids from WH Freeman
- Cell Membranes animated tutorial from John Kyrk
Fats
Fats and oils are made from two kinds of molecules:
- glycerol (a type of alcohol)
- three fatty acids (so known as triglycerides)
Saturated fats: These types of fat are mostly derived from animal sources. There are single bonds between the carbons of their fatty acid tails, meaning that each carbon is bonded to maximum number of hydrogens possible. Therefore the hydrocarbon chains in these fatty acids are fairly straight and packed closely together. This is why saturated fats are solid at room temperature.
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Portions of this article originally appeared on Suite101 online magazine.
Page last updated: 5/2013
