Nucleus and ribosomes (article) | Khan Academy
Nucleus vs Nucleolus. Every organism has the most basic component of life, which is the cell, and in almost all cells there is the nucleus. Structure and function of the nucleus and ribosomes of a cell. In fact, that’s exactly what eukaryotic cells do with their genetic material, placing it in a membrane-enclosed repository called the nucleus. The nucleus (plural, nuclei) houses the cell’s genetic material, or DNA. Ribosomes are large complexes of protein and ribonucleic acid (RNA) responsible for protein synthesis when DNA from the nucleus is transcribed.
But what is the structure? Let's look at the outside of the nucleus first. The nucleus is surrounded by two separate membranes, an outer membrane and an inner membrane. Let's look at this structure up close. So, we have an outer membrane, and we have an inner membrane. These two membranes separate the nucleus from the cytoplasm, which is the liquid-filled space that makes up the majority of the cell, and all of the non-compartmentalized parts of the cell.
Essentially, the parts of the cell that aren't enclosed within an organelle. On the inside of the nucleus is what's called the nucleoplasm. In the nucleoplasm is the fluid inside the nucleus. And so these two, the cytoplasm and nucleoplasm, aren't continuous. However, a lot of the times, the stuff needs to be transported between the nucleoplasm and the cytoplasm.
And also, proteins in the cytoplasm need to be able to get into the nucleus, such as polymerases, which convert DNA into messenger RNA. So this transport of things like MRNA out of the nucleus, and protein into the nucleus, happens at a special complex called a nuclear pore.
How are the nucleus and the nucleolus different? | Socratic
And so there's another nuclear pore over here in my blown-up diagram of the outer and inner membranes. What's interesting about the nuclear pore, is that it spans both membranes, the outer membrane and the inner membrane, so that compounds in the cytoplasm can be transported into the nucleus, and compounds in the nucleus can be transported out.
But now, the cell has gone to a lot of trouble to create these two lipid membranes to isolate the nucleus from the rest of the cell. So the nuclear pore is actually very selective in what can be transported inside and out. And so the nuclear pore actually recognizes special signals on different proteins, and only with the presence of these signals, can proteins be transported into and out of the nucleus through the nuclear pore.
So the nucleus' primary function is to contain the cell's DNA, or chromosomes. But when you look at the nucleus up close, you see there is a very densely compacted area.
And this area is called the nucleolus. Just as the nucleus is kind of the center of the cell, the nucleolus is the center of the nucleus. Moreover, the nucleus is also responsible for generating genetic expression to monitor the proper activities of the entire cell. Meanwhile, the nucleolus is responsible for another essential function for the entire cell.
The nucleolus is responsible for the collection and transcription of RNA, particularly the ribosomal nucleic acid or rRNA.
Nucleus and ribosomes
Moreover, the nucleolus is responsible for the synthesis of ribosome which is essential to perform activities in the entire cell. Given that the nucleus is somewhat the mother of the nucleolus, the nucleus is also able to do the same action.
However, it focuses more on storing DNA and preserving the chromosomes inside of it. And speaking of chromosomes, the nucleus is the organelle that contains the chromosomes for cell reproduction. Meanwhile, the nucleolus is a dense, strained structure inside of the nucleus that contains ribosome.
Although the nucleolus is just somewhat a sub-organelle of the nucleus, the nucleolus still has three main regions. The first region is the fibrillar centers. This region is usually where the transcription of rDNA takes place. Surrounding the fibrillar centers are the dense fibrillar centers. This is where the modification and cleavage of rRNA happens. The dense, fibrillar centers are then bounded by the granular component.
The granular component is where the assembly of protein going to the ribosomal sub-units happens. The nucleus is the main organelle while the nucleolus is the sub-organelle.
The nucleus is membrane bound while the nucleolus is non-membrane bound.