{"id":4360,"date":"2019-06-17T18:05:10","date_gmt":"2019-06-17T18:05:10","guid":{"rendered":"https:\/\/pressbooks.ccconline.org\/acchumanbio\/chapter\/3-5-lipids-3\/"},"modified":"2023-11-30T17:49:50","modified_gmt":"2023-11-30T17:49:50","slug":"3-5-lipids-3","status":"publish","type":"chapter","link":"https:\/\/pressbooks.ccconline.org\/acchumanbio\/chapter\/3-5-lipids-3\/","title":{"raw":"3.5\u00a0Lipids","rendered":"3.5\u00a0Lipids"},"content":{"raw":"
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Yum!<\/span><\/h1>\r\n<\/div>\r\n\r\n[caption id=\"attachment_347\" align=\"alignright\" width=\"190\"]\"Image Figure 3.5.1 Lipids can be unhealthy if consumed in large quantities.<\/em>[\/caption]\r\n\r\nIt glistens with fat, from the cheese to the fries. Both cheese and fries are typically high-fat foods, so this meal is definitely not recommended if you are following a low-fat diet. We need some fats in our diet for good health, but too much of a good thing can be harmful to our health, no matter how\u00a0delicious\u00a0it tastes. What are fats? And why do we have such a love-hate relationship with them? Read on to find out.\r\n
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Lipids and Fatty Acids<\/h1>\r\nFats are actually a type of lipid.\u00a0<\/span>[pb_glossary id=\"5651\"]Lipids[\/pb_glossary]<\/strong>\u00a0are a major class of\u00a0biochemical compounds\u00a0that includes oils, as well as fats. Among other things, organisms use lipids to store\u00a0energy.<\/span>\r\n\r\n<\/div>\r\nLipid\u00a0molecules consist mainly of repeating units called\u00a0[pb_glossary id=\"5657\"]fatty acids[\/pb_glossary].<\/strong>\u00a0There are two types of fatty acids: saturated fatty acids and unsaturated fatty acids. Both types consist mainly of simple chains of carbon atoms bonded to one another and to hydrogen atoms. The two types of fatty acids differ in how many hydrogen atoms they contain\u00a0and\u00a0the number of\u00a0bonds between carbon atoms.\r\n
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3.5 Cultural Connection: Fats in Tanning<\/span><\/h1>\r\n

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\r\n\r\n[caption id=\"attachment_1566\" align=\"alignright\" width=\"434\"]\"Image Figure 3.5.2 The Plains First Nations used buffalo brains to tan their buffalo hides. These tanned hides where soft, flexible, and waterproof.<\/em>[\/caption]\r\n\r\nAncient civilizations all over the world have used fats in the hide tanning process.\u00a0 If raw hides (animal skins) aren't tanned, they get very brittle and can breakdown.\u00a0 Tanning results in a hide that is soft, flexible, and resists decay.\r\n\r\nOne method of tanning is called \"brain tanning\".\u00a0 It's name is quite self-explanatory \u2014 a mixture of boiled animal brains is used to tan a hide.\u00a0 A type of fat in the brain, called lecithin, is a natural tanning agent.\u00a0 Once the hide has been rubbed with the brain mixture, it is smoked and then it is ready for use!\r\n\r\nBrain tanning is preferred in many cultures because it creates hides which are waterproof and it doesn't create environmentally harmful byproducts.\r\n\r\n<\/div>\r\n<\/div>\r\n

Saturated Fatty Acids<\/h2>\r\nIn\u00a0[pb_glossary id=\"5693\"]saturated fatty acids[\/pb_glossary]<\/strong>, carbon atoms are bonded to as many hydrogen atoms as possible. All the carbon-to-carbon atoms share just single bonds between them. This causes the molecules to form straight chains, as shown in the figure below. The straight chains can be packed together very tightly, allowing them to store energy in a compact form. Saturated fatty acids have relatively high melting points, which explains why they are solids at room temperature. Animals use saturated fatty acids to store [pb_glossary id=\"5753\"]energy[\/pb_glossary].\u00a0 Some dietary examples of saturated fats include butter and lard.\r\n\r\n[caption id=\"attachment_355\" align=\"alignnone\" width=\"701\"]\"Diagram Figure 3.5.3 Fatty acids can be saturated, monounsaturated, or unsaturated. This affects their state (solid or liquid) at room temperature.<\/em>[\/caption]\r\n

Unsaturated Fatty Acids<\/h2>\r\nIn\u00a0[pb_glossary id=\"5685\"]unsaturated fatty acids[\/pb_glossary]<\/strong>, some carbon atoms are not bonded to as many hydrogen atoms as possible. Instead, they form double or even triple bonds with other carbon atoms. This causes the chains to bend (see Figure 3.5.3). The bent chains cannot be packed together very tightly. Unsaturated fatty acids have relatively low melting points, which explains why they are liquids at room temperature. Plants use unsaturated fatty acids to store energy.\r\n\r\nMonounsaturated fatty acids contain one less hydrogen\u00a0atom\u00a0than the same-length saturated fatty\u00a0acid\u00a0chain. Monounsaturated fatty acids are\u00a0liquids at room\u00a0temperature, but start to solidify at refrigerator temperatures. Good food sources of monounsaturated fats include olive\u00a0oils,\u00a0peanut oils, and avocados.\r\n\r\nPolyunsaturated fatty acids contain at least two fewer hydrogen atoms than the same-length saturated fatty\u00a0acid\u00a0chain. Polyunsaturated fatty acids are liquids at room temperature and remain in the\u00a0liquid\u00a0state in the refrigerator. Good food sources of polyunsaturated fats include\u00a0safflower oils, soybean oils, and many nuts and seeds.\r\n
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Types of Lipids<\/h1>\r\n<\/div>\r\nLipids may consist of fatty acids alone, or they may contain other\u00a0chemical components,\u00a0as well. For example, some lipids contain alcohol or phosphate groups. Types of lipids include\u00a0triglycerides,\u00a0phospholipids, and steroids. Each type has different functions in living things.\r\n

Triglycerides<\/h2>\r\n[pb_glossary id=\"5679\"]Triglycerides[\/pb_glossary]<\/strong> are formed by combining a molecule of glycerol with three fatty\u00a0acid\u00a0molecules, as shown\u00a0below.\u00a0Glycerol (also called glycerine) is a simple\u00a0compound\u00a0known as a sugar alcohol. It is a colourless, odorless\u00a0liquid\u00a0that is sweet tasting and nontoxic. Triglycerides are the main constituent of body fat in humans and other\u00a0animals. They are also found in fats derived from plants. There are many different types of triglycerides, with the main division being between those that contain saturated fatty acids and those that contain unsaturated fatty acids.\r\n\r\n[caption id=\"attachment_367\" align=\"alignright\" width=\"476\"]\"Image Figure 3.5.4 Triglycerides consist of a glycerol molecule (along the left side) with three attached fatty acids (coming off the right side). This diagram shows a saturated fatty acid, the storage form of fat in animals.<\/em>[\/caption]\r\n\r\n
\r\n\r\n \r\n\r\n<\/div>\r\nIn the human bloodstream, triglycerides play an important role in metabolism as energy sources and transporters of dietary fat. They contain more than twice as much energy as [pb_glossary id=\"5655\"]carbohydrates[\/pb_glossary], the other major source of energy in the diet. When you eat, your body converts any calories it doesn't need to use right away into triglycerides, which are stored in your fat cells. When you need energy between meals, hormones trigger the release of some of these stored triglycerides back into the bloodstream.\r\n

Phospholipids<\/h2>\r\n[caption id=\"attachment_372\" align=\"alignright\" width=\"203\"]\"Image Figure 3.5.5 A phospholipid is made up of a phosphate group connected to glycerol, which is connected to two fatty acids.<\/em>[\/caption]\r\n\r\n[pb_glossary id=\"368\"]Phospholipids[\/pb_glossary]<\/strong> are a major component of the cell membranes of all living things. Each phospholipid molecule has a \"tail\" consisting of two long fatty acids, and a \"head\" consisting of a phosphate group and glycerol molecule (see Figure 3.5.5). The phosphate group is a small, negatively-charged molecule causing it to be [pb_glossary id=\"5677\"]hydrophilic[\/pb_glossary], or attracted to water. The fatty acid tail of the phospholipid is [pb_glossary id=\"5675\"]hydrophobic[\/pb_glossary], or repelled by water. These properties allow phospholipids to form a two-layered cell membrane, which is also called a bilayer<\/strong>.\r\n\r\n \r\n\r\nAs shown in Figure 3.5.6, a phospholipid bilayer forms when many phospholipid molecules line up tail to tail, forming an inner and outer surface of [pb_glossary id=\"5677\"]hydrophilic[\/pb_glossary] heads. The hydrophyilic heads point toward both the watery extracellular space and the watery inside space (lumen) of the cell.\u00a0 The [pb_glossary id=\"5675\"]hydrophobic[\/pb_glossary] fatty acids are nestled in the inner space of the bilayer.\r\n\r\n[caption id=\"attachment_373\" align=\"alignnone\" width=\"306\"]\"Diagram Figure 3.5.6 Cell membranes consist of a double layer of phospholipid molecules.<\/em>[\/caption]\r\n\r\n
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Steroids<\/h2>\r\n<\/div>\r\n[pb_glossary id=\"375\"]Steroids[\/pb_glossary] <\/strong>are lipids with a ring structure. Each steroid has a core of 17 carbon atoms, which are arranged in four rings of five or six carbons each (pictured in Figure 3.5.7). Steroids vary by the other components attached to this four-ring core. Hundreds of steroids are found in plants, animals, and fungi, but most steroids have one of just two principal biological functions. Some steroids (such as cholesterol) are important components of cell membranes, while many other steroids are [pb_glossary id=\"5661\"]hormones<\/strong>[\/pb_glossary], which are messenger molecules. In humans, steroid hormones include cortisone \u2014 a fight-or-flight\u00a0hormone\u00a0\u2014 and the sex hormones estrogen, progesterone and testosterone.\r\n
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Feature: My\u00a0Human Body<\/span><\/h1>\r\n<\/div>\r\nDuring a routine checkup with your family doctor, your\u00a0blood\u00a0was collected for a\u00a0lipid\u00a0profile. The results are back, and your triglyceride level is 180 mg\/dL. Your doctor says this is a little high. A blood triglyceride level of 150 mg\/dL or lower is considered normal. Higher levels of triglycerides in the blood have been linked to an increased risk of atherosclerosis<\/a>,\u00a0heart\u00a0disease<\/a>, and stroke<\/a>.\r\n\r\n[caption id=\"attachment_378\" align=\"alignright\" width=\"398\"]\"Image Figure 3.5.8 Changing your diet can help keep blood lipid levels healthy.<\/em>[\/caption]\r\n\r\nIf a\u00a0blood\u00a0test reveals that you have high triglycerides, the levels can be lowered through healthy lifestyle choices and\/or prescription medications. Healthy lifestyle choices to control triglyceride levels include:\r\n