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Transcript
The Organic Macromolecules of Life Carbohydrates The night before a big event, many athletes “carb-load”, meaning they eat foods rich in carbohydrates. Why? Many carbohydrates provide a usable energy source. Your body breaks down carbohydrates and uses the energy in their chemical bonds to fuel the activities of life. Carbohydrates are a group of chemicals that include sugars, starches, and cellulose. Carbohydrates provide energy for organisms and they also provide structure for some organisms. For example, the cell walls of plants are made of carbohydrates, which gives them their characteristic box shape. Sugars, or saccharides, are relatively small, simple carbohydrates. Simple sugars are the easiest chemicals for your body to break down. Have you ever had a sudden burst of energy after eating something sweet? Sweet foods usually contain simple sugars that are easy for your body to break apart quickly. When your body needs energy quickly, it breaks down simple sugars. Sugars commonly come in two forms: monosaccharides (“single sugars) and disaccharides (“double sugars”), which are two monosaccharides bonded together. When sugars are bonded together, a larger sugar and water are formed. For example, glucose and fructose are two common monosaccharides. When glucose and fructose are joined together, sucrose (a disaccharide) and water are formed. Notice that all of these sugars end with the suffix –ose. The suffix –ose refers to sugar. Many monosaccharides and disaccharides can be linked together into more complex carbohydrates called polysaccharides (“many sugars”). Organisms form various complex carbohydrates for energy storage. Most plants store energy in a polysaccharide called starch. When you eat a potato for example, you are taking in the potato plant’s stored starch. Animals store energy in a polysaccharide called glycogen, which is formed in the muscles and the liver. When athletes carb-load before an event, they eat foods high in starches, which their bodies break down into simple sugars. Their livers and muscles convert the simple sugars into stored glycogen. The glycogen can then be broken down into simple sugars, which can be broken apart when energy is needed. Simple sugars can also be joined together to make structural carbohydrates, such as cellulose. You may not be familiar with the word cellulose, but cellulose is all around you – in desks, pencils, paper, and any other plant material you see. In fact, cellulose is one of the most abundant molecules on Earth. Lipids Carbohydrates are used for some energy storage. When energy needs to be stored for an even longer period of time, carbohydrates are converted into a different organic macromolecule – fat, which is a type of lipid. Lipids are a group of organic molecules that includes fats, oils, waxes, phospholipids and steroids. Generally speaking, waxes and fats are solids, whereas oils are liquids. Fats, oils and waxes are the most common lipids. Fats and oils provide long-term energy storage. Fats also act as insulation by helping to keep animals such as whales and penguins warm. Waxes provide a different kind of protection; they repel water. Fruits and leaves produce waxes to keep water in and thus prevent the plants from drying out. Ducks and other waterfowl produce waxes that makes their feathers waterproof. Phospholipids are important structural chemicals in cells. These molecules form the membranes, or outer protective covering, that surrounds cells. Phospholipids help control the substances that enter and exit cells.The last group of lipids, steroids, serves as either structural molecules or chemical messengers. Some steroids, such as cholesterol, are components of cell membranes and help give the cell structure. Although cholesterol is essential to life functions, too much of it can be harmful to your body. Other steroids serve as chemical messengers and carry messages from one part of the body to another. Many important lipids are formed from combinations of fatty acids and glycerol. Fatty acids are long chains of hydrogen and carbon atoms that have a carboxyl group attached at one end. A carboxyl group is a chemical group consisting of one carbon atom, one hydrogen atom, and two oxygen atoms. Glycerol, which is an organic alcohol, contains three carbon atoms, each of which is connected to a hydroxyl group. A hydroxyl group consists of one oxygen atom and one hydrogen atom. Many lipids are formed from the attachment of two or three fatty acids to one glycerol. When fatty acids and glycerol are joined together, a lipid and water are formed. When people speak about nutrition and health, they often refer to saturated vs. unsaturated fats. Lipids can be saturated or unsaturated molecules. Remember that fatty acids are made of several carbon atoms connected together in a chain. If every carbon atom in a fatty acid is joined to another carbon atom by just one, single bond, the fatty acid is saturated. If two bonds, called a double bond, join a pair of carbon atoms the fatty acid is unsaturated. Saturated fats are commonly found in meats and most dairy products. If a fatty acid contains several double bonds, it is said to be polyunsaturated. Polyunsaturated fats tend to be liquid at room temperature and are used in many cooking oils, such as sesame, peanut, and corn oil. Replacing saturated fats with unsaturated fats in your diet may help to prevent heat disease. Proteins More than one half of the dry weight of your body is made of proteins. Proteins are large, complex molecules composed of many smaller molecules called amino acids. Amino acids have an amino group on one end, an R group, and a carboxyl group on the other end. An amino group consists of one nitrogen atom and two hydrogen atoms. There are more than 20 amino acids found in living things. All of the amino acids have similar chemical structures, but they differ in a region of the molecule called the R group. The R group of each amino acid is unique to that particular amino acid. When several amino acids are joined together, a protein and water are formed. The bond that joins two amino acids together is called a peptide bond. A molecule of water is lost when a peptide bond is formed between two amino acids. A dipeptide is two amino acids joined together. A polypeptide is a long chain of several amino acids joined together. A complete protein contains one or more polypeptide chains and may contain a few other chemical groups that are important to the protein’s proper function. Proteins serve several functions in living organisms. They can be embedded in the cell membrane and pump molecules into and out of the cell, they are responsible for the ability of cells to move, and they make up hair, nails, and, muscles. Enzymes, a special category of proteins, help speed up the rates of chemical reactions in living things. In fact, the functions of proteins are at the very center of life itself. Nucleic Acids Killer bees are more aggressive when threatened than other types of bees. What makes these bees behave differently? Some of their characteristics (and some of yours) are inherited. Molecules called Nucleic acids control inherited characteristics. Nucleic acids are large, complex molecules that contain hereditary, or genetic, information. They are composed of many smaller molecules called nucleotides. Nucleotides are molecules that are built of three different parts: a special 5-carbon sugar, a phosphate group that contains phosphorous, and a nitrogenous base that contains nitrogen. You will learn more about these structures later in the year during the DNA unit. When nucleotides are joined together, a nucleic acid and water are formed. There are two kinds of nucleic acids – deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). DNA and RNA differ in their structures and functions. Similar to the blueprint for a builder, DNA carries the instructions that control the activities of a cell. Similar to the builder, RNA uses those instructions to build proteins. Therefore, both DNA and RNA are essential for life processes because they are involved in the production of proteins, and proteins play a role in virtually every activity of every living organism.