Many people have always wondered why some of the signs that parents have are transmitted to the child (for example, eye color, hair color, face shape, and others). It has been proven by science that this transmission of a trait depends on genetic material, or DNA.
What is DNA?
Currently, deoxyribonucleic acid is understood to mean a complex compound responsible for the transmission of hereditary traits. This molecule is found in any cell of our body. The main signs of our body are programmed in it (a certain protein is responsible for the development of a particular sign).
What does it consist of? The composition of DNA includes complex compounds - nucleotides. A nucleotide is understood to mean a block or mini-compound containing 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 via nitrogen bases according to the principle of complementarity.
In addition, it can be considered that genes are a part of DNA - certain nucleotide sequences responsible for protein synthesis. What chemical structural features does deoxyribonucleic acid have?
Nucleotide
As was said, the main structural unit of deoxyribonucleic acid is the nucleotide. This is a complex formation. The composition of the DNA nucleotide is as follows.
Five-component sugar is located in the center of the nucleotide (in DNA it is deoxyribose, unlike RNA, which contains ribose). A nitrogenous base is attached to it, of which 5 types are distinguished: adenine, guanine, thymine, uracil and cytosine. In addition, each nucleotide also contains a phosphoric acid residue.
The composition of DNA includes only those nucleotides that have the indicated structural units.
All nucleotides are arranged in a chain and follow each other. Grouped in triplets (three nucleotides each), they form a sequence in which each triplet corresponds to a specific amino acid. The result is a chain.
They are combined among themselves due to the bonds of nitrogenous bases. The main connection between the nucleotides of parallel chains is hydrogen.
Nucleotide sequences are the basis of genes. Violation in their structure leads to a malfunction in protein synthesis and the manifestation of mutations. The DNA contains identical genes that are determined in almost all people and distinguish them from other organisms.
Nucleotide modification
In some cases, modification of the nitrogen base is used to more stable transmission of a particular trait. The chemical composition of DNA changes due to the addition of a methyl group (CH3). Such a modification (on one nucleotide) allows one to stabilize gene expression and transmission of traits to daughter cells.
Such an “improvement” in the structure of the molecule in no way affects the combination of nitrogen bases.
This modification is also used in the inactivation of the X chromosome. As a result, Barra bodies are formed.
With enhanced carcinogenesis, DNA analysis shows that the nucleotide chain was methylated on many bases. In the observations, it was noted that methylated cytosine is usually the source of the mutation. Usually, in a tumor process, demethylation can help stop the process, but due to its complexity, this reaction is not carried out.
DNA structure
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 a DNA molecule begins at the 5'-end and ends at the 3'-end. The second chain, located opposite, is constructed in the same way, only spatially the molecules are one opposite 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 helix. It is caused by the presence of hydrogen bonds between nucleotides located opposite each other. A hydrogen bond is formed between complementary nitrogenous bases (for example, only thymine can be opposite the first chain adenine, and cytosine or uracil opposite the guanine). This accuracy is due to the fact that the construction of the second chain occurs on the basis of the first, so there is an exact correspondence between the nitrogenous bases.
Molecule synthesis
How is a DNA molecule formed?
In the cycle of its formation, three stages are distinguished:
- Disconnection of chains.
- Attaching synthesizing units to one of the chains.
- Building the second chain on the principle of complementarity.
At the stage of separation of the molecule, the main role is played by enzymes - DNA gyrase. These enzymes are focused on the destruction of hydrogen bonds between chains.
After the chains diverge, the main synthesizing enzyme, DNA polymerase, comes into play. Its accession is observed in section 5 '. Further, this enzyme moves towards the 3'-end, simultaneously attaching the necessary nucleotides with the corresponding nitrogen bases. Having reached a certain site (terminator) at the 3'-end, the polymerase is disconnected from the original chain.
After a daughter chain has formed, a hydrogen bond forms between the bases, which holds the newly formed DNA molecule together.
Where can I find this molecule?
If you delve into the structure of cells and tissues, you can see that DNA is mainly contained in the cell nucleus. The nucleus is responsible for the formation of new, daughter, cells or their clones. In this case, the hereditary information contained in it is divided between the newly formed cells evenly (clones form) or in parts (such a phenomenon can often be observed with meiosis). Damage to 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 mitochondria. In them, the DNA is somewhat different from that in the nucleus (mitochondrial deoxyribonucleic acid has a ring shape and performs several other functions).
The molecule itself can be secreted from any cells of the body (a smear from the inside of the cheek or blood is most often used for research). There is no genetic material only in the exfoliating epithelium and some blood cells (red blood cells).
Functions
The composition of a DNA molecule determines its function of transmitting information from generation to generation. This occurs due to the synthesis of certain proteins, causing the manifestation of a particular genotypic (internal) or phenotypic (external - for example, eye or hair color) trait.
Information is transmitted through its implementation from the genetic code. Based on the information encoded in the genetic code, specific informational, ribosomal, and transport RNAs are generated. Each of them is responsible for a certain action - informational RNA is used for protein synthesis, the ribosomal RNA is involved in the assembly of protein molecules, and the transport one forms the corresponding proteins.
Any malfunction in their work or a change in structure leads to a violation of the function performed and the appearance of atypical signs (mutations).
A DNA paternity test allows you to determine the presence of related characters between people.
Genetic tests
What can genetic material research be used for now?
DNA analysis is used to determine many factors or changes in the body.
First of all, the study allows us to determine the presence of congenital, inherited diseases. Such diseases include Down syndrome, autism, Marfan syndrome.
DNA can also be examined to determine kinship ties. The paternity test has long been widely used in many, especially legal, processes. This study is prescribed when determining the genetic relationship between illegitimate children. Often, applicants for the inheritance test pass this test when questions arise from the authorities.