Chromatin Structure: Regulation & Modifications

Chromatin Structure: Regulation & Modifications
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  • 0:00 Histones Are Involved…
  • 1:05 Chemical Modifications
  • 2:01 Epigenetic Inheritance
  • 3:17 Lesson Summary
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Lesson Transcript
Instructor: Sarah Friedl

Sarah has two Master's, one in Zoology and one in GIS, a Bachelor's in Biology, and has taught college level Physical Science and Biology.

While your DNA consists of many, many genes, each cell only expresses a few specific ones at a time. Mechanisms are in place to regulate which genes are turned on or off in each cell, as well as whether those instructions should be passed on to new cells.

Histones Are Involved in Gene Expression

Your body is made up of trillons and trillions of cells. You may already know that many of those cells are different from each other; your lungs are different from your muscles, bones, nerves, cartilage, toenails, ect. But did you know that almost all of your many trillions of cells have the exact same genome? What makes them different is how those genes are expressed. In fact, only a scant few genes are expressed on a cell at a given time and the genes that are expressed can even change over time.

Almost all of the cells genes can be found in an organisms' chromosomes, and the material that makes up a chromosome is called chromatin. DNA is incredibly long, thousands of times more than the diameter of the nucleus it lives in. What helps pack that DNA so tightly that it fits inside the nucleus are tiny proteins called histones. Histones not only compact DNA into a manageable size, they also regulate chromatin within the chromosome. They're small but mighty!

Chemical Modifications

Histones are very important components of a chromosome because they influence gene expression. For example, when histones are modified with either the addition or removal of certain chemical groups, histones bind more tightly or more loosely to DNA, which then effects which genes are expressed and which are not.

Histones are not the only ones having all the fun though. DNA itself can be modified and one specific way is called DNA methylation. This is when a methyl group (CH3) is added to DNA bases. During this process the sequence of the bases themselves aren't changed but addition of a methyl group may prevent a gene from being expressed. In fact, removing extra methyl group can actually turn on a gene. Don't worry though, DNA methylation is a good thing. As it turns out, improper DNA methylation may cause abnormal development in embryos.

Epigenetic Inheritance

What's even more incredible is that methylated genes often stay methylated throughout multiple cell divisions, leading to methylation patterns that are passed on and inherited by other cells. Inheritance of a trait like this that doesn't involve the DNA sequence is called epigenetic inheritance. These are modifications to the chromatin; not the DNA itself, so they aren't permanent, like DNA mutations are. In fact, they even have been known to be reversed.

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