Name A diagram of a hypothetical operon in bacteria is shown below The bacterial cells need enzymes A and B to breakdown a rare toxic compound X DUE WEDNESDAY 10 22 2014 AT 9 45AM ONLINE Fall 2014 7 012 Problem Set 4 20 Points total Question 1 5 5 points reg Promoter for regulator protein O region Enzyme B Enzyme A Promoter for genes encoding enzymes A and B a Assume that the regulator protein Reg binds to the O region to influence transcription of enzymes A and B You discover that enzymes A and B are only expressed when the bacterial cells encounter compound X Why do you think this might be advantageous for the cell In other words why might the bacteria not express enzymes A and B even when compound X is not present b You grow bacterial cells of an unknown genetic background on agar medium containing compound X What will you observe if the bacterial cells express enzymes A and B What will you see if they do not c You discover that the Reg protein binds to compound X Propose two different models that would allow the presence of compound X to alter the expression of enzymes A and B This would be advantageous for the cell because it would be a waste of energy to have enzymes A and B be expressed all of the time If enzymes A and B are expressed compound X can be broken down If enzymes A and B are not expressed compound X cannot be broken down Model 1 In this case the Reg protein acts as the repressor and binds to X and is unable to bind to the operator therefore transcription can occur Model 2 X binds to Reg which binds to the operon allowing the expression 1 Name d Imagine that you identified a mutant bacterium that cannot survive in the presence of compound X You later map this mutation to the promoter region for enzymes A and B Can this information help you eliminate any of your models in part c Explain e Imagine that you were to identify a lossOofOfunction mutant that fails to express the enzymes A and B in the presence compound X Assume that the location of the mutation is in the O region and the lossOofOfunction mutation means this region can no longer associate with the Reg protein Can either of your models for part c be eliminated as an option Explain This cannot help me eliminate either of the models given this information because we do not know what region the mutation occurred in This means that we can eliminate model 1 as an option because we know that the mutation has to do with the O region where activation occurs Question 2 1 5 points Question 3 7 5 Go to the MITx edX site https lms mitx mit edu courses MITx 7 012 2014 Fall about and log into your 7 012X account Navigate to Courseware Within Week 6 you will find a section labeled Problem Set 4OREQUIRED You must complete this section Your TA can check that you completed this through the 7 012x site so you do not need to submit any work here Protein A is a transmembrane protein that is found on the plasma membrane of a eukaryotic cell a Use the terms below to describe the path that protein A takes from the moment it has been translated to the moment protein A reaches its final destination in a cell You do not need to describe the process in detailOsimply list the cellular locations in the correct sequence You might use terms several times or not at all Plasma membrane Lysosome Vesicles Nucleus Mitochondria Endoplasmic Reticulum Cytosol Golgi apparatus Protein A immediately after translation is in the cytosol where it interacts with ribosomes The protein then recognizes the signal sequence and goes to the Endoplasmic reticulum From the ER the protein goes to the Golgi Apparatus via budding when the membrane of the ER forms a capsule The protein is then transported in a vesicle to the plasma membrane 2 Signal recognition particle recognizes and targets speci c proteins to the endoplasmic reticulum Translocation channel the complex that transports nascent proteins with a targeting signal sequence into the lumen of the ER from the cytosol Name b List two proteins mentioned in lecture that are important for the targeting of all nascent proteins to the endoplasmic reticulum and define their function c A schematic of protein A is shown below Two of its regions are highlighted in gray Those two regions are the only ones of their kind in this protein i e this protein has only one Region 1 and only one Region 2 No other sequences similar to Region 1 or 2 exist in this protein To characterize the function of each region you construct mutants in which the gray regions are deleted individually The effect of these deletions on the localization of the protein are shown below N terminal C terminal Region1 Region2 Region Deleted from Protein A Protein Localization Region 1 Cytoplasm Secreted protein Region 2 Describe the function of each region d Based on the information from Part 3c can you predict the orientation of the normal version of protein A on the plasma membrane Will the N terminus of the protein face the cytosol or the outside the cell What about its C terminus In region 1 the signal sequence is encoded When this signal is deleted the protein localization is in the cytoplasm by default In region 2 the transmembrane domain is encoded When this signal is deleted the protein will be secreted If the normal version of protein A is produced the N terminus of the protein will face the the outside of the cell because it enters the ER rst Therefore we can conclude that the C terminus will face the cytosol because it enters the ER last 3 Name e You want to change the targeting of protein A so that it localizes to the cytosol instead of the plasma membrane You are considering the following approaches to achieve this 1ORemove the ER signal sequence in protein A 2O Mutate the gene encoding for the Signal Recognition Particle SRP so that SRP is no longer functional Which option would you choose Explain your reasoning I would choose option 1 because if there is no ER signal sequence in protein A it will certainly stay in the cytosol Question 4 3 5 points You have identified 5 promising new drugs and want to develop them for human use Their modes of action are listed below Drug 1 blocks RNAOdependent RNA polymerases Drug 2 blocks DNAOdependent RNA polymerases Drug 3 blocks RNAOdependent DNA polymerases Drug 4 blocks DNAOdependent DNA polymerases Drug 5 blocks ribosomes a Which of these five drugs could be used to specifically block a ssRNA strand virus that incorporates into the host cell genome like HIV without affecting the host cell
View Full Document
Unlocking...