Are Ribosomes Found In Nucleus? 7 Facts You Should Know


Ribosomes are the protein manufacturing machine like organelle that is present in a cell. Let us now discuss more on the prevalence of ribosomes inside a cell.

Ribosomes are not found primarily in nucleus, but the nucleus is the site were the ribosomes are being manufactured. Nucleus is a significant organelle that contains all the genetic or hereditary information and materials. Nucleus is like the heart of the cell

The nucleus consists of few components which are the nucleolus, nuclear membrane, chromatin, chromosomes and many more. The nucleolus is the manufacturer of the ribosomal parts.

Ribosomes are manufactured inside of the nucleolus which is present in the nuclear membrane and then soon transported to cytoplasm and other organelles.

Are ribosomes found in nucleolus?

Nucleolus is the biggest organelle inside the nuclear organelle which is present inside the nuclear membrane. Let’s explore more on this.

Ribosomes are found in nucleolus. To be more precise, the answer is partially yes. The nucleolus is the organelle inside the nuclear membrane where the ribosomes are being made or manufactured. Ribosomes do not stay there but they are produced and transported to cytoplasm.

We already know that the ribosomal structure have 2 subunits. They are, the ribosomal subunit which is small, known as the small subunit and the ribosomal subunit which is large, known as the large subunit.

  • The prokaryotic ribosomes have 70s ribosomes (S- Svedberg ).
  • The eukaryotic ribosomes have 80S ribosomes (S- Svedberg ).
  • Prokaryotic ribosome are 50S and 30S which is the 70S complex
  • Eukaryotic ribosome are 60S and 40S which is the 80S complex.

Which type of ribosomes are found in the cell?

Ribosomes are of different types based on their working mechanisms. Let us have a clear view on each ribosomes.

  • Bacterial Ribosomes: Ribosomes that are found in bacterial cells have a sedimentation coefficient of 70S.
  • Mitochondrial Ribosome: There are mitochondrial ribosomes, which are called mitoribosomes. There are several types of mitoribosomes, such as 73S mitoribosomes in fungi, 78S mitoribosomes in plants (e.g., corn), and 60S mitoribosomes in mammals. In general, mitoribosomes are referred to be as the 70S.
  • Plastidial ribosome: Plastidial ribosomes or plastidoribosomes are ribosomes found in chloroplasts. Plants with higher levels of plastidoribosomes have 70S.
  • Nuclear Ribosome: The nucleus contains ribonucleoprotein particles called nuclear ribosomes. A nucleolar ribosome is a ribonucleoprotein particle with a diameter of 150-200 * found in the nucleolus.
  • Cytoplasmic ribosome: The cytoplasm contains large ribosomal particles called cytoplasmic ribosomes.

Explain more on the functions of ribosomes found in the cell:

Every organisms needs protein for their functioning, ribosomes aid in the manufacturing of these protein. Below we can find the various functions of ribosomes.

  • Ribosomes are responsible for protein synthesis (translation-process of synthesizing proteins). 
  • Ribosomes are the sites of biological protein synthesis in all living cells.
  • The ribosomes also act as transporters of synthesized proteins.
  •  The cytoplasm contains free ribosomes that synthesize proteins that are essential for protoplasm formation.
  • In the biochemical process of the transfer of peptide and hydrolysis of peptide, the catalyst or the process speeding up material is the organelle ribosomes.
  • The amino acid chains or the multiple peptide chain called the polypeptide chain are guarded against the enzymes which utilizes proteins called the protease or proteolytic enzyme as they flow through a sequence of the ribosome large subunit.

Explanation on the chemical composition of ribosomes:

Every molecule is made up of unique chemical segments which will distinguish it from other chemical molecule. Let’s discuss on the various chemical composition of each ribosomes.

Ribosomes consist of the ribosomal RNA which are represented as rRNA and the second component is ribosomal protein. 60% of ribosomes constitute of ribosomal RNA or the rRNA and 40% of the ribosomes are of ribosomal proteins.

Prokaryotic ribosomes:

The prokaryotic ribosomes or the 70S ribosomes have three types of rRNA and they are 23S rRNA, 16S rRNA, 5S rRNA which has around 3300 nucleotides, 1650 nucleotides, 120 nucleotides respectively.

Eukaryotic ribosomes:

The eukaryotic ribosomes or the 80S ribosomes consist of four types of rRNA and they are 28S rRNA, 18S rRNA, 5.8S rRNA, 5S rRNA which has 4700 nucleotides, 1900 nucleotides, 160 nucleotides, 120 nucleotides respectively.

Structure of ribosomes found in the nucleus:

The structure of the ribosomes can be assumed as a sandwich for better understanding. We can now have a look at the structure with the diagram.

  • The ribosome is an oblate spheroid structure and the most abundant organelle in a cell.
  • Approximately 250 Å  is the diameter of each ribosome.
  • In current research, each ribosome is said to be porous, moist rich, and made up of two unequal subunits, one larger and one smaller. 
  • There are two subunits. The larger one is dome-shaped or cup-shaped (140-160 *), while the smaller one is oblate-ellipsoidal (90-110 Å).
  • The small subunit is situated over the large subunit and is about equally half the size of the larger subunit.
are ribosomes found in nucleus
Structure of Ribosomes
Image credits: Wikimedia
  • There are two subunits in a 70S ribosome, 50S and 30S. 
  • In comparison, the molecular weight of the larger 50S subunit is about 1.8 * 106 Daltons, while the smaller 30S subunit is about 0.9 × 106 Daltons
  • In contrast, the 80S ribosome also contains two subunits, 60S and 40S.
  • Molecular weight: 60S subunit is 1.5-1.8 * 106 Daltons
  • Molecular weight: 40S subunit is 3-3.5 * 106 Daltons.

Does the nucleus produce ribosomes?

We know that a nucleus has a nucleolus in it. Here we will discuss more on the production of ribosomes.

Nucleus do not produce ribosomes but the nucleolus do! Though, nucleolus is present inside the nucleus we can not say that ribosomes are being produced by nucleus. Nucleolus produces the ribosomes and are the site of synthesis for ribosomes.

Nucleus being a large organelle performs endless prioritized tasks. In case of nucleolus, their sole function is to produce the ribosomes and this is why it is said that the nucleolus produces the ribosomes and not the nucleus.

Nucleus is a complex organelle with multiple function, as referred already they are like the heart of the cell. The presence of ribosomes is only during their manufacturing process and of course they are produced in the nucleolus.

Explain the number of ribosomes?

Ribosomes are infinite in a cell. Let’s discuss the count of ribosomes.

It is said that about 20000-30000 number of ribosomes are present in the E.coli, which is a single cell organism and in case of the mammalian cells, there is a possibility that approximately around 10 million ribosomes are present so the number of ribosomes are countless.

E.coli, which is the smallest cell among all cells has so much number of ribosomes so, when it comes to other organisms cells like plasma, liver cells, nerve cells and also in yeast cells, their count are infinite.

Where does the ribosomes occur and how?

Ribosomes are of two forms and let’s have a deeper view on their occurrence and availability.

  • We can observe ribosomes in cells of prokaryotes as well as eukaryotes.
  • Ribosomes are often found scattered freely in the cytoplasm of prokaryotic cells. 
  • The ribosome either dwell freely floating in the cytoplasmic space like in the organisms like yeast cells, meristematic plant tissues, lymphocytes, embryonic nerve cells, etc.
  • Ribosomes also will be adhered to the outer layer of the endoplasmic reticulum membrane and nucleus membrane like pancreatic cells, serous cells, plasma cells, Nissl bodies, hepatic parenchymal cells.
  • Functional ribosomes (that ones where active protein synthesis are performed) are attached to the membranes of the endoplasmic reticulum and other organelles.
  • The free ribosome is a ribosome that is not adhered to the endoplasmic reticulum or any other organelles and they float freely.
  •  Ribosomes are free-floating structures in the cell that synthesize proteins that are needed for intracellular utilization and storage.

Conclusion:

The article ‘Are Ribosomes Found In Nucleus? 9 Facts You Should Know’ explains in detail about the organelle nucleus and the presence of ribosomes in it. It also explains on the type and subunit of the ribosomes with their occurrence and function and chemical composition.

Sugaprabha Prasath

Hello, I am Sugaprabha Prasath, a Postgraduate in the field of Microbiology. I am an active member in Indian association of applied microbiology (IAAM). I have research experience in preclinicals (Zebra fish), bacterial enzymology and nanotechnology. I have published 2 research articles in an International journal and a few more yet to be published, 2 sequences submitted in NCBI-GENBANK. I am good at clearly explaining the concepts in biology both basic and advance level. My area of specialization is biotechnology, microbiology, enzymology, molecular biology, pharmacovigilance. Apart from academics, I love gardening and being with plants and animals. My linkedin profile- https://www.linkedin.com/in/sugaprabha-prasath-66937b1b3/

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