I'm going to say here that a cell membrane separates the interior of the cell from the external environment. We're going to say they're mainly composed of glycerophospholipids as well as sphingolipids. They have what we call a selectively permeable membrane, so that means it controls what goes into and out of the cell. And we take a look here, we have what is called our lipid bilayer. This represents the exterior of the cell, this represents the interior of our cell. We're going to say that we have our polar heads here, we have the nonpolar tails in the center, and then we have polar heads again. This lipid bilayer will help to control the flow of what goes into and out of our cell.
Cell Membranes - Video Tutorials & Practice Problems
Cell Membranes Concept 1
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Cell Membranes Concept 2
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Now when it comes to our membrane structure, we follow what's called a fluid mosaic model. Here, this is a model for representing the general structure of a cell membrane. Now, when we say the word fluid, we're going to say the lipid bilayer is not rigid but fluid and dynamic. We're going to say here, phospholipids in the lipid bilayer do not fit closely together due to kinks in the fatty acid chains. So here we have our phospholipid, and we're going to say that we have the polar heads orienting themselves on the externals, and then we have our hydrophobic tails on the interior of forming this lipid bilayer.
Now, Mosaic is basically the lipid bilayer also containing proteins, carbohydrates, and cholesterol molecules. If we take a look here, we're going to say that these two structures at the top represent our carbohydrate side chains. We have here, 4 fused rings together which means it's a steroid and specifically, it would be cholesterol. Next, we have here, this is called an integral protein. And if we're talking about integral proteins, we're going to say they extend through the entire bilayer and appear on both sides. We're going to say next, we have our peripheral proteins, They're associated with our with just one side. Our peripheral protein will be this green blob right here. It doesn't cut all the way through to over here like the integral proteins would.
We have our carbohydrate side chains that we talked about up top. These extend into the extracellular fluid, and they're responsible for cell recognition and communication. Now, we talked about these 4 fused rings here representing a steroid, but specifically cholesterol. So remember, cholesterol here resides within a bilayer and increases membrane strength based on how much cholesterol we have there. And then in terms of this, remember we talked about this being the polar heads, we have our non-polar tails, our hydrophobic tails in the inside, and then we have our polar heads over here. This would give us a good description of what we mean by a fluid mosaic model.
Cell Membranes Example 1
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In this example question, it asks which one of the following is not a component of cell membranes? Here, cholesterol. We've talked about cholesterol, which is represented by our 4 fused rings as being a key component of a cell membrane, and it helps with the membrane's strength based on the amount of cholesterol within it. So, this is a part. Sphingomyelins. We talked about our phospholipids helping to create the lipid bilayer. A phospholipid can also be in the form of sphingomyelin. So, sphingomyelins are a type of phospholipid. Proteins. Now, we said that proteins are part of our cell membrane, they can exist as integral proteins which are found on both sides, or they can be peripheral proteins that are only found on one side. The answer here would be waxes. Waxes do not represent a component of a cell membrane. So, here, our final answer would be option d.
Which one of the following components of a cell membrane extends through its entire thickness?
Cholesterol
Peripheral proteins
Integral protein
Sphingomyelin
Keeping in mind that unsaturated fatty acids form kinks in the phospholipid tails, what would happen if all of the unsaturated fatty acids in a lipid bilayer were replaced with saturated fatty acids?
It will become more fluid.
Its fluidity will be significantly reduced.
There will be no effect on its fluidity.
The lipid bilayer will become resistant to oxidation.