What Is Cytoplasm and Its Function?

We start by providing a basic definition of cytoplasm. The cytoplasm is the internal environment of cells. It is not an organelle like the other parts that make up the cell, but rather it is an aqueous medium for these organelles. With the exception of the nucleus, these organelles are considered constituent parts of the cytoplasm.

Cytoplasm is found both in eukaryotic cells (those with a true nucleus) and prokaryotic cells (those without a true nucleus). It is essentially everything within the cell membrane (plasma membrane) which is not the nucleus in eukaryotic cells. In prokaryotic cells, the cytoplasm encompasses the entire cell content within the cell membrane. The cytoplasm's ability to provide a medium for organelles is crucial for cellular organization and function.

Discover more about what are cell organelles and their function.

Now we have a definition of cytoplasm, we can understand it better by looking at the following cytoplasmic characteristics:

• The cytoplasm is liquid in consistency and has no specific shape. This liquid consistency is described as a colloidal solution or dispersion, i.e. it contains particles dispersed within it. These particles are sugars, mineral salts with ions, lipids, amino acids to form proteins, nucleotides, vitamins and transfer RNA. It is made up of 70% water, with the remainder consisting of the aforementioned biomolecules. This unique composition allows the cytoplasm to facilitate various biochemical reactions effectively.
  
  
• The cytoplasm is delimited by the inner surface of the cell membrane. It is compartmentalized into what we call organelles. Each of these cellular organelles has particular characteristics and its own functions. You can see the location of the cytoplasm within a cell in the cytoplasm diagram below.
  
  
• The cytoplasm of eukaryotic cells is different from the cytoplasm of prokaryotic cells which can be observed in their structure. In eukaryotic cells, the cytoplasm is between the cell membrane and the nuclear membrane. On the contrary, in prokaryotic cells, it includes everything in the cell membrane due to the absence of a nucleus. This structural difference has significant implications for cellular processes and complexity.
  
  
• Another important difference between eukaryotic and prokaryotic cells is that in prokaryotic cells almost all metabolic reactions occur in the cytoplasm. In eukaryotes, some occur in the cytoplasm but others occur in the organelles. This localization of metabolic activities illustrates the evolutionary adaptation of cells to optimize processes.
  
  
• Prokaryotic cells are also differentiated from eukaryotic cells by the organelles that are immersed within the cytoplasm. In the prokaryotic cell, there are the nucleoid, plasmids, ribosomes, inclusion bodies, thylakoids in photosynthetic organisms and accessory organelles. In eukaryotic cells, the organelles present arranged in the cytoplasm are the nucleus, ribosomes, mitochondria, rough endoplasmic reticulum, smooth endoplasmic reticulum, Golgi apparatus, lysosomes, peroxisomes and accessory processes.

We can find out more about important processes within cells in our explanation of the difference between DNA and RNA molecules.

With these characteristics in mind, we can look more closely at the function of cytoplasm within living cells:

• The main function of the cytoplasm is to contain the cellular organelles, providing them support so they can carry out their functions. Thanks to the cytoplasm, the organelles do not float, but are held and contained in their place. This containment ensures that cellular processes are carried out efficiently and effectively.
  
  
• A large part of the cellular metabolic processes and biochemical processes essential for the life of organisms occur in the cytoplasm, such as glycolysis (i.e. breakdown of glucose to produce energy). This is how the cytoplasm plays a role in cellular transport since the components formed within the organelles use the cytoplasm as a pathway for molecules. The cytoplasm thus acts as a conduit for the distribution and communication of molecules within the cell.
  
  
• The cytoplasm also serves as a transport medium for all the products that are manufactured within the cell. Since they have to move from one place to another, it is the cytoplasm that fulfills this function. This transportation is vital for maintaining cellular homeostasis and facilitating intracellular communication.
  
  
• It also serves to organize cell division, especially thanks to the cytoskeleton that orders the organelles during the formation of a new cell. You may be interested in this article about the phases of the cell cycle which explains these processes in more detail. This organization is crucial for ensuring that cellular division occurs smoothly and accurately.
  
  
• Other important processes that occur within the cytoplasm include cellular respiration, cell signaling, and protein synthesis. These processes highlight the cytoplasm's role in maintaining the cell's vitality and functionality.

Learn about some of the many processes which are carried out within cells by reading our explanation of the differences between anabolism and catabolism.

The cytoplasm consists of two main components which are the following:

• Cytoplasmic matrix, cytosol or hyaloplasm: the colloidal solution composed of liquid and dispersed particles. Among them we have the biomolecules already mentioned and cytoplasmic inclusions. The latter are dispersed and inert inconstant structures that serve as food reserves, products of cellular excretion or even pigments. It is made up of 70% water. The presence of these inclusions allows cells to store and utilize resources efficiently.
  
  
• Cytoskeleton: a network of filaments formed by proteins that holds organelles. If they did not exist, these cellular components would float within the cell without order or support. Cells are not always immobile, since organelles, chromosomes, and cellular contents tend to move. This is achieved thanks to the flexibility of the cytoskeleton that allows such movement. The cytoskeleton is essential for maintaining cellular integrity and facilitating dynamic cellular processes.

There are differences between the prokaryotic and eukaryotic cytoskeleton. The eukaryote is made up of microtubules made of tubulin, microfilaments of myosin and actin, and intermediate filaments made of various proteins. The cytoskeleton of prokaryotes is made up of classified proteins called MreB and ParM, WACA proteins, crescentin, and FtsZ. The functioning of the proteins of prokaryotes and eukaryotes are analogous to each other, fulfilling the same purposes of support and movement. This parallel evolution underscores the importance of the cytoskeleton in diverse cellular contexts.

We can also differentiate specific areas within the cytoplasm which are of differing consistencies. These are the following:

• Ectoplasm: it is the region closest to the internal cellular membrane, i.e. it is the outermost part of the cytoplasm. It has a dense gel-like consistency. It is rich in filaments that give it such consistency. It serves to give more support to the ends of the cell. This structural feature is crucial for maintaining cell shape and facilitating interaction with the external environment.
  
  
• Endoplasm: is the innermost part of the cytoplasm, where the organelles are. It has a more liquid consistency in relation to ectoplasm. This more fluid nature allows for efficient movement and interaction of organelles.

Although the terms cytoplasm and cytosol sound quite similar, they are two different things. Cytosol is the aqueous solution with dispersed elements and is part of the cytoplasm. This means that the cytosol is one of the many components of the cytoplasm. Conversely, the cytoplasm incorporates the entire cytosol together with the cytoskeleton. Understanding this distinction is essential for grasping the complexity and organization of cellular structures.

Now that you know what is cytoplasm and its function, don't miss this article on the different types of cells and their function.

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