Cytosol vs Cytoplasm in a cell: Differences and Similarities

The comparison of the cytosol vs cytoplasm is required because the cytosol is usually confused with the cytoplasm. Hence, it is essential to demonstrate that these two entities are different.

The cytosol and cytoplasm are components of the cell and may be similar in their form. However, the cytosol is not the same as the cytoplasm, rather it is the intracellular fluid present in the cytoplasm of the cell.

In biology, the cell is the smallest unit of life that makes up the tissues of living organisms. Humans have more than 30 trillion cells and each cell is made up of 3 main parts which include the nucleus, cytoplasm, and cell membrane. The nucleus of the cell is the structure that contains most of the cell’s DNA and nucleolus. It is in the nucleus that the RNA is made too. The cell membrane, on the other hand, surrounds the cell and regulates the substances that enter and exit the cell. Then, the cytoplasm is the fluid that contains other cell parts and organelles that carry out specific functions. It is in this cytoplasm that most chemical reactions and proteins of the cells are made.

The cytosol is a component of the cytoplasm in the cell

However, this cytoplasm as an intracellular fluid has another fluid component in it which is the cytosol. Hence, the cytosol and cytoplasm are both solutions in the cell of organisms. To understand their difference better, let’s look at each entity individually: its definition, structure, location, and function in the cell.

Definition

What is Cytoplasm?

The cytoplasm is a thick fluid that fills the cell which is enclosed by the cell membrane. This fluid contains the cytosol together with ions, filaments, macromolecular structures, and organelles. In a eukaryotic cell, the cytoplasm consists of all the material outside the nucleus and inside the cell.

Virtually all the organelles in eukaryotic cells like the endoplasmic reticulum, nucleus, and mitochondria are located in the cytoplasm of the cells. Then, the portion of this cytoplasm that is not contained in the organelles is called the cytosol. The cytosol is then the matrix that surrounds these organelles in a eukaryotic cell. The movement of the cytoplasm in plants around vacuoles is called cytoplasmic streaming. With the help of cytoplasmic streaming, the cytoplasm within the cell allows various materials to move around within the cell.

Composition and structure

The cytoplasm may seem to have no form or structure. Contrary to what it seems, the cytoplasm is highly organized and a framework of protein scaffolds known as cytoskeleton gives the cytoplasm and cell their structure. The main constituents of the cytoplasm include the cytosol, organelles, and cytoplasmic inclusions. The cytoplasm is involved in large cellular activities such as nuclear division or glycolysis.

Since the cytosol consists mainly of water and is a portion of the cytoplasm, thus, water is the largest component of the cytoplasm. This fluid consists of water, inorganic salts, sugars, and other organic components. It is made up of 80% water with other substances like nucleic acids, lipids, enzymes, amino acids, non-organic ions, carbohydrates, and lightweight molecular compounds. Also, it contains dissolved salts and nutrients that allow the water components to be easily absorbed by the cell.

As mentioned earlier, the cytoplasm is composed of various organelles. These organelles form the cytoskeleton and endomembrane system. Furthermore, this fluid is divided into two regions- endoplasm and ectoplasm. The endoplasm is the inner concentrated region of the cytoplasm whereas, the ectoplasm (cell cortex) is the outer region of the cytoplasm. This endoplasm is described as the granular mass in the cytoplasm while the ectoplasm is described as the surrounding lucid layer. This fluid is an excellent conductor of electricity.

What is Cytosol?

In eukaryotic cells, the cytosol is a component of the cytoplasm that surrounds organelles in the cytoplasm. Hence, the cytosol can be defined as an aqueous solution that is a portion of the cytoplasm in which organelles, proteins, and other cell structures float in.  This is one of the liquids in the cells of organisms (intracellular fluid ICF) and it is the matrix that surrounds these organelles in a eukaryotic cell. Another name for the cytosol is groundplasm or cytoplasmic matrix.

There are membrane-bound organelles that float in the cytosol even though the interior of these organelles is not considered as part of the cytosol. For instance, membrane-bound organelles such as nuclei, chloroplasts, mitochondria, and others within the cells possess their own internal fluid that is separate and different from the cytosol.

Composition and structure

The cytosol is said to have structure and organization as membranes separate it into compartments. This complex solution contains proteins, mRNA, amino acids, ribosomes, ions, sugars, messenger molecules, etc. Conclusively, the main constituents of the cytosol include ions, water, and molecules.

In organisms, the proportion of the cell volume that comprises the cytosol varies among them. For instance, in a bacterial cell, the cytosol forms the bulk of the cell structure whereas, in plant cells, it is not the cytosol that forms the bulk of the cell structure but the large central vacuole. However, the composition of the cytosol is mostly of dissolved ions, water, and molecules. These molecules include small molecules and large water-soluble molecules like proteins.

This matrix is a complex mixture of organic molecules and substances dissolved in water. Therefore, water is the largest component of the cytosol. This complex solution contains proteins, mRNA, amino acids, ribosomes, ions, sugars, messenger molecules, etc. In the cytosol, the concentration of sodium ions and potassium ions is different compared to the ions in the extracellular fluid. These differences in the ion levels play a role in cellular activities such as cell signaling, osmoregulation, and the generation of action potentials in excitable cells like the nerve, endocrine, and muscle cells.

Its properties and composition allow the functions of life to occur. This matrix also contains a large number of macromolecules and how the molecules behave can be altered through macromolecular crowding. The cytosol is said to have structure and organization as membranes separate it into compartments. It has multiple levels of organization which include concentration gradients of small molecules like calcium, large complexes of enzymes that work together and function in metabolic pathways, and protein complexes like carboxysomes and proteasomes that enclose and differentiate parts of the cytosol.

Location

Where is the cytoplasm located in a cell?

The location of the cytoplasm varies amongst cell types. In eukaryotes, it is located between the nuclear membrane and the cell membrane. Since eukaryotic cells have a membrane-bound nucleus, the other components of the cell are separated from the nucleus by the nuclear envelope. This is why the cytoplasm is restricted to the space between the cell membrane and nuclear membrane.

In prokaryotic cells, the location of the cytoplasm is different because these cells lack a true nucleus unlike in eukaryotic cells. You can read the difference between prokaryotic and eukaryotic cells for a better understanding of the contrast between these two cell types. In the prokaryotic cell, there is no nuclear membrane to separate the genome from other cell components. Due to this, the cytoplasm occupies the entire cell environment that is within the plasma membrane.

Therefore, all the cell components and organelles of the procaryotic cells as well as the genetic material are suspended in the cytoplasm. However, in regard to location, the cytoplasm is divided into two layers which include the ectoplasm and endoplasm. The endoplasm is the inner concentrated region of the cytoplasm whereas, the ectoplasm is the outer region of the cytoplasm.

Where is the cytosol located in a cell?

The cytosol is located within the cytoplasm where it surrounds all organelles that are embedded or suspended in the cytoplasm. This means there are membrane-bound organelles that float in the cytosol even though the interior of these organelles is not considered as part of the cytosol. It is therefore important to note that organelles such as nuclei, chloroplasts, mitochondria, and others within the cells possess their own internal fluid that is separate and different from the cytosol.

Function

What does the cytoplasm do?

  • The cytoplasm through structures known as vesicles, transport and remove waste products from the cells.
  • The Golgi apparatus and endoplasmic reticulum which make up the endomembrane system of the cytoplasm are involved in the transportation of substances such as lipids and proteins respectively in the cell.
  • This matrix helps to maintain the structure and shape of the cell: The cytoplasm contributes to the general shape of the cell. As a viscous matrix made of water, it does this by exerting a turgor pressure against the cell membrane.
  • It also contributes to the shape and structure of the cell through its cytoskeleton which is composed of microtubules and microfilaments.
  • The cytoplasm protects the internal components of the cell as it acts as a barrier between the external and internal environment of the cell.
  • It also serves as a cushion that absorbs some shock that can damage organelles.
  • Various molecules float in the cytoplasm and are stored in it. Some of these molecules include fats, starch, lipids, etc which can be used to build several structures of the cells. Adipocytes, for example, are cells that store lipids in their cytoplasm.
  • The cytoplasm function as a site for enzymatic reactions and metabolic activities as several enzymes can be seen in the cytoplasm.
  • Another function of the cytoplasm is that it aids in the movement, growth, and division of cells.
  • Cellular respiration, anaerobic respiration or glycolysis, and the translation of mRNA into proteins on ribosomes all take place in the cytoplasm.
  • The cytoplasm has monomers that generate the cytoskeleton that gives the cell its shape.
  • It also helps to create order and organization within the cell as it embeds different organelles to specific locations in the cell.
  • The cytoplasm has a solid glass structure that freezes large organelles in place.

What does the cytosol do?

  • The main function of the cytosol is that it serves as a medium for intracellular processes.
  • It contains the proteins, ions, and other components for cytosolic activities.
  • The cytosol function in signal transduction: During the process of signal transduction, messenger molecules may diffuse through the cytosol to alter the functioning of organelles, enzymes, or DNA transcription. These messengers may be from one part of the cell to another part or from outside the cell.
  • This matrix facilitates the transportation of metabolites from place to place in the cell. It transports the metabolites from their site of production to where they are needed.
  • Through the cytosol, water-soluble molecules like amino acids diffuse freely while large hydrophobic molecules such as fatty acids and sterols are transported through the cytosol by specific binding proteins.
  • Through vesicles in the cytosol, some molecules that are subjected to endocytosis are transported.
  • Another major function of the cytosol is that it plays a role in prokaryotic metabolism. Also, almost all life functions of the prokaryotic cells as well as glycolysis, DNA transcription, and replication take place in the cytosol.
  • In eukaryotic cells, a large proportion of metabolism takes place in the cytosol. In the cells of mammals, about half of the proteins are localized to the cytosol.
  • Even in yeast, the majority of its metabolic processes and metabolites take place in this matrix.
  • In the animal cell, it is in this matrix that the major metabolic pathways take place. These metabolic pathways include glycolysis, protein biosynthesis, gluconeogenesis, and the pentose phosphate pathway.
  • The cytosol function in enzyme activities: In order for enzymes to work properly, they need certain salt concentrations, pH levels, and other environmental conditions and in the cytosol, there are concentrations of some ions that give enzymes a favorable environment to function.
  • In mitosis, after the breakdown of the nuclear membrane, the cytosol functions as a site for many cytokinesis processes.
  • The cytosol function in the cell to give it and the organelles structural support. Thereby, the majority of cells depend on the volume of cytosol in order to create their shape as well as space for chemicals to move within the cell.

Differences between Cytosol and Cytoplasm

A table showing the difference between Cytosol and cytoplasm
(Cytosol vs Cytoplasm)
Cytosol
Cytoplasm
Definition
The cytosol is an aqueous solution that is a portion of the cytoplasm in which organelles, proteins, and other cell structures float in
The cytoplasm is a thick fluid that fills the cell which is enclosed by the cell membrane.
Description
It is the fluid portion of the cytoplasm that surrounds the organelles in the cell
It is the fluid that contains all the components of the cell within the cell membrane except the nucleus.
Composition
This matrix is composed of water, small and large water-soluble molecules, soluble ions, and proteins.
This matrix is composed of water, lipids, carbohydrates, amino acids, nucleic acids, enzymes, and non-inorganic ions.
Diversity
The diversity of the components of the cytosol is low compared to the cytoplasm
The diversity of the components of the cytoplasm is high compared to the cytosol
Proportion of size
The cytosol is a portion of the cytoplasm, so its size proportion is less in the cell
Since the cytosol is contained in the cytoplasm, the size proportion of this matrix is more in the cell
Location
The cytosol is located within the cytoplasm where it surrounds all organelles that are embedded or suspended in the cytoplasm.
In prokaryotic cells, the cytoplasm occupies the entire cell environment that is within the cell membrane. In eukaryotes, it is located between the nuclear membrane and the cell membrane.
Components
The main component of this matrix include ions, water, and molecules.
The main components of this matrix include the cytosol, organelles, and cytoplasmic inclusions
Metabolism
In prokaryotic cells, all the chemical reactions occur in this matrix. It facilitates the transportation of metabolites in eukaryotic cells from the site of production to where they are needed.
This matrix transport and remove waste products from the cells. It is involved in large cellular activities such as cell division and glycolysis.
Functions
For efficient metabolism, this matrix concentrates its dissolved molecules into the correct position. It concentrates molecules in the correct portions of the cytoplasm
This matrix freezes the organelles in place, ensuring efficient metabolism.
Organization and structure
The major organizational levels of this matrix are concentration gradients, protein complexes, protein
compartments and cytoskeletal sieving
This matrix is divided into endoplasm and ectoplasm. The endoplasm is the inner concentrated region of the cytoplasm whereas, the ectoplasm is the outer region of the cytoplasm

Similarities

  • They are the matrix found in the cell.
  • Water is the most abundant component found in the cytosol and cytoplasm.
  • They both function in the transportation of molecules, signal transduction, cytokinesis, and nuclear division.

Conclusion

From the definition of the cytosol and cytoplasm, it can be seen that they are both intracellular fluids and constituents of the cell. However, it is noted that the cytosol is part of the cytoplasm and the cytoplasm is a component of the cell that is surrounded by the cell membrane.

Hence, the main difference between the cytosol and cytoplasm is that the cytosol is the matrix that is a component of the cell’s cytoplasm while the cytoplasm is the fluid component of the cell that is outside the nucleus but inside the cell which is surrounded by the cell membrane.

The cytosol is the intracellular fluid of the cell whereas, the cytoplasm contains all the components of the cell within the cell membrane except the nucleus. Thereby, the main constituents of the cytoplasm include the cytosol, organelles, and cytoplasmic inclusions whereas the cytosol is made up mainly of water, ions, and molecules.

These two fluids have different organizational levels in the cell. The cytosol is made up of protein compartments, concentration gradients, protein complexes, and cytoskeletal sieving. Whereas, the cytoplasm is divided into endoplasm and ectoplasm. The endoplasm is the granular mass in the cytoplasm and the ectoplasm is described as the surrounding lucid layer.

It is seen that even though the cytosol and cytoplasm are both fluids in the cell, they have their different specific function as well as common function in the cell. The cytosol concentrates its dissolved molecules into the correct position for efficient metabolism. While it concentrates molecules in the correct portions of the cytoplasm, the cytoplasm freezes organelles in place, ensuring efficient metabolism. However, they both play a role in the transportation of molecules, signal transduction, cytokinesis, and nuclear division.

Therefore, the cytosol and the cytoplasm both form the dynamic solution in the cell. Hence, the diversity of both the soluble and insoluble particles are high in the cytoplasm since the cytosol is a portion of the cytoplasm.