Lipids may be defined as hydrophobic or amphiphilic small molecules.3 An amphiphile is a chemical compound possessing both hydrophilic (water-loving, polar) and lipophilic (fat-loving) properties. The amphiphilic nature of some lipids allows them to form structures such as vesicles. Lipids, together with carbohydrates, proteins and nucleic acids, are one of the four major classes of biologically essential organic molecules found in all living organisms; their amounts and quality in diet are able to influence cell, tissue and body physiology. Although fat is stored mainly in adipose tissue, most cells that contain mitochondria also have fat globules in them. Lipids can be categorized into three main types: triglycerides, steroids and phospholipids. Triglycerides, or triacylglycerols, are lipids you obtain from food sources of fat, such as cooking oils, butter and animal fat. Triglycerides provide insulation that keeps you warm while protecting your internal organs with a layer of padding. They also play a role how your body uses vitamins. When you don’t burn all the calories you consume, they’re converted to triglycerides and stored for future use. If you regularly eat more calories than you burn or eat too much food rich in fats, your triglyceride level could become too high and pose a health risk.3 Triacylglycerols are stored as fat droplets in large amounts in vertebrate fat cells, and in plants as oils in the seeds. Steroids are a type of lipid that includes hormones and cholesterol. Cholesterol is produced by the body and consumed through food, and it plays a role in the production of hormones. Hormones include the sex hormones estrogen and testosterone, as well as your other hormones like adrenaline, cortisol and progesterone. Cholesterol, the most abundant steroid lipid in the body, is required in every cell in the body. It plays a role in cell repair and the formation of new cells. However, too much cholesterol is a bad thing. When it combines with other compounds in your blood, it can build up as plaque in your arteries, blocking blood flow to and from the heart. Having a high cholesterol level increases your risk of cardiovascular disease. Phospholipids are derivatives of triglycerides. They are very similar to them but slightly different on a molecular level. Half of each molecule is water-soluble and the other is not, which causes them to react differently than triglycerides. Located on cell membranes, they form double-layered membranes with the water-soluble molecules on the outside of the cell membrane and the water-insoluble molecules in the inside. These lipids are responsible for protecting and insulating cells.
Free or unesterified fatty acids are ubiquitous if minor components of all living tissues. In animals, much of the dietary lipid is hydrolysed to free acids before it is absorbed and utilized for lipid synthesis. Intact lipids in tissues can be hydrolysed to free acids by a variety of lipolytic enzymes, before being metabolized in various ways including oxidation, desaturation, elongation or re-esterification. As free acids can interact with a wide range of enzyme systems in both specific and nonspecific ways, they must be rapidly sequestered in tissues by various means to ensure that their activities are closely regulated. Free fatty acids have potent antimicrobial, antiviral and antifungal properties, and they exert such effects in some living systems, especially the skin and mucosa of the lung. As they are powerful detergents and will inhibit very many enzyme systems in a nonspecific manner, it is not clear whether the biocidal properties are also nonspecific. Unsaturated fatty acids seem to have the greatest effects, but this may be because they can insert more readily into membranes. At high concentrations in vitro, free fatty acids are known to perturb membrane structures, but cytotoxic effects come into play before this can become relevant. Saponification is a process by which triglycerides are reacted with sodium or potassium hydroxide (lye) to produce glycerol and a fatty acid salt, called soap.3 The triglycerides are most often animal fats or vegetable oils. When sodium hydroxide is used, a hard soap is produced. Using potassium hydroxide results in a soft soap. Lipids that contain fatty acid ester linkages can undergo hydrolysis. This reaction is catalyzed by a strong acid or base. Saponification is the alkaline hydrolysis of the fatty acid esters
Phospholipids or Phosphatids are compound containing fatty acids and glycerol in addition to a phosphoric acid, nitrogen bases and other substituents. They usually possess one hydrophilic head and tow non-polar tails. They are called polar lipids and are amphipathic in nature. Phospholipids can be phosphoglycerides, phosphoinositides and phosphosphingosides. Waxes are a diverse class of organic compounds that are hydrophobic, malleable solids near ambient temperatures. Waxes are organic compounds that characteristically consist of long alkyl chains. A wax is a simple lipid that is an ester of a long-chain alcohol and a fatty acid. The alcohol may be made up of 12-32 carbon atoms. They may also include various functional groups such as fatty acids, primary and secondary long chain alcohols, unsaturated bonds, aromatics, amides, ketones, and aldehydes. Sphingolipids have the same overall shape as phosphoglycerides but have different chemistry, using sphingosine in place of glycerol. Sphingosine is a chemical compound which has a long hydrocarbon tail similar to fatty acids attached to a structure that is similar to the amino acid serine. Sphingolipids are known to regulate activity in cells, such as immune responses, production of cells, and development of specialized cells. Although these are under the spatial and temporal control, it was recently discovered that sphingosine kinases will be focused on therapeutic effects on enzymes for people with cancer and other conditions. Sphingolipids are commonly believed to protect the cell surface against harmful environmental factors by forming a mechanically stable and chemically resistant outer leaflet of the plasma membrane lipid bilayer.
Many enzymes are simple proteins consisting entirely of one or more amino acid chains. Other enzymes contain a non-protein component called a cofactor that is necessary for the enzyme’s proper functioning. Cofactors are small molecules or compounds that bind to enzymes and allow the enzymes to function. Cofactors are not proteins nor amino acids. There are two types of cofactors: inorganic ions and organic molecules known as coenzymes. Most coenzymes are vitamins or are derived from vitamins. Enzymes catalyze many type of reactions. However, most of the enzymes require the presence of cofactors in order to be active. Vitamins are critical organic molecules necessary for life. Despite their vital importance, they cannot be synthesized by animals and they must be acquired through diet, whether they are obtained from food or through supplemental vitamins. This odd characteristic may have evolved because of the biological complexity of vitamin synthesis; it is more efficient to obtain vitamins in food in trace amounts than to develop the numerous enzymes necessary to synthesize vitamins. In addition, vitamins must be molecularly modified after ingestion before they can be used in the body. Vitamins can act as coenzymes, signaling molecules, antioxidants, and hormones, as well as serving various other functions. Vitamin deficiency can lead to conditions such as: scurvy from lack of Vitamin C, and eye damage from lack of Vitamin A. In fact, many activated carriers in metabolism are derived from vitamins, including carriers important for redox reactions, such as electron transport (FADH2, for example), and carbon dioxide transfer (biotin). Because of the critical roles vitamins play in the functioning of the human body, they are an essential topic of study despite the low vitamin requirements of most animals. Vitamins that are soluble in fat or lipids and are absorbed into the body through the intestinal tract or more specifically the small intestines. Some fat-soluble vitamins are vitamins A, D, E, and K. Main areas in which fat-soluble vitamins are stored are the liver and adipose tissues. Fat-soluble vitamins except for vitamin K, are stored for long periods at a time and then excreted after this long duration of time has passed. For this reason overdosing on fat-soluble vitamins is highly feasible if ingested at high, toxic levels and it could possibly lead to hypervitaminosis.
When you are injured, a complicated process of inflammation and blood clotting is triggered. Prostaglandins are a group of lipids that are part of this process. Problems with prostaglandins can limit the healing process, cause increased inflammation and pain, and impact your overall health. Prostaglandins are hormones created during a chemical reaction at the site where an injury or other issue occurs. They are unique among hormones because unlike most of the chemical messengers, they are not secreted from a gland, but rather are created at the time they are needed directly where the problem exists.
1) Bruce Alberts, A. J. (2007). Molecular Biology of the Cell.
2) Van Holde KE, M. C. (1996). Biochemistry. Menlo Park, California: Benjamin/Cummings Pub. Co., Inc.
3) NV, B. (2002). Medical Biochemistry. San Diego: Harcourt/Academic Press.
4) Suman Khowala, D. V. (2008, June 4). Biomolecules: (introduction, structure & function) . Retrieved from http://nsdl.niscair.res.in/jspui/bitstream/123456789/802/1/Carbohydrates.pdf
5) H. M. Asif, M. A. (2011, January 21). Carbohydrates. Retrieved from International Research Journal of Biochemistry and Bioinformatics: http://www.interesjournals.org/full-articles/carbohydrates.pdf?view=inline