The cell membrane, also known as the plasma membrane, is the part of the cell that separates the cell’s insides from the external environment.
Cell membranes protect the cell from outside factors, allowing it to thrive in its environment. Inside the cell membrane is the nucleus, though the membrane itself consists of a semipermeable lipid bilayer.
To find out more about the cell membrane, just keep reading.
What Is The Cell Membrane?
As previously mentioned, the cell membrane is also called the plasma membrane. This part of a cell is responsible for protecting the interior of the cell.
This part of the cell was only discovered in the 1890s, and in 1915, it was given chemical components. The primary component identified were proteins.
In more recent years, humans have gained a better understanding of cells, including cell or plasma membranes. The Fluid Mosaic Model was put forward to explain this membrane, and is still used today.
This model describes the cell membrane as if it were made up of a mosaic of components.
In the membrane are things like carbohydrates, proteins, cholesterol, and phospholipids. All of these varying components give the structure a fluid character.
Cell Membrane Structure
The thickness of cell membranes typically range anywhere from 5 to 10 nm. Compared to human red blood cells, which are typically 8 µm, the plasma membrane is absolutely tiny.
The thickness of a human red blood cell is roughly 1,000 times wider than that of the cell membrane.
There are four primary components of a cell membrane. These are as follows: lipids (which includes cholesterol and phospholipids), proteins, and carbohydrates.
Phospholipids are molecules that are made up of glycerol, two fatty acids, and one phosphate-linked head group.
A cell or plasma membrane is typically made up of two layers. These layers are made of phospholipid, and have their tails pointing in. This arrangement is known as a phospholipid bilayer.
In the core of the membrane, you can find cholesterol (which is another lipid). This lipid is made up of four carbon rings that are fused together, and are typically found alongside phospholipids.
The carbohydrate, lipid, and protein proportions within the cell membrane will vary depending on the type of cell you are examining.
In a normal human cell, however, you would expect to see that protein accounts for roughly 50% of the plasma membrane’s overall composition mass.
All lipids in a normal human cell should make up around 40% of the composition mass, and carbohydrates only around 10% of the overall mass.
However, the concentrations of lipids and proteins can vary in different cell membranes.
A good example of this would be to look at myelin (a specialized outgrowth of cells responsible for insulating the axons in the peripheral nerves). Myelin typically contains roughly 76% lipid and only 18% protein.
When you compare these composition masses to the inner membrane of mitochondria cells, there is roughly a composition of 76% protein and only 24% lipids.
If you were to look at the plasma membrane within human red blood cells, the composition mass should be around 20% of lipids.
What Does The Cell Membrane Do?
The cell membrane does more than protect the interior of the cell. The plasma membrane is also responsible for transporting nutrients into the cell and removing toxic substances from the cell itself.
This membrane also contains proteins. These proteins will then, in turn, interact with various other cells.
These proteins on the plasma membrane can be glycoproteins or lipid proteins. Glycoproteins are proteins that are full of sugar and a protein moiety, whereas lipid proteins are full of fat.
The proteins that are stuck to the plasma or cell membrane will then allow for any cell to interact with another cell.
Cell membranes also provide structural support for the cell as a whole. There are actually many different types of cell membranes, just as there are many different types of cells.
Generally, the plasma membrane has a lot of cholesterol as its lipid component. However, this can vary across cells.
As there are millions of different plants, microbes, and organisms, there are lots of different types of cells. Even bacteria cells and algae will have differing characteristics and protective mechanisms.
In these cases, the cell wall isn’t the outermost layer. Here, the cell wall would be surrounded by another structure that is a lot stronger and more durable than the plasma membrane.
This is the case so that they can survive in much harsher conditions without being affected too much.
A Summary
To summarize, the cell membrane, or plasma membrane, protects the inside of the cell from external forces.
The thickness of these cell membranes are 1,000 times smaller than the thickness of a human red blood cell, making them incredibly tiny.
Not only does the cell membrane protect the inside of the cell, but it also provides structural support. This membrane is made up of four primary components: phospholipid, protein, cholesterol, and carbohydrates.
The composition mass of cell membranes can vary greatly, even within the same organism. For example, myelin typically contains roughly 76% lipid and only 18% protein.
When you compare these composition masses to the inner membrane of mitochondria cells, there is roughly a composition of 76% protein and only 24% lipids.
If you were to look at the plasma membrane within human red blood cells, the composition mass should be around 20% of lipids. As such, cell function has a direct relationship with the composition mass.
The cell membrane is responsible not only for providing protection to the cell and retaining structure, but much more. It allows gasses through to the cell, and gets rid of harmful or toxic gasses to protect the cell.
Proteins on the cell membrane allow the cell to interact with other cells, too.
It’s important to note that the cell membrane is not the outermost layer in all things. For example, in plants and bacteria, there is another barrier that surrounds the plasma membrane.
This added layer is there to ensure that the cell is able to survive harsher conditions.
Ever since I was a little girl, I have been fascinated by science. Every holiday I would ask for the newest science kit, and spend weeks learning with it.
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