Introduction:
Peptide hormones are synthesized like other protein molecules. They are 3 to ≥ 200 amino acid long chains. Insulin is the large peptide hormone (protein) secreted by the pancreatic islets. The insulin gene is transcribed into the mRNA molecule that codes for insulin protein. Ribosomes bind and read the mRNA molecule and synthesize peptide with the help of tRNA. The rough endoplasmic reticulum and Golgi complex modify the amino acid peptide to mature hormone (protein). The middle portion of the proinsulin (single amino acid chain) is known as the connecting peptide. The connecting peptide (31 amino acids long) is removed from the proinsulin, and the two polypeptide (30 and 21 amino acids long) chains are linked by disulfide bridges to produce the mature insulin molecule.
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ANATOMY AND PHYSIOLOGY THE UNITY OF FORM
- The hormone insulin enhances the transport of glucose (sugar) from the blood into most body cells. Its secretion is controlled by a negative-feedback system between the concentration of glucose in the blood and the insulin-secreting cells. Therefore, which of the following statements is correct? A decrease in blood glucose concentration stimulates insulin secretion, which in turn further towers blood glucose concentration. An increase in blood glucose concentration stimulates insulin secretion, which in turn lowers blood glucose concentration. A decrease in blood glucose concentration stimulates insulin secretion, which in turn increases blood glucose concentration. An increase in blood glucose concentration stimulates insulin secretion, which in turn further increases blood glucose concentration. None of the preceding is correct.arrow_forwardA. What is the difference between preproinsulin and proinsulin? B. What is cleaved out of proinsulin to allow the mature insulin molecule to be formed? C. What is the C peptide and why is it medically significant? D. What is the purpose of the signal sequence and why isn’t it present in the mature insulin molecule?arrow_forwardWhere are the receptors for insulin located?a. in the pancreatic beta cellsb. in the blood plasmac. on the target-cell membraned. in the target-cell cytoplasme. in the target-cell nucleusarrow_forward
- Which of the following statements about insulin is true? a. Insulin acts as a transport protein, cany in g glucose across the cell membrane. b. Insulin facilitates the movement of inti acellular glucose transporters to the cell membrane. c. Insulin stimulates the breakdown of stored glycogen into glucose. d. Insulin stimulates the kidneys to reabsorb glucose into the bloodstream.arrow_forwardWhich of the following statements about insulin is not true? a. The insulin receptor has tyrosine kinase activity. b. Insulin increases fat synthesis in adipose cells. c. Insulin increases glycogen synthesis d. Insulin increases gluconeogenesis reactions.arrow_forwardWhich of these does insulin do? A. It helps the intestines digest glucose. B. It helps glucose enter cells. C. It converts glucose into glutamate. D. It converts stored fats into glucose.arrow_forward
- Define the following terms:a. second messengerb. desensitizationc. target celld. insulin resistancee. adenylate cyclasearrow_forwardBased on your understanding of the binding of insulin, select all of the following events that you would expect to occur in muscle cells due to insulin binding to receptors.Group of answer choices a. Glycogen synthesis is activated b. PFK is stabilized in the R-state and glycolysis is activated c. GLUT4 (transporters) are increased in concentration at the plasma membrane d. Fructose 2,6-bisphosphate increased levels aid in stabilization of the T-state fructose 1,6-bisphosphatase e. Gluconeogenesis is activated in response to elevated fructose 2,6-bisphosphate levels f. Phosphorylation cascades allow for covalent modifications that would aid in the breakdown of glycogen to allow for increased levels of glucose 6-phosphate in the cell g. Hexokinase is inhibited so glucose will not be brought into the cell in high amounts h. Glycogen breakdown pathway is inactivatedarrow_forwardWhich of the following classes of compounds stimulates the release of insulin from pancreatic β-cells? a. Thiourylenes b. Biguanides c. Progestins d. Sulfonylureas e. α-Glucosides inhibitorsarrow_forward
- 1a) In a healthy mammal, which one of the following will lead indirectly to increased production of glycogen in liver cells? A. a reduction in insulin output B. a high glucose content in the diet C. an increase in thyroxine production D. a reduction in the amino acid concentration in the blood B) What effect would be caused by cutting the sympathetic nerve fibres to the heart? A. a decrease in the heartbeat rate B. a decrease in the length of the diastole phase C. a decrease in the length of the systole phase D. a decrease in the stroke volume c) If the nerve fibres within the septum are damaged, which phase of the cardiac cycle will be affected? A. ventricular diastole B. ventricular systole C. atrial systole D. atrial diastolarrow_forwardWhich of the following statements concerning insulin is NOT true? a. Insulin can increase glycogen synthesis. b. The presence of insulin can increase glucose uptake. c. Insulin can increase the secretion of epinephrine. d. It is secreted by the beta cell of pancreas. e. Glucose in blood can up-regulate the secretion of insulin.arrow_forwardInsulin therapy has all of the following effects, except:A. Increases concentration of free fatty acids in blood plasma B. Stimulates glucose uptake by tissuesC. Inhibits lipolysisD. Activates protein synthesisarrow_forward
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