- Why are Ribosomes important to the cell?
- There are 7 important functions of Ribosomes in the cell. These are mentioned below:
- 1. Ribosomes bring together mRNA and tRNAs to catalyze protein synthesis
- 2. Ribosomes are required for the growth of the cell
- 3. Free Ribosomes located in the cytoplasm create proteins that can be used within the cell
- 4. Bound Ribosomes create proteins that leave out of the cell
- 5. Ribosomes remain in close association with the Endoplasmic Reticulum and the Golgi apparatus to facilitate proper protein synthesis and transportation
- 6. Ribosomes are required to create various Enzymes
- 7. Ribosomes are required to bring genetic information via reproduction
Why are Ribosomes important to the cell?
Ribosomes are the macromolecules inside the cell. Some often term these as tiny cell organelles that don’t have any membrane.
These ribosomes are present in both eukaryotic and prokaryotic cells and function significantly in the production of proteins for the cell.
The proteins that are produced due to the involvement of the ribosomes via the process of protein synthesis are used in the growth, division, and maintenance of the cell and its structure.
Some of the proteins are also exported out of the cells for carrying out the various metabolic activities of the biological body in eukaryotes.
Anything inside the cell from the cell membrane, cell wall, organelle envelope, structure of mitochondria, endoplasmic reticulum, etc. are made up of components of proteins.
So, if ribosomes wouldn’t have been there then the structure and working of the cell wouldn’t been possible to maintain and keep intact.
Ribosomes are actually the biocatalysts that take part in the synthesis of proteins. That is they can read the coding of mRNA and then can catalyze the peptide bond formation of the chain of the amino acids to produce proteins with the help of tRNAs.
We all know that each ribosome consists of two subunits. Each subunit comprises ribosomal RNAs (rRNAs) and ribosomal proteins (r-proteins).
The rRNAs seem to be responsible for most enzymatic activities, whereas the r-proteins are proposed to have largely structural roles, but when combined together they carry out the translation of genes
Below, we have provided 7 important functions/roles of ribosomes in the cells. Also note that protein synthesis is the main role of ribosomes, and the rest of the other roles are just related or dependent either directly or indirectly on protein synthesis.
There are 7 important functions of Ribosomes in the cell. These are mentioned below:
1. Ribosomes bring together mRNA and tRNAs to catalyze protein synthesis
As already said, ribosomes are those macromolecules that take part in protein synthesis by catalyzing the formation of proteins.
It has been seen that when ribosomes are not active, they split into the two separate subunits, one large and one small subunit, and float freely in the cytoplasm.
And, as the protein synthesis begins, one small and one large subunit come together to form an active ribosome and catalyze the translation of mRNA to proteins.
Translation occurs at particular sites within the cytoplasm. One large subunit sits on top of the Start Codon of mRNA, and the one small subunit sits at the bottom at the same Start Codon position of mRNA.
tRNA also gets attached to the mRNA. Each tRNA molecule has two distinct ends, one of which binds to a specific amino acid, and the other which binds to the corresponding mRNA codon.
In this way, it covers the mRNA strand from top and bottom forming the ribosomal structure. As the ribosome is formed it starts translation that is the synthesis of proteins from the Start Codon end of mRNA to the Stop Codon end of mRNA.
The smaller subunit reads the coding of mRNA, and the larger subunit functions to link the amino acids with peptide bonds to form various protein chains.
tRNAs function there is to carry amino acids to the ribosome and join with their complementary codons.
2. Ribosomes are required for the growth of the cell
We all know that proteins are required for the structure, function, and regulation of the body’s tissues and organs.
And as, ribosome catalyzes the function of protein formation, therefore it can also be said that ribosomes take part in the cell growth.
A rapidly growing mammalian cell can contain about 10 million ribosomes, that’s how important ribosomes are.
And, they are actively involved in the formation of proteins that are required for the maintenance of the cell and its function.
Ribosomes can join up amino acids at a rate of 200 amino acids per minute. Small proteins can therefore be made fairly quickly, but two to three hours are needed for larger proteins such as the massive 30,000 amino acid muscle protein Titin.
Ribosomes itself are made of ribosomal proteins that fall into various energy-consuming enzyme families including ATP-dependent RNA helicases, AAA-ATPases, GTPases, and Kinases.
So, almost 60% of the cell’s energy is spent on ribosome production and maintenance. And, the cell is ready to spend the energy because it’s worth the production of ribosomes for the sustainability, growth, and division of the cell.
For instance, the proteins that include kinases and cyclins can regulate and help in the cell growth by properly running the cell cycle that leads to replication and division of the cell.
Another example is the Retinoblastoma protein that regulates cell proliferation, differentiation, and endoreduplication in plants.
All of these and many other proteins can only be synthesized when the ribosomes are there and actively working in the cell.
3. Free Ribosomes located in the cytoplasm create proteins that can be used within the cell
In eukaryotes, there are two types of ribosomes that are formed: Free Ribosomes and Bound Ribosomes.
Free Ribosomes are located freely in the cytoplasm and create proteins that can be used within the cell.
In simple words, the free ribosomes are able to move throughout the cell and can continuously synthesize proteins by translation of genes that are released into the cytoplasm and used within the cell.
It is also very important to note that free ribosomes remain excluded from the cell nucleus and other organelles, and can only work in the cytoplasm strictly.
We all know that the cell itself is made up of proteins and the proteins produced by free ribosomes are used to make the cytoplasm gelatinous, create the supportive structure of the cytoskeleton, make the structure of mitochondria, chloroplasts, cell membrane, etc.
In simple words, anything that you can imagine of made up of proteins inside the cell is due to the involvement of free ribosomes. Without free ribosomes, the various components of the cell could not function.
Just for example, mitochondrial proteins like UCP2, UCP3, including 1100 to 1400 other distinct mitochondrial proteins are generally involved in the mitochondrial function like carrying out reactions of the electron transport chain.
4. Bound Ribosomes create proteins that leave out of the cell
Another type of ribosomes are the bound ribosomes. These are also known as attached ribosomes.
Bound Ribosomes are the membrane-bound ribosomes that remain attached to the outer membrane of the Rough Endoplasmic Reticulum and create proteins that leave out of the cell.
The outer surface of the Rough Endoplasmic Reticulum (RER) is rough due to the presence of ribosomes attached to it.
These bound ribosomes not only create proteins that can leave out of the cell immediately but can also create proteins that will be stored in units called vesicles for future delivery outside of the cell.
These vesicles contain proteins and lipids together with the cytoplasmic liquid that is meant for delivery to targeted destinations outside of the cell naturally during the processes of secretion (exocytosis).
Just for example, the pancreas cells can produce and secrete enzymes (enzymes are made up of proteins) in the small intestine, that are important for digestion of food.
These pancreatic enzymes include trypsin and chymotrypsin to digest proteins, amylase to digest carbohydrates, and lipase to break down fats.
So, how are these enzymes (made up of proteins) are produced to be transported out of the cell. It’s because of the presence of many bound ribosomes inside the pancreatic cells.
It is also to be noted that there are more bound ribosomes present in the cells like brain cells, pancreatic cells, etc. as compared to the other normal cells of the body.
It’s because they are more actively involved in the production and secretion of numerous proteins in the form of various enzymes, hormones, etc.
5. Ribosomes remain in close association with the Endoplasmic Reticulum and the Golgi apparatus to facilitate proper protein synthesis and transportation
Yes, the ribosomes remain in close association with the Endoplasmic Reticulum and the Golgi apparatus to facilitate proper protein synthesis and transportation.
This function is related to the function we have studied in point number 4.
You can better call it as the Endomembrane system, that includes the cell organelles like Rough endoplasmic reticulum (ER), Golgi apparatus, Lysosomes, and Vacuoles together with the involvement of bound ribosomes.
Meaning that the ribosome will produce the proteins and those other cell organelles that are included in the endomembrane system will work together to modify, package, and transport lipids and proteins out of the cell.
The Rough Endoplasmic Reticulum due to the presence of bound ribosomes will produce proteins along with the modification of various other proteins such as the addition of carbohydrate side chains, etc.
These proteins gets packaged along with lipids and a bit of the cytoplasmic liquid inside the structure of various vesicles. And, these vesicles will be stored inside the Golgi Apparatus.
Such sorting, tagging, packaging, and distribution to form vesicles takes place in the Golgi apparatus.
Those vesicles that will leave the Golgi apparatus will form the lysosome. The lysosome contains digestive enzymes that are naturally occurring and can be found in bodily secretions such as tears, saliva, and milk.
Plant cells will contain vacuoles. These vacuoles are somewhat larger vesicles with water containing inorganic and organic molecules including enzymes in solution.
The plasma membrane is also part of the endomembrane system, as the plasma membrane also interacts with the other endomembrane organelles to take out the contents stored in the vesicles.
Thus, overall if you see, the ribosomes will create the proteins that are to be transported out of the cell either by exocytosis or indirectly by endocytosis. These proteins along with other biomolecules will be stored, packaged, and transported with the active involvement of the organelles of the endomembrane system.
6. Ribosomes are required to create various Enzymes
We all know that enzymes are made up of proteins. Each enzyme is made by joining together about 100 and 1,000 amino acids in a very specific and unique order.
Enzymes are important as they are the biological catalysts that speed up the rate of various chemical reactions taking place inside the cell by lowering down the activation energy of the biomolecules taking part in the chemical reaction.
These protein-based catalysts can catalyze all kinds of chemical reactions that are involved in growth, blood coagulation, cell healing, immunity, breathing, digestion, reproduction, and many other biological activities.
Ribosomes particularly the bound ribosomes are majorly involved in protein synthesis, as these are the sites of protein synthesis and enzymes, as they are involved in the polymerization of amino acids to form proteins.
For example, the pancreas is responsible for creating several digestive enzymes and the cells that produce these enzymes contain many ribosomes.
Another example is that the mucous cells lining the intestinal wall are actively involved in the production of maltase enzymes.
Maltose is made of two glucose molecules bonded together. The maltase enzyme is a protein that is perfectly shaped to accept a maltose molecule and break the bond.
7. Ribosomes are required to bring genetic information via reproduction
It is to be noted that ribosomes are not self-replicating and so can’t be passed in the form of genes from the parents to offspring.
But the genes that are the segments of DNA when gets passed to the offspring, there in the offspring cells the ribosomes are produced actively by ribosome biogenesis to take part in the cellular metabolic activities of the offspring.
Inside the nucleolus of the offspring’s cells, the production of rRNA from rDNA takes place. And, in the cytoplasm the production of 200+ ribosomal proteins takes place from ribosomal mRNA segments.
These rRNA binds with the various ribosomal proteins to form the subunits of ribosomal inside the nucleolus of the offspring’s cells.
These subunits come out of the nucleolus and the nucleus via the nuclear membrane and get assembled in the cytoplasm to translate the various mRNA segments of the offspring’s genes leading to the production of various proteins.
As the proteins produced will bring out the genetic changes in the body of the offspring. Thus, we can also say that ribosomes are required to bring genetic information via reproduction.