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

Membrane proteins are crucial for various cellular functions. Integral membrane proteins span the phospholipid bilayer, while peripheral membrane proteins are located on the membrane's surface. Key functions include recognition for cell identification, anchorage connecting the cytoskeleton to the extracellular matrix, transduction as receptors for signaling molecules, transport across membranes, linkage between cells, and enzymatic activity. Understanding these roles is essential for grasping cellular interactions and processes, including transport mechanisms and signal transduction pathways.

Types of Membrane Proteins

So from our last lesson video, we know that proteins are a major component of biological membranes. And so here in this video, we're going to talk about some of the types of membrane proteins. And really, we're going to focus on 2 main types of membrane-associated proteins, and notice we have them numbered down below, number 1 and number 2. And so the very first membrane protein that we're going to talk about are the integral membrane proteins. And so the integral membrane proteins, as their name implies with the integral part here, are integrated into the cell membrane.

And usually, the integral membrane proteins are going to be spanning the entire phospholipid bilayer. And so if we take a look at our image down below, notice that this purple protein that you see right here that's embedded within this phospholipid bilayer, is an integral membrane protein because it's integrated into the phospholipid bilayer. And it's also spanning the entire phospholipid bilayer. Notice that it has an intracellular portion towards the inside of the cell. It also has an extracellular portion that's towards the outside of the cell, and it has this portion here that is completely integrated into the membrane.

And so that's why number 1 here is going to be an integral membrane protein. Now the second type of membrane protein that we're going to talk about are the peripheral membrane proteins. And so the peripheral membrane proteins, as their name implies with the peripheral part, are proteins that are going to be found on the periphery or, in other words, proteins found on the perimeter or on the outside of the cell membrane. And so if we take a look down below at this image over here, notice that this green protein that we see here is not fully integrated into the membrane. Instead, it remains on the periphery or the perimeter of the cell membrane.

And so this is going to make this green protein a peripheral membrane protein. Now these membrane proteins can have all kinds of different functions. And so in our next lesson video, we'll talk about some of their functions. So I'll see you all there.

Membrane Protein Functions

In this video, we're going to talk about some of the functions of membrane proteins—or what exactly do these membrane proteins actually do? Well, it turns out that membrane-associated proteins can actually perform a wide variety of functions. They can do so many different things and we're not going to talk about every single function that membrane proteins have, but some of those functions include the following functions that we have in this table down below. Now notice over here on the left-hand side we have this little baby rattle and the reason for that is that hopefully this little rattle will help jog your memories of some of the membrane protein functions that we have in this table here. And the reason for that is because the first letter of each of these functions is going to spell the word 'rattle', and so here what we have are the letters that spell the word 'rattle'.

And so hopefully this little rattle over here will help jog your memories of some of the membrane protein functions. Now the first function that we have here is recognition, and so membrane proteins can be used for recognition to mark cells for identification, very similar to how your ID in your wallet marks you for identification. Now membrane proteins can also be used for anchorage where the cell's cytoskeleton and the extracellular matrix can be anchored together. And so here what we have is a little image of an anchor to remind you of that function. Now membrane proteins can also be important for transduction, essentially allowing signals, acting as receptors for signalling molecules.

And here what we have is a little receptor showing you that they can be used to detect signals. Now membrane proteins can also be really important for transport. Moving forward in our course, we're going to talk a lot more about transport across membranes. And so, the transport here is just molecular transport across a membrane. Very similar to how cars can be used for transportation, membrane proteins can also be used for transportation.

Now membrane proteins are also really important for linkage, essentially connecting two cells together via a protein linkage, just like these two little paper clips are connected together, in that fashion. And then last but not least, proteins in the membrane can be used as enzymes, and so many types of enzymatic processes can be catalyzed by membrane proteins. And so here what we have is a little enzymatic reaction, and we'll get to talk more about enzymes, a little bit later in our course. But for now, this here concludes our brief introduction to some of the membrane protein functions and we'll be able to get some practice applying these concepts as we move forward throughout our course. So I'll see you guys 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 membrane proteins and peripheral membrane 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 are not embedded within the lipid bilayer. These proteins can be found on either the inner or outer surface of the cell membrane and are typically attached to integral proteins or the lipid bilayer itself.

What functions do membrane proteins perform?

Membrane proteins perform a variety of essential functions, including:

• Recognition: Marking cells for identification.
• Anchorage: Connecting the cytoskeleton to the extracellular matrix.
• Transduction: Acting as receptors for signaling molecules.
• Transport: Facilitating the movement of molecules across the membrane.
• Linkage: Connecting two cells together.
• Enzymatic activity: Catalyzing biochemical reactions.

These functions are crucial for cellular interactions, communication, and various physiological processes.

How do integral membrane proteins differ from peripheral membrane proteins?

Integral membrane proteins differ from peripheral membrane proteins in their location and structure. Integral membrane proteins are embedded within the phospholipid bilayer and often span the entire membrane, having both intracellular and extracellular portions. They are integrated into the membrane and can interact with the hydrophobic core of the lipid bilayer. Peripheral membrane proteins, however, are located on the surface of the membrane and are not embedded within the lipid bilayer. They are typically attached to integral proteins or the lipid bilayer itself and can be found on either the inner or outer surface of the cell membrane.

What role do membrane proteins play in cell recognition?

Membrane proteins play a crucial role in cell recognition by marking cells for identification. This function is essential for the immune system to distinguish between self and non-self cells, preventing the immune system from attacking the body's own cells. Recognition proteins, often glycoproteins, have carbohydrate chains that serve as unique identifiers, similar to an ID card. These identifiers allow cells to communicate and interact appropriately, ensuring proper immune responses and cellular interactions.

Why is the function of transport important for membrane proteins?

The function of transport is important for membrane proteins because it facilitates the movement of molecules across the cell membrane. This is essential for maintaining cellular homeostasis, nutrient uptake, waste removal, and ion balance. Transport proteins, such as channels and carriers, enable specific molecules to pass through the membrane, either passively or actively. Passive transport does not require energy and moves molecules down their concentration gradient, while active transport requires energy to move molecules against their concentration gradient. This selective transport is vital for the cell's survival and proper functioning.