What are the 3 stages of a signal transduction cascade?
Show
Select your languageSuggested languages for you: Signal Transduction Pathways Organisms continually take in and interpret chemical signals from our environment. Living cells are also constantly exchanging signals with each other. Such signals are crucial for maintaining cell health and function and for initiating biological processes including cell division and cell death. In this article, we will discuss how these signals are transmitted within the cell through signal transduction pathways. We will also go through various examples of signal transduction pathways and some of the diagrams. Signal transduction pathway definitionThe term signal transduction pathway is used to describe the branched molecular network through which signaling molecules are sequentially activated (or deactivated) to carry out a specific cellular function. The signal transduction pathway is set off when a ligand binds to a cell-surface receptor during cell signaling. The three stages of cell signaling and the signal transduction pathwayCell signaling is the process by which a cell responds to messages from its external environment through protein receptors. When a ligand binds to a receptor--a protein that is found inside or on the surface of the target cell--a signal is transmitted, triggering a specific cellular process. A signal transduction pathway has three basic stages:
Signal transduction pathway diagram and stepsThe process of signal transduction is depicted in Figure 1 below. Cell Signaling Steps: Signal ReceptionMolecules that deliver signals are called ligands, while the protein molecules in the cell to which ligands bind are called receptors. When a ligand binds to an internal receptor, the signal does not need to be passed onto other receptors or messengers. On the other hand, when a ligand binds to a cell-surface receptor, the signal is passed on to other molecules in a process called signal transduction. Cell Signaling Steps: Signal TransductionIn a signal transduction pathway, second messengers, enzymes, and activated proteins interact with specific proteins, which are consequently activated in a chain reaction that converts extracellular signals to intracellular signals and ultimately triggers a specific cellular response. Interactions that take place before a certain point are called upstream events, while those that take place after such point are called downstream events. Most of the cell's proteins can influence downstream processes depending on the conditions within the cell. The interaction of two or more signaling pathways can cause a single pathway to branch off toward different endpoints. In addition, the same ligands are frequently involved in the transmission of different signals in different cell types. The difference in response is linked to variations in protein expression among cell types. Another factor is the signal integration of the pathways, which occurs when signals from two or more separate cell-surface receptors combine to trigger the same cell response. Enzymatic cascades can also enhance the impact of extracellular signals. The signal may be initiated when a single ligand binds to a single receptor. However, the activation of an enzyme-linked receptor can activate several copies of a signaling cascade component, amplifying the signal. Because of these complications, a signal transduction pathway can be better described as a branching network than a linear chain. Once the signal is relayed from the external environment of the cell into the inner surface of the plasma membrane, it can take two major routes toward the cell interior depending on the type of receptor that is activated, that is, by second messenger or by protein recruitment. Via second messengerThe first type of receptor transmits a signal from its cytoplasmic region to an adjacent enzyme–called an effector–which produces a second messenger. Second messengers are small intracellular mediators that either activate or deactivate certain proteins. It can either diffuse through the cytosol or stay embedded in the plasma membrane. Second messengers tend to be more prominent in the signaling pathway when a rapid, widespread response is needed. An example of a second messenger is the calcium ion (Ca2+) which, in response to a signal, is released in large quantities and quickly diffused through the cytosol. Calcium ions are responsible for the mediation and coordination of skeletal muscle cell contraction. Like calcium ions, other water-soluble second messengers including cAMP and cGMP diffuse through the cytosol. On the other hand, lipid-soluble messengers such as diacylglycerol (DAG) diffuse through the interior of the plasma membranewhere other key signaling proteins are embedded. Second messengers are named as such because extracellular signaling molecules (such as hormones) are considered the “first messengers”. However the term second messenger may be misleading because there could be over ten messengers in a signaling pathway, and the so-called second messenger can actually be the seventh messenger. Via protein recruitmentThe second type of receptor transmits a signal by changing the shape of its cytoplasmic region to become a recruiting station for signaling proteins. Such proteins interact with each other or with components of the plasma membrane. Whereas second messengers are small and are able to diffuse quickly and broadly, proteins are much larger and less mobile. This means proteins cannot rapidly relay and amplify signals. However, they are able to perform more complex signaling roles. This is because proteins have the capacity to carry out specific interactions with other proteins. They also show binding specificity for ligands and other molecules. Furthermore, their activity can be regulated. Cell Signaling Steps: Intracellular signaling pathwayWhen the signal is transmitted (whether by second messenger or protein recruitment) a protein at the start of an intracellular signaling pathway is activated. Each signaling pathway consists of a number of unique proteins that function sequentially. The majority of signaling proteins are proteins with several domains, which enable them to engage with a variety of players simultaneously or sequentially. As such, while it is often described as a linear chain, in reality, the signal transduction pathway is more often a branching network that allows for the integration, diversification, and modification of responses. Proteins in a signaling pathway tend to function by changing the shape of the next protein in the series, which either activates or inhibits that protein. These shape changes are usually done by protein kinases that add phosphate groups. Protein kinases are like the "on switch" of the signal transduction pathway--when a protein kinase phosphorylates (or adds a phosphate group to) another protein, it triggers a chain reaction and causes proteins to be phosphorylated one after the other. On the other hand, there are also protein phosphatases that dephosphorylate or remove phosphate groups from other proteins which deactivates protein kinases. They basically function as the "off switch" of the signal transduction pathway. To make sure that the cellular response is properly regulated when the signal is no longer present, it is crucial to turn off the signal transduction pathway. Dephosphorylation also frees up protein kinases for future use, allowing the cell to react again to subsequent signals. Cell Signaling Steps: Cellular ResponseSignals transmitted eventually reach target proteins that are responsible for specific cellular processes. The response caused by the target protein can lead to modifications such as:
Termination of signalingSignaling can be terminated by eliminating the extracellular messenger molecule. This is carried out by specific enzymes that destroy corresponding molecules. There are also cases in which active receptors are internalized by the cell and degraded together with its ligand. Signal transduction pathways often interact with one another; when they do, they perform logical operations to trigger a response. For example, a response could require a logical "AND" (meaning all pathways involved must be active in order to trigger the response). A different response could require a logical "OR" in which the activation of either pathway would lead to the response. Signal transduction pathway examples: two important typesNow that we have discussed the basics of the signal transduction pathway, let’s move on to specific examples of signaling transduction pathways. Here we will discuss the JAK-STAT pathway that plays a role in the transcription of the casein gene during milk production. We will also discuss the Hedgehog Pathway which plays an important role in limb and neural differentiation in vertebrates. JAK-STAT pathwayReceptor kinases are a type of membrane-bound receptor protein capable of phosphorylation (adding phospate groups to other proteins). Receptor tyrosine kinases (RTK) are receptor kinases that add phosphate groups to tyrosine residue. RTK are activated when a ligand binds to it, causing the RTK to undergo dimerization (two molecules forming a chemical bond), which then activates its phosphorylation function. The JAK-STAT pathway transmits information from the cell membrane to the nucleus. It plays an important role in the activation of the gene called casein during milk production. STAT–which stands for signal transducers and activators of transcription–proteins make up the transcription factors that are phosphorylated by some receptor tyrosine kinases (RTK) such as the JAK family. An endocrine factor called prolactin binds to the extracellular domains of prolactin receptors, resulting in their dimerization. Each of these receptors have a JAK protein kinase bound to them, and with these JAK proteins now brought together, they can phosphorylate the receptors in various sites. The JAK proteins transform receptors into an RTK. With this, the receptors are now ready to phosphorylate inactive STATs, resulting in their dimerization. The dimers formed are actually the active form of the STAT transcription factors, so they are ready to be moved to the nucleus where they will bind to certain parts of DNA. In the case of milk production, these transcription factors will bind to the upstream promoter elements of casein, which initiates its transcription. The Hedgehog PathwayMembers of the Hedgehog protein family bind to protein receptors known as Patched. Patched proteins bind to a signal transducer, the Smoothened protein, and prevents it from functioning. If Hedgehog does not bind to Patched, the Smoothened protein is not active, and a protein called Cubitus interruptus (Ci) is tethered to the responding cell’s microtubules. The Ci is cleaved while on the microtubules in a way that allows a segment to enter the nucleus and function as a transcriptional repressor. This segment of the Ci protein inhibits transcription by attaching to the enhancers and promoters of specific genes. On the other hand, if Hedgehog binds to Patched, the Patched protein's shape changes so that it no longer inhibits Smootshened. The entire Ci protein can now move to the nucleus and function as a transcriptional activator of the same genes it would have otherwise repressed. In vertebrates, the Hedgehog pathway is crucial for limb and neural differentiation. Mice that were bred to be homozygous for a mutant allele of Sonic Hedgehog showed severe limb deformities in addition to cyclopia, or having a single eye in the middle of the forehead (Fig. 2). Fig. 2: Image depicting two different types of cyclopia. Signal Transduction Pathways - Key takeaways
References
Frequently Asked Questions about Signal Transduction PathwaysSignal transduction pathways enable signals to be relayed from the external environment to the inside of the cell, triggering specific responses such as cell division and cell death. The term signal transduction pathway is used to describe the branched molecular network through which signaling molecules are sequentially activated (or deactivated) to carry out a specific cellular function. Protein phosphatases dephosphorylate or remove phosphate groups from other proteins, which deactivates protein kinases. They basically function as the "off switch" of the signal transduction pathway. The three steps to a signal transduction pathway are reception, transduction, and response. Signal transduction pathways often interact with one another; when they do, they perform logical operations to trigger a response. For example, a response could require a logical "AND" (meaning all pathways involved must be active in order to trigger the response). A different response could require a logical "OR" in which the activation of either pathway would lead to the response. Final Signal Transduction Pathways Quiz
Question This process can be described as a self-destruct mechanism that allows cells to die in a controlled way, preventing potentially harmful molecules from escaping the cell. Show answer
Question During this process, cells that die swell, burst, and empty their contents onto their neighbors. Show answer
Question During this process, a type of white blood cell envelopes and destroys a foreign substance or removes dead cells. This process plays a role in preventing the contents of dying cells from being released. Show answer
Question What enzyme initiates apoptosis by cleaving specific proteins in the nucleus and cytoplasm? Show answer
Question Explain the process of caspase cascade. Show answer Answer Caspases are enzymes that cleave specific proteins in the nucleus and cytoplasm. Caspases can be found in all cells as inactive precursors that are activated via cleavage by other caspases. Active caspases cleave and activate other procaspases, resulting in what is called a caspase cascade. Show question
Question Explain how the mitochondrial process works. Show answer Answer For cell damage to trigger apoptosis, a gene called p53 is required to start the transcription of genes that stimulate the release of cytochrome c--an electron carrier protein--from mitochondria. Once cytochrome c is forced out of mitochondria and into the cytosol, it interacts and activates the adaptor protein Apaf-1. Most forms of apoptosis utilize this mitochondrial pathway of procaspase activation to start, speed up, or intensify the caspase cascade. Show question
Question Immune cells called T-cells are used by the immune system to target and destroy foreign macromolecules and particles by binding to them. How does the development of T-cells trigger apoptosis? Show answer Answer T-cells normally don't target self-proteins (those produced by their own bodies). If they do, it can result in autoimmune disease. For this reason, immature T-cells are screened to see whether they attach to so-called self-proteins so that they can develop the ability to distinguish between self and non-self. Should the T-cell receptor attach to self-proteins, the cell initiates apoptosis to kill any potentially harmful cells. Show question
Question How is the activation of the apoptosis pathway regulated? Show answer Answer The apoptosis pathway is regulated by intracellular and extracellular signals that promote or suppress activation. Show question
Question Explain how apoptosis plays a role in the formation of mouse paws. Show answer Answer During the embryonic development of mice, apoptosis occurs in the cells in between individual fingers. As such, cell death sculpts their paws by causing the individual fingers to break apart from what is initially a spade-like structure. Show question
Question How is apoptosis related to cancer? Show answer Answer When apoptosis does not function properly, cells with potentially dangerous mutations may not be eliminated. Instead, such cells can grow uncontrollably, leading to the formation of a tumor. This happens because some sensors in cancer cells may fail to recognize signals that trigger apoptosis. Show question
Question What is cellular blebbing? Show answer Answer Cellular blebbing is a feature of a cell undergoing apoptosis in which the plasma membrane forms bulges. Show question
Question What gene is required to trigger apoptosis in the mitochondrial pathway? Show answer
Question Explain the role of the IAP family in regulating apoptosis. Show answer Answer The inhibitor of apoptosis (IAP) family prevents cell death in two ways: first, by binding to certain procaspases, they stop them from activating, and second, by binding to caspases, they stop them from being active. The efficacy of the death activation mechanism is considerably increased when mitochondria release cytochrome c to activate Apaf-1 together with a protein that inhibits IAPs. Show question
Question Why is it important to regulate apoptosis? Show answer Answer A cell cannot turn back once it has reached a key stage along the road to its demise because the caspase cascade is not only destructive but also self-amplifying. As
such, it is important that mechanisms that regulate apoptosis are in place. Show question
Question When do cells undergo apoptosis? Show answer
Question Explain why a signal transduction pathway is more of a branching network than a linear chain. Show answer Answer Each signaling pathway consists of a number of unique proteins that function sequentially. The majority of signaling proteins are proteins with several domains, which enables them to engage with a variety of players simultaneously or sequentially. Thus, the signal transduction pathway is more often a branching network that allows for the integration, diversification, and modification of responses. Show question
Question What is a signal transduction pathway? Show answer Answer The term signal transduction pathway is used to describe the branched molecular network through which signaling molecules are sequentially activated (or deactivated) to carry out a specific cellular function. Show question
Question In which of the following stages of the signal transduction pathway does the cell detect the ligand after it binds to a receptor protein on the cell surface? Show answer
Question Briefly describe what happens during the signal transduction stage. Show answer Answer The signaling molecule changes the receptor protein. The signal is relayed by each molecule changing the next molecule in the pathway. Show question
Question Molecules that induce cell signaling are called ____. Show answer
Question What are the two major routes that the signal can take once it is on the interior side of the cell membrane? Show answer Answer Once the signal is relayed from the external environment of the cell into the inner surface of the plasma membrane, it can take two major routes toward the cell interior depending on the type of receptor that is activated, that is, by second messenger or by protein recruitment. Show question
Question How are water soluble second messengers transported within the cell? Show answer Answer Water-soluble second messengers diffuse through the cytosol. Show question
Question How are lipid soluble second messengers transported within the cell? Show answer Answer Lipid-soluble second messengers diffuse through the interior of the plasma membrane where other key signaling proteins are embedded. Show question
Question Compare the response rate between second messenger and a signaling protein. Show answer Answer Second messengers tend to be more prominent in the signaling pathway when a rapid, widespread response is needed. Whereas second messengers are small and are able to diffuse quickly and broadly, proteins are much larger and less mobile. This means proteins cannot rapidly relay and amplify signals. Show question
Question What is the role of protein kinases in the signal transduction pathway? Show answer Answer Protein kinases phosphorylate the succeeding protein. They basically function as an "on switch" of the signal transduction pathway. Show question
Question What is the role of protein phosphatases in the signal transduction pathway? Show answer Answer Protein phosphatases dephosphorylate the succeeding protein. They basically function as an "off switch" of the signal transduction pathway. Show question
Question Why are protein phosphatases important to the signal transduction pathway? Show answer Answer To make sure that the cellular response is properly regulated when the signal is no longer present, it is crucial to turn off the signal transduction pathway. Dephosphorylation also frees up protein kinases for future use, allowing the cell to react again to subsequent signals. Show question
Question Why is the term "second messenger" misleading? Show answer Answer The term second messenger may be misleading because there could be over ten messengers in a signaling pathway, and the so-called second messenger can actually be the seventh messenger. Show question
Question How is signal transduction terminated? Show answer Answer Signaling can be terminated by eliminating the extracellular messenger molecule. This is carried out by specific enzymes that destroy corresponding molecules. There are also cases in which active receptors are internalized by the cell and degraded together with its ligand. Show question
Question What does it mean for receptors to have multiple domains? Show answer Answer Each receptor spans the plasma membrane, meaning each receptor has extracellular, transmembrane, and cytoplasmic domains. Show question
Question What does it mean when we say that ligands and receptors exhibit specificity? Cite an example. Show answer Answer Both ligands and receptors have a high level of specificity: typically, a ligand binds to a specific receptor. For example, growth factor receptors bind growth factors, and dopamine receptors bind dopamine. Show question
Question Where are internal receptors found? Show answer
Question What are the three major categories of cell-surface receptors? Show answer Answer Ion channel-linked receptors Show question
Question Explain how ion channel receptors work. Show answer Answer Ion channel protein receptors work by binding a ligand and then opening a channel across the plasma membrane. When a ligand attaches to the extracellular region of the channel, the proteins undergo shape change to accommodate the entry of ions like sodium, calcium, and hydrogen. Show question
Question Where are enzyme-linked protein receptors found? Show answer
Question How do enzyme-linked receptors interact with enzymes? Show answer Answer Some have an intracellular domain that interacts with enzymes while others have an intracellular domain that is, in itself, an enzyme. Show question
Question What is the difference between internal and cell surface receptors? Show answer Answer Internal receptors are found in the cytoplasm, while cell surface receptors span the plasma membrane. Show question
Question What is a G protein coupled receptor? Show answer Answer G protein coupled receptors work by binding a ligand and then activating a type of membrane protein known as G protein, which then interacts with an ion channel or an enzyme in the plasma membrane. Show question
Question Internal receptors typically interact with what type of molecules? Show answer
Question Explain how a G protein coupled receptor works. Show answer Answer When G protein coupled receptors bind ligands, the GEF domain catalyzes Gα to bind GTP. Gα-GTP dissociates from the Gβγ, some Gα subunits stimulate the activities of subsequent enzymes in the series, while others inhibit them Show question
Question In cell signaling, molecules that deliver signals are called ____. Show answer
Question Receptors are usually what kind of biological molecule? Show answer
Question Where do signals come from? Show answer Answer From cells in other parts of the organism Show question
Question What is autophosphorylation? Show answer Answer Autophosphorylation refers to the the process by which the receptor attaches phosphates onto itself. Show question
Question What happens when ligands bind to the extracellular region of two adjacent tyrosine kinase receptors? Show answer Answer The tyrosine kinase receptors dimerize. Show question
Question Ligands are also known as Show answer
Question When a ligand binds to a receptor, a signal travels across the membrane and into the cytoplasm; the continuation of a signal in this manner is known as __. Show answer
Question Ligands that bind with __ are not required to enter the cell. Show answer
Question What type of ligands diffuse through the plasma membrane and bind to internal receptors? Show answer
Question What type of ligands cannot diffuse through the plasma membrane and have to undergo signal transduction? Show answer Discover the right content for your subjectsNo need to cheat if you have everything you need to succeed! Packed into one app!Study PlanBe perfectly prepared on time with an individual plan. QuizzesTest your knowledge with gamified quizzes. FlashcardsCreate and find flashcards in record time. NotesCreate beautiful notes faster than ever before. Study SetsHave all your study materials in one place. DocumentsUpload unlimited documents and save them online. Study AnalyticsIdentify your study strength and weaknesses. Weekly GoalsSet individual study goals and earn points reaching them. Smart RemindersStop procrastinating with our study reminders. RewardsEarn points, unlock badges and level up while studying. Magic MarkerCreate flashcards in notes completely automatically. Smart FormattingCreate the most beautiful study materials using our templates. Sign up to highlight and take notes. It’s 100% free. What are the 3 stages of signal transduction?The signal transduction process links the signal molecule and the receptor protein to bring about a cellular response. 2. What are the 3 steps of signal transduction? Reception, Transduction, and Response are the three steps in the process of signal transduction.
What are signal transduction cascades?Signal transduction is the process through which cells communicate with the external environment, interpret stimuli and respond to them. This mechanism is controlled by signaling cascades, which play the role of intracellular transmitter, being able to transmit biochemical information between cell membrane and nucleus.
What is the process of signal transduction?Signal transduction is the process in which binding of an extracellular messenger to the cell surface receptor is translated into changes in biochemistry, cell biology, and gene transcription that make it possible for the cell to respond to the information that was received.
|