Archaeal Cell Membranes - Online Tutor, Practice Problems & Exam Prep

Archaeal cell membranes differ significantly from bacterial and eukaryotic membranes. Archaeal lipids feature hydrophobic tails made of isoprene units instead of fatty acids, and they utilize ether linkages, enhancing resistance to heat and chemicals. These membranes can form bilayers with Glycerol Diether Lipids or monolayers with diglyceraltetraether lipids, crucial for extremophiles in harsh environments. The bilayer consists of two isoprene chains per head group, while the monolayer has two head groups linked by four ether linkages, providing increased rigidity and stability under extreme conditions.

Archaeal Cell Membranes

This video, we're going to begin our lesson on archaeal cell membranes. Archaeal membrane lipids actually differ from bacterial and eukaryotic membrane lipids in two significant ways that we have numbered down below, 1 and 2. The first significant way that archaeal membrane lipids differ from bacterial and eukaryotic membrane lipids is that archaeal membrane lipids have hydrophobic tails that consist of repeating isoprene lipids. These isoprene lipids, where isoprene is a 5-carbon hydrocarbon molecule, are not fatty acids. Recall that bacterial and eukaryotic membrane lipids do consist of fatty acids. If we take a look at our image down below, we can get a better understanding of this. Notice on the left-hand side we're focusing in on the bacterial and Eukaryotic Membrane Lipids, which mainly consist of these phospholipids. They have a Glycerophosphate head group and then have these fatty acid tails, down below. Now notice that with the archaeal membrane lipids, which we have over here on the right, that they also have a Glycerophosphate head just like the bacterial and eukaryotic membrane lipids do. However, notice looking at their hydrophobic tails that they do not consist of fatty acids. Instead, the archaeal membrane hydrophobic tails consist of isoprene chains, isoprene lipids and again isoprene is this molecule that you see here and so you can see that multiple isoprene units are being linked together to create the hydrophobic tail. So that's one way that the two membranes differ.

The second significant way that archaeal membrane lipids differ from bacterial and eukaryotic membrane lipids is that instead of having an ester linkage, they have an ether linkage. The ether linkage is what connects the hydrophobic tails to the Glycerophosphate head group. These ether linkages are actually more resistant to heat and chemical toxins than ester linkages are. This can help some archaea be extremophiles and be able to tolerate extreme conditions like immense amounts of heat as well as high pressures and other conditions. If we take a look at our image down below, once again we can get a better understanding of this. Notice that with the bacterial and eukaryotic membrane, lipids, that there is an ester linkage highlighted here in yellow that connects the Glycerophosphate head group to the fatty acid tails. However, with the archaeal membrane lipids, notice that the Glycerophosphate head group is connected to the hydrophobic tails, the isoprene chains, via an ether linkage. This ether linkage, notice, is missing a carbonyl group. And so, the carbonyl group that is missing here, once again, is what's going to allow this to become an ether linkage and make these archaeal membrane lipids more resistant to heat and chemicals and things of that nature.

This here concludes our brief introduction to archaeal cell membranes, and we'll be able to get some more practice applying these concepts as we move forward. So I'll see you all in our next video.

Cell membranes composed of glycerol-ether lipids biosynthesized from isoprene units are characteristic of:

• A. Bacteria.
• B. Eukayrotes.
• C. Archaea.
• D. Protists.

Which of the following statements is FALSE?

• A. The hydrophobic tails of archaeal membranes are repeating isoprene units.
• B. The glycerophosphate head & fatty acid tail of bacterial membranes are linked by an ester linkage.
• C. The glycerophosphate head & fatty acid tail of eukaryotic membranes are linked by an ether linkage.
• D. The glycerophosphate head & fatty acid tail of archaeal membranes are linked by an ether linkage.
• E. The hydrophobic tails of bacterial membranes are long fatty acid chains.

Types of Archaeal Membrane Lipids

This video, we're going to talk a little bit about the different types of archaeal membrane lipids. And so recall from our previous lesson video that archaeal membrane lipids are made of repeating units of isoprene lipids, rather than fatty acids like bacterial and eukaryotic membranes are made of. Now these archaeal membrane lipids that are made up of these isoprene units can form either bilayers where the membrane is made up of 2 layers of lipids, similar to how bacteria and eukaryotic membranes are bilayers, or the archaeal membrane lipids could form these monolayers, where the membrane would consist of just one single layer of lipids. And this all depends on the type of lipid that's being used in the archaeal membrane. Now the bilayers are going to have 2 hydrocarbon isoprene chains attached to a single head group. And this is going to be formed by these specific lipids called Glycerol Diether Lipids. Now it's that there's going to be just one glycerol molecule, and there are going to be 2 ethers, 2 ether linkages. So the root di is a root that means 2. And so, if we take a look at our image down below over here on the left hand side, we're showing you how archaeolipids can form bilayers, where there are 2 layers of lipids forming the membrane. So notice that here is the first layer of lipid and down below here we have the second layer of lipids forming this bilayer membrane. And so this is really similar to the membranes that we saw with bacteria and eukarya. Now notice zooming into these molecules here, notice that they are separate molecules, and these are Glycerol Diether Lipids. Again, the glycerol part means that there's only 1 Glycerophosphate head, and the diether means that there are 2 ether groups, one here and one here. And so this is going to be, one Glycerol Diether Lipid. Now notice down below we're showing you another Glycerol Diether Lipid because once again it has 1 Glycerophosphate head and 2 ethers. But notice that these 2 Glycerol Diether Lipids are separate from one another, and that's what creates the bilayer. Now on the other hand, the monolayers are going to have 2 really long hydrocarbon isoprene chains that are connected to actually 2 head groups. And this is going to be formed by these lipids called diglycerotetraether lipids. The di root once again means that there are 2 Glycerophosphate heads. And the tetra is a root that means 4. And so there are going to be 4 ether linkages in this molecule. And so if we take a look at our image down below over here on the right hand side, notice that we're showing you an archaeal lipid, how archaeolipids can form a monolayer. And so notice here that instead of having 2 layers of lipids there's just one single layer because these molecules are attached, to each other vertically. And so notice over here we're zooming in to show you one of these molecules. It's a diglycerotetraether lipid. Once again, the di root means that there are 2 glycerol groups or glycerophosphate heads here and here, and then the tetra is a root that means 4. And so tetra ether means that there are 4 ether linkages, 1, 2, 3, and 4 ether linkages. And so notice that this is just one single molecule rather than 2 molecules like what we had on the left. And so, this is what creates this monolayer. Now the formation of these monolayers, is going to be really critical in extremely hot temperatures because it helps to increase the membrane rigidity and therefore protect the cell in these extremely hot temperatures. And so by being capable of forming these monolayers using these diglyceride tetraether lipids, these archaeal membranes, are going to be more resistant and allow some archaea to be extremophiles and survive in extreme conditions such as extremely hot temperatures. And so this here concludes our brief lesson on the different types of archaeal membrane lipids and we'll be able to get some practice applying this concept as we move forward. So I'll see you all in our next video.

Thermophilic archaea may have tetraether lipids that:

• A. Form bilayer membranes.
• B. Form monolayer membranes.
• C. Bind to and protect their DNA.
• D. Form more stable tri-layer membranes.

Which of the following statements is true?

• A. Eukaryotic cell membranes form monolayer in extremely hot temperatures.
• B. Archaeal cell membranes contain cholesterol making them more rigid than eukaryotic cells.
• C. Archaeal cells membranes can form bilayers or monolayers depending on environmental temperatures.
• D. Bacterial cell membranes contain cholesterol making them more rigid than eukaryotic cells.
• E. Bacterial cell membranes can form bilayers or monolayers.

Here’s what students ask on this topic:

What are the main differences between archaeal and bacterial cell membranes?

Archaeal cell membranes differ from bacterial cell membranes in two significant ways. First, archaeal membranes have hydrophobic tails made of repeating isoprene units, whereas bacterial membranes have fatty acid tails. Isoprene is a 5-carbon hydrocarbon molecule, making archaeal lipids distinct. Second, archaeal membranes use ether linkages to connect the hydrophobic tails to the glycerophosphate head group, while bacterial membranes use ester linkages. Ether linkages are more resistant to heat and chemical toxins, allowing some archaea to thrive in extreme environments. These differences contribute to the unique properties of archaeal membranes, such as increased stability and rigidity under harsh conditions.

How do archaeal membrane lipids contribute to extremophiles' survival in harsh environments?

Archaeal membrane lipids contribute to extremophiles' survival in harsh environments through their unique structure. The hydrophobic tails of archaeal lipids are made of isoprene units, which are more stable than fatty acids. Additionally, these lipids are connected to the glycerophosphate head group via ether linkages, which are more resistant to heat and chemical toxins compared to ester linkages found in bacterial and eukaryotic membranes. Some archaeal membranes can form monolayers using diglyceraltetraether lipids, which provide increased rigidity and stability, crucial for surviving extremely hot temperatures. These adaptations enable extremophiles to thrive in environments with high heat, pressure, and chemical stress.

What are the types of archaeal membrane lipids and their structures?

Archaeal membrane lipids can form either bilayers or monolayers, depending on their structure. Bilayers are formed by glycerol diether lipids, which have two isoprene chains attached to a single glycerophosphate head group. These lipids are similar to bacterial and eukaryotic membranes but use ether linkages. Monolayers are formed by diglyceraltetraether lipids, which have two glycerophosphate head groups connected by four ether linkages and two long isoprene chains. The monolayer structure provides increased membrane rigidity, essential for survival in extremely hot environments. These structural variations allow archaeal membranes to adapt to different environmental conditions.

Why are ether linkages in archaeal membranes more resistant to heat and chemicals?

Ether linkages in archaeal membranes are more resistant to heat and chemicals due to their chemical structure. Unlike ester linkages, ether linkages lack a carbonyl group, making them less reactive and more stable under extreme conditions. This increased stability helps maintain membrane integrity in high temperatures and harsh chemical environments. The resistance provided by ether linkages is crucial for archaea, especially extremophiles, allowing them to survive and thrive in environments that would be detrimental to organisms with ester-linked membranes, such as those found in bacteria and eukaryotes.

How do archaeal monolayers differ from bilayers in terms of structure and function?

Archaeal monolayers and bilayers differ in both structure and function. Bilayers are formed by glycerol diether lipids, which consist of two isoprene chains attached to a single glycerophosphate head group, creating two separate lipid layers. In contrast, monolayers are formed by diglyceraltetraether lipids, which have two glycerophosphate head groups connected by four ether linkages and two long isoprene chains, resulting in a single continuous layer. Monolayers provide increased membrane rigidity and stability, essential for survival in extremely hot environments. This structural difference allows monolayers to better protect archaeal cells under harsh conditions compared to bilayers.