próteinhormones

Protein hormones are a class of hormones synthesized from amino acids. They are peptides or proteins that are secreted by endocrine glands and travel through the bloodstream to target cells, where they bind to specific receptors on the cell surface. This binding initiates a cascade of intracellular events that ultimately alter the cell's function. Unlike steroid hormones, which can pass through the cell membrane, protein hormones cannot easily cross the lipid bilayer and therefore rely on cell surface receptors to exert their effects.

Examples of protein hormones include insulin, glucagon, growth hormone, and follicle-stimulating hormone. Insulin, produced by the pancreas, regulates blood glucose levels by promoting glucose uptake and storage. Glucagon, also from the pancreas, has the opposite effect, raising blood glucose by stimulating glycogenolysis and gluconeogenesis. Growth hormone, secreted by the pituitary gland, promotes growth and cell reproduction. Follicle-stimulating hormone, another pituitary hormone, plays a crucial role in reproductive processes.

The synthesis of protein hormones involves transcription of DNA into messenger RNA (mRNA), followed by translation of mRNA into a polypeptide chain. This initial polypeptide is often a precursor molecule that undergoes further processing, such as cleavage and folding, to become the mature, active hormone. Protein hormones are generally soluble in water, which facilitates their transport in the blood. Their action is typically rapid but short-lived, as they are broken down by enzymes in the blood or within target cells. The regulation of protein hormone secretion is often controlled by feedback mechanisms, where the levels of the hormone or its downstream effects influence further release.