Across all the cells in our body is a copy of the DNA - the blueprint that determines how each cell develops to create a unique you. A common question is how does it differentiate between the various forms and functions of the 37 trillion cells in each of us.

A recent feature from Live Science set out to explain how a minute structure could handle such variety and complexity in its cell development tasks. It explains that like most of the processes and actions of DNA, its differentiation between different cell types is also a highly regulated process. For eukaryotic-celled organisms or those whose cell nuclei are clearly distinguishable, a "central dogma" could explain how the DNA serves as the manual for complex cell development.

As the DNA relays information to the messenger RNA (mRNA), it becomes the roadmap that cells follow on which proteins are to be produced. But how does the DNA tell the mRNA where and when to produce which cells?

DNA methylation
(Photo: Christoph Bock, Max Planck Institute for Informatics via Wikimedia Commons)
This image shows a DNA molecule that is methylated on both strands on the center cytosine. DNA methylation plays an important role in epigenetic gene regulation in development and cancer.

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Understanding the Transcription Factor in the DNA

According to Karen Reddy, assistant professor of biological chemistry at Johns Hopkins University School of Medicine, a special protein called a transcription factor is in charge of identifying which genes are activated. An overview article from the Reference Module in Biomedical Sciences describes the transaction factor as key proteins that bind to the DNA. They also possess a specific domain that interacts with the RNA, regulating the amount of mRNA generated by a single gene.

But where does this transcription factor come from? And how does it know what to do?

"Lots of transcription factors are reused from cell to cell to cell," Karen Reddy explains in her Live Science interview. One transcription factor can go on and activate different gene types in different cell types. Furthermore, this process remains controlled and ordered thanks to the neatly packaged DNA in different cell types - a trait described by each cell's chromatin landscapes.

Chromatin is a complex made from DNA, RNA, and other proteins that function together to wrap up long DNA strands. The nature of how the DNA is packaged is generally known as the chromatin landscape. This landscape determines which genes are more exposed, posing them for transcription factor activation. On the other hand, other genes are repressed also depending on the landscape. Reddy additionally explains that there is "cross talk" between the transcription factor and the chromatin landscape.

Other Elements That Affect Gene Expression

The Johns Hopkins assistant professor further noted that there are still many other factors that affect gene expression, such as a promoter protein that can turn genes on or off - one whose ability to do so depends on its location relative to the genes it should be targeting.

Additionally, there are other processes that could affect the resulting DNA, such as chemical groups that alter the form and function of the strand. As an example, the Live Science feature cited the addition of a methyl group to a nucleotide, which contains the building blocks of DNA, such as cytosine, in a process called DNA methylation. A 2015 review appearing in the journal Cureus examines that DNA methylation helps keep humans from over-expressing specific gene families that could cause serious conditions.


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