Cell Nucleus — Structure & Function

What Is the Nucleus?

The nucleus is the control center of the cell. Think of it like cell headquarters. The big boss, our DNA, works there and directs the rest of the cell's activities.

Remember that a distinguishing feature of eukaryotic cells is that they have a nucleus, as opposed to prokaryotic cells, which do not have a nucleus.

Let's take a look at the structure of the nucleus and then talk about a few of its parts.

In addition to housing the nucleolus (defined in the pink box above), a cell's nucleus stores its genetic material in the form of DNA.

However, the DNA doesn't always look the same. In its off-time (when the cell is just doing its normal job), a cell's DNA is in the form of chromatin.

When a cell is in the process of dividing, however, its chromatin condenses or tightens into X-shapes called chromosomes.

Key Vocabulary:

1. Nucleus
2. Nucleolus
3. Nuclear envelope
4. DNA
5. Chromosome
6. Chromatin

What Is in the Nucleus?

The nucleus is an organelle only present in eukaryotes. It is sort of like the president of the United States. It is heavily guarded, very powerful, and keeps a lot of important information.

The nucleus is so important because it stores your blueprint—that is, the genetic information that makes you who you are. This genetic information is called DNA and is essential for the process of protein synthesis. In the nucleus, the DNA stays in a loose form called chromatin. When the cell divides, the DNA condenses into chromosomes.

The nucleus is encased in a nuclear envelope, similar to the cell membrane. The nuclear envelope is a double membrane with little nuclear pores in it that let certain things in and out. Because this organelle is so important, the nuclear membrane has to be able to protect the contents of the nucleus.

In the center of the nucleus is the nucleolus. In the image above, the nucleolus is the little, round ball that sort of looks like the pit of a peach. The nucleolus is an extremely condensed region of chromatin (packaged DNA) where ribosomes are formed.

The nucleoplasm is a gel-like substance that fills in all the space inside the nucleus that the nucleolus does not fill. Chromatin floats around in the nucleoplasm.

The Brain of the Cell

The nucleus is considered the brain of the cell. The nucleus of every cell contains DNA, the hereditary information for an organism.

Even though every cell contains the organism's entire genome, each cell only expresses the parts of DNA that it needs to function. What is expressed in each cell is determined by the nucleus. The nucleus also controls the cell's individual functions such as cell growth, protein synthesis, cell division, and reproduction.

The nucleus consists of:

• Nuclear Envelope - Composed of two membranes

Outer membrane - Studded with ribosomes and has nuclear pores to transport materials into and out of the nucleus

Inner membrane - Also contains nuclear pores to transport proteins and RNA into and out of the nucleus

• Chromatin - A coiled form of DNA in the nucleus. It can further condense into chromosomes when the cell is dividing. It also contains all the information the cell needs to string together amino acids and form proteins

• Nucleolus - A dense substructure that forms around repeating sequences of DNA that code for rRNA

• Nucleoplasm - Performs a role similar to that of the cytoplasm (holding essential nutrients)

• Nuclear lamina - A network of proteins that gives the nucleus structure

(Video) Nucleus

by learnbiologically

This video gives an overview of the parts and purpose of the nucleus.

(Video) What's in a Nucleus?

by MacmillanUSA

The nucleus is the brain of the cell, but what exactly is in it? This short video explains what you'll find in the nucleus and what purpose each of those things has.

The nucleus is a membrane-bound organelle. The double membrane, called the nuclear envelope, protects the contents of the nucleus. Within the nucleus is our DNA. Most of the time, DNA is stored in a semi-loose mess called chromatin. When a cell divides, the chromatin condenses and forms chromosomes.

Our genetic code actually exists in two forms: DNA and RNA. DNA is a blueprint for protein synthesis. This is important because our proteins make us who we are. During protein synthesis, DNA is read to make an mRNA molecule. The mRNA then exits the nucleus and heads to the endoplasmic reticulum. It is then translated into amino acids, which make up proteins.