Tour of an Animal Cell The Endomembrane System

ch 7, 8 and 9 19 of 51 Tour of an Animal Cell: The Endomembrane System Eukaryotic cells have an integrated network of organelles, including the endoplasmic reticulum (ER), the Golgi apparatus, and lysosomes, which is collectively referred to as the endomembrane system. The endomembrane system serves a variety of functions within the cell, including protein synthesis and transport, metabolism of lipids, and detoxification. Before beginning this tutorial, watch the Endomembrane System animation. Part A - Organelles of the endomembrane system The various parts of the endomembrane system serve different functions in the cell. In this activity, you will identify the roles of each part of the endomembrane system. Drag each function to the appropriate bin. 6/13/2019, 11:24 AM ch 7, 8 and 9 20 of 51 Hint 1. Cisternal maturation Cisternal maturation is the process by which the cisternae of the Golgi apparatus progress from the cis face to the trans face. Hint 2. Which organelle of the endomembrane system functions in protein synthesis? The part of the endomembrane system that is studded with ribosomes for protein synthesis is the _____. ANSWER: Golgi apparatus rough ER smooth ER Hint 3. In what ways is the endomembrane system similar to a factory? The endomembrane system performs so many different functions in the cell that it is often compared to a factory with elaborate assembly lines and shipping capabilities. Drag the terms on the left to the appropriate blanks on the right to complete the sentences. Not all terms will be used. ANSWER: Reset Help 1. The production department of the endomembrane system, where lipids and proteins are made, is the endoplasmic reticulum (ER) . 2. The Golgi apparatus serves as the finishing and shipping area for products of the endomembrane system. This organelle adds molecular identification tags, or shipping codes, to plasma membrane products bound for other parts of the cell. 3. A lysosome is a recycling center in the cell because it breaks down damaged organelles and returns organic monomers to the cytosol. 4. Like a shipping container or truck, a vesicle transports materials between various parts of the endomembrane system. ANSWER: 6/13/2019, 11:24 AM ch 7, 8 and 9 21 of 51 Reset Help Part B - Sites of protein synthesis All proteins are synthesized by ribosomes in the cell. Some ribosomes float freely in the cytosol, while others are bound to the surface of the endoplasmic reticulum. Most proteins made by free ribosomes function in the cytosol. Proteins made by bound ribosomes either function within the endomembrane system or pass through it and are secreted from the cell. Which of the following proteins are synthesized by bound ribosomes? Select all that apply. Hint 1. How to approach this problem To determine whether a protein is synthesized by free ribosomes or bound ribosomes, be sure to consider where the protein ultimately ends up. In general, there are two classes of proteins: those that function in the cytoplasm or in environments that are in direct contact with the cytoplasm (Note that although the nucleus is enveloped by two membranes, the interior is still considered to be in direct contact with the cytoplasm via the numerous pores that allow transport between these two environments.) 6/13/2019, 11:24 AM ch 7, 8 and 9 22 of 51 those that function in locations separated from the cytoplasm by a cellular membrane The proteins in the first class are synthesized by free ribosomes; they will ultimately function in the cytoplasm or within the nucleus. The proteins in the second class are synthesized by bound ribosomes; they will ultimately reside in or pass through the endomembrane system. Hint 2. Where in the cell are nuclear proteins made? Some proteins must pass into and out of the nucleus to regulate a variety of activities, including the synthesis of DNA, RNA, and ribosomes. Which of the following pathways would a protein destined for the interior of the nucleus follow? ANSWER: The protein is translated on free ribosomes and then passes between the lipids of the nuclear envelope to enter the nucleus. The protein is translated at the surface of the rough ER and then moves from the interior of the ER to the interior of the nucleus. The protein is translated at the surface of the rough ER, is packaged into a vesicle, and the vesicle fuses with the nuclear envelope, depositing the protein inside. The protein is translated on free ribosomes and then passes through the pore complex to enter the nucleus. ANSWER: insulin actin ribosomal protein DNA polymerase lysosomal enzyme ER protein Part C - The pathway of secretory proteins Proteins that are secreted from a eukaryotic cell must first travel through the endomembrane system. Drag the labels onto the diagram to identify the path a secretory protein follows from synthesis to secretion. Not all labels will be used. Hint 1. How to approach this problem Not all of the labels will be used in the flowchart. Review the functions of each organelle listed and eliminate the organelles not involved in the synthesis, modification, or transport of secretory proteins. Then place the remaining organelles in the correct order. Hint 2. Where are the organelles of the endomembrane system located? Knowing the structure and locations of the compartments that make up the endomembrane system can help you understand how substances move within and between the organelles. Drag the labels to their appropriate locations on the diagram. ANSWER: 6/13/2019, 11:24 AM ch 7, 8 and 9 23 of 51 Reset Help Hint 3. How does cargo move through the Golgi? As cargo passes through the Golgi apparatus, it is modified in a step-wise manner prior to being transported to the plasma membrane or to other locations in the endomembrane system. These distinct modifications are based on the presence of different Golgi enzymes in each cisterna. Complete this sentence. Cargo leaves the endoplasmic reticulum and is sent to the _____ Golgi cisterna, which then matures through the redistribution of enzymes to become a _____ Golgi cisterna and eventually the _____ Golgi cisterna. ANSWER: trans; medial; cis medial; cis; trans cis; trans; medial cis; medial; trans ANSWER: 6/13/2019, 11:24 AM ch 7, 8 and 9 24 of 51 Reset Help Part D - Pulse-chase experiments and protein location Scientists can track the movement of proteins through the endomembrane system using an approach known as a pulse-chase experiment. This experiment involves the “pulse” phase: Cells are exposed to a high concentration of a radioactively labeled amino acid for a short period to tag proteins that are being synthesized. the “chase” phase: Any unincorporated radioactively labeled amino acids are washed away and large amounts of the same, but unlabeled, amino acid are added. Only those proteins synthesized during the brief pulse phase are radioactively tagged. These tagged proteins can be tracked through the chase period to determine their location in the cell. The data below were obtained from a pulse-chase experiment in which cells were examined at different times during the chase period. The numbers represent the radioactivity (measured in counts per minute) recorded at each of the indicated sites. The higher the number, the greater the radioactivity. Time ER 3 minutes 162 7 Golgi 21 Cytoplasm 5 Lysosomes Extracellular space 4 20 minutes 73 88 17 10 8 60 minutes 9 35 14 112 13 120 minutes 11 23 18 151 10 Based on these data, what is the most likely function of the cells in this experiment? Hint 1. Understanding the pulse-chase experiment The pulse-chase experiment is similar to fitting newly synthesized proteins with identification collars, much as one would do in the field to track animals. By using a chase, this cohort of newly synthesized proteins can be tracked as they move to different regions of the cell, without any subsequently synthesized proteins complicating the results. By tracking these proteins over time, the target region where the proteins function can be identified based on the concentration of radioactivity. Hint 2. How can the results of this experiment be represented graphically? The data from this experiment can be represented in line graphs. The change in radioactivity in each part of the cell has been plotted over time. Time ER Golgi Cytoplasm Lysosomes Extracellular space 6/13/2019, 11:24 AM ch 7, 8 and 9 25 of 51 3 minutes 162 7 21 5 4 20 minutes 73 88 17 10 8 60 minutes 9 35 14 112 13 120 minutes 11 23 18 151 10 Drag a label to the target beneath each graph to indicate which part of the cell the graph represents. Labels can be used once or not at all. ANSWER: Reset Help Hint 3. What is phagocytosis? Some cells ingest smaller particles through the process of phagocytosis. Which of the following are true statements about phagocytosis, the vesicles formed during phagocytosis (called phagosomes, or food vacuoles), and the fate of the ingested particles? Select all that apply. ANSWER: Lysosomes fuse with phagosomes formed during phagocytosis. Phagosomes by themselves can digest the ingested particles into molecules the cell can use. The contents of phagosomes are digested with the help of hydrolytic enzymes in lysosomes. Phagocytosis occurs when part of the cell’s plasma membrane engulfs a particle, forming a phagosome. Phagocytosis only occurs in protists. ANSWER: secretion muscle contraction phagocytosis detoxification 6/13/2019, 11:24 AM ch 7, 8 and 9 26 of 51 Activity: Regulation: Negative and Positive Feedback Click here to complete this activity. Then answer the questions. Part A Which of these is an example of negative feedback? ANSWER: As a blood clot begins to form, the process of its formation gets faster and faster. After you eat, glucagon stimulates an increase in blood sugar levels. After you eat, insulin stimulates the lowering of blood sugar levels. The digestive enzyme pepsinogen is converted to pepsin by the action of hydrochloric acid; pepsin itself can then convert pepsinogen into pepsin. Once labor begins, contractions increase in frequency and intensity. . 6/13/2019, 11:24 AM