Question

35. Insulin is a peptide (protein) hormone secreted by B-cells located in the pancreas. To be protein) hormone used to regulate the level of glucose in the bloodstream. It is produced and performed. cated in the pancreas. To better understand how insulin is secreted, the following experiments were a. The mature me mature mRNA for insulin encodes a protein that is 110 amino acids in length. If the genes t is 110 amino acids in length. If the gene is translated in a cell- "E extract (meaning a solution containing ribosomes, the mRNA and charged tRNAS was used the protein Ius long. However when insulin is purified from the media of cultured pancreas cells, insulin is only long. Describe a specific process that occurs during the normal trafficking and secretion of insulin which could account for this size discrepancy. (3 pts) The mature mRNA is 10 amino acids long, whereas the purified insulin is 75 amino acids long due to the process of splicing. After mRNA is produced, there are regions that are "nonsense" and are not needed. The se are spliced, out bu spliceosomes and other proteins and enzymes so that only the exong lactually coding and necessary) part is joined to gether and utilized .. b. You are working with different strains of laboratory mice that have a predisposition for developing diabetes, in other words, these mice do not seem to be able to respond to insulin normally. You sequence the gene for insulin in the lab mice strains, but find no mutations in the gene for insulin. You are able to track insulin in each mouse strain and your findings are below. Complete the table below to explain the mis-trafficking of insulin. (9 pts) Mice have vesicles with insulin, but no secretion of insulin into the extracellular space. Describe the defect in trafficking that would result in this observation. The acceptor compartment (plasma membrane) might not have the tethering proteins to attach to the Rab protein of the vesicle to allow for v-SNARES and t-SNARES to find one another and allow for the release of insulin from the resides. Mice have no vesicles at all, but insulin can be detected in the ER. Why? Mice have the ER signal sequence and transmembrane domain to allow it to why go to the ER but with absence of vesicles/ the insulin cannot be transported to the plasma membrane and extracellular space.

Answer 1

a) The mature mRNA codes 110 amino acids Song wherease the purified insulin is 75 amino acids. due to post translat- ional modification, once and postein is synthesized, it contain some signal sequences to reach its destination. from Protein MRNA of insulin contain ER recognition signal sequences. once it reached into ER, then these signal sequences are need to be removed by peptidases when the Signal sequences are cleared from protein (insulin) then it is transposted to the Golgi for modification Proper folding of protein is necessary before transportation to the Golgi body. So, amino acids number can be reduced. b). Mice have no vesicles at all, but insulin can be detected in the ER because mice insulin contain ER recognition signal sequences and insulin reached to the ER but may be ER unable to foom COPI coated Vesicle which is needed to trampost insulin. from ER to Golgi body. Vesicles are not able to from or binch off from ER membrane.