Ribosomes

Introduction

A human being is a marvel in itself and there are so many wonderful things that happens in a human body. Almost everyone knows that we are made up of cells, but most of us do not have the idea about the different organelles, the cells are made of.

One such wonderful organelle is called ribosomes.

If you look at a cell under the microscope, you will always find Ribosomes. Ribosome got its name from the “Rib” in “ribonucleic acid” the chemical in the cell which helps Ribosomes make protein. 

Ribosomes

They are present in cells of both Humans, Plants and Animals. These are basically organelles that you will find in a cell of every type. Organelles are an important part of cells and are responsible for various functions in it. Some other organelles that are present in the body are the nucleus and mitochondria. 

Ribosomes as Discrete Organelles

Ribosomes are very different from other types of organelles because unlike others, they do not have a protective membrane around them. This thing is quite rare because almost every organelle has a protective layering.

As a science experiment, if you look at a cell under microscope you will see small dots floating around within the cell. The tiny dots are Ribosomes and are present in almost all parts of the cell. 

One very interesting fact about Ribosomes is that they are located very differently in plants and animal cells than they are in the human cells. In plants and animal cells you will only be able to see Ribosomes near the nucleus organelles and the endoplasmic reticulum.

Importance of Ribosomes

Ribosomes carry out some of the most integral parts of our bodily functions. They are so tiny that even in just a single cell there are as many as 10 million of them. Can you believe that? 10 million ribosomes in a single cell? The number of ribosomes in a single cell emphasize on their importance. 

Our cells need Ribosomes to make proteins in our bodies. Proteins are created through peptide bonds by Ribosomes. They are one of the fastest organelles and can break down more than 5 amino acids every single second for the production of a new protein. 

This process is even faster in Ribosomes found in Animal cells as they can add more than a million amino acids every second! 

Ribosomes as Protein Factories

Proteins are needed by our cells to perform many important functions. More than 20 percent of our body is proteins which makes it the second most abundant element in our body after water. Without proteins, our body will not be able to gain the nutrition that it needs. Protein is also needed by the enzymes in our body. If Ribosomes did not produce proteins for our body, then it will lead to a deficiency and our cells and enzymes will not be able to function properly.  

Plants, Animals and Human cells are not the only cells that contain these small Ribosomes. Even cells of bacteria need them to function properly. If you ever look at a bacteria cell, you will be able to locate Ribosomes by looking within the cytoplasm as they float around freely. 

Structure and Composition of Ribosomes

A ribosome is composed of more than 70 different kinds of proteins. Along with this, they are also composed of nucleic acid molecules of four different kinds. 

Main composition of a Ribosome includes RNA and proteins. 

These two are present in a balanced ratio and make up most of a Ribosome. The two main parts of Ribosome are divided into two subunits called the large subunit and the small subunit.

The large subunit

The large subunit is where the “translation” process takes place. This is the subunit where amino acids are actually broken down to make proteins. It is referred to as “60S” when talking about the composition of eukaryotic cells and as “50S” when talking about the composition of prokaryotic cells. 

Eukaryotic cells are present in all animals and plant cells and have a membrane-bound nucleus. They are also bigger in size than prokaryotic cells and therefore also have bigger sized Ribosomes. Prokaryotic cells are unicellular organisms and have a very simpler structure compared to eukaryotic cells. Also, Prokaryotic cells do not have mitochondria and are commonly present in Bacteria.

The Small Subunit

The small subunit is not called “Small” because its small in size but because of its smaller size relative to the larger subunit. It is responsible for the function of reading and translating the information about the “building blocks” in amino acids. These two subunits interact together when proteins are needed by the cell. Therefore, both the large and small subunit help in the creation of new proteins. Similar to the large subunit, it is also referred differently for eukaryotic cells and prokaryotic cells as its respective names are “40S” and “50S”.

There are two different types of Ribosomes found in different types of Cells and they both have different compositions. 

Difference between the 70S and 80S ribosomes

  • The 80S ribosomes have less rRNA and more protein as their respective ratio is 40: 60. Whereas, the 70S ribosomes have more rRNA and less protein in the ratio of 60:40. 
  • 80S Ribosomes are mainly produced within the nucleolus of the cells whereas, the 70S ribosomes are produced in the cytoplasm of prokaryotic cells. 
  • Because 80S ribosomes are larger in size they also have 18 more protein molecules than the 70S Ribosomes. They have 40 protein molecules in the larger subunit and 33 molecules in the small subunit. Whereas, the 70S Ribosomes only have 34 protein molecules in the large subunit and only 21 in the small subunit.

Process of Protein Synthesis

Now that we know what Ribosomes are made of, lets learn about their functions and how they actually make proteins.

Protein production is one of the most critical part of a cell. Without making proteins the cells in the body will not be able to survive. Our body is dependent on protein to function properly. Ribosomes help cells remain in a healthy condition by reacting with other parts of the cell. One such part is the nucleus, the cell’s nucleus and Ribosomes work together to make proteins.

This complete process of making proteins is called “Translation” and uses amino acids in the body for its successful operation.

To understand the process better, imagine that amino acids are “Small building blocks” and these small building blocks can be broken down and then reassembled. Naturally, the amino acids are not present in the correct order. Or you can say the small blocks in it are not aligned properly in order to turn into proteins. Ribosomes break down these small building blocks and rearranges them in the structure of a protein. The end result is that our cells get Proteins that are more specifically known as mRNA Proteins.

Role of RNA

Ribosomes are the only organelles that can interact with the RNA in the body to receive instructions from it. This is why cells need them, because Ribosomes are the only part in cells that can read the sequence of each small block in amino acids and they can “translate” these sequences into the sequence of proteins. The RNA (Ribonucleic acid) gives it instructions about how to rearrange the blocks to create proteins.

The “Translation” process Explained

The translation process is very complex, and Ribosomes have to interact with many different parts and chemicals present in the cell in order to finally create a protein. Let us look at details of every step involved:

  • First, the mRNA present in the Ribosome signals to the subunits that the cell needs new proteins.
  • This causes them to merge together and interact with each other.
  • To start the process, ribosomes need “codons” which are present in the RNA.
  • Once the Codons are located, they give Ribosomes instruction about how to rearrange and assemble the small building blocks in the right way so that they turn into proteins.
  • The Ribosome attaches each amino acid together, one after another which finally results in a protein being made.
  • The RNA waits for the right rearrangement to complete and as soon as the right sequence is completed by the Ribosomes. The RNA signals to them to stop attaching any more amino acids because the protein is now ready and does not need more amino acids.

Just like proteins are created through a process. Ribosomes are also created in the cell. Their place of production is a specific area in the nucleus called the nucleolus. 

Other functions of Ribosomes

Other than making proteins, Ribosomes are also responsible for creating digestive enzymes. This is mainly done by Ribosomes that are attached to the endoplasmic reticulum. 

Fun Facts about Ribosomes

  • Ribosomes were discovered in the year 1974 by three scientists and they also won a Nobel Prize for this discovery.
  • The discovery of Ribosomes helped many scientists to understand the functions of our cells and bodies in more detail. Firstly, scientist did not believe that ribosomes could actually make proteins, but later on the fact has been established. 
  • The scientists who discovered Ribosomes were Albert Claude, Christian de Duve, and  Emil Palade. They have been rewarded for the discovery of ribosomes because It helped the scientist all over the globe to understand the functioning of a cell and human body in general, perfectly.
  • Because Ribosomes are so important for making proteins in the body they are also known as “Protein Factories”. This name is so famous that most students around the globe call ribosomes by protein factories.
  • If Ribosomes did not make protein in our cells than many cellular activities in our body will start to dysfunction such as damage to our body and cells will not be healed quickly. 

For instance, let us say that you cut your finger while cutting onion. Right after the cut your body gets into the healing process. This happens because of the help of ribosomes and proteins. Without these two things clotting could not happen, and there was a chance that you could bled to death.

  • In some cells Ribosomes are free to move and float around everywhere while in others they are only attached to the cell’s organelles. 
  • Not all Ribosomes are alike, there are two different types including the 80S type which is only found in eukaryotic cells and the 70S which is only found in prokaryotic cells.
  • The Ribosomes found in eukaryotic cells are bigger in size than the Ribosomes found in prokaryotic cells.
  • A ribosome is so small in size that they can be as tiny as only 20 nanometers. Despite being tiny in size, they helped making the most amazing thing in our body – the proteins.
  • They are the only unique type of organelles that do not have a protective membrane. Almost every other organelle has a protective layering.
  • There are always two types of Ribosomes in a cell. One is always attached to the endoplasmic reticulum while the other floats around freely within the cytoplasm. 
  • Because they are the only organelles in a cell that can make proteins, they are widely used for making antibiotics. The antibiotics we consume on a daily basis when we are sick or in the midst of diseases is all because of ribosomes. These organelles have done a huge favor on a medical industry.
  • A single Ribosome is made up of three different types of RNA and they all help in making proteins. Such as the mRNA helps it to break and arrange the proteins and the tRNA finally synthesizes the protein into its final form. 
  • Scientists distinguish between different types of Ribosomes by the unique colors of their components. 

Conclusion

Human cell cannot function properly without the help of organelles. On the one hand we have mitochondria, that helps providing the necessary energy to our body. On the other hand, we have ribosomes, that help in making proteins. 

Ribosomes help to keep us alive in the most beautiful way and that is why they are considered a viable organelle in the human body.

References

  1. Denise R. Ferrier, Lippincott Illustrated Reviews, Biochemistry, Ed. 6th
  2. Rodwell, Kennelly, Harper’s Illustrated Biochemistry, Ed. 30th