Signal Transduction Definition
This section focuses on how organisms adapt to changing environmental situations by using signal transduction pathways. Before diving into some of the complicated signal transduction routes that organisms really employ, the phrases “signalling cascade,” “phosphorylation cascade,” and “secondary messengers” will be discussed in this section. Following that, we’ll examine various individual pathways, including the WNT, RTK, and cortisol pathways. Despite the fact that these routes are highly distinct, we’ll look at the aspects they have in common and the cellular reactions they cause. Most significantly, we’ll learn how these signalling pathways may trigger genetic reactions that can alter a cell’s phenotypic or even cause it to die (cell death).
Signal Transduction Overview
Your mother sends you a text message. After school, she’ll pick you and your buddy up and take you to the movies. Although your pal is just a few seats away, their phone is dead. How can you deliver this message to your buddy without disturbing the class? Of course, you leave them a letter!
The communications sent in this situation are extremely similar to those sent by your body’s cells to communicate and coordinate their activity. Like delivering a letter to a buddy, all the signals your body sends must transit via signal transduction pathways. The signal transduction routes used by your body, on the other hand, are much more intricate. Furthermore, signal transduction pathway ideas will undoubtedly be on the AP exam. So stay with us as we go over every detail of signal transduction pathways!
Signal Transduction Pathways
Let’s go over some of the terms and motifs we’ll be seeing before diving into some extremely intricate signal transduction pathways. Watch our video on section 4.2 – Introduction to Signal Transduction if you need a refresher on these words or subjects.
The receipt of a signal is the starting point for all signal transduction pathways. This signal might be a ligand or a physical signal from the environment, such as a light ray, sound wave, or even tactile contact. Regardless of the signal, the receptor protein undergoes a conformational change as a result of its receipt. This may result in a broad range of cytoplasmic responses, a process known as signal transduction.
This conformational shift usually activates another enzyme. This enzyme performs a single action that results in a cellular response in a few cases. This enzyme, on the other hand, is far more likely to activate a variety of second messenger molecules, such as cyclic-AMP. In a phosphorylation cascade, these molecules often convey phosphate groups to other enzymes, resulting in the activation of millions of proteins and enzymes throughout the cell.
The crucial thing to understand here is that when it comes to signal transduction pathways, there is an almost unlimited variety. Though we’ll go through a few particular instances in the slides that follow, the AP test might question you about an entirely different approach. Look for the common parts of the signal transduction pathway provided in these situations, and you should be able to answer the question!
The WNT pathway is one that has been preserved across the animal kingdom. The word “WNT” is a mix of wingless (a gene mutant originally detected in fruit flies) and integrated (a gene mutation first recognised in humans) (a homolog gene found in other animals). This molecule was given the moniker WNT since both of these genes generate the same glycoprotein signal molecule.
Let’s start with the events that occur before a WNT signal molecule is received. Without getting too technical, beta-catenin is a chemical that can trigger gene expression. Beta-catenin is broken down by a set of proteins in the cytoplasm. The beta-catenin destruction complex is a collection of proteins. Beta-catenin is broken down and unable to activate any genes as long as this compound is present.
The WNT signal molecule is introduced. These chemicals interact with a receptor protein called frizzled, which is secreted by numerous cells during embryogenesis and organism development. The Dishevelled (Dvl) protein and the Axin protein attach to the frizzled receptor protein as a result of the conformational shift, breaking apart the beta-catenin destruction complex. Beta-catenin may now reach the nucleus and activate particular genes, since it is no longer eliminated.
However, this is only one of the numerous routes that a WNT signal molecule might activate. A WNT signal molecule, for example, may control how much glucose is taken in response to an insulin signal. The WNT pathway is hypothesised to have a role in the development of insulin resistance in people with type 2 diabetes.
Consider another well-known system, the RTK pathway, which is named for the receptor molecules that drive it. Despite the fact that there are hundreds of distinct types of receptor-tyrosine-kinase proteins that react to various growth factors and hormones, they all work in the same way to initiate a signal transduction pathway.
Individual RTK proteins are usually found on the cell membrane. When a growth factor or other signal molecule attaches to the extracellular receptor domain of an RTK protein, two RTK proteins join together in a process called dimerization. The two RTK proteins come together during this step. The protein’s tyrosine kinase domain accomplishes exactly what its name suggests: it phosphorylates tyrosine amino acids in each protein’s tail region. In a phosphorylation signalling cascade, these phosphorylated tyrosines may then send the phosphate groups to a vast variety of additional proteins.
The JAK/STAT pathway, for example, works as follows. The RTK receptor proteins are linked to the JAK proteins. When a signal is received and dimerization occurs, the JAK proteins are the first to be phosphorylated. The phosphate groups are passed on by JAK proteins to STAT proteins, which subsequently form complexes that stimulate the transcription of numerous genes in the nucleus.
While the JAK/STAT pathway is only one of several that RKT proteins and their signal molecules may activate, it does demonstrate the complicated patterns of phosphorylation cascades that can occur.
Cortisol Signalling Pathway
You’ll find something intriguing if you look at the cortisol signalling pathway. Cortisol receptors are found in the cytoplasm rather than on the cell membrane. Cortisol, on the other hand, is a lipid-based steroid hormone that easily passes through cell membranes. Other lipid-based hormones and their receptor proteins are in the same boat.
The complete protein and cortisol combination reaches the nucleus when cortisol binds to its receptor protein and begins the process of transcription of particular genes. As a result, the cortisol signalling route is one of the most basic we’ve discussed. The cortisol pathway is fascinating because it induces such a wide range of reactions in various cell types.
Consider the following: Cortisol, sometimes known as the “stress hormone,” is a hormone that is produced in a stressful situation. When the adrenal glands receive hormone signals from the brain, they make this one hormone. During stressful situations, substantial amounts of cortisol are released into the circulation, causing a variety of consequences in various tissues.
When cortisol binds to cells in the liver, for example, it triggers gluconeogenesis, a process that produces new glucose molecules and releases them into the circulation. This provides the energy that a stressed creature needs to continue fighting. It prevents muscles from absorbing amino acids, allowing them to be used for energy as well. If cortisol levels stay high for an extended length of time, muscle cells may be programmed to die-a process known as apoptosis! This provides energy to the organism by breaking down proteins, but it also weakens it.
Cortisol may also impair your immune system, allowing you to avoid dealing with inflammation when under stress. However, if you have high levels of cortisol in your system, you are more likely to get ill. Cortisol, like many other hormones, is fantastic when it’s in the appropriate quantity but deadly when it’s too much!