Insulin is the example of

Peptide Hormones

The correct answer is option 1. Peptide Hormones.

Peptide hormones are a class of hormones composed of amino acids. They are synthesized as larger precursor molecules known as prohormones, which undergo post-translational modifications to become biologically active. Insulin is one such peptide hormone, and it serves as an excellent example to illustrate the characteristics and functions of peptide hormones.

1. Structure of Insulin:

Insulin is a polypeptide hormone composed of two peptide chains linked by disulfide bonds. These chains are called the A chain and the B chain. The A chain contains 21 amino acids, while the B chain contains 30 amino acids. The disulfide bonds between the A and B chains help stabilize the structure of insulin.

2. Synthesis and Processing:

Insulin is synthesized in the beta cells of the pancreas as a larger precursor molecule called preproinsulin. Preproinsulin undergoes cleavage to form proinsulin, which contains the A and B chains connected by a C peptide. Post-translational processing involves the removal of the C peptide to produce mature insulin. This processing occurs within the secretory vesicles of the beta cells.

3. Release and Regulation:

Insulin is released from pancreatic beta cells in response to elevated blood glucose levels, typically after a meal. Glucose stimulates the beta cells to release insulin via a process involving glucose uptake, metabolism and increased intracellular ATP levels. Insulin secretion is also regulated by other factors such as amino acids, hormones (e.g., glucagon, incretins), and neural signals.

4. Functions:

Insulin plays a central role in regulating glucose metabolism and maintaining blood glucose homeostasis. Its primary functions include:

• Facilitating the uptake of glucose into cells, particularly muscle and adipose tissue, by promoting the translocation of glucose transporters (GLUT4) to the cell membrane.
• Stimulating the conversion of glucose into glycogen (glycogenesis) in the liver and muscle, thereby promoting glycogen storage.
• Inhibiting gluconeogenesis (the production of glucose from non-carbohydrate sources) and glycogenolysis (the breakdown of glycogen into glucose), thereby reducing blood glucose levels.
• Modulating lipid metabolism by promoting lipogenesis (the synthesis of fatty acids and triglycerides) and inhibiting lipolysis (the breakdown of triglycerides into fatty acids and glycerol).

5. Physiological Effects:

Insulin deficiency or insensitivity (insulin resistance) leads to impaired glucose uptake, resulting in elevated blood glucose levels (hyperglycemia), a hallmark of diabetes mellitus. Type 1 diabetes is characterized by autoimmune destruction of beta cells, leading to insulin deficiency, while type 2 diabetes involves insulin resistance and relative insulin deficiency.

In summary, insulin is a peptide hormone synthesized in the pancreas that regulates glucose metabolism by promoting glucose uptake, storage, and utilization. Its structure, synthesis, release, regulation, and functions exemplify the characteristics of peptide hormones. Understanding the role of insulin is essential for managing diabetes and maintaining overall metabolic health.