BEIJING, Nov. 4 (Xinhua) — Dna (DNA) is a life-sustaining medicine, like a guidebook for protein production, according tomedia reports. The manual is written in only four letters: A, G, T, and C, corresponding to four bases: adenine (A), thymus (T), ostrich (G), and cytosine (C). These four letters, or base pairs, are combined in a specific way in a long strand of DNA to form a gene.
Genes are tiny pieces of DNA that record the information needed to produce proteins through a transcription process. These proteins are essential for the development and survival of living things.
In 1990, several laboratories decided to work together to crack the genetic instructions that make up human DNA, known as the Human Genome Project. By the end of the project in April 2003, we had finally unveiled the human blueprint drawn by nature.
Chromosomes are made up of DNA strands.
With the Human Genome Project, scientists have finally developed a digital concept of human DNA. The results showed that human cells contained a total of 3 billion pairs of base pairs, compressed into 23 pairs of chromosomes. Each of the 20,000 to 25,000 genes corresponds to about 100 million base pairs and is responsible for coding a range of proteins, each of which has its own unique function. Across the genome, only 1% to 2% of the DNA responsible for protein encoding is responsible.
The remaining 98% to 99% are not responsible for coding any proteins and are therefore named “non-coding DNA”. Because scientists believe that protein synthesis is the main role of DNA, this part of the DNA is also called “junk DNA.” But the question is, as the “recipe” of life, why is there so many pages of junk in DNA?
Is it garbage or hasn’t been found yet?
The cutting mechanism of mRNA.
Synthetic protein is not as simple as cooking according to a recipe. Proteins need to be tweed by DNA to be synthesized because the enzymes that synthesize proteins cannot read DNA directly. The contents of the DNA are copied to a molecule called messenger RNA (mRNA). Like DNA, mRNA has four base pairs, but thymus (T) is replaced by uracil (U). In addition, mRNA is a single-stranded structure, not a double-stranded structure like DNA.
During transcription, mRNA is cut into pieces and then reassessed. This process is called RNA scissors. This process is caused by the fact that some of the gene fragments are meaningless “from a protein perspective”. These fragments are called “introns”. During RNA cutting, these fragments are culled and discarded, and can be said to have been discarded during transcription.
DNA and RNA.
For decades, these uncoded fragments have puzzled scientists. They are scattered among genes and do not seem to have any obvious effect, and many scientists consider them worthless. In 1972, geneticist Susumu Ohno invented the term “junk DNA” to describe “waste” in such DNA. At the time, these DNAs were also known as “selfish DNA” because they seemed to exist entirely for their own sake and did nothing to contribute to the survival of organisms.
However, some scientists believe that we should not rush to label these DNA as “useless”. If you only know ten of these words when you read the original English text of this article, can you say that all the other words are useless nonsense? Similarly, scientists believe that the function of these so-called “junk DNA” may just not have been discovered.
What is the function of “junk DNA”?
The researchers decided to compare the human genome with a vast database of other animal genomes. The technique is called Comparative Genomics. As a result, researchers were shocked to find that some fragments of junk DNA had not changed for thousands of years. The retention of these fragments of DNA suggests that uncoded DNA is to some extent critical to the survival of living things. As a result, the DNA was preserved through “positive selection” during evolution because if the fragments mutated, they could be harmful to the organism.
For example, between 65 and 75 million years ago, mice and humans took two different evolutionary paths from the same ancestor. The researchers found that only 20 percent of all remaining DNA was responsible for protein encoding, and most of the DNA actually belonged to non-coding areas of the genome.
The Human Genome Project Timeline.
However, the Encyclopedia of DNA Components (ENCODE), released after the end of the Human Genome Project, cast a negative vote on the “useless” of junk DNA. ENCODE is a collaboration between laboratories under the sponsorship of the National Human Genome Research Institute. The Human Genome Project aims to interpret the blueprint for human existence, while ENCODE seeks to find out which fragments of the blueprint are really useful.
The Human Genome Project uses DNA sequencing to crack the human genome, while the ENCODE project examines other components such as RNA by sequencing RNA and looking for fragments of DNA that can be altered by chemicals or proteins. The results of this project suggest that the chemical activity of DNA fragments may give us some tips on what functions they might have.
Remember, genes carry the information needed to synthesize proteins that ultimately perform cellular functions. The amount of protein a given gene can eventually synthesize is determined by its gene expression (i.e., the ability to use information compiled in the gene to guide protein synthesis).
The core principle of gene expression.
Specific proteins, transcription factors, or chemicals can bind to DNA to change when and how genes are expressed. Scientists have found that some “junk DNA” contains DNA that regulates genes, which can determine when and how genes are activated or turned off. They can also be used as a place for transcription factors to bind to DNA and regulate the transcription process. Non-coded DNA contains several different regulatory factors, including:
Promoters: If you liken a gene to a light bulb, the starter sequence is its switch. The launcher provides the protein with a place to initiate the transcription process and also switches the opening and closing of the transcription-related components. Genes that cannot be synthesized do not contain starters and are located at the front end of the encoded gene sequence.
The mechanism by which the initiater functions.
Enhancers: Proteins that assist in the process of activating transcription bind to enhanced subsethics. The enhancer acts like a catalyst in a chemical reaction. Transcription can occur even without enhanced subsethres, but is more efficient in the case of enhancers. The enhancer may be at the end of the gene sequence, or it may be far away from the gene sequence.
Enhanced sub-role mechanisms.
Silencers: In contrast to enhancers, silencers bind to proteins that inhibit transcription, preventing overexpression of a gene and causing protein excess. Similar to enhancers, the distance between the silencing child and the gene sequence is also far and near.
The mechanism of the role of the silencer.
The enhancer and the silencer combine to act like a fan regulator. It’s just that they control not the fan speed, but the degree of gene expression. The combination of protein and enhancer is equivalent to turning the wind speed to maximum, while binding to the silencer is equivalent to “stopping” the fan.
Several “functions” of non-coded DNA are listed above. So what about non-coding DNA that doesn’t count as functional DNA sequences?
A “functional” DNA sequence controls gene expression, the number of proteins synthesized by a particular gene sequence. It is the differences in protein composition that give each cell unique function. Therefore, since each cell contains the same genome and DNA, it is up to the level of gene expression to determine whether a cell belongs to an endotred cell, an immune cell, a nerve cell, and so on.
To explain this innate variability, the ENCODE team practiced this technique in several types of cells. Therefore, according to the above definition of “functionality”, “junk DNA” has an absolute effect on gene expression. The results of the ENCODE project show that we know very little about the mysterious non-coding regions of the genome.
In 2012, the ENCODE project team revealed that more than 80% of gene base pairs exhibit biochemical activity. As a result, there must be more than 1% of biologically functioning DNA. The project found a large number of previously unrecognized signals and “switches”, like tattoos, embedded throughwhere in human DNA.
Since the ENCODE project published its findings, scientists have found a link between uncoded DNA sequences and a variety of biological processes and human diseases. The researchers speculate that these sequences may be related to the development of our thumbs and even the uterus in the opposite direction. A paper published in the journal Cancer Genes also showed that a piece of non-coded DNA can regulate gene expression and ultimately affect the risk of prostate and breast cancer. Therefore, the function of cracking the so-called “junk DNA” has now become a great research field.
It should be noted here, however, that the ENCODE project’s definition of “functional” has been hotly debated. Many scientists point out that the results of the ENCODE project are misleading and far overestimated. They argue that the mere binding of proteins to DNA, or chemical changes, is not enough to suggest that the DNA sequence must have played a meaningful role. In organisms, the binding of some DNA to proteins is a random event that has no significance. This undoubtedly adds to the doubt about the results of the ENCODE project release.
The voices of these criticisms are not unreasonable. More research is needed to quantify the function of non-coded DNA. However, there is no objection to the fact that “junk DNA is not rubbish at all”.