why the hormones that work by binding to cell membrane acts through secondary messengers
Hormones that work by binding to cell membrane receptors act through secondary messengers because they are unable to enter the cell directly. These hormones, known as polar or water-soluble hormones, are composed of large molecules that are unable to diffuse through the hydrophobic lipid bilayer of the cell membrane.
To exert their effects, these hormones bind to specific receptors on the cell membrane. Upon hormone binding, the receptor undergoes a conformational change, leading to the activation of a secondary messenger system within the cell. This secondary messenger system relays the signal from the hormone receptor to the appropriate target molecules inside the cell.
The most common secondary messengers involved in cell signaling are cyclic adenosine monophosphate (cAMP), inositol trisphosphate (IP3), and diacylglycerol (DAG). These molecules are small and/or lipid-soluble, allowing them to diffuse through the cell's interior and activate or inhibit various intracellular signaling pathways.
By utilizing secondary messengers, hormone signaling cascades can amplify the initial signal and regulate a wide range of cellular processes. These include gene transcription, enzyme activation, ion channel opening/closing, and cellular metabolism. Moreover, the use of secondary messengers allows for the fine-tuning of cellular responses and the integration of multiple signals to coordinate complex physiological processes.
Hormones that work by binding to cell membranes act through secondary messengers because they are unable to freely enter the target cell due to their hydrophilic (water-loving) nature. These hormones primarily include peptide hormones and catecholamines (such as adrenaline and noradrenaline).
When these hormones bind to specific receptors on the cell membrane, they initiate a cascade of cellular events known as signal transduction pathways. This is where secondary messengers come into play.
Secondary messengers are small molecules or ions that act as intermediaries in the signaling pathways activated by hormone binding. They relay the hormonal signal from the cell surface to the interior of the cell, amplifying and modulating the signal along the way.
Common secondary messengers include cyclic adenosine monophosphate (cAMP), inositol trisphosphate (IP3), and calcium ions (Ca2+).
Upon hormone binding, the receptor undergoes a conformational change, which activates a G protein (guanine nucleotide-binding protein) attached to the receptor on the inside of the membrane. The activated G protein then activates an enzyme called adenylate cyclase, which converts adenosine triphosphate (ATP) to cAMP.
cAMP, in turn, activates protein kinase A (PKA), which phosphorylates specific target proteins within the cell, leading to various cellular responses. This signaling mechanism allows for amplification, as one hormone molecule binding to a receptor can activate multiple secondary messengers, which can then activate multiple protein kinase A enzymes.
Overall, the use of secondary messengers in hormone signaling allows for rapid and efficient signal transduction across the cell membrane, facilitating the transmission of information and promoting diverse physiological responses within the target cell.
Hormones that work by binding to cell membranes typically act through secondary messengers because they cannot directly enter the cell due to their hydrophilic (water-loving) nature. These hormones, known as hydrophilic hormones or peptide hormones, include insulin, glucagon, and many others.
To understand how these hormones act, let's break it down step by step:
1. Hormone binding: When a hydrophilic hormone, such as insulin, reaches its target cell, it binds to specific receptor proteins located on the cell membrane.
2. Activation of G-proteins: Once the hormone binds to its receptor, it triggers the activation of a specialized protein called a G-protein, which is attached to the inner side of the cell membrane.
3. Activation of adenylyl cyclase: The activated G-protein then stimulates an enzyme called adenylyl cyclase, which is also present on the inner side of the cell membrane.
4. Production of secondary messengers: Adenylyl cyclase generates cyclic adenosine monophosphate (cAMP) as a secondary messenger. cAMP serves as a crucial signaling molecule that transmits the hormone's message from the cell membrane to various intracellular targets.
5. Activation of protein kinases: cAMP activates protein kinases, which are enzymes responsible for adding phosphate groups to other proteins. These phosphorylated proteins then trigger a cascade of events within the cell.
6. Cellular response: The phosphorylated proteins initiate a series of intracellular reactions that eventually lead to a specific cellular response, such as changes in gene expression, enzyme activity, or ion channel opening, depending on the hormone and target cell type.
So, the hormones that bind to cell membranes act through secondary messengers, such as cAMP, to relay their message into the cell and initiate specific cellular responses. This mechanism allows for amplification of the hormone signal and enables the coordinated regulation of various cellular processes in response to hormonal stimuli.