In biology, cells have fundamental or basic properties for living systems because all organisms are composed of cells. There are two types of cells, namely prokaryotes and eukaryotes.
Archaea and Bacteria consist of prokaryotic cells, while fungi, protists, animals and plants are included in eukaryotes. The main difference between eukaryotic and prokaryotic cells is the presence of Deoxyribo Nucleic Acid (DNA), as reflected in both types of cells.
Most of the DNA in eukaryotic cells is in an organelle called the nucleus, which is bounded by a double membrane. Meanwhile, DNA in prokaryotic cells is concentrated in an area not covered by a membrane, called the nucleoid.
The interior of prokaryotic cells on the other hand is called cytoplasm. The term is also used to refer to the area between the nucleus and the plasma membrane in eukaryotic cells. One of the characteristics of eukaryotic cells is that the nucleus is surrounded by a nuclear membrane.
Understanding Nucleolus
The nucleolus (also known as the cell nucleus) is the most prominent structure in the nucleus that does not divide. When viewed under an electron microscope, it appears as a mass of dark colored granules and the fibers are joined to parts of the chromatin.
The nucleolus is a membrane-bound structure consisting of nucleic acids and proteins in the cell nucleus. Alberts, et al (2002) also stated that the nucleolus is a true nuclear subcompartment that is not covered by a membrane. Champe, et al (2005) also clarified that the nucleolus is a subdominant nucleus that makes up ribosomal subunits in eukaryotic cells.
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Nucleolus Function
In general, animal cell components consist of:
- Nucleolus.
- Cell nucleus.
- Ribosomes (small dots as part of number 5).
- Vesicles.
- Rough endoplasmic reticulum.
- Golgi body.
- Cytoskeleton.
- Smooth endoplasmic reticulum.
- Mitochondria.
- Vacuoles.
- Cytosol (fluid containing organelles consisting of cytoplasm).
- Lysosomes.
- Centrosome.
- Cell membrane.
The function of the nucleolus is to synthesize various types of Ribonucleic Acid (RNA) molecules which function in the ribosome assembly process. Another function is to build ribosomes and be involved in the protein synthesis process. The nucleolus is inside the nucleus. The other parts of the nucleus are chromatin granules, nuclear membrane, and nuclear sap (nuclear fluid or nucleoplasm).
The functions of the nucleolus in animal cells include:
- The nucleolus has a role in forming ribosomal subunits. Ribosomes are cell components that form proteins from all amino acids, while subunits are parts of ribosomes that can increase transfer RNA (tRNA) and amino acids. Its function is to assemble amino acids into peptides into RNA. RNA is a biological molecule that plays a role in decoding, coding, regulation, and gene expression.
- The nucleolus is a protein producer for animals. Proteins on the other hand are complex organic compounds that have very high molecular capacity and are polymers of amino acid monomers, which are linked to each other by peptide bonds. The benefits of protein for animals are also very diverse, starting from forming bones, skin and blood.
- The nucleolus is a regulator of nutrient metabolism processes. This is because the nucleolus takes in every nutrient it gets. The cell nucleus also has its own function, namely the cell can understand genetic information or form RNA intermediaries and produce proteins.
- The nucleolus is one of the most important components as the main moving element. This is because the nucleolus has a function in regulating the flow of proteins. Protein itself is a very important substance for the body. So, every animal also needs protein. In fact, not only animals need protein, humans also need it so that their lives remain healthy forever.
There are many functions of the nucleus for animals, starting from regulating metabolism and the flow of proteins, making ribosomal subunits and RNA, providing nutrition, and strengthening bones.
The function of the nucleolus in animals is responsible for the process of protein formation, while its function in plants is as a place for RNA synthesis to take place.
Location of the Nucleolus
Nucleoli can be found in eukaryotic cells, including plant and animal cells. Sometimes, there are two or more nucleoli in the nucleus, depending on the type and stage in the cell’s reproductive cycle.
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Nucleolus Structure
The structure of the nucleolus will be visible under electron microscope observation which is larger than the size of the chromatin grains. The nucleolus is where gene transcription takes place, from which rRNA (ribosomal RNA) molecules are obtained.
rRNA is a type of RNA which is the material that forms ribosomes. The RNA content in the nucleus is not constant when compared to other parts of the nucleus, which is estimated at 5% – 20%.
The size of the nucleolus changes in the number of granular components during ribosomal gene copying. When synthesizing proteins, the nucleolus reaches 25% of the total capacity of the nucleus.
During interphase, the nucleolus is clearly visible. Furthermore, just before mitosis, the nucleolus breaks down and becomes small fragments which finally disappear when metaphase occurs.
The nucleolus disappears along with the formation of chromosomes and the cessation of RNA synthesis. At the end of telophase, the nucleolus begins to appear again as fine grains which over time will fuse to form one or more nucleoli. This can happen because the chromosomes have formed and RNA synthesis begins to stop.
The nucleolus consists of deoxyribonucleic acid (DNA), ribonucleic acid (RNA), and proteins found in eukaryotic cells. The structure of the nucleolus is the same in animal and plant cells. As reported on the Byjus page , eukaryotic cells have a well-ordered structure with four main ultrastructural components. These components include:
- The fibrillar center, which is the place where ribosomal proteins are formed or where rDNA takes place.
- Granular components, namely components that have rRNA and bind to ribosomal proteins before ribosomes are formed.
- Dense fibrillar components, namely components that have newly transcribed RNA linked to ribosomal proteins.
- Nucleolar vacuoles, which are components that only exist in plant cells.
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