1.2 The Nucleus and DNA

Introduction

You reviewed the structures within plant and animal cells—all except the nucleus. There are some important things to learn about the nucleus, and you will be looking at this organelle in more depth than the others.

Why is the Nucleus so Important?

You won't find the nucleus in just any cell. For example, bacteria are prokaryotic (this means “before the nucleus”). These cells do not have a nucleus, although they do still have DNA. They also have no membrane-bound organelles, such as chloroplasts or mitochondria.

On the other hand, eukaryotic organisms (animals, plants and fungi) do have nuclei in their cells.

Structure

Notice in this diagram that a membrane surrounds the nucleus, and that there are holes or pores, in this membrane. The membrane around the nucleus is similar to the cell membrane because both allow only certain substances to pass through.

Function

The nucleus is often called the 'control center' for a cell, but what does this really mean?

Structure and Function of the Nucleus

Watch both videos for an introduction to the structure and function of the nucleus within a cell.

Summary

The nucleus is responsible for several important things:

• storage of DNA, which contains the “master set” of instructions for all of the cell's activities

• control of the cell's production of proteins by copying information from DNA

• containing the nucleolus, where ribosomes are made.

Red blood cells are the only type of human cells that have no nuclei.

What is DNA?

It's time to take a closer look at what's inside the nucleus-the nucleolus and the cell's DNA.

DNA stands for “deoxyribonucleic acid.” It is a code containing about three billion (that's 3 000 000 000!) bases.

The Most Famous Molecule

DNA is the chemical that carries genetic information from parents to offspring. Although DNA consists of very long strands of bases, there are only four types of bases. This means that the sequence in which they are strung together is very important.

This sequence of bases leads to the creation of proteins. In turn, those proteins determine the characteristics of an organism. Your unique DNA sequence, and the proteins it codes for, makes you different from all other forms of life on earth.

DNA molecules

The DNA molecule is a 'double helix' because it is made of two strands that wind around each other like ribbons. Bonding between base pairs connects these strands.

The structure of DNA itself is too small to see under a microscope, but it's easy to extract the larger 'strings' into which it is organized. 

PRACTICE: The Nucleus

DNA Extraction-Virtual Lab

This 'virtual lab' will allow you to perform a DNA extraction the way a microbiologist would. If you want to perform a real DNA extraction using your own kitchen, complete lab 1 and 2 in the 'Biology Projects' section.

Watch the video, then click on the Learn.Genetics. logo to try the lab.