Nucleosome: Definition & Structure

An error occurred trying to load this video.

Try refreshing the page, or contact customer support.

Coming up next: Nucleus: Definition & Function

You're on a roll. Keep up the good work!

Take Quiz Watch Next Lesson
 Replay
Your next lesson will play in 10 seconds
  • 0:00 What is a Nucleosome?
  • 0:53 Histones
  • 1:49 Nucleosomes and Types…
  • 3:20 Lesson Summary
Save Save Save

Want to watch this again later?

Log in or sign up to add this lesson to a Custom Course.

Log in or Sign up

Timeline
Autoplay
Autoplay
Speed Speed

Recommended Lessons and Courses for You

Lesson Transcript
Instructor
Shannon Compton

Shannon teaches Microbiology and has a Master's and a PhD in Biomedical Science. She also researches cancer and neurodegenerative diseases.

Expert Contributor
Amanda Robb

Amanda holds a Masters in Science from Tufts Medical School in Cellular and Molecular Physiology. She has taught high school Biology and Physics for 8 years.

Each of your cells has about 2 meters of linear DNA. This has to be packed into a nucleus roughly 10 micrometers in diameter. This means your nucleus must be excellent at packaging your genetic material! This lesson tells you how your DNA is packaged.

Nucleosomes, Chromatin, and Chromosomes

A nucleosome is a structure in your chromosomes, or bundled DNA. Each nucleosome has a core particle, DNA, and a linker protein. The proteins in the core particle and linker proteins are called histones. The DNA will wrap around the core particle about 1.65 times and is secured by the linker protein. This figure shows a drawing of a nucleosome.

Nucleosome Structure
Image of a nucleosome

About 200 bases of DNA are involved with each nucleosome. This includes the portion that is wrapped around the core and a bit of a tail region that connects to the next nucleosome. This arrangement is said to look like beads on a thread. Several nucleosomes together are called chromatin. Chromosomes are bundles of tightly packed chromatin. Humans have 23 pairs of chromosomes.

Histones

The protein portion of a nucleosome is made of histones. There are five major families of histones, which include H1, H2A, H2B, H3, H4, and H5. The core particle has eight total histones. One H2A and H2B bind together to form a dimer, or two proteins bound together. An H3 and an H4 will bind to also form a dimer. Next, one H3/H4 dimer binds to another H3/H4 dimer to form a tetramer, or four proteins bound together. Finally, an H2A/H2B dimer will bind an H3/H4 tetramer to create the core particle.

After DNA wraps around the core particle either H1 or H5 will bind. The purpose of H1 and H5 is to secure the DNA strand to the core particle. Either H1 or H5 can do this function.

Nucleosomes and Types of Chromatin

DNA arranged in nucleosomes is called chromatin. The histones in nucleosomes interact to form more complex structures of chromatin. As a result, there are several types of chromatin. The type depends on the phase of the cell cycle and how much the genes in a particular region of DNA are needed for cell function.

When a cell prepares to divide it must first compact its DNA into chromosomes. This ensures that the DNA is not broken and helps ensure transfer into daughter cells. DNA in this form is called chromosomal chromatin.

To unlock this lesson you must be a Study.com Member.
Create your account

Additional Activities

Nucleosome Model

In this activity, students are going to be applying their knowledge of the nucleosome to create two three dimensional models and comparing them. In order to do this, you should have a variety of supplies on hand that students can use for their models, such as clay, wire, beads, pipe cleaners, string, glue, tape, pom poms, and anything else you'd like to include. The more supplies are offered, the more creative your models will be.

Examples:

For example, a student might use the beads on a string analogy, and actually create a tetramer of histone proteins with beads. The wire could be twisted to look like the DNA helix, and then wrapped around the tetramer twice, as shown in the lesson. Students could also create a more involved double helix shape from pipe cleaners or paper, and wrap them around clay histone proteins.

Student Instructions:

Now that you're familiar with the shape of nucleosomes, it's time to build your own with craft supplies. In this activity, you'll be building two different models from craft supplies that represent a nucleosome, then comparing the accuracy of your models. Check out the criteria for success on how to create your models. Then, once you've created two different models, answer the questions below.

Criteria For Success for Nucleosome Models:

  • Two different models are created, each with different combinations of craft supplies
  • Models include an 8-histone core with the appropriate histone proteins and H1
  • Model includes a double-stranded helix of DNA

Questions:

  • Compare your two models of the nucleosomes. What was similar and what was different between the two models?
  • Which model was a more accurate representation of a nucleosome and why do you think that?
  • Is there anything you could do to make your model more accurate? Why or why not?

Expected Results

Students should be able to create two models using different supplies. This shows students that scientific concepts can be represented in a variety of ways and encourages creativity and critical thinking. To evaluate the more realistic model, students should look for details like the different histones included in the model, the double helix shape of DNA, and accuracy compared to the image in the lesson. Students might think that they could include more nucleosomes to make the model more accurate or house them in a nucleus, as in a real cell.

Register to view this lesson

Are you a student or a teacher?

Unlock Your Education

See for yourself why 30 million people use Study.com

Become a Study.com member and start learning now.
Become a Member  Back
What teachers are saying about Study.com
Try it risk-free for 30 days

Earning College Credit

Did you know… We have over 200 college courses that prepare you to earn credit by exam that is accepted by over 1,500 colleges and universities. You can test out of the first two years of college and save thousands off your degree. Anyone can earn credit-by-exam regardless of age or education level.

To learn more, visit our Earning Credit Page

Transferring credit to the school of your choice

Not sure what college you want to attend yet? Study.com has thousands of articles about every imaginable degree, area of study and career path that can help you find the school that's right for you.

Create an account to start this course today
Try it risk-free for 30 days!
Create an account
Support