Introduction to Biosignaling - Online Tutor, Practice Problems & Exam Prep

Biosignaling involves the ability of living cells to produce, receive, and respond to external signals, facilitating cellular communication. Key components include ligands, which bind to specific receptors, initiating signal transduction—a process converting extracellular signals into intracellular responses. Common features of biosignaling systems include specificity, amplification, modularity, adaptation, and integration. Kinases, particularly serine-threonine and tyrosine kinases, play crucial roles by phosphorylating target proteins, altering their activity. Understanding these pathways is essential for grasping cellular responses and interactions in biological systems.

Introduction to Biosignaling

In this video, we're going to begin our introduction to bio signaling. And so bio signaling, as you can see, has the root word "bio", which of course we know means life. And so bio signaling is really just the signaling of life. It is defined as the ability for all living cells to produce, receive, and respond to external signals and conditions. Bio signaling really allows cells to respond to stimuli and also allows for effective cellular communication between cells.

If we take a look at our image down below right here, you can see we have a little representation to help you guys better understand bio signaling. Over here, what we have is our cell, which you'll notice, is our signaling cell. Our signaling cell really acts almost like an archer, which has a bow and arrow pointed at another cell. The signaling cell is going to produce some kind of signal or ligand such as this molecule that we see right here. This ligand has the ability to diffuse to different areas. This ligand will make its way over to another cell over here, and this cell is going to have the appropriate receptor in its plasma membrane that will bind the ligand. This cell over here is referred to as the target cell because it has the specific receptor for this specific ligand that was released. You can see we have the little target symbol over here to remind you guys of that.

You can see that the ligand binding to the receptor is going to cause a cascade of intracellular events within the target cell that ultimately leads to a cellular response. This is a form of cell communication because we have one cell over here producing a signal and causing a cellular response within a different target cell. We'll be able to see examples of bio signaling as we move forward in our course.

Over here on the right hand side, what we have is just a small list of some examples of different types of bio signaling molecules. These ligands, these bio signaling molecules here, could be antigens, growth factors, hormones, light, mechanical touch, neurotransmitters, and much more. Again, this is just a small list. Moving forward in our course, we'll be able to see different examples of different types of bio signaling molecules. But for now, this here concludes our introduction to bio signaling. In our next lesson video, we'll talk about signal transduction. So, I'll see you guys there.

Introduction to Biosignaling

In this video, we're going to introduce signal transduction. Now signal transduction is really just a cell process that, as its name implies, transduces or converts extracellular signals or extracellular information into an intracellular chemical change or an intracellular response. And so really signal transduction requires a minimum of at least 2 key components which we'll talk about down below. Now normally, signal transduction includes more than just these 2 key components, but here we're just introducing the bare minimum key components that would be required for signal transduction. And so this first key component is going to be a ligand. And of course, we've covered in our previous lesson videos what a ligand is. So we already know that a ligand is a small molecule that specifically binds and forms a complex with another biomolecule. And in this context of signal transduction and bio signaling, this biomolecule is going to be a receptor protein. And really that leads us to our second key component, which is going to be the receptor. And again, this receptor is typically going to be an integral membrane protein that's embedded within the cell's plasma membrane. And this receptor protein is going to undergo a change, a conformational change upon ligand binding. And so this ligand is going to bind to the receptor and then the receptor is going to undergo a conformational change. And at that point, after the conformational change, that opens up a lot of different possibilities for the continuation of signal transduction.

If you take a look at our image down below over here on the left-hand side, you can get a better idea of signal transduction. And so notice that at the top here, this blue molecule represents our ligand or our primary messenger since this is really the first molecule that's going to elicit the signal transduction pathway. And so this ligand of course is going to bind very very specifically and form a complex with this receptor that we have down below. And again, the receptor is typically going to be an integral membrane protein that is embedded within the cell's plasma membrane as you see here. And of course, once the ligand binds the receptor is going to undergo a conformational change. And again, once the receptor undergoes a conformational change, that opens up a lot of different subsequent possibilities. Here, what we're showing is that the conformational change leads to the activation of an effector enzyme and then this effector enzyme produces a secondary messenger that diffuses into the cytoplasm and ultimately leads to this cell response, the generation of a cell response. And so really all of the events that we see taking place right here would be an example of signal transduction because, again, signal transduction is when the cell transduces or converts extracellular signals like the ligand or the primary messenger and converts this extracellular signal into a chemical change or a chemical response, ultimately a cell response. And this is the process that would lead to that cell response, and so that is what's referred to as signal transduction.

Moving forward in our course, we'll be able to talk about lots of different examples and specific examples of signal transduction. Now what's also really, really important to note here is that the receptor ligand interactions or the interactions between this ligand and this receptor right here, are actually protein ligand interactions. And you might recall that way back in our previous lesson videos, we actually covered protein ligand interactions in a lot of detail. And so because receptor ligand interactions are protein ligand interactions, everything that we talked about in protein ligand interactions also applies to receptor ligand interactions. And so if you don't remember anything about protein ligand interactions, please be sure to go check out those older lesson videos because, again, all of the information in the protein ligand interactions videos also applies here to receptor ligand interactions.

If we take a look at our image over here on the right hand side, these images should look familiar to you guys, somewhat familiar to you guys, from our protein ligand interaction videos. And so notice here what we have is our free receptor, symbolized by r, and over here what we have is our free ligand symbolized by l. And of course, the receptor and the ligand can bind to each other to form a receptor ligand complex, r l. And notice that this is a reversible reaction, which means that it can proceed in the forward direction, but it can also proceed in the reverse direction. And it's possible for the receptor and the ligand to dissociate from each other. And so notice down below, because, again, this is a reversible reaction, that means that the dissociation equilibrium constant k_d also applies here. And so recall that the k_d is just the equilibrium constant for the dissociation of the receptor ligand complex. And because it's the equilibrium constant, we know that it's going to be the concentration of the product of the products over the concentration of the reactants. And so for the reverse reaction here, the products are going to be the free receptor and the free ligand. And of course, for this reverse reaction, the reactant is going to be the receptor ligand complex, and so that's why it's in this format. And again, these are all older concepts that we talked about in our previous lesson video. So if this looks completely foreign to you guys, please make sure to go back and check out those older lesson videos. And so this here concludes our introduction to signal transduction and moving forward we'll be able to get a little bit of practice applying these concepts and I'll see you guys in our next video.

A sample of cells has a total receptor concentration of 10 mM and a free ligand concentration of 15 mM. If 25% of the receptors are occupied with ligand under these conditions, calculate the receptor-ligand dissociation constant (K_d).

• A. 7 mM.
• B. 38 mM.
• C. 12 mM.
• D. 45 mM.

Which hormone from the plot below shows the highest binding affinity for the receptor?

• A. Hormone X.
• B. Hormone Y.
• C. Hormone Z.

Introduction to Biosignaling

So moving forward in our course, we're going to talk about a lot of different biosignalling transduction systems. But before we move forward in our course and talk about the details of all of those biosignalling transduction systems, it's important to take a step back and look at the common features that all of these biosignalling transduction systems share. And so here in this video, we're going to talk about the 5 features that pretty much all biosignalling transduction systems share. And so you can see that we have each of these 5 features numbered down below in our table. And over here on the right, what we have is images to portray each of those features. Now the very first feature here is specificity, which is really exactly what it sounds like, and it's referring to this idea that receptor ligand interactions are super, super specific. And so what this means is that receptors will not just respond to any ligand, they will only bind and respond to very specific ligands. And so over here in this image, you can see that we have our receptor, and notice that the circular green ligand here is perfectly shaped and fit for this receptor. And notice that this red square-shaped ligand over here is not fit for this receptor. And so the receptor will not respond to this ligand, however, it will respond to the circular green ligand. And so that's exactly what this idea is referring to, that the receptor-ligand interactions are super specific to each other.

And so moving on to the second feature here, what we have is amplification, which is also exactly what it sounds like, that signals will get amplified. And so this is the idea that even if you have just one single receptor-ligand interaction, ultimately that one single receptor-ligand interaction will lead to many downstream interactions. And so over here on the right hand side, you can see the portrayal of this particular feature of amplification. And so notice here we have our ligand binding to the receptor and that represents our single receptor-ligand interaction. But, ultimately, we know that it's going to lead to many, many downstream interactions, and so you can see that, ultimately, it could lead to 1 molecule getting activated, which would activate 2 molecules and then each of those would activate 2 more. And ultimately, what happens is you get many, many molecules that are affected through the interaction of just one single receptor-ligand interaction. And so that shows the amplification of the single signal.

Now our third feature here that pretty much all biosignalling transduction systems share is modularity. And this is the idea that a system's components are modular and they can be modulated or they can be modified in order to elicit many different responses, and they can be modified for many different uses. And so over here on the right, we can see a portrayal of that idea. And so notice that we have our single receptor-ligand interaction. But the biosignalling transduction system could entail modifications, and so there's one pathway that could lead to an active enzyme, which would lead to cell response number 1. But then of course the same exact receptor-ligand interaction could be modified so that its signal transduction leads to the inactivation of an enzyme, perhaps through phosphorylation like as we're showing here. And that inactivation of the enzyme could lead to cell response number 2. And so ultimately, what we're seeing here is that a biosignalling transduction system can be modulated for many uses to elicit different cell responses.

So now moving on to feature number 4, it is adaptation. And, of course, this is exactly what it sounds like, that a biosignalling transduction system can actually adapt to several different scenarios, and it can do this through positive and negative feedback regulation. And so if we take a look at this image over here, notice we're showing you again our ligand-receptor interaction right here. And notice that this signal transduction system leads to the activation of all these different enzymes, which ultimately leads to product f over here. But if product f is getting overproduced, product f can actually come back and inhibit this receptor-ligand interaction, so that it can help decrease the production of f. And so this is a way for the system to adapt to the scenario where f is overproduced. And this is showing an example of negative feedback regulation since it's inhibiting this receptor-ligand interaction, but this could also occur through positive feedback regulation as well.

And so our fifth and final feature that all biosignalling transduction systems share is integration. And, of course, this is the idea that a system can actually integrate with other systems. And so, it can therefore produce a unified and scaled cellular response, especially if these two systems are producing opposite cell response effects. And so notice over here in this image, we have 2 different biosignalling transduction systems. We have this purple and green receptor-ligand interaction, and then we have this blue and red receptor-ligand interaction. And so notice that these 2 biosignalling systems can be integrated in order to create a unified and scaled, appropriately scaled cell response. And we'll be able to see ideas of integration as we move forward in our course as well.

And so really this here concludes our lesson on the 5 features of biosignalling transduction systems, and we'll be able to see examples of all of these five features as we move forward in our course and talk about specific biosignalling transduction systems. And so that concludes this video and I'll see you guys in our next one.

Which of the following statements regarding signal transduction pathways in cells is FALSE?

• A. A ligand, such as a hormone, binds to a specific cell surface receptor on a target cell.
• B. Signal transduction cascades, often involving protein kinases, amplify a signal intracellularly.
• C. A receptor changes conformation upon ligand binding, transmitting a signal across the cell membrane.
• D. Signal transduction cascades directly transmit a single stimulus to one, single target, identically in all cells.
• E. Phosphatases remove phosphoryl groups from polypeptides, regulating a cell's response.

Introduction to Biosignaling

So as we move forward in our course and talk about different types of biosignaling pathways, what we're going to see is that these enzymes called kinases actually play a large role in biosignaling. These kinase enzymes help to create the cell response that's associated with bio signaling. Now moving forward in our course, we're going to see different types of kinases, and that's the main focus of this video. Recall that way back in some of our previous lesson videos when we talked about different types of enzymes, we already covered kinases. We already have an idea that kinases are just enzymes that phosphorylate or add phosphate groups to their substrates, and they do this by utilizing or hydrolyzing ATP.

When kinases phosphorylate their substrates within cells, it's actually a really big deal. The reason that it's such a big deal is because the phosphorylation of target proteins leads to altered activity of the target protein. By alteration of activity, what we really mean is that it could lead to either the activation of that target protein or it could lead to the inhibition of that target protein. However, there's no solid way to predict whether phosphorylation is going to activate or inhibit a particular target protein. It's going to be different on a case-by-case basis, and you should never assume that phosphorylation will lead to activation or inhibition. Instead, what you should assume is that phosphorylation will lead to altered activity of that target.

Again, as we move forward in our course, we're going to see different types of kinases. Two of the most common classes of kinases are the serine-threonine kinases and the tyrosine kinases. The serine-threonine kinases, as their name implies, are kinases that phosphorylate either serine and/or threonine residues on their target proteins. It turns out that serine-threonine kinases make up about 25% or one fourth of all kinases, which is a pretty large percentage if one out of four of all kinases are going to be serine-threonine kinases. Serine-threonine kinases are definitely a class of kinase that you should be familiar with moving forward in our course.

The second common class of kinase are the tyrosine kinases. As their name implies, these are kinases that phosphorylate the amino acid residue tyrosine on their targets. Notice that down below, on the left-hand side, we're showing you the serine threonine kinases, and then over here in the image on the right-hand side, we're showing you the tyrosine kinases. Focusing on the serine-threonine kinases, they will either phosphorylate the amino acid residue serine or threonine. These serine-threonine kinases will utilize ATP and hydrolyze ATP to ADP, and in the process, they take that phosphate group and add it onto their targets at these particular residues creating phosphoserine or phosphothreonine. This phosphorylation of these residues leads to altered activity of that target.

Over here on the right, we're showing you the tyrosine kinase. Tyrosine kinases are going to phosphorylate the amino acid residue tyrosine on their target proteins. In the process, they utilize and hydrolyze ATP to ADP while adding a phosphate group to the tyrosine residue. We can add in our negative charges and this here represents the phosphate group, and this is phosphotyrosine. The phosphorylation of this residue could be a big deal because it alters the activity of that target protein. As we move forward in our course, we'll see serine-threonine kinases and tyrosine kinases. Keep these in mind as we move forward in our course. But for now, this concludes our introduction to the types of kinases, and I'll see you guys in our next video.

Why is the activation of a protein kinase an important step in signal transduction?

• A. Kinases bind to receptors and prevent binding of the ligand.
• B. Kinases prevent signal amplification by degrading specific enzymes in the cell.
• C. Kinases can activate or inactivate proteins by phosphorylation.
• D. Kinases are secreted by a cell as a signaling molecule.

Introduction to Biosignaling

So again, as we move forward in our course beyond this point, we're going to talk about a lot of different types of biosignalling pathways. And what we'll realize is that these different biosignalling pathways utilize different types of biosignalling receptors. And so really that's the main focus of this video, to introduce these different types of biosignalling receptors. So really there are 2 major types of integral membrane protein receptors that you guys should know that are involved in most signal transduction pathways. So the first major type is the G protein-coupled receptors or the GPCR for short. And so here in this blank, we can fill in GPCR. And the second major types are the receptor Tyrosine Kinases or the RTK for short. So over here we can fill in RTK. Now again, as we move forward in our course, we'll see specific examples of G coupled protein receptors receptor Tyrosine Kinases or RTKs. But for now, we're just introducing these receptors. Now what's important to note is that the GPCRs and the RTKs will actually transduce extracellular signals via fundamentally different mechanisms. And again, that's why we're going to cover each of these types of receptors separately in their own individual videos as we move forward in our course. And so down below in our example notice that we're going to introduce the GPCR and the RTK, and so the image over here on the left is showing the GPCR signaling, and so notice that we have the ligand up above and the GPCR is this protein that we see embedded within the membrane, and later in our course we'll see that this GPCR associates with what's known as a G protein. But again, don't worry too much about this now because we're going to talk about this in more detail later in our course. For now, what you could do is just get an idea of how we're going to portray the GPCR, moving forward in our course. And then over here on the right, what we're showing you is the RTK biosignalling receptor. And so again, the ligands are up above and you can see that the receptor here for the RTKs actually has these 2 different, monomer units. And again, don't focus too much on the details here because we're going to revisit RTKs later in our course. Really, the major takeaway is that we're going to be talking about 2 major types of biosignalling receptors, the GPCRs and the RTKs, and this is kind of what they're going to look like moving forward, and this is what the RTKs are going to look like moving forward. And so this here concludes our introduction to the 2 types of biosignalling receptors, GPCRs and RTKs, and I'll see you guys in our next video.

Introduction to Biosignaling

In this video, we're going to introduce our map of the lesson on biosignaling pathways, which is down below right here. Now, as we move forward in our course and talk about different biosignaling pathways, what we'll see is that these biosignaling pathways can really be grouped into 3 different categories that we have color-coded here by their backgrounds. And so we have this green background over here on the far left, and these are biosignaling pathways that utilize G protein-coupled receptors or GPCRs. Then notice over here in the middle with the pink background, we have biosignaling pathways that utilize Receptor Tyrosine Kinases or RTKs. And then over here on the far right, what we have is biosignaling pathways that utilize lipid hormones. And so again, as we move forward in our course, we'll talk about biosignaling pathways that are in each of these groups.

Now, just like the maps that we saw in some of our previous lesson videos, this map was specifically constructed so that it is a reflection of our lesson on biosignaling. And so what that means is that we're going to explore this map in a similar way that we explored the maps in our previous lesson videos. And so we're going to explore the left branches first, and we're going to continue to explore left branches until we've explored all of the left branches, and then we'll start to zoom out and explore the right branches. And then once we've explored all the branches in that pathway, we'll go ahead and move on to our new branch, again exploring to the left first, in the same fashion that we did in our previous lesson videos.

Now, one thing to note that's different about this map is that we've intentionally left these interactive blanks here throughout the map. And so we've done that because when we move through the course, we're going to revisit this map and fill in these interactive blanks. And so you can expect to revisit this map of the lesson on biosignaling pathways several times as we move forward in our course. And so again, we're going to start by exploring the leftmost branches. So, in our next lesson video, you should expect to cover G protein-coupled receptors or GPCRs. And that's exactly what we're going to do. So I'll see you guys in our next video.

Here’s what students ask on this topic:

What is biosignaling and why is it important for cellular communication?

Biosignaling refers to the process by which living cells produce, receive, and respond to external signals. This process is crucial for cellular communication, allowing cells to respond to various stimuli and coordinate their activities. Biosignaling involves ligands (signaling molecules) binding to specific receptors on target cells, initiating a cascade of intracellular events that lead to a cellular response. This mechanism ensures that cells can adapt to their environment, regulate their functions, and maintain homeostasis. Understanding biosignaling is essential for comprehending how cells interact and respond to changes, which is fundamental in fields like medicine and biotechnology.

What are the key components of signal transduction in biosignaling?

Signal transduction in biosignaling involves converting extracellular signals into intracellular responses. The key components include:

• Ligand: A signaling molecule that binds specifically to a receptor.
• Receptor: Typically an integral membrane protein that undergoes a conformational change upon ligand binding.
• Effector Enzyme: Activated by the receptor, it produces secondary messengers.
• Secondary Messengers: Molecules that propagate the signal within the cell, leading to a cellular response.

These components work together to ensure that external signals are accurately transmitted and elicit appropriate cellular responses.

What are the common features shared by all biosignaling transduction systems?

All biosignaling transduction systems share five common features:

• Specificity: Receptors are highly specific to their ligands.
• Amplification: A single ligand-receptor interaction can trigger multiple downstream effects.
• Modularity: Components can be modified for different responses.
• Adaptation: Systems can adjust to different scenarios via feedback regulation.
• Integration: Different signaling pathways can integrate to produce a unified response.

These features ensure that biosignaling pathways are efficient, adaptable, and capable of precise regulation.

What roles do kinases play in biosignaling pathways?

Kinases are enzymes that play crucial roles in biosignaling pathways by phosphorylating target proteins, which alters their activity. This phosphorylation can either activate or inhibit the target protein, depending on the specific context. Two common classes of kinases are:

• Serine-Threonine Kinases: Phosphorylate serine or threonine residues on target proteins.
• Tyrosine Kinases: Phosphorylate tyrosine residues on target proteins.

Phosphorylation by kinases is a key regulatory mechanism in signal transduction, affecting various cellular processes such as growth, differentiation, and metabolism.

What are the two major types of biosignaling receptors involved in signal transduction pathways?

The two major types of biosignaling receptors involved in signal transduction pathways are:

• G Protein-Coupled Receptors (GPCRs): These receptors interact with G proteins to transduce signals.
• Receptor Tyrosine Kinases (RTKs): These receptors have intrinsic kinase activity and phosphorylate tyrosine residues on target proteins.

Both types of receptors transduce extracellular signals via different mechanisms, leading to various cellular responses. Understanding these receptors is essential for studying how cells communicate and respond to their environment.