A copy of DNA is contained in the nucleus of all 37.2 trillion cells. Theoretically, these cells all have the same blueprint, so they have the same functionality.So how DNA For example, do you know if it is in a blood cell or a sensory cell? How do you know which genes need to be “switched on”? How do cells know and perform their functions?
Like everything related to DNA, it is a multifactorial and highly regulated process.In humans and other organisms Eukaryotic cells A concept called the “central dogma” describes how DNA acts as an instruction manual. DNA informs messenger RNA (mRNA) and is used as a roadmap for protein production. Therefore, transcribing the correct portion of DNA into mRNA is only the first step in ensuring that the cell has all the proteins it needs.
A special protein called a transcription factor turns on the gene, said Karen Reddy, an assistant professor of biology. Chemistry At John Hopkins University School of Medicine. Transcription factors bind to DNA and increase or decrease the expression of certain genes. But that raises the question: where do transcription factors come from?
“Many transcription factors are being reused from cell to cell,” Reddy told Live Science. It’s like using the same parts in another car. One transcription factor can have different activations gene With different cell types. For example, the transcription factor used by the sensory cells called Olf-1 is the same as the transcription factor Ebf-1 used to designate B cells. We also know that transcription factors activate various genes in these cells. This is because DNA is organized and packaged differently in different cell types.
In the nucleus, DNA, proteins, RNA It works together to package long strands of DNA. This complex is called chromatin. The way DNA is wrapped around a complex of proteins called histones, and the chemical modification of those histones, is called the chromatin landscape. This affects which genes are more or less exposed. In a given cell type, some genes are ready for activation by transcription factors because of how they are exposed in the chromatin structure, Reddy said. Others are either oppressed or hidden by the chromatin landscape. These can still be turned on, but first, sufficient transcription factors and chromatin modifiers are needed to alter the chromatin structure and reveal them.
“There is crosstalk between the chromatin landscape and the world of transcription factors,” Reddy said.
Covering both of these elements is the 3D architecture of the cell nucleus, how chromatin is folded and organized in the nucleus. This folding facilitates the interaction between the genes that need to be expressed and the factors that increase their expression. The active (or required) portion of DNA for a particular cell type is grouped near the center, and the inactive section is closer to the outside of the nucleus.
Several factors that control how a gene is expressed, such as a promoter that can turn a gene on and off, are in the immediate vicinity of the gene. However, other factors, such as tissue-specific enhancers that increase gene expression, can be far away from the genes that need to be enhanced for the cell. The foldable or 3D architecture brings enhancers closer to the gene of interest, Reddy said.
Finally, there is the process of making more long-term changes to the DNA itself. For example, DNA methylation involves adding a methyl group to nucleotides (DNA “building block” cytosine and its backbone) and is generally associated with gene repression, Reddy said. DNA methylation is transmitted from generation to generation, affecting which genes are turned on or off in certain types of cells and preventing overexpression of certain genes. This can lead to conditions such as neuropathy and cardiovascular conditions.Illness, according to a 2015 review of the journal Cureus..
According to Lady, all these levels (DNA methylation, chromatin landscape, folding, transcription factors) are important regulatory steps for the expression of essential genes at the right place and at the right time. “Both of these levels of control are confused by diseases like cancer.”
The good news is that these regulatory factors back up each other. “It’s okay as a cell because something can go wrong and these processes reinforce each other,” Lady said.
Originally published in Live Science.
How does DNA know what work to do in each cell?
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