For example, they help keep aquatic birds and mammals dry because of their water-repelling nature. Lipids are also the building blocks of many hormones and are an important constituent of the plasma membrane. Lipids include fats, oils, waxes, phospholipids, and steroids. A fat molecule, such as a triglyceride, consists of two main components—glycerol and fatty acids. Glycerol is an organic compound with three carbon atoms, five hydrogen atoms, and three hydroxyl —OH groups. In a fat molecule, a fatty acid is attached to each of the three oxygen atoms in the —OH groups of the glycerol molecule with a covalent bond.
During this covalent bond formation, three water molecules are released. The three fatty acids in the fat may be similar or dissimilar. These fats are also called triglycerides because they have three fatty acids.
Some fatty acids have common names that specify their origin. For example, palmitic acid, a saturated fatty acid, is derived from the palm tree. Arachidic acid is derived from Arachis hypogaea , the scientific name for peanuts. Fatty acids may be saturated or unsaturated. In a fatty acid chain, if there are only single bonds between neighboring carbons in the hydrocarbon chain, the fatty acid is saturated.
Saturated fatty acids are saturated with hydrogen; in other words, the number of hydrogen atoms attached to the carbon skeleton is maximized. When the hydrocarbon chain contains a double bond, the fatty acid is an unsaturated fatty acid. Most unsaturated fats are liquid at room temperature and are called oils.
If there is one double bond in the molecule, then it is known as a monounsaturated fat e. Saturated fats tend to get packed tightly and are solid at room temperature. Animal fats with stearic acid and palmitic acid contained in meat, and the fat with butyric acid contained in butter, are examples of saturated fats.
Mammals store fats in specialized cells called adipocytes, where globules of fat occupy most of the cell.
In plants, fat or oil is stored in seeds and is used as a source of energy during embryonic development. Unsaturated fats or oils are usually of plant origin and contain unsaturated fatty acids.
Olive oil, corn oil, canola oil, and cod liver oil are examples of unsaturated fats. Unsaturated fats help to improve blood cholesterol levels, whereas saturated fats contribute to plaque formation in the arteries, which increases the risk of a heart attack. In the food industry, oils are artificially hydrogenated to make them semi-solid, leading to less spoilage and increased shelf life.
Simply speaking, hydrogen gas is bubbled through oils to solidify them. During this hydrogenation process, double bonds of the cis -conformation in the hydrocarbon chain may be converted to double bonds in the trans -conformation. This forms a trans -fat from a cis -fat. The orientation of the double bonds affects the chemical properties of the fat. Margarine, some types of peanut butter, and shortening are examples of artificially hydrogenated trans -fats.
Many fast food restaurants have recently eliminated the use of trans -fats, and U. Essential fatty acids are fatty acids that are required but not synthesized by the human body. Consequently, they must be supplemented through the diet. Omega-3 fatty acids fall into this category and are one of only two known essential fatty acids for humans the other being omega-6 fatty acids.
They are a type of polyunsaturated fat and are called omega-3 fatty acids because the third carbon from the end of the fatty acid participates in a double bond. Salmon, trout, and tuna are good sources of omega-3 fatty acids.
Omega-3 fatty acids are important in brain function and normal growth and development. They may also prevent heart disease and reduce the risk of cancer. Like carbohydrates, fats have received a lot of bad publicity. However, fats do have important functions.
Fats serve as long-term energy storage. They also provide insulation for the body. Phospholipids are the major constituent of the plasma membrane. Like fats, they are composed of fatty acid chains attached to a glycerol or similar backbone. Instead of three fatty acids attached, however, there are two fatty acids and the third carbon of the glycerol backbone is bound to a phosphate group.
The phosphate group is modified by the addition of an alcohol. A phospholipid has both hydrophobic and hydrophilic regions. The fatty acid chains are hydrophobic and exclude themselves from water, whereas the phosphate is hydrophilic and interacts with water. Cells are surrounded by a membrane, which has a bilayer of phospholipids. The fatty acids of phospholipids face inside, away from water, whereas the phosphate group can face either the outside environment or the inside of the cell, which are both aqueous.
Because fat is the most calorie dense food and having a storable, high calorie compact energy source would be important to survival. The nature of its fat also made it an important trade good. Like salmon, ooligan returns to its birth stream after years at sea. Its arrival in the early spring made it the first fresh food of the year. As you learned above all fats are hydrophobic water hating. To isolate the fat, the fish is boiled and the floating fat skimmed off. Importantly it is a solid grease at room temperature.
Because it is low in polyunsaturated fats which oxidize and spoil quickly it can be stored for later use and used as a trade item. Its composition is said to make it as healthy as olive oil, or better as it has omega 3 fatty acids that reduce risk for diabetes and stroke. It also is rich in three fat soluble vitamins A, E and K. Unlike the phospholipids and fats discussed earlier, steroids have a ring structure.
Although they do not resemble other lipids, they are grouped with them because they are also hydrophobic. All steroids have four, linked carbon rings and several of them, like cholesterol, have a short tail. Cholesterol is a steroid. Cholesterol is mainly synthesized in the liver and is the precursor of many steroid hormones, such as testosterone and estradiol. It resembles the structure of starch, but it more highly branched, with branch points occurring every 8 to 14 glucose residues.
License: CC-BY 3. Polypeptides , or proteins, are the polymer that results from the linkage of amino acids. There are 20 different naturally occurring amino acids that can be linked together by peptide bonds to form the primary structure of the protein. Peptide bonds are formed through what is essentially the reversal of the hydrolysis reaction and is called a condensation reaction. In this case, the bond is formed with the elimination of a water molecule.
The resulting CO-NH linkage is called an amide linkage , or peptide bond. The tertiary structure of a protein is the three-dimensional arrangement of the atoms, whereas the quaternary structure is the interaction of protein subunits, usually linked by disulfide bonds.
An example of a protein with a quaternary structure is hemoglobin , consisting of four subunits linked together. Nucleic acids are the polymers of nucleotides , which are ubiquitous molecules that possess considerable structural diversity. The four most common nucleotides are :. A nucleic acid is formed when the nitrogen atoms N9 of purines and N1 of pyrimidines form bonds to a five-carbon sugar, either ribose or deoxyribose. The bulk of the nucleotides in any cell are found in their polymer forms, as either DNA or RNA , whose primary function is information storage and transfer.
Perhaps the most well-known nucleotide is adenosine triphosphate ATP , a molecule containing adenine, ribose, and a triphosphate group. Lipids , or fats, are carboxylic acids with long-chain hydrocarbon side groups, whose physical properties are determined by their length and level of saturation.
Fatty acids usually occur in esterified form as major components in the natural compounds, where the most prominent forms arise as the C 16 and C 18 palmitic, oleic, linoleic, and stearic acids. Most fatty acids have an even number of carbon atoms because they are biosynthesized by the addition of C 2 units acetyl-CoA. Triacylglycerols function as energy reserves and contain three esterified fatty acids. They are the highly efficient storage form of metabolic energy because they are less oxidized than carbohydrates or proteins.
This allows them to yield significantly more energy when they are completely oxidized during cellular respiration. Such large, complex molecules do not dissolve well in water. Glycogen is also made by linking together glucose molecules. Like starch, it is used by animals to store sugar and provide energy. It is similar to amylopectin in structure, but branched with a C1-to-C6 glycosidic bond about every ten glucose units.
Click here to. Components of Cells. The Macromolecules. The phosphate group, the base, and the sugar make up a complete nucleotide. More specifically, a guanine only pairs with a cytosine forming three hydrogen bonds, indicated by the green circle , and an adenine only pairs with a thymine forming two hydrogen bonds, indicated by the red circle.
The fatty acids attach to the glycerol molecule by a covalent ester bond. The long hydrocarbon chain of each fatty acid makes the triglyceride molecule nonpolar and hydrophobic. It is called a saturated fatty acid, because all the carbon atoms in the chain are single bonded to each other and are fully "saturated" with hydrogen atoms.
In this process, oleic acid is formed by adding two carbon atoms to palmitic acid, and then by inserting a double bond between carbons 9 and Because oleic acid has one double bond, it is considered a monounsaturated fatty acid.
The double bonds kink these molecules and prevent them from packing tightly together. The loose packing results in triglycerides that are liquid at room temperature. Mammals cannot make linoleic acid; it is required in the diet. The covalent bonds form by condensation reactions in which water is a byproduct. They provide a concentrated store of energy. A macromolecule's structure is intimately connected with its function.
Consider, for example, a nucleic acid.
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