3.4 Cell Nucleus

Learning Objectives

Describe the features and function of the cell’s nucleus.

Introduction

Where is your DNA?

You may know that a criminal can easily leave DNA at a crime scene. How? DNA is found in every cell of your body. In each cell there is a nucleus, which is home to your DNA. So if a criminal has a cut and blood is left at the crime scene, or a hair falls out and is left behind, then DNA will also be left at the scene.

Guided Learning

The Nucleus

The nucleus is only found in eukaryotic cells. It contains most of the genetic material (the DNA) of the cell. The genetic material of the nucleus is like a set of instructions. These instructions tell the cell how to build molecules needed for the cell to function properly. That is, the DNA tells the cell how to build molecules needed for life. The nucleus is surrounded by the nuclear envelope, a double membrane (two bilayers) that controls what goes in and out of the nucleus. The nucleus also has holes embedded in the nuclear envelope. These holes are nuclear pores, and they allow things to flow out of the nucleus.

Chromosomes

Inside of the nucleus, you will find the chromosomes. Chromosomes are strands of DNA wrapped around proteins. They contain genes, or small units of genetic material. Human cells have 46 chromosomes.

Nucleolus

The nucleus of many cells also contains a central region called the nucleolus. The job of the nucleolus is to build ribosomes. These ribosomes flow out the nuclear pores into the cytoplasm. Ribosomes are organelles that make proteins in the cytoplasm. See the composition of the nucleus pictured below (Figure below).

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In eukaryotic cells, the DNA is kept in the nucleus. The nucleus is surrounded by a double membrane called the nuclear envelope. Within the nucleus is the nucleolus.

Review

The nucleus contains the genetic material of the cell.
The genetic material of the cell is found in chromosomes, DNA wrapped around proteins.
The nucleolus, which makes ribosomes, is also within the nucleus.