1 Metabolism Exam 3: Lipids1. Know the concepts surrounding fatty acids; saturation, cis versus trans configurations, nomenclature, chain length, essentiality- First off, fatty acids are merely a methyl group (CH3), a long repeating chain of carbons, and a carboxcylic acid (COOH) group. This carbon chain can be from anywhere to four carbons up to 24, and this will determine the type of fatty acid that it is. Once the chain is longer than 14 carbons, this is usually the cut off for when the fatty acid is nutritionally important.- This chain is made up of repeating carbons, and if there are not any double bonds between each consecutive carbon, it will have hydrogens attached. If there are no double bonds between any of the carbons, then that will mean that each carbon will have 2 hydrogens—it will be saturated with hydrogens. This is what we call a saturated fat, and these the fats that are linked to coronary heart disease. Some examples that you should know (for the test!) are coconut oil, butter, and load. Monounsaturated will have one—thus the word mono—double bond in the carbon chain. Likewise, polyunsaturated will have more than one double bond. Examples of monounsaturated are olive oil, canola oil, and peanut oil. Polyunsaturated examples are sunflower oil, corn oil, soybean oil, and cottonseed oil. (No idea that that last one was an oil)- Now if you look at a saturated carbon (remember that it has 2 hydrogens attached), these hydrogens can be on the same side—called cis---or on the opposite side—called trans. Trans fatty acids are the fats that people should avoid at all times. Now the reason that saturated fats are used, yet they are horrible for our body, is because the more saturated a fat is, the longer its shelf life is. Companies have a technique called hydrogenation where they add carbons to a fatty acid to make it saturated. This will preserve the food item longer on the shelf and make it stay Tony Berardi2“fresh looking” longer. This is what why processed foods takes years to spoil. Fun side fact. - For the nomenclature, follow this method and you will easily name any fatty acid: First count how many carbons are in the fatty acid, including the carbon in the methyl and carboxy group. This is your base name. Then count the number of double bonds. And note where the first or all the double bonds are. Then depending on what side of the chain you started counting the double bonds, this is how it is named---the methyl is the omega (referred to as “n” or “w”) and the carboxy is the alpha end (referred to as Δ). Then once you pick an end to count from, the first double bond is noted if from the “n” side, and if you name it from the Δ side, you put down every double bond location. So an example: What does the name 20:3n:8 mean? The 20 is how many carbons there are. The 3 is the number of double bonds and the “n” refers to the fact that it is being named from the methyl end, so the 8 is what carbon the first double bond isat. How about 20:3Δ6,9,12? 20 is the number of carbons, 3 is the number of double bonds, then the Δ signifies that we are counting from the carboxy end, so the 6,9, and 12 is where the double bonds are at the respective carbons. So there are two ways to name a fatty acid, depending from which end you start at (Those two namesare of the same fatty acid).- Lastly, the body lacks the enzyme to create bonds after the ninth carbon from the Δ end, so since we cannot make these fatty acids, what do you think they are called? Essential fatty acids! There are two of them and they are called linoleic (18:2n:6, 18:2Δ9,12, or omega 6) and linolenic acid (18:3n:3, 18:3Δ6,9,12 or omega 3). In the body, these fatty acids are metabolized to something called eicosanoids, and these modulate blood pressure, platelet aggregation, the immune system, the nervous system, and smooth muscle contraction. So pretty important roles. 2. Be able to name fatty acidsTony Berardi3- Simply follow that pattern above, and you will be naming any fatty acid you want. They also have the scientific names, but who cares for this class. Let’s decipher the essential fatty acids to make sure we got it. Linoleic acid or omega6 is 18:2Δ9,12. So this means that there are 18 carbons and 2 double bonds. The double bonds are counted from the carboxy end, and they appear on the ninth and twelfth carbon. Alternatively, you can name it as 18:2n:3, so 18 carbons, 2 double bonds, and named from the methyl end, so the first double bond is at the third carbon And for linolenic acid or omega six, we have 18:3Δ6,9,12. 18 carbons, 3 double bonds, and counting from the carboxy end, they are at the sixth, ninth, and the twelfth carbon. Or 18:3n:6. Counting from the methyl end, the first double bond is atthe sixth position.- So now you can name any fatty acid and will not miss these questions on the test! The only trick might be when she throws in “w” instead of n”. It’s the same thing, just a different name for the same thing. 3. Know the functions and examples of eicosanoids, sterols, and phospholipids- This question will go over why fatty acids are essential for the body and how a diet with absolutely no fat is a horrible idea. - First, you have those essential fatty acid, linoleic (omega 6) and linolenic acid (omega 3) are metabolized to the eicosanoids, which regulate a whole host of events. These function in the cell that they are metabolized in. This are divided into the prostacyclins, the thromboxanes, and the leukotriens. You will need to know the function of each for the exam. So prostacyclins act on the endothelium as vasodilators and platelet anti-aggregation (break up platelets), thromboxanes act on the platelets to help them aggregate over an injury and as a vasoconstrictor, and the leukotrienes act on the leukocytes, so they help lower inflammation and help the vascular beds contract. There is another class called the Tony Berardi4prostaglandins that act on any endothelium in many cells to contract or relax the smooth muscle. o Now for how they are metabolized in the body: Say you have a linoleic acid (omega 6) hanging around. This reacts with an enzyme called Δ6 desaturase---very easy to remember, because all it does is add a double bond at the sixth carbon from the carboxy end---so now there are three double bonds. This product acts with elongase---just like the name says, it elongates the chain. So adds two
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