Although the molecule of a protein is a chain formed by a series of amino acid groups, it is not straight, but three-dimensional. Pen × fun × Pavilion www. ｂｉｑｕｇｅ。 ｉｎｆｏ

Oh, by the way, the proteins of all living things on Earth are made up of amino acid groups, and there are not many types of these amino acids, only twenty in total.

There is a method of observing the structure of matter in the microscopic world called X-ray diffraction. X-rays are used to irradiate the measured substance, and the arrangement of atoms inside the object is judged according to the image formed by the refracted rays. Based on this, the structure of a keratin was analyzed, and the helical structure of the protein was proposed.

Further analysis of the cause of this is the role of a weak bond - hydrogen bond - which is about 10% of the covalent bond. The polypeptide chain is pulled by its many hydrogen bonds, forming a spiral-shaped trend. Although the individual hydrogen bonds are weak, many hydrogen bonds work together to keep the polypeptide chain in a stable state.

This three-dimensional shape structure is known as the secondary structure of proteins. Did you think of the double helix structure of DNA, the reason is the same.

When amino acids are combined into peptide chains, the R groups on each amino acid group become the side chains of the main chain. These sidechains have different properties. Like alanine, phenylalanine, etc., their groups have no electropolarity, and water molecules have no attraction and are hydrophobic. But the side chains of some amino acids, such as serine, threonine, their groups and water molecules will produce attraction and are hydrophilic. There are also glutamic acid and aspartic acid, which are not only hydrophilic, but also acidic. Lysine, on the other hand, is not only hydrophilic, but also alkaline.

Therefore, on polypeptide molecules with different amino acid sequences, various side chains are in different positions and spatial relationships, attracting or repelling each other. Some can form certain chemical bonds and combine; Some side chains are hydrophobic, so they are alienated from the external water environment and involved in the interior of the molecule; Some side chains are close to the external water environment due to their hydrophilicity. These factors will cause the polypeptide to further bend and wound on the basis of the secondary structure, forming a clumpy-shaped tertiary structure of the protein.

If several of these peptide chains are aggregated together to form a fixed molecular group, they become the quaternary structure of the protein.

In this way, protein molecules with higher order structure may form various convex and concave three-dimensional shapes, and through various chemical bonds, they can form specific three-dimensional mosaicism with large and small molecules of various objects, and play a variety of irreplaceable biological roles. The most fundamental condition for these three-dimensional shapes is the primary structure of the protein.

If we take an example, we can more easily understand the meaning of these structures.

The red substance in the blood has been studied in depth, and now we all know that it is hemoglobin. This iron-containing protein is responsible for the red color of the blood.

The role of hemoglobin is to carry oxygen from the lungs to the tissues, which in turn helps transport carbon dioxide from the tissues to the lungs and excrete them from the body.

Human hemoglobin has a molecular weight of 66,800, which means that it weighs as much as 66,800 hydrogen atoms. It is composed of two peptide chains each, one with 141 amino acid groups and one with 146 amino acid groups.

The order in which these amino acid groups are arranged is the primary structure of human hemoglobin.

These peptide chains exhibit a helical structure, which is the secondary structure.

While these peptide chains themselves are spiral-shaped structures, they are coiled in a certain direction, forming a tertiary structure. The peptide chain of each hemoglobin is roughly spherical after being curled.

Between the peptide chains with tertiary structure, many side chains can be docked in close proximity to play a certain connecting role, so that the peptide chains are further aggregated to form a quaternary structure. For hemoglobin, the four peptide chains are linked together like four globules stuck together in a tetrahedral formation. Each globule is called a subunit of hemoglobin.

The most important point is that the tertiary and quaternary structures of human hemoglobin are very stable. No, this hemoglobin subunit is spherical, the other is pie-shaped, this quaternary structure is tetrahedral and the other is a dragon. The tertiary and quaternary structures are very stable and identical, so all hemoglobins have the same physiological function.

In fact, physiologically speaking, the role of hemoglobin is to transport oxygen from the lungs to the tissues, and then to the lungs to carry carbon dioxide from the tissues. Why is it necessary to form such a large and complex molecule in the process of biological evolution?

People have studied the process of hemoglobin binding to oxygen and found that when hemoglobin is combined with oxygen, it does not produce redox reaction, and the iron in hemoglobin is bivalent regardless of oxygen binding or deoxygenation. So this phenomenon is called oxygenation and deoxygenation, not redox.

By measuring the rate at which oxygenated hemoglobin releases oxygenated hemoglobin, scientists found that when oxygenated hemoglobin enters the capillaries and tissues, the oxygen pressure of the environment drops, and hemoglobin begins to release oxygen, and once hemoglobin begins to release oxygen, the process of releasing oxygen will be accelerated.

When hemoglobin returns to the lungs, it is easier for oxygen to bind further once it begins to bind. This is important for the blood to absorb oxygen adequately and to release it completely in the tissues. This result is known as the Boa effect.

After scientists used X-ray crystallography to compare the structure of oxygenated and deoxygenated hemoglobin, it is believed that the binding and detachment of one heme group and oxygen in hemoglobin are accompanied by small changes in the position of the peptide chain, and the interaction of some amino acid groups on the peptide chain can affect other heme groups and accelerate their binding and detachment from oxygen. Therefore, hemoglobin is likened to an efficient oxygen pump.

This shows that the position of the peptide chain is not constant, it acts non-stop like a real device. We can think of an amino acid group as a part, and a hemoglobin molecule is a complex machine made up of 572 parts. It is constantly and efficiently transporting oxygen and carbon dioxide through the human body.

Efforts were made to explore, and by 1968, information on the amino acid sequences of hemoglobin and myoglobin of several mammals had been collected. Overall, they are somewhat different from human hemoglobin, but the 'pockets' that hold the heme group are almost always the same.

By 1970, Huber of the Max Planck Institute for Protein Research in Germany had published a paper on the structure of hemoglobin in insects. The amino acid sequences of insect and vertebrate hemoglobin are very different, but the folding of the tertiary structure of the peptide chain is said to be strikingly similar.

This situation shows that in the biological world, the oxygen pumps produced by different manufacturers may be different in size, color and material, but the structure and principle are the same. This can also prove that all life on Earth has a common origin.

From this, we can see that the reason why a protein can have a certain physiological function is due to its complex tertiary and quaternary structure. The most fundamental thing is that the various bonds are unbalanced, resulting in mutual attraction and repulsion. A variety of microscopic biological tools have been produced based on this.

What Yuan Qidong thinks about is how to use the expression of three-dimensional force field to reasonably simplify the structure of this microscopic biological tool, so that it can be easily analyzed and utilized.

Moreover, there are about 39,000 human genes, and people have not yet fully understood the tertiary and quaternary structures of all these genes.

Just when these things filled Yuan Qidong's head, Du Xiaomei's kick made these things merge. Thankfully, it's a blend of things, not a mess.

It took Yuan Qidong two days to figure out the three-dimensional molecular force field structure of more than 500 proteins. Around him, several computer experts such as Dongxi, Nanbei, and Tie Jingang were constantly busy, constantly simulating the three-dimensional structure proposed by Yuan Qidong on the computer, and then further using the three-dimensional force field to express it as a microscopic biological tool.

On the evening of the third day, Xue'er forced Yuan Qidong to stop working, and he got out of that state of excitement. However, his goal has basically been achieved, because these more than 500 kinds of protein can be said to be the most basic thing. With the three-dimensional force field structure diagram of these microscopic biological tools, it will be much faster and more accurate to analyze the process of living organisms. It is also easier to derive the three-dimensional force field structure of other proteins.

The rest of the work can be assigned to other people, and he can easily do it for two days.

It's really hard for him to remember so many genetic structures. That stuff was boring.

In fact, Yuan Qidong has further ideas. The structure of these kinds of proteins is all naturally occurring and is a masterpiece of nature.

But because it's natural, there's a lot of stuff in it that is superfluous or imperfect. This is easy to understand, no matter how round a natural stone is, there is no artificial circle. Naturally-grown rice is not as productive as artificially grown.

So Yuan Qidong decided to have time to design some completely new proteins, which were more efficient and simpler, or had more special uses.