Types of Membrane Proteins - Online Tutor, Practice Problems & Exam Prep

Membrane proteins are essential for various cellular functions, categorized into integral and peripheral proteins. Integral proteins span the phospholipid bilayer, while peripheral proteins are located on the membrane's surface. Their functions include recognition for cell identification, anchorage to the extracellular matrix, signal transduction, transport of molecules, linkage between cells, and enzymatic activity. Understanding these roles is crucial for grasping cellular interactions and processes, highlighting the importance of membrane proteins in maintaining cellular integrity and communication.

Types of Membrane Proteins

So from our last lesson video, we already know that proteins are a critical component of biological membranes, and so in this video, we're going to focus on some of the different types of membrane proteins. And really, there are two main types of membrane-associated proteins that you should be familiar with, and notice down below we're numbering them number 1 and number 2. And of course, the numbers up above in the text correspond with the numbers that you see down below in the image.

The first type of membrane protein that you should be familiar with are the integral membrane proteins. These integral membrane proteins, as their name implies, are going to be integrated or embedded within the cell membrane and usually will be spanning the entire phospholipid bilayer. If we take a look at our image down below, notice we're showing you a biological membrane right here, and notice that towards the top is the outside of the cell and towards the bottom is the inside of the cell. You'll notice we've got this purple protein here that is completely integrated and is spanning the entire biological membrane. It has an intracellular portion of the protein that's facing towards the inside of the cell, an extracellular portion of the protein that's towards the outside of the cell and then, of course, it has an integrated region, and so this is why we call this an integral membrane protein.

Now, the other type of membrane protein is the peripheral membrane proteins. The peripheral membrane proteins, as their name implies, are proteins that are found on the periphery, or in other words, proteins found on the perimeter of the biological membrane. They will not span the membrane like the integral membrane proteins do. If we take a look at our image down below, notice right over here we're showing you an example of a peripheral membrane protein. This protein is only going to have an extracellular portion on the outside of the cell. It is not integrated or embedded in the phospholipid bilayer and does not have an intracellular portion. It is on the perimeter, it is a peripheral membrane protein. Peripheral membrane proteins can either be on the extracellular side or the outside of the cell, but you could also potentially have another peripheral membrane protein on the inside or the intracellular side of the biological membrane. That's important to keep in mind.

These membrane proteins, whether they are integral or peripheral, can have a wide variety of different functions, and so moving forward in our next video, we'll get to talk more about the functions of these membrane proteins. So I'll see you all in our next video.

Membrane Protein Functions

In this video, we're going to talk about some of the different types of functions that membrane proteins can have or what these membrane proteins actually do. Membrane associated proteins can perform a wide variety of functions. They can do so many different types of things, and so we're not going to cover every single function that membrane proteins can have, but some of those functions are included in the following table that you see down below. Notice on the left-hand side over here, we're showing you this little baby rattle, and that's because hopefully, by remembering "rattle," it'll help jog your memory of some of the membrane protein functions that we have in this table. The reason for that is because the first letter of each of these membrane protein functions spells out the word "rattle," as you can see right here. Again, that's why we have this rattle here just to help jog your memories.

The very first membrane protein function that we have listed here is recognition, and this is because membrane proteins can mark a cell for identification. Just like a driver's license can mark you for identification, membrane proteins can mark cells for identification and help cells distinguish one cell from another cell. The next protein function that we have here is anchorage, and some membrane proteins can anchor the cell cytoskeleton to the extracellular matrix or the ECM. Cell cytoskeleton and ECM anchoring is a critical function in some scenarios, and over here on the right, we're showing you a little image of an anchor to remind you of that function.

The third function that we have here is transduction, and this is when some membrane proteins serve as receptors for signaling molecules, allowing for bio-signaling to take place. Transduction basically allows a signal on the outside of the cell to affect the metabolism of the cell on the inside. Over here, we're showing you a little receptor just to remind you of that function. The fourth function that we have here is transport, and some membrane proteins can help with molecular transport across the membrane, which is a function that we'll get to talk more about moving forward in our course. Just like vehicles like cars can be used to transport objects, membrane proteins, in some cases, can also be used to transport objects across the membrane.

The fifth function that we have is linkage, and some membrane proteins can connect to cells via a protein linkage. We did talk about some cell junctions in some of our previous lesson videos, and so over here, just like these two pieces of a chain are being linked together, some membrane proteins can link together to neighboring cells. Last but not least, the final function that we have listed here is enzymes. Some membrane proteins can serve as enzymes to speed up chemical reactions, and so many types of enzymatic processes can rely on these membrane proteins to serve as enzymes. Over here, we're showing you a little basic enzymatic reaction, just to remind you of that function.

Once again, by remembering the word "rattle," hopefully, this will help you jog your memory of some of these membrane protein functions that are in this table. This concludes our brief lesson on membrane protein functions, and we'll be able to get some practice applying these concepts as we move forward. So, I'll see you all in our next video.

Which of the following is NOT a function of membrane proteins?

• A. Transducing signals from the environment into the cell.
• B. Synthesizing proteins.
• C. Anchoring the cell cytoskeleton and extracellular matrix.
• D. Marking cells for recognition.

Here’s what students ask on this topic:

What are the main types of membrane proteins?

The main types of membrane proteins are integral and peripheral proteins. Integral membrane proteins are embedded within the phospholipid bilayer and often span the entire membrane, having both intracellular and extracellular portions. Peripheral membrane proteins, on the other hand, are located on the surface of the membrane and do not span the bilayer. They can be found on either the extracellular or intracellular side of the membrane. These proteins play crucial roles in various cellular functions, including transport, signal transduction, and cell recognition.

What functions do membrane proteins perform?

Membrane proteins perform a variety of essential functions. These include:

• Recognition: Marking cells for identification.
• Anchorage: Anchoring the cell cytoskeleton to the extracellular matrix.
• Transduction: Serving as receptors for signaling molecules.
• Transport: Facilitating molecular transport across the membrane.
• Linkage: Connecting cells via protein linkages.
• Enzymatic Activity: Acting as enzymes to speed up chemical reactions.

These functions are crucial for cellular interactions and processes, helping maintain cellular integrity and communication.

How do integral and peripheral membrane proteins differ in their structure and location?

Integral membrane proteins are embedded within the phospholipid bilayer and often span the entire membrane, having both intracellular and extracellular portions. This allows them to interact with both the inside and outside of the cell. Peripheral membrane proteins, however, are located on the surface of the membrane and do not span the bilayer. They can be found on either the extracellular or intracellular side of the membrane. This structural difference influences their specific roles and interactions within the cell.

Why is the function of recognition important for membrane proteins?

The function of recognition is crucial for membrane proteins because it allows cells to identify and distinguish themselves from other cells. This is similar to how a driver's license identifies a person. Recognition proteins mark cells for identification, which is essential for immune responses, tissue formation, and cellular communication. Without proper recognition, cells could not effectively interact with their environment or other cells, leading to potential issues in immune function and tissue organization.

What role do membrane proteins play in signal transduction?

In signal transduction, membrane proteins act as receptors for signaling molecules. When a signaling molecule binds to a receptor protein on the cell membrane, it triggers a series of intracellular events that affect the cell's metabolism and function. This process allows cells to respond to external signals, such as hormones or neurotransmitters, and is crucial for maintaining homeostasis and coordinating cellular activities. Signal transduction pathways are vital for processes like growth, differentiation, and immune responses.