Bio 100 Reading for Enzyme, Lipids, and DNA Instructor Deborah Bird Page | 1ENZYME READING Introduction Enzymes are critical to every chemical reaction that occurs in your body. Enzymes act as catalysts, that is, they speed up chemical reactions but are not used up themselves in the process. Enzymes increase the rate of chemical reactions. Enzymes are made of protein, and all proteins, including enzymes, work best in an environment within a certain range of temperature and pH. Each enzyme has its own specific ideal range, and exposure to higher-than-ideal temperatures or different pHs, for example, can cause proteins to unravel, making them useless. When this happens, we say the protein is denatured. For example, egg white is made of a protein called albumin. When the egg is cooked, the albumin denatures. Cold temperatures usually don’t denature proteins, but the chemical reactions catalyzed by enzymes slow down and proceed much more slowly. An example of how enzymes work and their importance is the ingestion, digestion and absorption, excretion of food along with the metabolism needed to support these processes. Before it can be used for energy, the food you eat has to be digested. Digestion is the mechanical and chemical breakdown of food into molecular subunits which can be used by cells. Digestion begins in your mouth with the mechanical breakdown of food. The chemical changes that will take place begin here too. When you swallow, food moves from your mouth, through your esophagus, and into your stomach, where the breakdown continues. Food leaves your stomach and passes through your small and large intestines. Material that cannot be broken down leaves the large intestine after much of the water used for digestion is reabsorbed. Beginning in your mouth, but more in your stomach and small intestine, proteins called enzymes break food down, allowing the chemicals released to be absorbed by your blood stream, which transports these chemicals to individual cells where they are used by the cells to make ATP and to build new molecules. The material that an enzyme acts on is called its substrate. Each kind of enzyme works on onlyBio 100 Reading for Enzyme, Lipids, and DNA Instructor Deborah Bird Page | 2one kind of substrate, which we call substrate specificity. Although there are only twenty different kinds of amino acids used to make proteins such as enzymes, these amino acids can be precisely arranged in different amounts and sequences to produce a huge number of different proteins. Each enzyme is specific for one kind of substrate because the enzyme binds to the substrate, and the shape of the enzyme must conform to the shape of the substrate molecule. The substrate molecule binds to the enzyme at a region called the active site. Once the enzyme has acted on the substrate and converted it to the product, the enzyme can bind with another substrate molecule and the process is repeated, often thousands of times per minute. Once food is broken down, the usable subunits are delivered by your circulatory system to individual cells, where they are first processed in the cytoplasm, and then used by organelles called mitochondria. Mitochondria are bean-shaped organelles formed of a double membrane surrounding a semifluid matrix. The inner membrane is rich in proteins involved in the production of ATP (adenosine triphosphate), the energy molecule used by all cells. The process of using nutrient molecules to make ATP is called cellular respiration. Besides carrying out cellular respiration, plants can also MAKE an especially important fuel molecule, a sugar called glucose, by photosynthesis. During cellular respiration, cells use fuel molecules produced by digestion, especially the sugar glucose (C6H12O6), and oxygen (O2) and to make ATP and produce carbon dioxide (CO2) andBio 100 Reading for Enzyme, Lipids, and DNA Instructor Deborah Bird Page | 3water (H2O) as byproducts. This is how the oxygen you breathe in as used and where the carbon dioxide you breathe out comes from. The ATP produced can then be used as power for the cell in all its activities. Cellular respiration occurs in eukaryotic cells such as plant and animal cells and in many bacteria as well. The process can be summarized by the chemical equation C6H12O6 + 6O2 –> 6CO2 + 6H2O + ~36 ATP Glucose is energy rich, but oxygen and carbon dioxide are energy poor. The energy released by the breakdown of glucose is used to synthesize ATP, and ATP is also energy rich. We measure this energy in Calories, the same Calories listed on food labels. When a person consumes more Calories than are used, the excess energy is stored as fat, and the person gains weight. When fewer Calories are consumed than are used, the difference is made up by using energy stored as fat. When this happens, the person loses weight. Your heart rate is related to metabolic processes because each contraction moves oxygen-rich blood through your body, and returns oxygen-poor blood to your lungs to be reoxygenated. Remember, the oxygen is used to “burn” the fuel molecules (mostly glucose) to make ATP. Lipids Lipids have many essential functions in living organisms, including forming cell membranes, forming hormones, and storing energy. To stay alive, we must consume lipids in our diet, usually in the form of triglycerides (also called fats). Unfortunately, some of us consume too much fat in our diet, which is part of the reason that heart disease is the number one killer in our society. We hear that unsaturated fats are good for us (in moderation), but what is the difference between saturated and unsaturated fats? - In saturated fats, the fatty acids have only single bonds (no double bonds) between the carbon atoms. Saturated fats have the maximum number of hydrogen atoms -- they are “saturated” with hydrogen atoms. - In unsaturated fats, there is at least one double bond in at least one of the fatty acids. The presence of the double bond means fewer hydrogen atoms. Unsaturated fats can be either monounsaturated or polyunsaturated. - Monounsaturated fats have only one double bond. - Polyunsaturated fats have more than one double bonds. These structural differences affect the physical characteristics of fats. - Since saturated fats have only single bonds in the fatty acids, the fatty acid chains are straight and can pack together more tightly. Therefore, saturated fats are usually solid at room