# Insulin: Structure, Function, and Regulation This document outlines the biochemical properties, physiological functions, and importance of insulin in metabolic regulation. ## Structure of Insulin Insulin is a protein hormone that is produced by the pancreas. Its structure is essential to its function. * **Composition:** It consists of two separate polypeptide chains connected by disulfide bonds: * The **alpha chain** (A chain) contains 21 amino acids. * The **beta chain** (B chain) contains 30 amino acids. * **Molecular Weight:** The molecular weight of human insulin is approximately $5,808\ \mathrm{g/mol}$. ## Function of Insulin in Metabolism Insulin's primary role is to regulate the metabolism of carbohydrates and fats in the body. After a meal, the body releases insulin to manage the influx of glucose. * **Glucose Uptake:** Insulin signals to the liver, muscles, and fat cells to absorb glucose from the blood, which can then be used for energy. * **Energy Storage:** It promotes the storage of excess glucose in two primary forms: 1. **Glycogen:** Glucose is stored as glycogen in the liver and muscles for short-term energy needs. 2. **Triglycerides:** In adipose tissue, glucose is converted and stored as triglycerides for long-term energy. * **Fat Metabolism:** Insulin prevents the body from breaking down and using fat for energy when glucose levels are sufficient. ## Blood Sugar Regulation Insulin is the key hormone for lowering blood sugar levels. However, the body also has mechanisms to raise blood sugar when it is too low. * **Low Blood Sugar Response:** When blood sugar levels drop, the body initiates **glycogenolysis**, the breakdown of stored glycogen in the liver to release glucose back into the bloodstream. ## Insulin Deficiency: Diabetes Mellitus A malfunction in the insulin system leads to a serious metabolic disorder. * **Definition:** **Diabetes mellitus** is a disorder in which the body either does not produce enough insulin or does not respond normally to the insulin it produces. * **Consequence:** This leads to abnormally high blood sugar levels, a condition known as hyperglycemia, which can cause significant health complications over time.