Davidson BIO 111 - Unit I Cellular Communication

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SG 1 Unit I: Cellular Communication Living beings can be composed of a single cell (e.g., bacteria, cyanobacteria, and protists such as Paramecium and Chlamydomonas (a single-celled, photosynthetic organism that you will meet in lab)) or many cells. Not surprisingly, organisms composed of many cells are called multicellular organisms. An adult human is a very organized collection of about 70 trillion cells. (If you counted these cells at a rate of one cell per second, it would take you over two million years to count every cell in your body.) With a few exceptions (e.g., red blood cells), each individual cell in a multicellular organism is a living entity with a complete set of genes and life maintenance equipment. Each cell maintains its own existence in addition to making a vital contribution to the life of the multicellular organism. In order for multicellular organisms to function properly, their cells must communicate. For instance, your muscles must contract when your brain sends a message to contract. Your salivary glands must secrete a lot of saliva when there is food in your mouth and only a little saliva at other times. Your heart rate must increase when you exercise, but not when you sleep. Unit I focuses on how cells communicate with each other in order to coordinate their functions and maintain the organism. While we will focus most closely on cellular communication in multicellular creatures, you should keep in mind that communication is very important to unicellular creatures as well. For instance, unicellular organisms must swim toward nutrition or sunlight if they are photosynthetic and must be able to sense when conditions are right to reproduce. In this unit, we will examine four examples of cellular communication: 1) how liver cells secrete glucose 2) how cardiac muscle increases force 3) how neurons tell muscles to contract 4) how an egg knows it is fertilized Each system uses a slightly different communication system, and taken together, these four systems represent many of the cellular communication systems scientists understand thus far.  Overview Reading Note: Yes, five chapters is a lot, but keep in mind this is overview reading and should be briefly skimmed at this point. These chapters will be discussed throughout this unit, and we will go into more detail as indicated by “Focused Reading.’ You do not need to learn every detail in this reading now – just try to get a sense of the topics we will encounter. • Chapter 2 • Small Molecules and the.... • Chapter 3 • Proteins, Carbohydrates… • Chapter 4 • Nucleic Acids… • Chapter 6 • Cell Membranes • Chapter 7 • Cell Signaling and Communication The Liver Produces Glucose in Response to Stress Glucose (C6H1206) is the primary sugar that biological creatures use as fuel. Humans, like other creatures, burn (oxidize) this sugar into carbon dioxide (C02) and water (H20), using the energy released by this oxidation process to perform life's many functions (discussed in detail in Unit III). To ensure that cells have enough glucose to burn (and, therefore, enough energy to perform essential functions), the body maintains a constant supply of it in the blood (about 1 mg glucose per 1 ml blood).  Focused Reading Note: Whenever you see the heading “focused reading” you should read these short sections of your textbook carefully BEFORE continuing to read in this Study Guide. • p 40-42 "The structures…" to “3.1 Recap” • p 49-53 “3.3 What are…” to “Chemically…”  thelifewire.com Reading • Animated Tutorial 3.1 • Macromolecules (just consider the carbohydrate subsection for now)SG 2  Web Reading • Carbohydrate section of CancerQuest http://www.cancerquest.org/index.cfm?page=32 However, our bodies respond to stressful stimuli by increasing the blood glucose level to ensure enough fuel to fight or flee from what is scaring us. This extra sugar comes from glucose stores in the liver. During meals, glucose enters the body, is transported in the blood, and is removed from the blood and stored for later use by the liver. To store glucose, the liver attaches many of the sugar molecules together (polymerizes them) to form a large storage molecule called glycogen. When glucose is needed (either because you haven't eaten for a while or because you are scared), these big glucose polymers will be broken down into individual glucose molecules (monomers), which will be dumped into the blood to provide fuel for all of the cells of the body. ❖ Study Questions: Note: You will frequently encounter “study questions” throughout this Study Guide. Some answers to study questions can be found within in the preceding Study Guide text, but many answers will come from assigned text and/or web reading. You do not need to submit written answers to these study questions, but you should be prepared to discuss study questions in class and on exams. 1. What is glucose used for in biological creatures? What is the function of glycogen? What is the relationship between glucose and glycogen? Why does your liver go to the trouble of converting glucose to glycogen then back to glucose? (Why not store glucose?) 2. What is a polymer? What is a monomer? Is glucose a polymer or monomer? What is glycogen? Explain. What is a monosaccharide? A disaccharide? A polysaccharide? An oligosaccharide? Be able to recognize a monosaccharide and polysaccharide when you see one drawn. 3. Glucose molecules are joined together to form glycogen by a process called dehydration synthesis (or condensation synthesis). Glycogen is broken down to form glucose by the process of hydrolysis. "Hydro-" means water and “lysis” means to break apart. What does water have to do with these two processes? Be able to illustrate both of these reactions including the breaking or forming of bonds and the involvement of water


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