Bacterial & Eukaryotic Cell Membranes - Online Tutor, Practice Problems & Exam Prep

Bacterial and eukaryotic cell membranes primarily consist of phospholipids, featuring a glycerophosphate head and hydrophobic fatty acid tails connected by ester linkages. Cholesterol, found only in animal membranes, enhances membrane rigidity and forms lipid rafts, which are crucial for bio-signaling. Understanding these structural differences is essential for grasping cellular functions and interactions, particularly in distinguishing between bacterial and eukaryotic cells. The unique lipid compositions of archaeal membranes will be addressed separately.

Bacterial & Eukaryotic Cell Membranes

In this video, we're going to begin our lesson on bacterial and eukaryotic cell membranes. One thing to note is that in this video, we're not really going to talk about archaeal cell membranes, because the membranes of archaea are a little bit different. We'll talk about those separately in a different video. For now, we're focusing mainly on bacterial and eukaryotic cell membranes. Recall from our previous lesson videos that the major component of cell membranes are phospholipids. Both bacterial and eukaryotic phospholipids have what's known as a glycerophosphate head, and they also have these fatty acid tails. Sometimes the glycerophosphate head is just called the head, and the acid tails are sometimes just referred to as the tails. Recall also from our previous lesson videos that phospholipids are amphipathic molecules. The term amphipathic means that they have both hydrophilic and hydrophobic groups. Hydrophilic means water-loving, which is going to be the hydrophilic glycerophosphate head. The hydrophobic part is going to be the fatty acid tails or the hydrophobic tails for short.

If we take a look at our image down below, notice on the left-hand side we're showing you a lipid bilayer, a phospholipid bilayer. We're zooming in to just one specific phospholipid here to look at the phospholipid structure. Notice that the phospholipid structure, which is just represented as this circle with two tails coming off, can also be represented with its complex chemical structure, which you see over here. Notice that the circular part, which is represented right here in this box, is referring to the glycerophosphate head or the head of the phospholipid. Notice that this green box down here is along with these green tails coming off, these are referring to the fatty acid tails. One thing that's also really important to note here is that the fatty acid tails, which you see down below, are connected to the glycerophosphate head by these linkages known as ester linkages. What you see here highlighted in yellow are the ester linkages. This is important because these ester linkages are unique to only bacterial and eukaryotic phospholipids because archaeal phospholipids tend to use ether linkages, which is a different type of linkage than an ester linkage. We'll talk more about the ether linkage and the archaeal cell membranes later in a different video. But for now, this here concludes our brief introduction to bacterial and eukaryotic cell membranes. As we move forward, we'll continue to learn more and more about these membranes. I'll see you all in our next video.

Cholesterol in Animal Membranes

In this video, we're going to focus on cholesterol in animal membranes. And so, only animal membranes have a molecule known as cholesterol, which is a molecule that is going to help make the membranes a lot more rigid than bacterial membranes. There are specific regions within membranes known as lipid rafts, and these lipid rafts are really just dense regions of cholesterol that can move laterally together through the fluid membrane. You can imagine them as little dense regions that are going to be, somewhat acting like a raft in an ocean of phospholipids. If we take a look at our image down below, we can get a better understanding of this. Notice on the left we're focusing on bacterial cell membranes which are mainly made up of phospholipids, with proteins embedded in them, but notice that there is the absence of cholesterol. So cholesterol is absent and we're representing cholesterol as this molecule that you see right here. Bacterial cell membranes do not have cholesterol. However, eukaryotic cell membranes, mainly animal cell membranes, do have cholesterol and so cholesterol is present in animal cell membranes. You can see cholesterol embedded throughout the membrane along with the phospholipids and other proteins as well. And dense regions that have lots of cholesterol can create these lipid rafts and this lipid raft region right here would stay somewhat together and could move laterally within the membrane within this ocean of phospholipids. Lipid rafts can have a lot of important implications in bio signaling and in other processes as well. But here, what we're focusing on mainly is that animal cell membranes have cholesterol, whereas bacterial cell membranes do not have cholesterol. Now our archael cell membranes are going to have a unique type of lipid composition and so they're going to be different than the membranes of bacteria or eukaryote. We'll talk more about the archael cell membranes later in a different video.

______ is a chemical found in eukaryotic cell membranes that regulates fluidity in extreme temperatures.

• A. Phospholipid.
• B. Glycerophosphate.
• C. Glucose.
• D. Cholesterol.

Here’s what students ask on this topic:

What are the main components of bacterial and eukaryotic cell membranes?

The main components of bacterial and eukaryotic cell membranes are phospholipids. These phospholipids consist of a glycerophosphate head, which is hydrophilic (water-loving), and hydrophobic (water-fearing) fatty acid tails. The glycerophosphate head and fatty acid tails are connected by ester linkages. In addition to phospholipids, eukaryotic cell membranes, particularly in animals, contain cholesterol, which helps to make the membranes more rigid. Bacterial cell membranes, however, do not contain cholesterol. Proteins are also embedded within these membranes, playing various roles in cellular functions and interactions.

How does cholesterol affect animal cell membranes?

Cholesterol in animal cell membranes plays a crucial role in enhancing membrane rigidity and stability. It is embedded within the phospholipid bilayer and helps to reduce membrane fluidity, making the membrane less permeable to very small water-soluble molecules that might otherwise pass freely through. Cholesterol also contributes to the formation of lipid rafts, which are dense regions of cholesterol and phospholipids that move laterally within the membrane. These lipid rafts are important for bio-signaling and other cellular processes.

What is the difference between ester linkages and ether linkages in cell membranes?

Ester linkages and ether linkages are types of chemical bonds that connect the glycerophosphate head to the fatty acid tails in phospholipids. In bacterial and eukaryotic cell membranes, the glycerophosphate head is connected to the fatty acid tails by ester linkages. These ester linkages are characterized by the bond between a carbonyl group and an oxygen atom. In contrast, archaeal cell membranes use ether linkages, where the bond is between an oxygen atom and two carbon atoms. This difference in linkage types contributes to the unique properties of archaeal membranes compared to bacterial and eukaryotic membranes.

What are lipid rafts and what is their function in cell membranes?

Lipid rafts are specialized, dense regions within cell membranes that are rich in cholesterol and sphingolipids. These rafts can move laterally within the fluid membrane, acting like small, stable platforms. Lipid rafts play a significant role in bio-signaling, as they can compartmentalize cellular processes by bringing together specific proteins and lipids involved in signaling pathways. This organization helps in the efficient transmission of signals across the cell membrane, influencing various cellular functions such as immune responses, cell adhesion, and membrane trafficking.

Why do bacterial cell membranes lack cholesterol?

Bacterial cell membranes lack cholesterol because bacteria have evolved different mechanisms to maintain membrane fluidity and stability. Instead of cholesterol, bacteria use other types of lipids and proteins to achieve similar effects. For example, bacterial membranes often contain hopanoids, which are pentacyclic compounds that help stabilize the membrane. The absence of cholesterol in bacterial membranes is one of the key differences between bacterial and eukaryotic cell membranes, with cholesterol being a characteristic feature of animal cell membranes.