Fundamentals of Human Nutrition/Glycerol and fatty acids
12.3 Glycerol and Fatty Acids
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Glycerol and Fatty Acids are components of triglycerides. Triglycerides are a type of lipid, or fat, primarily responsible for taste and texture of foods, energy storage, supplying essential fatty acids, and carrying fat-soluble compounds. They account for most of the fat found in your body and in your foods (Ikechik, 2009, Introduction section, para. 1). Most commonly, triglycerides are found as saturated fat in foods such as meat, butter, and high-fat dairy products. It is important to recognize what happens to these triglycerides after consumption. To understand how triglycerides are metabolized, it is essential to understand that a triglyceride is made of a glycerol and a fatty acid (Ikechik, 2009, Glyceride breakdown section, para. 2) A triglyceride is made up of a three carbon chain with five hydrogens and three hydroxyl groups. This is glycerol. There is also a hydrocarbon chain, or fatty acid (“Lipid molecules,” 2015). Digestion of triglycerides begins in the stomach. First, triglycerides are broken into the two components described above, glycerol and fatty acids. One triglyceride will be broken into 1 glycerol and 3 fatty acids during a hydrolytic reaction that is catalyzed by the enzyme, lipase (Smith, 2015, Chemical metabolism section, para. 3). Next, the glycerol and fatty acid will move to the small intestine so that they can be absorbed into blood circulation. Griffin (2009) explains that the glycerol and fatty acid will pack together to form a chylomicron, whose role will be to transport the triglycerides to the liver. The liver will send the fats to the muscle cell for energy or the adipose fat cell for storage (p.1). Fatty acids and glycerol are stored in adipose fat in complex forms, such as triglycerides until they are needed for metabolic processes. (Wolfe, E382) The two components of the triglyceride take on different roles in metabolism. Although both have the potential to be stored as fat, Griffin (2009) explains that Glycerol is the only component of the triglyceride that has the ability to is be converted to glucose, while fatty acids are primarily stored as fat (p.1). The explanation for this becomes clear when studying how each component is metabolized. Glycerol is first broken down into pyruvate. Once converted into pyruvate, it can undergo the anabolic process gluconeogenesis to synthesize glucose. It is important to recognize when this process would occur. This reaction occurs when an individual has a low blood glucose level, often caused by a lack of carbohydrates in the diet. For this reason, it is important to have glycerol and fatty acid stores to ensure that metabolic processes can be maintained in times of fasting. (Physiol, 15) On the other hand, the fatty acid component of the triglyceride will be broken down into acetyl CoA in a process called fatty acid oxidization. Griffin (2009) explains that this is the catabolic process in which fatty acids are broken down into acetyl CoA (p. 2-3). This process begins when coenzyme A binds to the end of a fatty acid chain. Next, coenzyme A will take two carbons from the fatty acid’s hydrocarbon chain and detach from the rest of the chain to form acetyl CoA and a shorter fatty acid. This process happens with the help of the coenzymes, FAD and NAD which are oxidized in the electron transport chain to FADH and NADH. After the fatty acid is broken down into acetyl CoA, it will enter into the Krebs cycle where it will produce ATP (Ross, 2014).
Griffin, B.A. (2009). Lipid metabolism. Surgery, 29, 1-5. doi:10.1016/j.mpsur.2008.12.003 Ikechik. (2009, November). How is a triglyceride broken down?. Retrieved from http://www.livestrong.com/article/31619-triglyceride-broken-down/ Lipid Molecules. (2015, July 21). Boundless Biology. Retrieved from https://www.boundless.com/biology/textbooks/boundless-biology-textbook/biological-macromolecules-3/lipids-55/lipid-molecules-298-11431/ Smith, Y. (2015, June 14). What are triglycerides?. News Medical. Retrieved from www.news-medical.net/health/What-are-triglycerides.aspx Whitney, E.N., & Rolfes, S.R. (2014). Understanding nutrition. Stamford, CT: Cengage.Learning. This section is being edited by Julia Branton