Does that mean that all the information about a person has been hidden in DNA? Is this information like an accurate design drawing that can accurately describe every cell and function of the human body? Can an extinct creature be restored by computer simulation only by relying on DNA information? Today, let's study this misunderstanding that may be acquiesced in everyone's mind.
The amount of genetic information is surprisingly small.
First of all, ask a question: how much information does the human gene have in total? How many cells does the human body have?
A: There are about 365,438+600 million DNA base pairs. Because there are only four types of base pairs, the smallest one can be expressed by two digits, so the total data volume is about 790 million bytes, or about 790 trillion. This is not a very large amount of data. A VCD A few decades ago, a badly pasted movie was about this big.
DNA is transparent and can only be observed when it divides, so it is called 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 less than the number of cells, and it is impossible to even record where each cell is, let alone the connection of nerve cells, the control of development cycle and the rhythm of metabolism. How did you accomplish such an amazing feat with only a little information?
To answer such a question, we need to recall the content of a biology class in junior high school, so let's start thinking from there!
Look at auxin again
Do you still remember the research on plant phototropism in junior high school chemistry? Auxin, a hormone chemically called indoleacetic acid, determines that the tips of plants will grow in the direction of stronger light. Auxin is secreted by the coleoptile at the top of the plant and transported downwards. Light irradiation will cause concentration difference between the sunny side and the backlight side of the stem (protein with auxin transporter embedded in the cell membrane will be excited and activated under light irradiation, and the activated protein will transport auxin outside the cell, while the backlight side cells without "pumping" auxin will retain auxin). In areas with high auxin concentration, cells expand more, which makes the backlight side of plants longer than the light side.
phototropism
And auxin has another function-apical advantage. On the trunk, high concentration of auxin grows fast, while on the branches, the higher the auxin, the slower the growth. Therefore, the branches closer to the terminal buds will grow slowly, thus forming the spire structure of many plants.
So now there are three questions:
Why does the top secrete growth hormone?
Why do the same chemical components show different effects?
After all, what does auxin do?
Gene expression of cell differentiation
To explain these problems, we should talk about cell differentiation from gene expression.
Auxin is a hormone. Hormones are called hormones because these chemicals bind to specific protein in cells. When they combine, protein will be activated, which will affect the transcription and expression of DNA in the nucleus. That is to say, although every cell contains all the genes, only some of them are active. Protein, who participates in the synthesis of specific genes, will make cells present specific shapes and structures, so the somatic cells of our multicellular organisms have ever-changing shapes and extremely rich functions, which is called cell differentiation.
So where did the receptor protein come from? It is synthesized by DNA transcription and translation. Well, is there a wonderful feeling? There is an interactive relationship between them, with genes influencing protein and protein influencing genes.
Moreover, hormone is only one factor that can affect the expression of basic groups, and there are many natural factors, such as the first differentiation during the development of birds' embryos-from blastocyst to gastrula, which is influenced by four signal transmitters: bone morphogenetic protein, fibroblast growth factor, knot signal protein and Wnt signal protein, resulting in asymmetry between the proximal and distal axes, thus making embryonic cells polar curl. In human terms, these words are: roll to the nutritious side (egg yolk direction). After curling, these cells will begin to differentiate in different directions, and endoderm, mesoderm and ectoderm will appear, and they will further differentiate into all tissues and organs of larvae.
The gastrula is extremely curly,
Therefore, three questions about auxin are well explained: because cells are differentiated, the functions of cells in different tissues are different, and only the growing tip cells will express their genes for synthesizing auxin;
Moreover, because the differentiated cells have different functions and different receptor proteins, the same hormone can even produce the opposite effect;
Auxin plays a role by regulating DNA expression and other biochemical reactions through receptor proteins. If we directly say that the essence is realized by participating in complex biochemical reactions.
Too many possibilities to simulate.
From the above, we can already see some clues. Genes never directly regulate a specific trait as you think. A gene is only responsible for producing a protein, and how this protein participates in the development of organisms and what kind of effect it will have is determined by the "comprehensive environment" (as small as the specific chemical composition in each cell, as large as the intensity and gravity of cosmic rays).
This is a very interesting concept, that is to say, gene expression affects the comprehensive environment to some extent, and the comprehensive environment will shape gene expression. The interaction between them is a circular logic that is connected from beginning to end and contains countless parameters. It is impossible to calculate by mathematical logic. You should know that there are as many as1.7408965065903x10172 (174000...* * 65438+.
Metaphor of workplace and cell
Next, I will come up with a metaphor that I have been thinking about all night to help readers who are still at a loss understand how efficient genes are in cell regulation.
I compare each cell to an office cubicle, where employees and everything else are the collection of all biochemical reaction substances in the cell, and genes are the tool kits in the drawer.
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That's about it.
Now everyone is working hard, because the first five tips after coming are all on the desktop, which says "work must be read" After understanding the contents of these tips, everyone began to work-input the files that kept coming into the computer.
The fifth tip only recorded an instruction, "Look at the east partition of your desk after entering a file", but nothing was seen except a board, of course, nothing would happen.
The change happened at sunrise, and a beautiful ray of sunshine shone through the window, and wonderful things happened here. After entering another document, the employee sitting by the window looked up at the partition according to the procedure, but this time it was different. They found words on the partition. It turns out that there is a watermark in the partition similar to that used on paper money. If there is no light, you can't see. The partition says "Open the Kit 7 in the left drawer" (the analogy here is the influence of light on cell differentiation).
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Watermark in the dollar, Franklin
So while everyone was still typing documents, several people had quietly started other work. Kit 7 contains only one sentence "Open the second drawer on the left and finish the work". There are several approval documents in the second drawer on the left. After the approval, you will find a piece of paper below, which reads "Distribute the above documents to others" and "Left First Drawer Opening Kit 4 1".
Although these files sent to other people also record all kinds of the same information, the operations performed are different because of everyone's specific situation. For example, there is an instruction that "people who enter more than 40 files open suite 2 13", and people sitting far from the door do not receive enough distribution, and less than this number will not respond to this instruction (the analogy here is the polarization of cells).
In this way, after several rounds, everyone in the office began to perform different jobs, and with the deepening of the work progress, everyone's work content will become more and more different. They will increase manpower, open up new departments and start new businesses, from an office with dozens of people to a huge company with hundreds of trillions of employees.
Abide by world laws
Now, let's analyze the story just now Gene is a tool kit, which contains two kinds of information, namely "specific working methods" and "instructions". Both kinds of information are realized by synthesizing protein. But can the final result be judged only by the information recorded in the kit? I can't. If you think about it carefully, you will find that most of the information is provided by some material and environmental information already existing in cells, such as why everyone can type? The second drawer on the left is open. Why are there several documents? Why do you get more access by sitting near the door? This information determines that the gene will not be put into the specific environment, and I don't know what kind of results will be produced.
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The door of truth in The Alchemist of Steel has nothing to do with this image, although the reproduction of life depends on "truth".
The fundamental reason why the instruction "People who enter more than 40 files open Suite 2 13" can be polarized is that there is only one door, and the distance of the door determines which employees will respond to the instruction. However, the number of doors, the location of doors, the size of doors, the opening and closing time of doors, the transmission frequency of files, and the processing speed of others are not recorded in the genes, and of course there is no need to record them. The realization condition of all this is because "the door is already here".
In other words, the reason why our creatures have developed like this is because most of the information comes from the physical laws and chemical laws in this universe. What genes do is put a small stone in it. What effect will this stone have? Whether it is silence or the Loch Ness monster, it will be given to the dark water.
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Exquisite, elegant, efficient and rare
Therefore, genes can play the music of life with little information, turn disorder into order, and create life from an inorganic world. To ask how this subtle and efficient logic is formed is actually very simple-it was tried, that's all.
The greatness of life lies in its rarity.
Although the universe is vast and rich in material, most of it is single and boring. There are more stars in the universe than sand on all beaches on earth, but how different are they from sand? Our earth is like a bright gem on the boundless beach, emitting charming brilliance. It is a blue ocean, an oxygen-rich and vibrant world, and it may be the only gem on all beaches in the world.