Let’s talk about dinosaurs

　　When it comes to those movies that will hit the box office in 2022, “Jurassic World 3” must have a place. Since its release in domestic theaters on June 10, “Jurassic World 3” has performed brilliantly and has become a force that should not be underestimated in the summer season. The box office finally exceeded 1 billion yuan.
　　As the final chapter of the “Jurassic” series, the lineup of “Jurassic World 3” is stronger than ever. In addition to the “old friends” Brontosaurus, Mosasaurus, and Tyrannosaurus rex, there also appeared the Pyroraptor in feathers, and the naughty and cute Velociraptor baby. Dinosaurs have always been an exciting topic, and it’s no wonder that some people are asking, “Is it possible to resurrect dinosaurs?”
　　The death of
　　DNA The idea of ​​​​reviving dinosaurs is very attractive, but the DNA of dinosaurs is difficult to find.
　　Speaking of biologists, you may naturally think of a group of people in white coats shaking glass tubes. In fact, biologists often “play rough”. In 2012, a research team led by Danish scientist Morton Allendorf started to drill. After sampling and analyzing 158 moa bones, they found that the half-life of DNA was 521 years.
　　Biology textbooks say that DNA looks like a spiral staircase. In fact, DNA and stairs have one more thing in common: They are both made of more basic materials. Stairs are made of steel, glass, stone, etc., and the basic building blocks of DNA are called deoxynucleotides. According to the different bases carried, deoxynucleotides can be divided into four categories: those with adenine (A), those with guanine (G), those with thymine (T), and those with cytosine (C). . The combination of steel, glass, and stone determines the shape of the stairs; similarly, the information carried by DNA essentially depends on the arrangement sequence of the four types of deoxynucleotides.
　　Between nucleotides, a cement-like binder is also needed. To be more specific, two forces are used: one is intramolecular forces, such as covalent bonds, that connect nucleotides into long chains; the other is intermolecular forces, such as hydrogen bonds and van der Waals forces, that connect two The long chains are linked together to form a double helix.
　　The problem is that these forces do not exist forever, but are affected by various factors, such as the amount of water, the intensity of ultraviolet light, whether the protein is “obedient”, and whether there are bacteria around. Healthy organisms have a relatively stable and orderly internal environment. When life comes to an end, the power to maintain order disappears, the connection between nucleotides will gradually collapse, and the genetic information carried by DNA will gradually disappear.
　　Every 521 years, half of the connections between nucleotides disappear. Based on this calculation, the DNA in the bones can be preserved for about 1.5 million years under ideal conditions. The extinction of the dinosaurs occurred approximately 66 million years ago, which means that it is almost impossible to find DNA in dinosaur fossils.
　　How DNA Works
　　So , could dinosaurs be resurrected without DNA?
　　You may blurt out: “Impossible, because DNA is the genetic material of organisms.” That’s right, except for special cases such as RNA viruses and prions, the genetic traits of most organisms are determined by DNA. So, how was it decided?
　　As the saying goes: “It’s difficult to adjust to everyone’s taste.” Taking coriander as an example, some people like it very much, while others avoid it. A 2012 study suggested that the difference may come from olfactory receptors. Olfactory receptors are a special class of proteins that bind to odor molecules in the air, which in turn activate neurons that give us specific sensations.
　　”Who” made these proteins? The main contributor is transfer RNA (tRNA). tRNA looks like a clover, and its function is like a forklift, which can transport amino acids to designated positions for assembly into proteins.
　　And “who” tells tRNA where to put amino acids? The mystery lies on the other end of the tRNA, with 3 bases distributed on it. As mentioned earlier, there are hydrogen bonds between two long strands of DNA. In fact, hydrogen bonding occurs between bases. The combination of bases is very specific. For example, among the four bases that make up DNA, adenine (A) goes hand in hand with thymine (T), and guanine (G) prefers cytosine (C).
　　When tRNA travels with amino acids, it will soon encounter a qualified “conductor”-messenger RNA (mRNA). mRNA looks like a single strand of DNA, but with fewer nucleotides. Or we can say that mRNA is like a ladder cut longitudinally. The rungs in the middle of the ladder are the bases from which the nucleotides protrude. Depending on the binding rules between bases, mRNA can direct tRNA to put amino acids in the right place.
　　mRNA also has 4 bases: adenine (A), guanine (G), cytosine (C), and uracil (U). Although uracil is somewhat different from thymine, they are completely identical in binding preference. Therefore, as long as DNA tells mRNA its nucleotide sequence, it can direct the synthesis of proteins through the above mechanism, and then use proteins to regulate various physiological activities, such as affecting our sense of food.
　　It is currently believed that the gene on chromosome 11 is closely related to the sense of smell. In addition, it also affects the development of nerves and the regulation of insulin. Nerve activity determines our emotions, and insulin is an important driver of energy metabolism, affecting the body’s ability to use nutrients.
　　Of course, genetic traits are important, but they are not the whole of life. For example, people with certain genes are more likely to suffer from cardiovascular and cerebrovascular diseases. However, controlling diet and paying attention to exercise can offset the influence of genes to a certain extent. As for intelligence, aspirations, and temperament, it is even more complicated, and the acquired influence is the decisive factor.
　　The growth of DNA
　　So , the next question came again: Why did most organisms choose DNA by coincidence? Genetic information is released roughly in the order from DNA to RNA to protein. Why go around in circles instead of using protein or RNA as the genetic material?
　　It may be a little troublesome to use protein directly. Taking humans as an example, there may be tens of thousands of proteins in a cell. As for how many kinds of proteins there are in our body, it is still unclear. In contrast, there are only 20 amino acids that make up human protein. Using DNA to record the combination of amino acids seems to be a long way around, but it is actually more efficient.
　　If you use RNA directly, you will encounter the problem of variation. The BA.5 strain of the new coronavirus was often mentioned in the news some time ago. What does “BA.5” mean? It can be understood as the number of the family tree. In order to accurately name the new coronavirus, scientists drew a “family tree” for them according to their genetic closeness. BA.5 is derived from the mutation of B.1.1.529, the father of the latter is B.1.1, and B.1.1 is the result of the mutation of the B.1 strain… In the process of transmission of genetic information, some changes are inevitable, This is why there are so many variants of the new coronavirus in less than 3 years.
　　DNA is much more stable, and double strands are equivalent to double insurance. And the longer the DNA, the more proteins it encodes. Some of these proteins check the arrangement of nucleotides in the DNA, and if something goes wrong, others fix it. So, on average, the chance of a nucleotide error in each round of DNA replication is only one in a billion.

　　The Birth of DNA After
　　knowing the excellence of DNA, it is easy to think of a question: Where did the original DNA come from?
　　First of all, where did nucleotides come from on the earth in the early years? Some scholars believe that it comes from meteorites. For example, in the 1960s, scientists detected bases such as adenine in meteorites. Some scholars also believe that they appeared naturally.
　　In 1953, American scholar Stanley Miller made a strange experimental device. The device is closed to avoid external pollution, and there are only some small molecular substances in it, such as water, hydrogen, methane, etc. So, too, was the composition of the primordial ocean, as it was then thought. In addition, the device has heating and discharging components to simulate the high temperature and lightning on the early earth. A week later, he detected many macromolecules in it, such as amino acids.
　　Regardless of whether it came from extraterrestrial or natural generation, in short, at a certain moment, macromolecular substances including nucleotides appeared on the earth. This leads to a new question: what forces make the nucleotides form long chains? Around 2000, scholars discovered that clay, such as montmorillonite, can promote nucleotide linkage.
　　You may not have seen montmorillonite, but you have probably eaten montmorillonite powder. When you have diarrhea, your doctor will prescribe this medicine. Smectite powder looks like flour and tastes a little sweet. If you put it under a microscope, you can see many small holes. Metal ions are hidden inside these small pores. For the human body, they can absorb harmful substances such as bacteria and viruses; if they encounter nucleotides, they will act as catalysts. Nucleotides in the early years may have become long or short chains under similar mechanisms.
　　Next, there is the question of evolution. If the primitive ocean is compared to a pot of soup, the early nucleotides and amino acids are like rice grains. Nucleotides are combined in a random manner, and there may be meaningless nucleotide chains, or they may just hang on amino acids like tRNA, and they may even appear in complex forms similar to mRNA. No matter which one, if there are free nucleotides nearby, they can replicate themselves under certain conditions; if not, the big deal will gradually disappear under the influence of time-why should they evolve in the direction of DNA?
　　In the early earth, there must have been a pair of “hands” responsible for screening nucleotide chains. With this in mind, some scholars set their sights on the bottom of the sea—about 4 billion years ago, in the deep depths of the bottom of the sea, the earth exposed its chest. Driven by magma, cold and heat, acid and alkali interweave to form a stone full of holes.
　　The earliest macromolecular substances appeared in these stones. Relying on the force between molecules or intramolecules, they began to combine blindly and evolved various forms. Over time, some of these nucleotide strands, like mRNA, have the ability to synthesize proteins. On the one hand, proteins can repair errors and make nucleotides more stable; on the other hand, they participate in substance metabolism and provide more raw materials for nucleotide replication. Therefore, when their offspring enter other holes along the small hole, they easily “beat” those nucleotide chains that only know how to use existing substances to copy themselves.
　　Asteroids fall to Earth from time to time, causing a cloud of dust that obscures the sky. The earth slowly has a magnetic field, which meets the solar wind at the north and south poles, sparking the dazzling aurora. The chain of nucleotides knows nothing of this, only that it replicates itself as faithfully as possible.
　　The first replication, nothing special happened; the second replication, still no major changes… After 500 million years of persistence, on a certain day 3.5 billion years ago, the first single-celled organism finally appeared .
　　Epilogue
　　There is a famous saying in “Jurassic Park”: “Life will always find a way.” DNA does not know how to judge, but only knows to tirelessly reproduce itself. It is this kind of tragic attempt that gave birth to everything in the world.
　　American psychologist Martin Seligman proposed a “learned helplessness theory”: put animals in an inescapable dilemma, they will gradually learn to be depressed, and even if the situation changes, they will not have the courage to try again . A similar phenomenon also occurs in humans. Because of repeated failures, people despair about sports, school, and even family life. They think it is impossible in their hearts and refuse to try again. This may be the price of being a higher animal. We will decide our behavior based on our past experience.
　　Perhaps, this is what understanding DNA means: understanding the grandeur of life is only possible by temporarily stepping outside the boundaries of the self.