Learning Guide Week 1: Cellular Organization

Learning Guide Week 1: Cellular Organization Welcome to BIOL230W. We will be starting the semester using cystic fibrosis as a case study to understand gene expression: the Central Dogma of Biology. This will include transcription, translation, and protein transport. We will also study genome and protein structure as we journey through our first seven weeks together. Learning Objectives • • • • • • • • • • • • Explore and outline the symptoms of cystic fibrosis. Hypothesize the mechanism that results in cystic fibrosis symptoms as related to structures in the cell. Identify the different parts of a phospholipid. Relate how the parts of the phospholipid contribute to its amphipathic characteristic and how the characteristics affects the formation of a phospholipid bilayer. Determine what types of molecules can diffuse through a membrane and why. Discuss the properties of a membrane that allow it to be selectively permeable. Define the process of osmosis. Define the three major categories of organelles and list example organelles. Describe the general evolutionary process of the nucleus and endomembrane system as related to FECA and LECA. Describe the major functions of the organelles of the endomembrane system. Relate the different cellular locations of the endomembrane system with function in gene expression (i.e., where does transcription/translation occur). Use a micrograph to analyze information related to the endomembrane system. Day 1 Small Group Activity: Symptoms of Cystic Fibrosis Below is a list of some of the symptoms associated with cystic fibrosis. Please use this list and Wikipedia/Google to answer the next questions. • • • • • • • • A persistent cough that produces thick mucus Difficulty breathing Repeated lung and sinus infections Chronic constipation Foul-smelling and/or greasy feces due to clogged pancreatic ducts Female infertility associated with thickened cervical mucus Malnutrition Hypoxia (lack of oxygen delivery to tissues) 1. Do you notice any similarities and/or relationships between these symptoms? 2. What type of tissue lines the lungs, digestive tract, reproductive tracts and makes the pancreas: epithelial, muscle, dense connective, or nervous? Use Wikipedia or Google to determine this answer if you do not know. 3. Can you hypothesize a common mechanism for these symptoms related to cells of epithelial tissue and transport of water? Day 2 Small Group Activity: Cell Membrane Structure and Transport Last class we learned that one symptom of cystic fibrosis is a thick mucus covering the epithelial cells associated with our respiratory tract. The epithelial cells are surrounded by a cell membrane composed of a phospholipid bilayer. 4. Draw a representation of a phospholipid (phosphate group, glycerol, fatty acids) and phospholipid bilayer (phosphate group, fatty acids, hydrophilic region, hydrophobic regions) in the space below. Label the listed parts of each structure. PHOSPHOLIPID PHOSPHOLIPID BILAYER 5. What characteristics of phospholipids cause them to assemble into a bilayer in an aqueous environment? 6. What feature(s) of the membrane allow it to be “selectively permeable” (i.e., allow some molecules to diffuse through and others not)? 7. Using the structure of the bilayer drawn above, discuss if the following molecules can diffuse across a membrane. • A small non-polar molecule: • A small polar molecule • A large polar molecule: • An ion: 8. Can water diffuse across a cell membrane? Please explain your answer. Osmosis is the diffusion of water through a semipermeable membrane from an area of low solute concentration (hypotonic solution) to an area of high solute concentration (hypertonic solution). The solute is typically polar or charged molecules that cannot cross the membrane. Cells use the active transport of solutes to move water; there is no cellular mechanism to actively transport water. If a cell is surrounded by extracellular fluid that has a higher concentration of solutes compared to the cytoplasm, the extracellular fluid is a hypertonic compared to the cell; water molecules tend to diffuse from the hypotonic cell into the hypertonic extracellular fluid. In contrast, if a cell is surrounded by a extracellular fluid that has a lower concentration of solutes compared to the cytoplasm, the extracellular fluid is hypotonic compared to the cell; water molecules tend to diffuse from extracellular fluid into the cells. 6. In the space below, draw a representation of a cell in a hypertonic extracellular fluid and a cell in a hypotonic extracellular fluid. Draw an arrow representing the diffusion of water for each cell. HYPERTONIC HYPOTONIC 7. Hypothesize how the process of osmosis in epithelial cells plays a role in the thick mucus found in cystic fibrosis patients. 8. If ions cannot pass through a membrane, how are they transported to drive osmosis? Summary Exercise: In the space below, please describe how a cell can regulate the water concentration of the extracellular environment using the transport of other molecules. Day 3 Mini-Lecture Questions 1. List three categories of organelles and underline the two that require membrane manipulation via proteins for formation. 2. Define FECA and LECA and compare and contrast the FECA and the LECA with respect to the nucleus, the mitochondria, and the chloroplast. 3. List the organelles involved with the production and export of proteins starting with the nucleus and ending with the cell membrane. This is going to help you with our discussion about cystic fibrosis. Small Group Activity: Symptoms of Cystic Fibrosis Scientists have identified a protein channel that when mutated leads to the symptoms of cystic fibrosis. Below are several transmission electron micrographs of cells that do not express the CFTR the protein (image A – referred to as CFPAC cells), cells that express the normal protein (image B – referred to as Wildtype or WT) or cells that express a mutated form of the protein (image C and D – referred to as ∆F508 CFTR). It may be helpful to label the images to make it easy to interpret them. Image from Yang, Yiping, et al. "The common variant of cystic fibrosis transmembrane conductance regulator is recognized by hsp70 and degraded in a pre-Golgi nonlysosomal compartment." Proceedings of the National Academy of Sciences 90.20 (1993): 9480-9484. Each cell type was fixed, process into very thin slices (picture slicing a potato or onion) and treated with an antibody that is specific to the identified protein. The antibody binds to and labels the WT or mutated form of the protein with a dark (black) stain. The thin slices are mounted on slides that can used by a transmission electron microscope. Please use the caption, knowledge from class or Google/Wikipedia to answer the following questions. 3. Transmission electron microscopy was used in this experiment. Using the first two paragraphs of the Wikipedia article “Transmission Electron Microscopy”, what advantage does transmission electron microscopy have compared to light microscopy? 4. Several organelles are labeled in the image with abbreviations. Please list the organelles shown and include major categories (i.e., proteinaceous, membrane-bound or endosymbiotic) and function based on what we discussed in class. An organelle we did not discuss in class is included: multivesicular body (MVB) which is like of vacuole in animal cells that can sort things that are entering or exiting the cell. 5. CFPAC cells are derived from a cystic fibrosis patient that does not synthesize the identified CF protein. What is the significance of showing the staining pattern of these cells (image A) in this experiment? (Hint – Why stain cells that are known to NOT express the protein?) 6. What organelles does the protein localize to in Image B? Remember you are looking for a dark staining pattern to indicate the location of the protein. You may need to you Image A as a comparison. 7. What organelle does the protein localize to in Image C and D? 8. Summarize the major difference between localization of the wildtype and the mutated protein? 9. Thinking about the general synthesis and transport of proteins, what might cause the differential localization pattern? (Hint – please consider where the normal protein is translated, cytoplasm vs. ER and how proteins move between organelles/plasma membrane after translation). Summary Exercise 1. Drawing from what you learned about the Central Dogma of biology and protein export in Biol110, draw a flow diagram indicating the order of events in these processes starting with DNA and ending with export of the protein outside the plasma membrane. 2. Highlight the step that is disrupted in the cells with the mutated CF protein discussed above.