Motor Proteins - Online Tutor, Practice Problems & Exam Prep

Motor proteins, such as myosin, kinesin, and dynein, utilize the cytoskeleton for movement, powered by ATP. Myosin moves along actin microfilaments, facilitating muscle contractions and transporting cargo. Kinesin transports vesicles toward the positively charged end of microtubules, while dynein moves in the opposite direction, toward the negatively charged end. Understanding these interactions is crucial for grasping cellular movement and transport mechanisms, highlighting the importance of the cytoskeleton in maintaining cellular function and structure.

Motor Proteins

In this video, we're going to begin our discussion on motor proteins. Motor proteins actually create movement using the cytoskeleton. Before we talk any more details about motor proteins, let's first do a quick recap on the cytoskeleton. Recall from way back in our previous lesson videos that the cytoskeleton consists of microfilaments, intermediate filaments, and microtubules. Below in the depiction of our cell here, you can see we've got the cell membrane. Inside our cell, you can see a lot of different structures, including the different structures of the cytoskeleton. You can see that we have microfilaments, we've got intermediate filaments, and we've got microtubules all within our cell. These cytoskeleton components function to provide cell shape. Here, you can see the distribution of the cytoskeleton in our cells. They provide cell shape. They also help to provide movement of cells. They can also provide transportation of molecules within the cell and can be involved in signaling as well because they can respond to external molecules and that can cause the cytoskeleton to shift inside. This is going to be important to remember the different components of cytoskeletons because different motor proteins will interact with different parts of the cytoskeleton. In our next lesson video, we'll be able to talk more about these motor proteins. I'll see you guys in that video.

Motor Proteins

So now that we've briefly covered the cytoskeleton, we can focus more on motor proteins. Motor proteins are proteins themselves that use energy in the form of ATP, and they use the cytoskeleton as tracks in order to create molecular movement. This molecular movement is responsible for muscle contractions which we'll talk a lot more about later in our course. They're also responsible for movements of individual cells through their environments and they're responsible for intracellular movement as well in terms of transportation of molecules and organelles within the cell. We'll also be able to talk more about this idea as we move forward in our course. Now, there are actually many different types of motor proteins, so we can't cover them all in this course, but some of the more well-characterized motor proteins that your professors might expect you guys to know are myosin, kinesin, and dynein. We've got the structures of these three motor proteins down below. The first one right here is myosin. The next one that we have here is kinesin. And then last but not least, over here on the far right, we have dynein. As we move forward in our course, we'll be able to talk more about each of these three different motor proteins. But I can tell you now that these three motor proteins are going to interact with different components of the cytoskeleton. Myosin is going to interact with microfilaments whereas kinesin and dynein are going to interact with microtubules. Again, we'll be able to talk more about that as we move forward in our course, starting with myosin. So I'll see you guys in our next video.

Motor Proteins

In this video, we're going to talk more about the motor protein myosin. So, myosin is specifically a motor protein that is going to move along thin actin microfilaments. And so myosin is responsible for transporting molecular cargo such as vesicles that might contain proteins or lipids or other macromolecules, and it's responsible for transporting this molecular cargo along the thin actin microfilaments. But the myosin protein, as we'll see later in our course, is also involved in muscle contractions. And so later when we talk more details about muscle contractions, we are going to see this myosin motor protein again. And so notice down below on the left-hand side, we're showing you a single myosin molecule and notice that at the tips here, we have these pinkish structures that are referred to as the myosin heads. And then, this, rest of the chain right here is referred to as the myosin tails. And so what's important to note is that many myosin molecules can actually aggregate together to form thick filaments. And so, what you can see here, this arrow represents protein aggregation where we can take multiple myosin molecules and organize them in this fashion right here to create the thick myosin filament. And so, this entire structure that we see here is referred to as thick myosin filament. And again, we are going to see thick myosin filament again later in our course when we talk about muscle contraction. So be sure to remember, the structure of the myosin motor protein. And so this concludes our introduction to the myosin motor protein and in our next lesson video, we'll be able to talk about kinesin. So I'll see you guys in that video.

Motor Proteins

In this video, we're going to talk about the motor protein kinesin, which interacts with microtubules. And so, it's important to know that microtubule subunits will actually assemble to make a polarized molecule with oppositely charged ends. If we take a look down below at our image, this microtubule right here that we see is a polarized molecule with oppositely charged ends. You can see that on the left-hand side, it has the negatively charged end, and on the right-hand side, it has a positively charged end. Kinesin is a motor protein that specifically moves towards the positively charged end of the microtubule. It can transport and pull molecular cargos such as vesicles or chromosomes along the microtubules, pulling the molecular cargo towards the positively charged end of the microtubule. As we'll see down below in our image, the kinesin heads are going to bind to the microtubule, motor protein. Notice that, the motor protein and the kinesin heads, which are down below here, are attached directly to the microtubule as we mentioned above, with the light chains, which are right here, attached to the molecular cargo, which is the vesicle up here. The kinesin motor protein is capable of pulling the vesicle or the molecular cargo towards the positively charged end of the microtubule. You can see that this arrow represents the direction of movement towards the positively charged end. Also, notice that the motor protein utilizes energy in the form of ATP to transport the molecular cargo.

If you haven't YouTubed kinesin, then it's something that you definitely want to do because it's remarkable to see these depictions of the kinesin heads walking along the microtubule. So, if you've never googled kinesin or YouTube kinesin, make sure to YouTube kinesin so that you can get a better understanding of its movement along the microtubules. One thing that helps me memorize the direction of Kinesin's movement, which is towards the positively charged end of the microtubule, is to note that 'kin' found in the word kinesin, is a word that means family. Up above, you can see that there's this nice-looking family here that is all happy, and that is something very positive. 'Kin,' which means family, is very positive, reminding me that kinesin moves towards the positively charged end of the microtubule. This concludes our lesson on Kinesin's movement towards the positively charged end of the microtubule. In our next lesson video, we'll be able to talk about dynein and its interactions with the microtubule. I'll see you guys in that video.

Motor Proteins

In this video, we're going to talk about the motor protein dynein, which also interacts with the microtubule. Dynein is essentially the opposite of the motor protein kinesin. Dynein is a motor protein that specifically moves towards the negatively charged end of the microtubule. This allows it to transport and pull molecular cargo, such as vesicles along the microtubules, but this time towards the negatively charged end, which is the opposite direction of kinesin. Dynein is responsible for the motion of eukaryotic flagella and cilia.

Below in our example, you can see that we've got our microtubule, which is a polarized molecule with a negatively charged end and a positively charged end. Notice that our motor protein dynein is moving in the opposite direction, towards the negatively charged end. It also utilizes energy in the form of ATP to move the vessel, the molecular cargo, again towards the negatively charged end.

One thing that helps me remember that dynein moves towards the negatively charged end of the microtubule is that dynein kinda sounds like dying. Dying, representing death, is not a good thing, so it's a negative thing. Noticing that dynein sounds like dying reminds me that dynein moves towards the negatively charged end of the microtubule.

This concludes our lesson on how dynein moves towards the negatively charged end of the microtubule, and we'll be able to get some practice utilizing the concepts that we've learned as we move forward in our course. So, I'll see you guys in our next video.

What are the common features of the motor proteins kinesin and dynein?

• A. Both types of motor proteins bind microtubules.
• B. Both types of motor proteins bind and hydrolyze ATP.
• C. Both types of motor proteins undergo conformational changes when they travel along the microtubule.
• D. Both types of motor proteins 'step' from one tubulin subunit to another.
• E. All of the above are true.

Your lab isolates a new type of motor protein, which is some version of either myosin, kinesin, or dynein but it is unclear exactly what type it is. You hypothesize that the motor protein is NOT myosin. Which of the following is a piece of evidence that would support your hypothesis?

• A. The protein was isolated by adding then purifying actin microfilaments that it was bound to.
• B. The protein was isolated by adding then purifying microtubules that it was bound to.
• C. The protein aggregated in solution.
• D. The protein did not have a vesicle attached to it when purified.

Here’s what students ask on this topic:

What are the main types of motor proteins and their functions?

The main types of motor proteins are myosin, kinesin, and dynein. Myosin moves along actin microfilaments and is crucial for muscle contractions and transporting molecular cargo such as vesicles. Kinesin moves towards the positively charged end of microtubules, transporting vesicles and other molecular cargo within the cell. Dynein, on the other hand, moves towards the negatively charged end of microtubules and is involved in the motion of eukaryotic flagella and cilia. All these motor proteins utilize ATP to power their movements, playing essential roles in cellular transport and structure maintenance.

How do motor proteins use ATP to create movement?

Motor proteins use ATP to create movement through a process called ATP hydrolysis. When ATP binds to a motor protein, it is hydrolyzed to ADP and an inorganic phosphate (Pi). This hydrolysis releases energy, causing a conformational change in the motor protein. This change allows the motor protein to 'walk' along the cytoskeletal filaments, such as actin microfilaments or microtubules, effectively transporting molecular cargo or facilitating cellular movements. The cycle of ATP binding, hydrolysis, and release is repeated, enabling continuous movement.

What is the role of myosin in muscle contraction?

Myosin plays a crucial role in muscle contraction by interacting with actin filaments. During muscle contraction, myosin heads bind to actin, forming cross-bridges. ATP binding to myosin causes it to detach from actin, and ATP hydrolysis provides the energy for the myosin head to pivot and reattach to a new position on the actin filament. This 'power stroke' pulls the actin filament towards the center of the sarcomere, shortening the muscle fiber and generating contraction. This process is repeated in a cycle, leading to muscle contraction.

How do kinesin and dynein differ in their movement along microtubules?

Kinesin and dynein differ in the direction they move along microtubules. Kinesin moves towards the positively charged end of the microtubule, which is typically towards the cell periphery. It transports vesicles, organelles, and other molecular cargo in this direction. Dynein, in contrast, moves towards the negatively charged end of the microtubule, which is usually towards the cell center. Dynein is involved in transporting cargo such as vesicles and is also responsible for the motion of eukaryotic flagella and cilia. Both proteins use ATP to power their movements.

What is the significance of the cytoskeleton in motor protein function?

The cytoskeleton is crucial for motor protein function as it provides the tracks along which motor proteins move. The cytoskeleton consists of microfilaments, intermediate filaments, and microtubules. Myosin interacts with actin microfilaments, while kinesin and dynein interact with microtubules. These interactions enable motor proteins to transport molecular cargo, facilitate cellular movements, and maintain cell shape and structure. The cytoskeleton's dynamic nature allows it to respond to cellular signals, further aiding in the regulation of motor protein activities and cellular functions.