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Difference Between Cell Membrane and Plasma Membrane
The cell membrane and plasma membrane are two terms that are often used interchangeably to describe the same structure. However, there are subtle differences between these two structures that are important to understand.
What is Cell Membrane?
The cell membrane is a type of plasma membrane that encloses the entire contents of a cell, including the cytoplasm and all the organelles.
The cell membrane is not always the outermost layer of the cell since plant cells also have a cell wall that further encloses the cell membrane.
Animal cells however have no cell wall and the cell membrane is the barrier between the inner contents of the cell and the external environment.
The cell membrane consists of a phospholipid bilayer that also contains integral proteins. Integral proteins often span the membrane and provide pathways for molecules to move through the membrane.
The membrane is selectively permeable, due to the presence of the lipids which are hydrophobic (repel water). The phosphate heads are hydrophilic (do not repel water) in comparison with the lipid tails.
The lipid tails are glycerol molecules. Other lipids in the membrane include cholesterol which helps provide some stiffness and support to the membrane.
A cell membrane is important in cytokinesis during cell division. In some organisms the membrane is modified with cilia for feeding and movement.
Knowledge of the structure of the cell membrane of microbes has allowed researchers to develop antimicrobial agents to attack pathogenic bacteria and fungi.
What is Plasma Membrane?
The plasma membrane is a membrane that surrounds individual organelles or the contents of a cell. The cell membrane is a type of plasma membrane that encloses the cell.
There are plasma membranes found surrounding both the cytoplasm and contents of a cell and surrounding individual organelles such as chloroplasts and mitochondria. This means that plasma membranes have several different functions depending on where they are located.
The structure of the membrane can vary depending on what it surrounds, whether that is the entire cell or an organelle in the cell.
Plasma membranes always provide a degree of protection regardless of what structure they are surrounding, and many also play a role in phosphorylation reactions.
A plasma membrane surrounding an organelle will have slightly different functions depending on what organelle it is enclosing.
Organelle plasma membranes still have selective-permeability and carefully control what substances pass into and out of an organelle, but the type of molecules needed by the organelle will differ.
The molecules that need to enter and leave a mitochondria compared with a chloroplast for instance, will be different at times because the organelles have different functions. For instance, pyruvate needs to enter mitochondria in order for aerobic cellular respiration to occur, while carbon dioxide needs to enter chloroplasts in order for photosynthesis to occur.
Differences: Cell Membrane and Plasma Membrane
One of the key differences between the cell membrane and plasma membrane is their location. The cell membrane can refer to the outermost layer of any type of cell, including both eukaryotic and prokaryotic cells, whereas the plasma membrane specifically refers to the outermost layer of a eukaryotic cell.
Another difference between these two structures is their composition. While both the cell membrane and plasma membrane are composed of a lipid bilayer, the plasma membrane contains a wider variety of proteins, including receptor proteins, transport proteins, and enzymes. These specialized proteins play important roles in various cellular processes such as cell signaling, nutrient uptake, and waste removal.
The plasma membrane also contains various carbohydrates that are attached to the proteins and lipids on its surface. These carbohydrates are involved in cell-cell recognition and play a crucial role in immune responses, allowing the immune system to distinguish between self and non-self cells.
One important feature of both the cell membrane and plasma membrane is their selectively permeable nature. This means that they are able to regulate the movement of molecules into and out of the cell. The lipid bilayer is impermeable to most polar molecules, including ions and large molecules such as proteins, but it is permeable to small nonpolar molecules such as oxygen and carbon dioxide. The specialized proteins on the plasma membrane allow for the selective transport of specific molecules, enabling the cell to maintain homeostasis and respond to its environment.
The following table highlights the major differences between Cell Membrane and Plasma Membrane:
Characteristics |
Cell Membrane |
Plasma Membrane |
|---|---|---|
Location |
The cell membrane is only found surrounding the contents of the cell. |
A plasma membrane can also be found surrounding certain organelles. |
Tonicity |
While a cell membrane is always involved in helping regulate tonicity. |
That is not the case for all plasma membranes. |
Feeding and movement |
A cell membrane can be modified in organisms to facilitate feeding and movement, for instance Paracemium has cilia for feeding and movement. | Other plasma membranes are not modified in this way. |
Conclusion
In summary, while the terms cell membrane and plasma membrane are often used interchangeably, there are important differences between these two structures. The cell membrane can refer to the outermost layer of any type of cell, whereas the plasma membrane specifically refers to the outermost layer of a eukaryotic cell. The plasma membrane contains a wider variety of specialized proteins and carbohydrates than the cell membrane.
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