What Is An Organelle?

An organelle is a general term for the small organs or subunits within a cell. Organelles are vital for the function of a cell and represent the various “workers” within the cell with specialized functions.

Organelles, or more accurately, cellular organelles are essential for understanding cells and cellular structure. Human beings, like other organisms, are made from millions of different cells. Every bodily function is carried out thanks to cells.

“A cell has a history; its structure is inherited, it grows, divides, and, as in the embryo of higher animals, the products of division differentiate on complex lines. Living cells, moreover, transmit all that is involved in their complex heredity.” — Frederick Gowland Hopkins

Everything from digesting food, blood pumping, storing fat, and the rest of bodily functions are the result of the electrical impulses that cells send out. All living creatures on our planet, from human beings to birds, insects, or even microorganisms are made from a cell. It does not matter how small or big the organism in question is. Each organism needs a complex structure in order to function and stay alive.

What Types of Cells Are There?

There are two types of cells: prokaryotic and eukaryotic cells. The main difference between these two types of cells is that prokaryotic cells do not have any membrane-bound nuclei, while eukaryotic cells do. Both types, however, have membranes, DNA (Deoxyribonucleic acid), and ribosomes, which allows them to create proteins.

In this article, we will just focus on eukaryotic cells, which are also known as eukaryotes. This is because prokaryotic cells or prokaryotes do not contain organelles.

Looking Inside Cells

If we looked inside a prokaryotic cell, we would find see a structure made of a membrane. This membrane-bound structure is what is known as an organelle.

  • The membrane that bounds the organelle is made from two layers of phospholipids. The function of this double layer is to insulate all the little compartments that are in every large cell.
  • Each of the compartments within organelles has a very specific function or task that it carries out.
  • The cell membrane also contains a liquid known as cytoplasm due to its viscosity. Organelles “live” in that viscous liquid.

What Are the Different Tasks That Organelles Do?

Let’s look at all the different organelles and the functions they carry out.

  • The nucleus is the organelle that takes care of storing DNA. DNA is the blueprint for every single organism.
  • Every protein in our bodies is blueprinted by our DNA. But before that happens, certain processes need to take place. All these processes take place in the cell’s nucleus. The nucleus is surrounded by a nuclear envelope. Once the transcription of the DNA has taken place within the nucleus, the membrane that surrounds it provides the necessary room so that the genetic information is protected. This membrane is also where all the molecules tasked with protecting the genetic information are stored.

“The cell of a higher organism contains a thousand different substances, arranged in a complex system.” — Herbert Spencer Jennings

  • This membrane has two layers made from four different sheets of liquid. These layers keep the nucleus separated from the cytoplasm. The space created by these layers is referred to as the perinuclear space.
  • The mitochondrion is the organelle that is responsible for producing energy. If we were to use an industrial metaphor to describe the mitochondrion, we could say that it is the cell’s powerplant.
  • The Smooth Endoplasmic Reticulum or SER is tasked with both producing lipids and with detoxification.
  • The Rough Endoplasmic Reticulum or RER is responsible for the production of protein. In particular, the protein that gets produced by the Rough Endoplasmic Reticulum is for export.
  • The Endoplasmic Reticulum is a plasma membrane located in the cell. When it RER folds itself, it creates a lumen, which is the name for the internal space, continuous with the perinuclear space.
  • There are two different kinds of endoplasmic reticulum, smooth and rough. The rough one is where the protein is produced, while the smooth one is where lipids (fats) are created.
  • The RER is considered rough because of the ribosomes that stud its surface.
  • Firstly, the protein is created inside before going through the process known as glycosylation. Glycosylation is what happens when the protein is folded and then tagged with a molecule.

But before the protein is ready for export out of the cell, it needs to be modified (or, in order words, it needs to get ready to be exported). The organelle responsible for this is called the Golgi apparatus.

Once the proteins have been produced by either rough or smooth endoplasmic reticulum, they are sent out by the Golgi apparatus. The Golgi packs the protein from the RER and puts them into the vesicles, which are small compartments made from a lipid bilayer charged with storing molecules. It is through these vesicles that the proteins get to the cell membrane or to be released outside the cell. But not all the molecules that enter the Golgi apparatus have the same fate. The proteins are tagged with different sugar molecules that determine their fate. The Golgi apparatus identifies the sugar molecules and uses that information to send the protein in question to one of the following four paths:

  • Cytosol
  • Cell membrane
  • Secretion
  • Lysosome

If a protein enters the Golgi apparatus in error, it is sent back where it came from using the cytosol. The cell membrane is used continuously. After the vesicle has been created, it goes to the cell membrane and both the cell membrane and the vesicle become fused. But there are some proteins that are supposed to be secreted on different parts of the body. In that case, before the vesicles are fused with the cell membrane, they accumulate. They are only released when they get a chemical signal. But that only happens when a large enough number of them has accumulated.

Finally, proteins get to an acidic organelle known as the lysosome. The lysosome hydrolyzes the contents of the lysosome thanks to their special enzymes.

“Our investigations were very fruitful. They led to the discovery of a new cell part, the lysosome, which received its name in 1955, and later of yet another organelle, the peroxime.” — Christian de Duve

The Smooth Endoplasmic Reticulum is tasked with making steroids and fat (lipids). So, they are not involved in the production (synthesis) of protein. The organelle that destroys lipid is called the peroxisome. The peroxisome is where the oxidative enzymes are stored. And finally, the lysosome is tasked with the destruction of protein.