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Nucleus: Definition & Function

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  • 0:00 Types of Nucleus
  • 0:40 Structure
  • 1:14 The Nucleus Protects DNA
  • 1:40 Nucleus Manages Many…
  • 3:30 Lesson Summary
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Lesson Transcript
Instructor: Angela Lynn Swafford

Lynn has a BS and MS in biology and has taught many college biology courses.

A nucleus is like the brain of your cells. In this lesson, you will learn about its various responsibilities, and then you can test how well you grasp this material by taking a quiz.

Types of Nucleus

The word 'nucleus' can refer to the center of an atom or the control center of a cell. This lesson will discuss the nucleus of a cell.

You have over 200 different types of cells in your body. Some can be really thin and long, like a nerve cell that runs all the way from your spinal cord to your foot. Some, like a fat cell, have a more rounded shape. No matter what your cells look like, there is one important thing they all have in common: a nucleus. This is a control center that is found inside all of your cells at some point during their life. A nucleus is responsible for determining and controlling what a cell looks like and what it does.

Structure

A nuclear envelope encloses the nucleus to keep it separate from surrounding materials in the cell. Sometimes substances need to move into or out of the nucleus, and this is possible because there are little holes in the nuclear envelope called nuclear pores. Inside the nucleus is at least one dark-colored mass called a nucleolus. DNA occupies most of the rest of the space inside a nucleus. DNA is genetic material that has the instructions necessary to build proteins. Proteins are responsible for helping with most activities in a cell.

The Nucleus Protects DNA

Your DNA is organized into about 20,000 genes, basically instruction manuals for our bodies. Without all of these genes, your body would not be able to make proteins. Proteins are absolutely necessary to make sure everything in your body is working properly. The nucleus helps protect your very important DNA. More specifically, the nuclear envelope keeps your genes separate from the other structures inside a cell.

Nucleus Manages Many Cellular Activities

The brain is your body's control center. The nucleus is a cell's control center. The nucleus oversees many processes that occur inside a cell. Let's take a look at some of them more closely.

  • DNA replication is a process of duplicating or doubling a cell's genetic material. DNA replication must occur before a cell can reproduce.
  • Cell division is when a cell reproduces or splits into two new cells. Each new cell gets one copy of the duplicated DNA.
  • Gene expression is the process of using the DNA in a gene to make a product, such as a protein. Every cell in your body has the same genes, but only some are used to make proteins. Only these genes are considered to be expressed, or turned on. It is these active genes that give a cell its specific function and shape.
  • Transcription is the process of creating RNA molecules using DNA instructions. This is the first step in making a protein. It involves producing three kinds of RNA:
    • mRNA is messenger RNA. It carries instructions for making a protein.
    • tRNA is transfer RNA. It assists with making proteins.
    • rRNA is ribosomal RNA. It also helps with building proteins, but it is the only RNA type to be transcribed, or made, in the nucleolus.

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