The composition of DNA ... Chemical composition of DNA

Many people have always wondered why some of the signs that are available to parents are passed on to the child (for example, eye color, hair, face shape and others). Science has proven that this transfer of trait depends on genetic material, or DNA.

What is DNA?

Currently, deoxyribonucleic acid is understood as a complex compound responsible for the transmission of hereditary traits. This molecule is contained in any cell of our body. It programmed the main features of our body (for the development of a characteristic corresponds to a certain protein).

What does it consist of? The DNA composition includes complex compounds - nucleotides. A nucleotide is a block or mini-compound that has a nitrogenous base, a phosphoric acid residue and sugar (in this case deoxyribose).

DNA is a double-stranded molecule in which each of the chains is connected to the other through nitrogen bases according to the principle of complementarity.

In addition, we can assume that the DNA consists of genes - certain nucleotide sequences responsible for protein synthesis. What chemical structural features does deoxyribonucleic acid have?

Nucleotide

As it was said, the basic structural unit of deoxyribonucleic acid is the nucleotide. This is a complex education. The DNA nucleotide composition is as follows.

At the center of the nucleotide is five-component sugar (in DNA it is deoxyribose, in contrast to RNA, which contains ribose). It is joined to the nitrogenous base, which are distinguished by 5 types: adenine, guanine, thymine, uracil and cytosine. In addition, each nucleotide also contains a phosphoric acid residue.

The DNA composition includes only those nucleotides that have the indicated structural units.

All nucleotides are arranged in a chain and follow each other. Grouped by triplets (three nucleotides), they form a sequence in which each triplet corresponds to a particular amino acid. As a result, a chain is formed.

They are combined among themselves due to the bonds of nitrogenous bases. The basic relationship between the nucleotides of the parallel chains is hydrogen.

Nucleotide sequences are the basis of genes. Violation in their structure leads to a failure in the synthesis of proteins and the manifestation of mutations. The DNA composition includes the same genes, which are determined practically in all people and distinguish them from other organisms.

Nucleotide modification

In some cases, the modification of the nitrogenous base is used for a more stable transmission of one or another characteristic. The chemical composition of DNA changes due to the addition of the methyl group (CH3). Such modification (on one nucleotide) allows to stabilize gene expression and transfer of signs to daughter cells.

Such an "improvement" in the structure of the molecule in no way affects the association of nitrogenous bases.

This modification is also used in the inactivation of the X chromosome. As a result, Barra's bodies are formed.

With increased carcinogenesis, DNA analysis shows that the nucleotide chain has been susceptible to methylation on many bases. In the observations, it was noted that the source of the mutation is usually methylated cytosine. Usually, in a tumor process, demethylation can help stop the process, but due to its complexity, this reaction is not carried out.

Structure of DNA

In the structure of the molecule, two types of structure are distinguished. The first type is a linear sequence formed by nucleotides. Their construction is subject to certain laws. The recording of nucleotides on the DNA molecule begins at the 5'-end and ends at the 3'-end. The second circuit, located opposite, is constructed in the same way, only in the spatial ratio of the molecule are one opposite to the other, and the 5 'end of one chain is located opposite the 3' end of the second.

The secondary structure of DNA is a spiral. It is caused by the presence of hydrogen bonds between nucleotides arranged opposite each other. The hydrogen bond is formed between complementary nitrogenous bases (for example, opposite to adenine of the first chain there can be only thymine, and in front of guanine - cytosine or uracil). This accuracy is due to the fact that the construction of the second chain occurs on the basis of the first, therefore an exact correspondence is observed between the nitrogen bases.

Synthesis of a molecule

How does the DNA molecule form?

In the cycle of its formation three stages are distinguished:

• Disconnection of circuits.
• Connection of synthesizing units to one of the circuits.
• Completion of the second chain according to the principle of complementarity.

At the stage of disintegration of the molecule, the main role is played by enzymes - DNA gyrase. These enzymes are oriented to the destruction of hydrogen bonds between the chains.

After the divergence of the chains, the main synthesizing enzyme, DNA polymerase, enters the case. Its attachment is observed in section 5 '. Further, this enzyme moves towards the 3'-end, simultaneously adding the necessary nucleotides with the corresponding nitrogenous bases. After reaching a specific site (terminator) at the 3'-end, the polymerase is disconnected from the original chain.

After the daughter chain was formed, a hydrogen bond forms between the bases, which also bonds the newly formed DNA molecule.

Where can I find this molecule?

If you go deeper into the structure of cells and tissues, you can see that the DNA is mostly contained in the nucleus of the cell. The nucleus is responsible for the formation of new, daughter cells, or their clones. In this case, hereditary information located in it, is divided between the newly formed cells evenly (clones are formed) or in parts (often this phenomenon can be observed in meiosis). The defeat of the nucleus entails a violation of the formation of new tissues, which leads to a mutation.

In addition, a special type of hereditary material is found in the mitochondria. In them, DNA differs somewhat from that in the nucleus (mitochondrial deoxyribonucleic acid has an annular shape and performs several other functions).

The molecule itself can be excreted from any body cells (for testing, a smear from the inside of the cheek or blood is used most often). There is no genetic material only in exfoliating epithelium and some blood cells (erythrocytes).

Functions

The composition of the DNA molecule makes it perform the function of transmitting information from generation to generation. This is due to the synthesis of certain proteins that cause the manifestation of a particular genotypic (internal) or phenotypic (external - for example, the color of the eyes or hair) sign.

The transfer of information is carried out through the implementation of it from the genetic code. Based on the information encrypted in the genetic code, specific information, ribosomal and transport RNAs are produced. Each of them is responsible for a certain action - information RNA is used for the synthesis of proteins, the ribosomal participates in the assembly of protein molecules, and the transport forms the corresponding proteins.

Any failure in their work or a change in structure leads to a disruption in the function performed and the appearance of atypical signs (mutations).

The DNA test for paternity allows you to determine the presence of related signs between people.

Genetic tests

Why can genetic research be used at present?

DNA analysis is used to determine many factors or changes in the body.

First of all, the study allows you to determine the presence of congenital, inherited diseases. Such diseases include Down syndrome, autism, Marfan syndrome.

DNA can also be examined to determine related relationships. The paternity test has long been widespread in many, primarily legal, processes. This study is assigned when determining the genetic relationship between children born out of wedlock. Often this test is handed over to applicants for inheritance when there are questions from the authorities.