The images below are from Human Physiology: An integrated Approach (7th ed). Use
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Question
The images below are from Human Physiology: An integrated Approach (7th ed). Use them to address the following questions about insulin and insulin signaling: 1 mRNA A. The image to the left illustrates the synthesis of a insulin, a peptide hormone. In your ow the numbered steps in the figure n words, describe what is happening at each of Preprohormone Ribosome Endoplasmic reticulum (ER) Signal sequence Transport vesicle Prohormone 2. 3 Golgi complex 4 Secretory vesicle Active hormone Cytoplasnm Peptide fragment Release signal ECF 5 Plasma Capillary endothelium To target ©2016 Pearson Education, Inc.Explanation / Answer
The synthesis of insulin in a step-wise manner is described as below :
Removal of its signal peptide during insertion into the endoplasmic reticulum generates proinsulin. Proinsulin consists of three domains: an amino-terminal B chain, a carboxy-terminal A chain and a connecting peptide in the middle known as the C peptide.
Within the endoplasmic reticulum, proinsulin is exposed to several specific endopeptidases which excise the C peptide, thereby generating the mature form of insulin.
Insulin and free C peptide are packed in the Golgi bodies into secretory granules which accumulate in the cytoplasm.
When the beta cell is appropriately stimulated, insulin is secreted from the cell by exocytosis.
The insulin then diffuses into small blood vessels of the pancreas. C peptide is also secreted into blood, but has no known biological activity.
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