Organic Macromolecules The Lipids

What are lipids Lipids are what are commonly referred to as fats. Waxes and oils are also lipids. Lipids are an essential part of the human diet. Typically our diet should consist of about 30% fat. Unfortunately, most Americans consume closer to 40% Why do you think people like food with so much fat in it?

What do we need lipids for anyway? The major function of lipids in our body is the storage of energy. Lipids contain a lot of energy in the form of chemical bond energy, just like carbohydrates do. One gram of fat holds twice as much chemical bond energy than one gram of carbohydrates.

Lipid functions continued Lipids are also important in the structure of the cell membrane,(it is a phospholipid bilayer) Steroid hormones (Testosterone, estrogen and progesterone). Transporting important molecules throughout the body (Cholesterol)

Elements present in lipids Just like the carbohydrates, lipids consist of carbon, hydrogen and oxygen, that’s it, nothing else. Unlike carbohydrates, there isn’t a specific ratio of Hydrogen to Oxygen. However it will always, always, always be greater than 2:1. Do you recall what other element(s) are found in amino acids?

Lipid monomers Just like proteins and carbohydrates, lipids are large molecules made up of smaller molecules. The building blocks of lipids are 1 molecule of glycerol, and (usually) 3 fatty acids. Phospholipids are made of glycerol, 2 fatty acids and 1 phosphate molecule.

Lipid Building blocks Glycerol is considered an alcohol. Every molecule of glycerol is exactly the same. It has 3 carbons, 3 OH groups, and 5 hydrogens. Molecular formula is C3H5(OH)3

Structural formula of Glycerol                                                                                                           

Fatty acids While there are different types of fatty acids, they all have some things in common. They consist of long chains of carbon and hydrogen, and they all contain a carboxyl functional group. It is this carboxyl group that gives the fatty acid it’s acidic properties. Can you remember where else we saw a carboxyl group?

Saturated versus Unsaturated. Not all fats are good for you. The bad ones consist of saturated fatty acids. These fatty acids are completed saturated with hydrogen atoms, and have no double bonds between carbon atoms. Stearic acid is saturated. Unsaturated fatty acids are not completely saturated because they contain a double bond between carbon atoms somewhere in the chain. Oleic acid is unsaturated. Polyunsaturated fats contain two or more double bonds between carbons. Linoleic acid is polyunsaturaed.

Structural formula of fatty acids

Why are saturated fats bad? It is because the form LDL (Low density lipoproteins). These molecules transfer cholesterol, but tend to deposit this cholesterol in your arteries, causing blockages. This can lead to heart disease. Unsaturated fatty acids form HDL (High density lipoproteins). These carry cholesterol to the liver, where it needs to be. LDL’s are sometimes referred to as bad cholesterol and HDL’s are referred to as good cholesterol.

Dehydration Synthesis Just like Proteins and Carbohydrates, lipids are formed through the process of dehydration synthesis. The general equation is 1 Glycerol + 3 fatty acids  1 Lipid + 3 molecules of water.

Animation of Dehydration Synthesis http://www2.nl.edu/jste/lipids.htm

Hydrolysis As we learned with proteiNs and carbohydrates, anything that is created by dehydration synthesis can be broken apart by hydrolysis. The equation for the hydrolysis of lipids would then be. 1 Lipid + 3 molecules H20  1 glycerol + 3 fatty acids

Trans-fatty acids The natural shape of lipids are what organic chemists refer to as the cis configuration. However lipids can also be made to take the trans configuration. In order to increase the shelf life and to make unsaturated fats solids at room temperature, unsaturated fats are changed into transfats through a process called partial hydrogenation.

Partial hydrogenation In this process, an unsaturated or polyunsaturated fatty acid has additional hydrogen atoms added to it, breaking some of the double bonds between carbons. This changes the shape of the molecule, and raises the melting point of the fat to over 110 degrees fahrenheit. It also extends the shelf life of the lipid.

What is the big deal about transfats? Because they have a higher melting point than normal cis fats, they stay solid in your relatively cool body. It makes it nearly impossible to “burn” this fat. Since the structure is changed, the enzymes, which are proteins remember, aren’t as effective at breaking them down into their building blocks.

Foods with transfats Here are some foods you may want to avoid or at least cut back on. cakes cookies margerine french fries potato chips When in doubt, read the label.

Health risks and Transfats Coronary heart disease. Alzheimer’s disease. Cancer. Diabetes. Liver disfunction. Infertility. Obesity.

Exit out ticket Now that you are experts on Lipids, complete this assignment and then…Enjoy your Lunch!