4c. The Nucleus [Beyond Books - Life Science: Part 1]

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4c. The Nucleus

Electron micrograph of the nucleus.

In a factory, the chief executive officer controls everything that happens. What would it be like to have this job in a cell factory?

You would have your own office (which would be nice) but you would also have many responsibilities. You would need to keep track of all the blueprints kept in your office. And you would tell the workers which products to build and when to build them.

The cell factory contains a large inventory of blueprints dating all the way to its founding. Some of these blueprints are out of date, and some are for parts and products that are no longer made. Part of your job would entail sorting through everything, finding the correct blueprints, copying them, and sending the copies out to the assembly line at the correct time.

When the factory gets too large, it is difficult to run properly; thus, another factory must be built. To prepare for this, you have to provide the new factory with its own set of all the blueprints.

Sounds a bit daunting? Now you may have a better appreciation for what the nucleus does in the cell.

Nuclear Function

The NUCLEUS, often referred to as the headquarters of the cell, controls all cell activity by regulating what proteins are made. It is a large ORGANELLE that is easily seen with a light microscope. The nuclear membrane contains the blueprints of the cell. The information for the manufacture of proteins is encoded in a series of bases along the DNA found in the nucleus.

All cells contain much more DNA than they actually use. A small percentage of this DNA is active, and the rest of it is outdated (or nonsense DNA) that the organism no longer uses. As a species evolves over time, mutations change the DNA. Just as outdated blueprints in a factory are kept on file, outdated genetic information is never thrown out. The entire evolutionary history of an organism is written in its DNA. The processes of transcription and translation (which will be discussed in more detail later) allow the cell to decode this information to construct proteins.

When a cell has grown to a certain size it becomes less efficient. To increase its productivity, the cell divides into two new cells in a process called mitosis. The mother cell must have two copies of its DNA to pass on to the daughter cells that are created. This ensures that every new cell has a correct and complete set of DNA blueprints.

Nucleus Structure

DNA transcription into mRNA (or "messenger RNA", a form of RNA) occurs in the nucleus.

The nucleus is composed of a nuclear membrane and nucleoplasm. The NUCLEAR MEMBRANE is a double membrane that contains the nucleoplasm. The NUCLEOPLASM contains CHROMATIN, a combination of DNA and proteins. Within the nucleoplasm, the NUCLEOLUS manufactures RIBOSOMES, structures in which proteins are assembled.

But where does protein production occur?

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