The information in DNA is like a design drawing, recording all the cells and structures of living things?

Every well-educated person now knows that the code of life is stored in several ultra-long organic molecular chains called DNA in each cell. Today, many commercial organizations have begun to promote DNA testing services , just a little bit of saliva can tell you a lot about your life.

Does that mean that all a person’s information is already hidden in DNA? Is this information like a sophisticated blueprint that accurately depicts every cell and function of the human body? Is it possible to reconstruct an extinct creature through computer simulation relying solely on DNA information? Today we will study this misunderstanding that may be the default in everyone's mind.

The amount of genetic information is surprisingly small

First of all, ask a question: How much information does human genes contain in total? How many cells does the human body have?

Answer: There are about 3.16 billion DNA base pairs in total human beings. Because there are only 4 types of base pairs, which can be represented by two bits at least, the total amount of data is about 7.9 Billion bytes (Bytes), approximately 790 megabytes (M Bytes). This is a not very large amount of data. In a VCD from decades ago, a very blurry movie was probably this large.

DNA is transparent and can only be stained and observed when dividing, so it is called a chromosome.

The human body has about 30 trillion cells.

Yes, the ratio of genes to cells is about 1:37974. The number of genes is far smaller than the number of cells, and it is not even possible to record where each cell is, let alone include the connections of nerve cells, the control of development cycles, and the rhythm of metabolism. How is it possible to accomplish such an amazing feat with just a little bit of information?

To answer such a question, we need to recall the content of a biology class we learned in junior high school, and let the thinking start from there!

Looking at auxin again

Do you still remember the research on plant phototropism in junior high school chemistry? Auxin - This hormone, chemically called indoleacetic acid, determines whether the tip of the plant will grow in the direction of stronger light. Auxin is secreted by the coleoptile at the tip of the plant and transported downward. The irradiation of light will cause a concentration difference between the light-facing and back-lit surfaces of the stem (a protein called auxin transporter is embedded in the cell membrane and will be endowed when exposed to light. can be activated. The activated protein will transport auxin out of the cell, while cells on the backlight side that do not "pump" auxin outward will retain auxin). In areas with higher auxin concentrations, cells will expand more. , so that the backlight side of the plant grows longer than the light side, showing phototropism.

Phototropism

Not only that, auxin also has another function - apical dominance. On the trunk, the higher the auxin concentration, the faster the growth, but on the branches, the higher the auxin concentration, the slower the growth. Therefore, branches closer to the terminal bud will grow more slowly, thus forming the pointed tower-shaped structure of many plants.

So now there are three questions:

Why is growth hormone secreted at the top?

Why do the same chemical ingredients show different effects?

After all, what is the effect of auxin?

Gene expression to cell differentiation

To explain these issues, we must start from gene expression to cell differentiation.

Growthin is a hormone. The reason why hormones are called hormones is because these chemicals bind to specific proteins in cells. After the two combine, the proteins are activated and in turn affect the processes in the cell nucleus. DNA transcription and expression. That is to say, although every cell contains all genes, only some of them are active. The proteins synthesized by the specific genes involved in the expression will cause the cells to show specific shapes and structures, so the somatic cells of our multicellular organisms The forms are ever-changing and the functions are extremely rich, which is called cell differentiation.

So where do receptor proteins come from? It is synthesized from DNA through transcription and translation.

Well, is there a strange feeling? There is a relationship between the two that can affect each other. Genes affect proteins, and proteins can affect genes.

Not only that, hormones are only one factor that can affect gene expression. There are also many naturally occurring influencing factors, such as the first differentiation during the development of bird embryos - from blastocyst to embryo. In the intestinal embryo, under the influence of four signal transmitters, including bone morphogenetic protein, fibroblast growth factor, nodal signaling protein, and Wnt signaling protein, proximal-abaxial asymmetry is produced, which causes polar curling of embryonic cells. In human terms, these sentences mean that the egg should be rolled toward whichever side is more nutritious (the direction of the yolk). After curling occurs, these cells will begin to differentiate in different directions, emerging as endoderm, mesoderm and ectoderm, which will further differentiate into all tissues and organs of the larvae.

The polar curl of the gastrula,

So the three questions about auxin are easily explained: Because the cells differentiate, the cell functions of each different tissue are different. Different, only the genes that synthesize auxin are expressed in the tip cells that are growing;

And because the differentiated cells have different functions and different receptor proteins, the same hormone can even play a complete role. The opposite effect;

The process of auxin is to regulate DNA expression and other biochemical reactions through receptor proteins. If we say it directly, its essence is achieved by participating in complex biochemical reactions.

Too many possibilities to simulate

Some clues can be seen from the above content. Genes never directly regulate a specific trait as everyone imagines. A gene is only responsible for producing one kind of protein, and how this protein participates in the development of organisms and what effects it will have are determined by the "comprehensive environment" (as small as the specific chemical composition inside each cell, as large as the intensity and intensity of cosmic rays) Gravity) ***determined by the same.

This is a very interesting concept, which means that the expression of genes affects the comprehensive environment to a certain extent, and the comprehensive environment will shape gene expression. The two interact with each other, forming a circular logic connected from end to end, which contains countless parameters. It is impossible to calculate using mathematical logic. You must know that a Go board of only 19 x 19 has as many as 1.7408965065903 x10^172 (174000...***170 0...0) layouts, which is more than all the layouts in the entire universe. The total number of atoms is much higher!

A metaphor between the workplace and cells

Now I will come up with a metaphor that I thought about all night long to help readers who are still confused understand the role of genes in cell regulation. How is efficiency achieved?

I liken each cell to an office cubicle. The employees and all other items sitting in it are the collection of all biochemical reaction substances in the cell, and genes are the tips in the drawer.

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That's about it

Now everyone is immersed in work, because the first 5 tips they have after arriving are placed there. "Must-read for work" was written on the desktop. After learning the contents of these tips, everyone started working - inputting the documents that were continuously sent to them into the computer.

The fifth tip only records one instruction: "Every time you finish entering a document, look at the partition of your desk to the east." But you didn't see anything except a board, of course nothing. It won't happen either.

The change happened at sunrise, a beautiful ray of sunlight shone in from the window, and something wonderful happened here. After the employee sitting by the window completed the document entry again, he raised his head and glanced at the partition according to the procedure, but this time it was different. They found words on the partition. It turned out that there was a watermark similar to that used on banknotes. It could not be seen without the transmission of light. The partition said "Open Tips 7 in the left drawer" (an analogy here) is the effect of light on cell differentiation).

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The watermark in the U.S. dollar, Franklin

So while everyone was still entering files, several people had quietly started other jobs. Tip 7 contains only one sentence: "Open the second drawer on the left and complete the work." There are several approval documents in the second drawer on the left. After the approval is completed, you will find a piece of paper underneath with these two sentences: "Complete the above Distribute the files to others", "Open the tip bag 41 in the left drawer".

Although these files sent to other people also record the same information, the operations performed are different because of each person's specific situation. For example, one of the instructions is "People who have entered more than 40 documents open the tip bag 213". People sitting far away from the door have not received enough distribution. If the number is insufficient, they will not respond to this instruction. (Here Analogous to polar differentiation of cells).

In this way, after several rounds, everyone in the office began to perform different tasks, and as the work progresses, the content of each person's work will become more and more different, and they will Increase manpower, open new departments, launch new businesses, and transform from an office with dozens of people into a huge company with tens of trillions of employees.

Cooperating with the laws of the world

Now let’s analyze the story just now. Genes are tips, which contain two types of information: “methods of specific work” and “instructions” , both types of information are realized through the synthesis of proteins. But can the final result be judged solely by relying on the information recorded in the tips? cannot. If you think about it carefully, you will find that most of the information is provided by some substances and environmental information that already exist in cells. For example, why can everyone type? Why do the drawers on the second left have several documents as soon as they are opened? Why do you get more chances to get in if you sit closer to the door? This information determines what kind of results the genes will produce unless they are put into a specific environment.

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The Gate of Truth in "Fullmetal Alchemist", although the reproduction of life also depends on "truth", it has nothing to do with this image.

The fundamental reason for achieving polarization through the instruction "Those who have entered more than 40 documents, open the tip bag 213" is that "there is only one door". The distance from the door determines which employees will respond to the instruction. . But "number of doors", "location of doors", "door size", "door opening and closing times", "file transfer frequency", "other people's processing speed" are not recorded in genes, of course No need to record either. The conditions for all this to be realized are simply because "the door is already here."

That is to say, the reason why our creatures develop like this is that most of the information comes from the physical and chemical laws of the universe. All Gene did was to put in a small pebble. What kind of effect this pebble would have, whether it would be silent or a Loch Ness Monster, would be left to the dark water below.

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Exquisite, elegant, efficient, rare

Therefore, genes only need a very small amount of information to play the music of life , transforming disorder into order, creating life from an inorganic world. If you want to ask how this exquisite and efficient logic is generated, it is actually very simple - it is just tried and tested.

The greatness of life lies in its rarity.

Although the universe is vast and rich in matter, most of it is single and boring. There are more stars in the universe than there are grains of sand on all the beaches on the earth, but how different are they from the sand? Our earth is like a bright gem on an endless beach. It exudes a charming luster. It is a blue ocean, rich in oxygen, and a world full of life. It is also probably the only one on all the beaches in the world. gem.