98% of human DNA is “junk”?

Our genetic manual contains instructions for proteins that make up the body and provide energy for it, but less than 2% of the human body’s DNA can encode proteins, and the remaining 98% of the DNA sequence is called “junk DNA”. Scientists have long believed that They are useless. These non-protein-coding DNA extensions look like gibberish in a manuscript—useless and may be forgotten by people. But the latest research shows that the “junk” part of our genome may still play an important role.

Meaningless “words”
Natural creatures have a unique “writing method”. Our genetic script uses only 4 letters: A, G, C, and T. The long combination of these letters constitutes our genes and determines the structure of proteins, but protein manufacturing The process is not as simple as reading a cooking recipe. Before combining the proteins, the DNA is transcribed into RNA, which is cut and reassembled into smaller pieces.

During the cutting process, non-coding “junk DNA” is discarded, which means that they will never participate in the production of protein. Why does the “instruction manual” of natural organisms carry so many seemingly unnecessary substances? This is a question that researchers are still thinking about. The most logical explanation is that “junk DNA” may not be useless.

The function of useless DNA
At the beginning of this century, the “Human Genome Project” gave people a comprehensive understanding of the human genetic script for the first time, but nearly 10 years after the project was completed, a team of more than 400 scientists released what they called the “Encyclopedia of DNA Elements.”

This international collaboration has explored the function of each gene in the genome. The results of this large-scale study require a re-evaluation of junk DNA. Although less than 2% of the genome can make proteins, about 80% of the genome can perform some sort of Features.

The DNA Element Encyclopedia has a broad definition of function. Any “biochemical activity” is a fair game-it can be transcribed into RNA, and even if the RNA is cut off in a later process, it can be identified as a functional sequence. But a lot of “junk DNA” does have an important role, including regulating how DNA is transcribed and where it turns into protein. If the protein code is a symphony note, then some non-coding sequences are like music conductors, affecting the rhythm of music.

But not all “junk DNA” has functions. A study published in the Journal of Cell Molecular Biology in 2008 showed that scientists eliminated the “junk DNA” in the yeast genome, and for specific genes, they removed the genetic content. Substances—the parts of DNA that are cut after transcription. Under laboratory conditions, the removal of gene introns has no significant effect on cells, which supports the view that they have no function.

However, research reports published in the journal Nature put forward the opposite view. When food is scarce, researchers have found that these sequences are essential for the survival of yeast. These studies believe that the usefulness of gene introns may depend on them. The environment in which it is located is far from the so-called “garbage”.

Useful garbage
In the past 10 years, other research advances have shown that “junk DNA” may only be misunderstood genetic material. Scientists have now linked various non-coding sequences with various biological processes (even human diseases), for example: researchers It is believed that these sequences are important factors for the development of the uterus and the opposing thumb.

In 2018, a study published in the Annals of Oncology showed that non-coding DNA fragments are like the volume knob of gene expression, and ultimately affect the formation of breast and prostate cancer; published in the Journal of Nature Genetics in 2019 A study showed that mutations outside the coding region of genes can cause autism.

Exploring non-coding sequences is one of the current research hotspots. More and more evidences show that these non-coding sequences may help overcome cancer. At present, this will be the most promising reverse tool for cancer diagnosis.

Although “junk DNA” has many functions, some researchers still believe that most of the genetic code is useless. Dan Groer, an evolutionary biologist at the University of Houston in the United States, believes that at least 75% of proteins have no function.

In order to obtain this data, Groer used a digital model to determine the usefulness of DNA. He considered harmful gene mutations (harmful genetic changes or double helix breaks). As time goes by, and the fertility rate continues to increase, we also get More genomes, so these mutations may be fatal. Groer evaluated in a paper published in “Genome Biology and Evolution” in 2017 that no more than a quarter of our genetic code has at most Functionality, if more than a quarter, we will accumulate fatal mutations at an uncontrollable rate.