Question

1. How do polypeptides have the following types of effects: autocrine, paracrine, and endocrine

2. If you experimentally increase the concentration of Na+ outside a cell while maintaing other ion concentrations as they were, what would happen to the cell's membrane potential? Can you please exaplin why?

a - membrane potential would increase b - membrane potential would decrease c - membrane potential would be unaffected d - depends on thermodynamy potential

Answer 1

1.The biological effects produced by by binding to cell surface receptors are called endocrine, autocrine, and paracrine effects, depending on the origin of the hormone. These effects are of some of the peptide/protein hormones .

(a). Autocrine effect ISLET AMYLOID POLYPEPTIDE (IAPP) IS a peptide hormone cosecreted with insulin from pancreatic b cells in response to several b-cell secretagogues, such as glucose (1, 2). IAPP exerts different functions at peripheral tissues (3), but its accumulation in the form of amyloid deposits in the pancreatic islets of humans is strongly associated with type 2 diabetes, most likely due to a progressive loss of b-cell mass and function (4–6).

(b) Paracrine effect: Gastrin is a polypeptide hormone that stimulates secretion of gastric acid (HCl) by the parietal cells of the stomach and aids in gastric motility. It is released by G cells in the pyloric antrum of the stomach, duodenum, and the pancreas. Gastrin binds to cholecystokinin B receptors to stimulate the release of histamines in enterochromaffin-like cells, and it induces the insertion of K⁺/H⁺ ATPase pumps into the apical membrane of parietal cells (which in turn increases H⁺ release into the stomach cavity). Its release is stimulated by peptides in the lumen of the stomach.

(c.) Endocrine effect: Examples of protein/polypeptide hormones include adrenocorticotropin (ACTH) from the pituitary, insulin from the pancreas, and parathyroid hormone (PTH). These hormones range in size from three amino acids (thyrotropin-releasing hormone) to considerably larger proteins with subunit structure (eg, luteinizing hormone). They are produced in their endocrine tissue of origin by transcription/translation of the gene coding for the hormone and synthesized initially as larger products (prepro- or pre-forms) that undergo processing to authentic hormone inside the cell before secretion. Polypeptide hormones act on their target cells by binding to receptors located on the cell surface. These receptors are proteins and glycoproteins embedded in the cell membrane that traverse the membrane at least once so that the receptor is exposed to both the extracellular and intracellular environments. There are several classes or types of cell surface hormone receptors that translate the hormonal message to the cell interior by different means.

2. c - membrane potential would be unaffected l