Signal Amplification: Videos & Practice Problems

Signal amplification occurs when a signaling molecule binds to its receptor, leading to a larger cellular response through the activation of multiple molecules. This process often involves protein kinases, which add phosphate groups to proteins, and protein phosphatases, which remove them. Phosphorylation cascades amplify signals through successive activation of kinases, enhancing the cellular response. Understanding these mechanisms is crucial for grasping cellular communication and response dynamics in biological systems.

Signal Amplification

In this video, we're going to introduce signal amplification. Once a signaling molecule binds to its receptor, that signal can be amplified inside of the cell in order to maximize the effect of the signal and generate a maximum cell response. If we take a look at our image down below over here on the left-hand side, notice that here we're showing you a cell's plasma membrane and down below we're showing you the cytoplasm or the inside of the cell, and up above with the blue background here we're showing you the outside of the cell with the extracellular fluid. Notice that embedded inside of the cell membrane here we have a receptor, and the signal molecule here in red, we know will bind to the receptor and cause a conformational change. In some scenarios, there may be no amplification at all, and if there's no amplification then that just means that not very many molecules are going to be activated. Here we're only showing you one molecule being activated. If there's only one molecule that's activated, typically that's going to lead to a smaller cellular response. With no amplification, there's a smaller cellular response. But in other scenarios, the signal can be amplified. Notice going in this direction we are showing you signal amplification. With signal amplification, many molecules are going to be activated and we have one signaling molecule that leads to the activation of many molecules and if many molecules become activated then the signal is being amplified and ultimately that's typically going to lead to a larger cellular response. Signal amplification allows for a larger cellular response so that response can be maximized.

It turns out that there are two types of enzymes that are commonly used to amplify the signal inside of the cell. These two types of enzymes are called protein kinases and protein phosphatases. Protein kinases are going to add a phosphate group to a substrate, and protein phosphatases, on the other hand, are going to remove a phosphate group from the substrate. Protein kinases and protein phosphatases are essentially doing the opposite of each other. Protein kinases add a phosphate group whereas protein phosphatases remove the phosphate group. Why is it so important to focus on this phosphorylation, the adding of a phosphate group? It's because phosphorylation, again the adding of a phosphate group to a substrate, is going to alter or change a protein's activity. How that protein's activity will be changed is going to depend on the specific protein, the specific scenario. But phosphorylation will typically lead to the alteration of a protein's activity either by turning the protein on or activating the protein or turning the protein off or deactivating the protein.

Down below, notice over here on the right-hand side of our image, notice that we're showing you a dephosphorylated protein over here on the left-hand side. This dephosphorylated protein does not have a phosphate group attached. However, the kinase enzyme is capable of, again, protein kinase is capable of adding a phosphate group to the substrate. The kinase enzyme is capable of taking the dephosphorylated protein and adding a phosphate group to it. Here we have a phosphorylated protein. The phosphate group typically the source is going to be ATP, getting hydrolyzed into ADP so, the phosphate group originates from the ATP. But ultimately kinases are going to add phosphate groups to get phosphorylated proteins and again phosphorylated proteins are going to have altered activity and so you can see the yellow border around the phosphorylated protein to represent that altered activity. This could represent the activation of this protein. If it's being activated, then it can be part of signal amplification. You could imagine that all of these proteins down below, over here in signal amplification, are proteins that are getting phosphorylated so that they become activated and generate a larger cellular response. When the cell wants to remove that cellular response, essentially dampen the cellular response or turn off the cellular response, then it needs a way to get rid of the altered activity. This is when phosphatases can be important because phosphatases are going to remove the phosphate group. You can see the phosphatase down below here is going to take the phosphorylated protein and remove the phosphate group. This ends up regenerating the dephosphorylated protein that we have here. These enzymes, protein kinases and protein phosphatases can be really important in signal amplification. This here concludes our introduction to signal amplification and we'll be able to get some practice applying these concepts as we move forward in our course. I'll see you all in our next video.

Kinases and phosphatases are essential to the cell because they:

• A. Are enzymes that synthesize proteins.
• B. Are enzymes that degrade proteins.
• C. Are enzymes that can turn proteins 'on' and/or 'off' through changes in phosphorylation.
• D. Are enzymes that can turn proteins 'on' and/or 'off' through changes in proton concentrations.
• E. None of the above.

Answer: (C)

What role do phosphatases play in signal transduction pathways?

• A. They phosphorylate proteins involved in signal transduction or cellular response.
• B. They activate protein kinases by phosphorylation.
• C. They amplify the signal molecule.
• D. They regulate the function of proteins involved in signal transduction pathways or cellular response.

Answer: (D)

Phosphorylation Cascades

In this video, we're going to introduce phosphorylation cascades. A phosphorylation cascade is when a series of protein kinases amplify a signal by successive phosphorylation events of different kinases. Ultimately, what we are saying is that kinases, which recall from our last video are just enzymes that add a phosphate group to a substrate, are capable of phosphorylating and activating other kinases. This leads to successive phosphorylation events for the amplification of a signal. Let's take a look at our image below of the phosphorylation signaling cascade. Notice once again, we're showing you a cell's plasma membrane right here, and below we're showing you the inside of the cell; above is, of course, the outside of the cell. Notice embedded in the plasma membrane here we have a signaling molecule that is going to be able to bind to the receptor and cause a conformational change.

In a phosphorylation signaling cascade what will happen is a kinase enzyme is going to become phosphorylated and activated in the presence of the signaling molecule binding to the receptor. This activated and phosphorylated kinase can go on to phosphorylate and activate yet another kinase. This kinase here can go on to phosphorylate and activate yet another kinase. Notice that this kinase is different from this one, which is different from this one and so this kinase here might be the one that is responsible for generating the cellular response. But ultimately, what we are seeing here is a phosphorylation cascade, which is really just defined by successive phosphorylation events, one after another, ultimately amplifying the signal to lead for a cellular response.

Phosphorylation cascades are a regular and normal part of many biosignalling pathways. This here concludes our introduction to phosphorylation cascades and, once again, we'll be able to get some practice as we move forward in our course. So, I'll see you all in our next video.

Phosphorylation cascades are useful signal transduction pathways because they ________.

• A. Allow proteins to be easily activated by adding or removing a phosphate group.
• B. Allow proteins to be easily deactivated by adding or removing a phosphate group.
• C. Amplify the original signal many times.
• D. All of the above.

Answer: (D)

Here’s what students ask on this topic:

What is signal amplification in cellular communication?

Signal amplification in cellular communication occurs when a signaling molecule binds to its receptor, leading to a larger cellular response through the activation of multiple molecules. This process often involves protein kinases, which add phosphate groups to proteins, and protein phosphatases, which remove them. The amplification allows a single signaling molecule to generate a significant cellular response, enhancing the efficiency and effectiveness of cellular communication. Understanding signal amplification is crucial for grasping how cells respond to external stimuli and regulate various biological processes.

How do protein kinases and protein phosphatases contribute to signal amplification?

Protein kinases and protein phosphatases play crucial roles in signal amplification. Protein kinases add phosphate groups to proteins, a process known as phosphorylation, which can activate or deactivate the target proteins. This activation often leads to a cascade of phosphorylation events, amplifying the initial signal. On the other hand, protein phosphatases remove phosphate groups, reversing the phosphorylation and thereby deactivating the proteins. The balance between these two types of enzymes ensures precise control over cellular responses, allowing for both amplification and termination of signals as needed.

What is a phosphorylation cascade and how does it amplify signals?

A phosphorylation cascade is a series of successive phosphorylation events involving multiple protein kinases. When a signaling molecule binds to its receptor, it activates a kinase, which then phosphorylates and activates another kinase. This process continues, with each activated kinase phosphorylating the next one in the sequence. This chain reaction amplifies the initial signal, leading to a robust cellular response. Phosphorylation cascades are a common mechanism in many biosignaling pathways, ensuring that even a small initial signal can produce a significant biological effect.

Why is phosphorylation important in signal transduction?

Phosphorylation is crucial in signal transduction because it regulates protein activity, thereby controlling various cellular processes. When a protein kinase adds a phosphate group to a protein, it can either activate or deactivate the protein, depending on the specific context. This modification alters the protein's function, enabling it to participate in signaling pathways. Phosphorylation allows for rapid and reversible changes in protein activity, making it an efficient way to transmit and amplify signals within the cell. This process is essential for cellular communication, growth, and response to external stimuli.

How do cells terminate amplified signals?

Cells terminate amplified signals primarily through the action of protein phosphatases, which remove phosphate groups from phosphorylated proteins. This dephosphorylation process deactivates the proteins involved in the signaling pathway, effectively dampening or stopping the cellular response. Additionally, cells can internalize and degrade receptors or signaling molecules, further ensuring that the signal is terminated. These mechanisms are crucial for maintaining cellular homeostasis and preventing overactivation, which could lead to detrimental effects such as uncontrolled cell growth or apoptosis.