Proteins: Form Equals Function Proteins are chains of amino acids that fold into three-dimensional shapes. Proteins come in a wide variety of amino acid sequences, sizes, and threedimensional structures, which reflect their diverse roles in nearly all cellular functions. Each protein has a particular structure necessary to bind and react with other molecules; thus, function is directly correlated to structure of the protein. For example, lactase is a protein (enzyme) that breaks down the sugar found in dairy products, lactose. Lactase must have a specific 3D shape that fits with lactose, like two pieces of a puzzle. This is oftentimes compared to a key fitting into a lock. If the protein doesn’t have the specific shape needed, it cannot attach to another molecule, and the reaction cannot take place. Carbohydrates: Form Equals Function Simple carbohydrates are relatively small molecules that the body can easily use for cellular respiration (to create ATP, or usable energy). In cellular respiration, one molecule of glucose can be broken down, therefore releasing the energy that is stored within the bonds right away. Complex carbohydrates are polymers made of many simple carbohydrates. We gave you three examples. The first, starch, provides energy for the plants that make them, and starch serves as the main food source for many animals. Humans and other animals produce enzymes (a protein) that can break down starch. Because starch is a long chain of simple carbohydrates, one piece can be broken off at a time to be used for energy (go through cellular respiration). In plants, this structure allows starch to be used throughout the day for energy and not all at once. The second complex carbohydrate, cellulose, provides structural support to plants. The monomers in cellulose form tight bonds, allowing flower stems and tree trunks to maintain their rigid, straight height. Humans do not produce an enzyme (a protein) that can digest cellulose, so it passes through the body undigested (meaning it is never used for energy because cellular respiration requires a simple carbohydrate). The third type of complex carbohydrate, glycogen, is a polymer of glucose and the storage form of carbohydrates in animals (humans too). When animals eat simple carbohydrates or starch, not all of the glucose may be needed right away. Your body will take the extra glucose and build a complex carbohydrate known as glycogen. This compact structure allows more glucose to be stored in cells for later use. Just like starch, the ends of a glycogen molecule can be used for energy when needed throughout the day. This is why you don’t have to eat food every time you need energy…your body stores the extra for later! Lipids (Fats): Form Equals Function There are many different types of lipids, but the one we are focusing on is the phospholipid, which is a molecule that makes up the majority of the cell membrane. An important property of lipid molecules is that they do not mix well with water. In the cell membrane, the lipid molecules are arranged into two layers (called the lipid bilayer). The parts of the phospholipids that have the highest tendency to interact with water (hydrophilic) are located toward the outside and inside of the cell. The parts of the phospholipids with the lowest tendency to interact with water (hydrophobic) are located toward the interior of the membrane. The interior part of the membrane prevents some molecules from entering the cell. Nucleic Acids: Form Equals Function Both DNA and RNA are nucleic acids. They are given this name because they are made up of nucleotides. The nucleotide is comprised of a phosphatesugar backbone and a nitrogen base as the “steps” of the twisted ladder. There are four nitrogen bases in DNA: adenine, thymine, cytosine, and guanine. Most people refer to these using four letters, A, T, C, and G. For example, to refer to a specific piece of DNA, we might write: AATTGCCTTTTAAAAA. The sequence of bases (letters) can code for many properties of the body’s cells. The cells can read this code. Some DNA sequences encode important information for the cell. The DNA code, or genetic code as it is called, is passed through the sperm and egg to the offspring. A single sperm cell contains about three billion bases consisting of A, T, G and C that follow each other in a well defined sequence along the strand of DNA. Each egg cell also contains three billion bases arranged in a well-defined sequence very similar, but not identical to the sperm. In essence, this structure creates compartments that allow each individual cell to control its internal environment, by letting certain substances move in or out of the cell. Temperature, water, minerals, nutrients, oxygen, pH levels, and other balances must be maintained in each cell in order to live. Just think, the cells in our stomach must maintain a very different environment than the cells of our heart muscle. We are able to do this because cell membranes are made out of lipids! DNA varies from one individual to another. These DNA variations can be used to identify people or at least distinguish one person from another because the specific sequence of DNA bases is what makes each person unique.