How is DNA Organized into Chromosomes? - Structure & Function

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  • 0:20 The Structure of Chromosomes
  • 1:25 Chromatin
  • 3:00 Function of DNA
  • 4:33 Genes
  • 5:48 Lesson Summary
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Lesson Transcript
Instructor: Greg Chin
Explore the structure of chromosomes and see how DNA fits inside the nucleus of the cell. In this lesson, you'll learn about histones, chromatin and nucleosomes.


Ahh, I think I'm going to be untangling these Christmas tree lights until New Year's! Well, at least I don't have it as bad the cell does. Can you believe the cell has three billion bases of DNA and it spends most of its time as tangled up as this?

The Structure of Chromosomes

So as you recall, DNA is the storehouse of information in the cell. DNA is organized into chromosomes and all of the DNA in the cell is referred to as the genome.

Definition of DNA
DNA Definition

DNA is a linear molecule; it's kind of like a string, kind of like our light strings that we're talking about. The difference here though, between our tangled Christmas tree lights and our DNA, is that we have three billion bases! That's a lot of string that's all got to be wadded up inside of the nucleus. So we've got to figure out a way to efficiently pack that DNA into the nucleus, one, so that it just fits inside of the nucleus, and two, so that we can actually access the information that DNA has to offer.

Illustration of wadded up DNA
Structure of Chromosomes

Chromatin

We have proteins that help us out with this job and they're called histones. Histones are proteins that are going to help package the DNA more efficiently. And what's going to happen is, if I have my histones here, we're basically just going to take our linear DNA molecule and we're going to roll it around the histones. By rolling it around these histones, the DNA has necessarily become shorter. If I have this long piece of DNA and if I'm rolling it up around balls, it's going to create a shorter length of linear molecule now that we have to fit inside the nucleus.

Scientists, we like to name things, so here we have the histone in the middle - the histone core - and this structure of histone and DNA, this little ball structure here, we refer to that as the nucleosome.

Illustration of histones and nucleosomes
Histones and nucleosomes

Now all of this DNA and protein organization, all the DNA rolled around the histone proteins, that's going to be called chromatin. Now, the nucleosomes are the basic subunit of the chromatin. What you can see if you were to look under a high powered microscope, is you'd see what looks like a beaded structure.

Function of DNA

So if I'm looking through the microscope and I have my cell and my nucleus, I'm going to see a lot of stringy looking things in here, and each of those stringy looking things are going to look like a beaded structure. It gets this beaded structure from the repeating segments of nucleosomes and linker DNA.

I said that it's going to be important not only to package the DNA into the cell, which organizing it into chromatin has helped us do, but I also said it's going to be important to be able to actually find information in the DNA. We said that DNA is a storehouse of information, and DNA is basically providing information to create different things that the cell's going to need. So if the cell needs microtubules, DNA is going to code for that. If the cell needs to make mitochondria, DNA is going to code for that.

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