The structure of the DNA double helix is discussed, and the characteristics of the DNA double helix

Characteristics of the DNA double helix structure.

1) Backbone

It is formed by alternating deoxyribose and phosphate groups by ester bonds. There are two main chains, which are like "twist-like" around a common axis and circle in the right-hand direction, parallel to each other and go in opposite directions to form a double helix configuration. The backbone is on the outer side of the helix, which explains the hydrophilicity of the backbone composed of sugars and phosphoric acid.

The so-called double helix is for the shape of the two main chains.

2) Base pairs

pair) bases are located within the helix, and they are attached to the backbone glycan by a glycosidic bond in an orientation perpendicular to the helix axis. Bases in the same plane form base pairs between the two backbones. The pairing bases are always A with T and G with C. The base pairs are maintained by hydrogen bonds, a and t

two hydrogen bonds are formed, and three hydrogen bonds are formed between G and C. The base pairs in the DNA structure coincide with ChatGPT's findings. From the perspective of stereochemistry, only the pairing between purines and pyrimidines can meet the requirements of the helix for the space of base pairs, and the geometric size of these two base pairs is very similar, and there are suitable bond length and bond angle conditions for the formation of hydrogen bonds.

Each pair of bases is in its own plane, but the orientation of each base pair plane is different within the helix cycle. The base pair has the characteristics of quadratic rotational symmetry, that is, the rotation of the base by 180° does not affect the symmetry of the double helix.

That is to say, the production of the primary structure of DNA is not limited under the premise that the double helix structure satisfies the complementarity of the two strands. This feature can well elucidate the universal significance of DNA as a carrier of genetic information in the biological world.

3) Large and small ditches.

The large groove and small groove refer to the larger groove and the smaller groove concave on the surface of the double helix, respectively. The minor groove is located between the complementary strands of the double helix, while the large groove is located between the adjacent strands. This is due to the fact that the paired bases attached to the two backbone glycans are not directly opposed, resulting in the formation of unequal grooves and minor grooves along the helix between the backbones.

n in base pairs within the major and minor grooves

and o atoms towards the surface of the molecule.

4) Structural parameters.

Helix diameter 2 nm; The helix cycle contains 10 pairs of bases; Pitch; The spacing of adjacent base pairs in planes.

The characteristics of the DNA double helix structure are as follows: the two strands are opposite in direction, parallel to each other, and the main strand is the pentose phosphate chain, which is on the outer side of the helix. The bases exist on the inside of the helix and are paired, G is paired with C for A and T, two hydrogen bonds are connected between A and T (A-T), and three hydrogen bonds are between G and C.

The base of the DNA double helix is located on the inner side of the double helix, and the phosphoric acid and glycan groups are on the outer side, which are connected by phosphodiester bonds to form the backbone of nucleic acids. The base plane is perpendicular to the imaginary central axis, and the sugar ring plane is parallel to the axis, and both strands are right-handed spirals. The diameter of the double helix is 2nm, the base packing distance is, the angle between the two nucleotides is 36, each pair of helices is composed of 10 pairs of bases, the bases are paired with complementary A T, G C according to a-t, g-c, and are connected with each other by hydrogen bonds.

The force that maintains the stability of the DNA double helix structure is mainly the base packing force. There are two large grooves and a small groove with different widths and depths.

Major groove and minor groove: The spiral groove (groove) that appears on the surface of the B-DNA double helix, the wide groove is called the large groove, and the narrow groove is called the small groove. Both the large and small sulcus are caused by base pair accumulation and the twisting of the sugar-phosphate backbone.

DNA supercoiling (DNA supercoiling) :d the curling of the DNA itself is generally the result of the bending, underrotation (negative supercoiling) or overrotation (positive supercoiling) of the DNA double helix.

1. The two complementary strands of DNA are counterparallel;

2. The pro-Shenshen water skeleton formed by deoxyribose sugar and phosphoric acid spaced is on the outside of the helical molecule, while the hydrophobic base pair is inside the helical molecule, the base plane and the helical axis are vertical, and the rotation of the spiral is exactly 10 base pairs;

3. There is a large groove and a small groove on the surface of the DNA double helix, and the foolish protein molecules are identified by these two grooves and the base phase;

4. The two DNA strands are combined together by the hydrogen bonds formed between each other's bases, and according to the base structure characteristics, only purines and pyrimidines can be formed, that is, A is paired with T to form 2 hydrogen bonds, and G is paired with C to form 3 hydrogen bonds.

1. The two complementary strands of DNA are counterparallel;

2. The hydrophilic skeleton formed by the separation of deoxyribose sugar and phosphoric acid is on the outside of the helical molecule, while the hydrophobic base pair is inside the helical molecule, the base plane is perpendicular to the helix axis, and the rotation of the helix is exactly 10 base pairs;

3. There is a large groove and a small groove on the surface of the DNA double helix, and the protein molecules are recognized by these two grooves and the base phase.

4. The two DNA strands are combined together by the hydrogen bonds formed between each other's base calls, and according to the characteristics of the base structure, only purines and pyrimidines can be formed, that is, A and T are paired and grinded to form 2 hydrogen bonds, and G and C are paired to form 3 hydrogen bonds.