In this lesson, we’ll learn what a eukaryotic cell is and what a nucleus is. We’ll also cover what the nucleus does in these cells and why it’s important.
Definition of a Eukaryote
The human genome project, cloning, and personalized medicine are all hot topics in the news lately.
What do all these exciting advances have in common? DNA! All cells have DNA, or genetic material that controls cell activities. Our DNA makes us who we are and gives us traits, like our height, skin color, and facial features. DNA is crucial for other, less noticeable traits as well, like keeping our blood vessels pumping blood and our diaphragm expanding and contracting to allow us to breathe. So as you can see, DNA is a very important part of our cells. Because of this, our cells house it in a structure called the nucleus.Cells with nuclei, like ours, are called eukaryotic.
Instead of leaving the DNA free floating in the cell like prokaryotes, or single-celled bacteria and similar organisms do, eukaryotes keep the DNA safe inside the nucleus. The nucleus has several important functions inside the cell, including storing DNA, copying DNA as needed, and making a cell structure called the ribosome. Before we get into the functions, let’s take a look at the structure and parts of the nucleus.
Definition of a Nucleus
The nucleus has something called a nuclear membrane, which is a double membrane separating it from the rest of the cell. Inside the nucleus, a thick goop called nucleoplasm fills the space. The nucleus has to let things in and out to do its job. This happens through gates called nuclear pores, which are the part of the cell that lets things in and out.
The nuclear pores, like guards at an important government building, are very strict. They won’t let anything without the right credentials in or out of the nucleus. Things in the cell have a nuclear import signal to send them into the nucleus or a nuclear export signal to send them out into the cell. Think of these signals like a badge, letting the guards know who has clearance to go where. These structures are all important to the three functions of the nucleus: storing DNA, copying DNA as needed, and making ribosomes at sites called nucleoli.
Let’s look more in detail at each of these functions now.
DNA is crucial to all cells. It holds all the instructions for each cell to do their job. If DNA is damaged, serious diseases can result in humans, such as heart disease, diabetes, and cancer.
Our cells want to keep the DNA safe, and they do this through the nucleus. Inside the nucleus, DNA isn’t just floating around loosely in the nucleoplasm. It is wound into neat, tight bundles using special proteins called histones. A single DNA strand is wrapped around a histone protein, and then those bead-like structures are carefully wrapped around each other again. The DNA is coiled in this precise manner for easier storage. Consider it like wrapping a ball of yarn.
It’s much easier to access all of your different yarns if they are wrapped neatly in a ball, compared to just tossing them in a box all together. This keeps the DNA safe, allows it to be stored in a small space despite its length, and keeps it organized for when the cell needs to access it.
Since DNA contains all the information for cells, when cells divide they want to make sure the new cell gets the same information. This is where DNA replication comes in. During DNA replication, proteins inside the nucleus make an exact copy of the DNA to be distributed to new cells.
DNA can also be copied to another molecule called RNA. RNA is a copy of DNA that leaves the nucleus for the cell to make protein. DNA is very important to the cell, and we wouldn’t want to move it around all the time. Thus, cells make a short copy of the information they need and ship it out of the nucleus through the nuclear pores.
The RNA goes to a structure called the ribosome. The ribosome reads the RNA and makes proteins the cell needs to function.
Those ribosomes that the RNA is shipped to are also made in the nucleus. Special structures inside the nucleus, called nucleoli, are the sites of ribosome production. Parts of the ribosome are made in the nucleus and exported through the nuclear pores. They go to the cytoplasm and assemble with other pieces, making fully functioning ribosomes to work as protein factories for the cell.
In summary, eukaryotic cells, like human cells, are cells that have a nucleus. And remember that DNA is the genetic material that controls cell activities. The nucleus is a structure that stores DNA, the genetic material of the cell. The nucleus is encased in a nuclear membrane, a double membrane separating it from the rest of the cell, and is filled with a thick goop called nucleoplasm.
The nuclear pores let materials in and out of the nucleus using nuclear import and export signals. The nucleus stores DNA in neat coils composed of histone proteins. When needed, the DNA can be unwound to be copied during DNA replication, which is when proteins inside the nucleus make an exact copy of the DNA to be distributed to new cells; or copied to RNA, which is a copy of DNA that leaves the nucleus for the cell to make protein. Nucleoli are sites of ribosome synthesis inside the nucleus.
These ribosomes read the RNA made in the nucleus to produce proteins needed for the cell.