Cytoplasm is the scientific name for one of the most common and important fluids in the human body, the one inside cells. It has the texture of jelly and it consists mostly of water and salt. It is found in every human cell, in all types of tissues and internal organs.
The name was invented in 1863 by Swiss scientist Rudolf von Kölliker. Initially, he considered cytoplasm to be the same thing as protoplasm. Later, the meaning of the term changed, covering every cell contents except the nucleus.
Cytoplasm makes up most of the cell content and is responsible for its shape and size. It anchors the organelles and fills the cell space, without it our body cells would be much smaller and nutrients couldn’t circulate between organelles. The enzymes that start metabolic processes inside the cells are all part of the cytoplasm. These enzymes also destroy toxins and other waste resulting from cellular activity. We can conclude that most of the important processes inside cells happen in the cytoplasm.
The main role of cytoplasm is to support the organelles inside cells in a suspended state, maintaining their structural integrity. The fluctuating concentrations of solutes make organelles unstable inside cytoplasm, they are not naturally fixed in place and would float freely without a mechanism to keep them stable. This is accomplished by a matrix of proteins that anchors and separates them from the rest of cytoplasm. The part of cytoplasm without any organelles is named cytosol, the protein network keeps it apart from them. Without it, the cellular forces as well as gravity would eventually make all of the organelles drop to the bottom of cells, which would severely impair their activity and cause health problems.
The second major role of cytoplasm is in the transport of all the supplies and products inside the cell. Cells function like small factories at a molecular level, they have a constant genetic and metabolic production. Cytoplasm ferries everything needed, mostly the energy feed required by the cells in order to survive but also more complex materials, such as the RNA components. In this role, cytoplasm also functions like a storage deposit. Basically, the materials just float inside until they are used, no special deposit facilities are required.
The third essential role of cytoplasm in the life of cells is to protect them and absorb shocks. As cells move inside the body, it is inevitable they will bounce with each other or hit other tissues. Cytoplasm shields the organelles from these shocks and acts like a safety layer in case of clash damage. The most fragile organelle, which needs the most protection, is named lysosome. Lysosome is home to several waste-processing enzymes but has a delicate structure. Without the buffer provided by cytoplasm, it would break on shock and spread these enzymes inside the entire cell, killing it from within.
The structure of cytoplasm can be roughly divided in two parts. The part near the edge is very dense and resembles jelly, being named plasmogel for this reason. The rest is much thinner, especially the part close to the cell nucleus which is almost liquefied, this part is called plasmosol. Overall, cytoplasm is made of organelles, cytosol and other particles that float in it.
Cytoplasm is colloidal due to a combination of both opaque granules and various organic molecules. This makes it have inconsistent staining properties. The basophilic parts are stained with basic dyes and are named ergatoplasm for this reason, while other areas can be opaque.
By far the most important part of cytoplasm is cytosol, which contributes around 70% of the total volume of every cell. It is basically a saline solution in which various organic compounds are floating. Water and salt makes up most of it, the rest are cytoskeleton filaments, as well as various organic and mineral molecules, some of which are soluble. Some examples include ribosomes, proteasomes, soluble proteins but also protein filaments structured as a matrix. The other part of cytoplasm, located near the core of the cell, is named endoplasm. It is a lot more fluid and granular compared to cytosol. The amount of fibers and soluble proteins can sometimes be very high, this causes cytoplasm to become saturated and can have important effects on the cell and the relation between the different components.
As for organelles, they got their name because they are somehow similar to the organs inside the body. Like their big counterparts, the little organs have specific roles in order to ensure the operation and survival of the cell. Organelles include endoplasmic reticulum, Golgi apparatus, vacuoles, lysosomes or mitochondria. In addition, plant cells also have chloroplasts. All of them can be found in cytosol, in a suspended state.
The other elements suspended in the cytosol are a wide array of particles collectively named cytoplasmic inclusions. These can be nutrients like starch or glucose, stored in the cell for later usage, or inorganic molecules (calcium oxalate crystals or silicon dioxide crystals in the case of plants). A very common inclusion is droplets of lipids. These can be found in prokaryotes and eukaryotes and serve as deposits for all types of lipids, including sterols and fatty acids. Droplets have a spherical share and consist of a mix of proteins and lipids. Specialized storage cells named adipocytes have a large number of droplets but they can be found in basically every type of cell.
Functions of cytoplasm
As already mentioned, cytoplasm serves three primary functions in the life of a cell. First of all, it provides an environment for organelles, the tiny formations that perform key duties. The second is to act as a transport medium for all the materials and waste related to the cell’s metabolism, as well as the genetic content. The fluid and jelly consistency of cytoplasm also makes it an excellent shock absorber, it shields the DNA and the organelles from damage during collisions.
Cytoplasm is so important in the life of a cell that any defects lead to its death. This is because all of the chemical reactions that sustain life take place in the cytoplasm, so its malfunctions break down the entire chain and no living creature is able to survive. All of the important enzymes of the cell reside inside cytoplasm. They separate nutrients into smaller molecules, which are then processed into energy by the mitochondria. Without them, organelles alone would be unable to break down glucose into pyrovate, the fuel of the cell’s energy needs. Cytoplasm is the medium where all of the organelles are located. While a protein matrix gives a cell its structure, it is cytoplasm that actually inflates the cell and defines its shape. Fatty acids, amino acid and sugar are produced inside the cytoplasm, which also plays a key role in the process of glycolysis. Cytokinesis, protein synthesis, anaerobic glycosis are other critical processes that take place inside the cytoplasm.
Organelles are tiny structures that replicate at a cellular level the main functions of the body: one is responsible for respiration, another of feeding and so on. Numerous other molecules float freely in the cytoplasm, most of them are insoluble nutrient particles that are just stored in there for later consumption. Another role of cytoplasm and the protein matrix inside it is to prevent the floating of organelles, which would otherwise all drop to the bottom.
Numerous biochemical transformations that are a key part of the magic of life actually happen at a low level inside the cell cytoplasm. It transports the cellular products and also grows in size at the same time as the host cell. It ferries oxygen to the cell and the enzymes that float inside it break down nutrients into small molecules that can be assimilated.