Many people have always wondered why some of the characteristics that parents have are transmitted to the child (for example, eye color, hair, face shape, and others). It has been scientifically proven that this transmission of a trait depends on the 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 found in every cell of our body. The main features of our body are programmed in it (a certain protein is responsible for the development of a particular feature).
What does it consist of? DNA is made up of complex compounds called nucleotides. A nucleotide is a block or mini-compound that contains a nitrogenous base, a phosphoric acid residue, and a sugar (in this case, deoxyribose).
DNA is a double-stranded molecule in which each of the chains is connected to the other through nitrogenous bases according to the principle of complementarity.
In addition, we can assume that DNA contains genes - certain nucleotide sequences responsible for protein synthesis. What are the chemical features of the structure of deoxyribonucleic acid?
Nucleotide
As mentioned, the basic structural unit of deoxyribonucleic acid is the nucleotide. This is a complex education. The composition of a DNA nucleotide is as follows.
At the center of the nucleotide is a five-component sugar (in DNA it is deoxyribose, unlike RNA, which contains ribose). It is joined by a nitrogenous base, of which there are 5 types: adenine, guanine, thymine, uracil and cytosine. In addition, each nucleotide also contains a phosphoric acid residue.
DNA contains 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 with each other due to the bonds of nitrogenous bases. The main bond between the nucleotides of 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. DNA contains the same genes that are determined in almost all people and distinguish them from other organisms.
Nucleotide modification
In some cases, for a more stable transfer of a particular trait, a modification of a nitrogenous base is used. The chemical composition of DNA is changed by the addition of a methyl group (CH3). Such a modification (on one nucleotide) allowsstabilize gene expression and transfer of traits to daughter cells.
Such an “improvement” of the structure of the molecule in no way affects the association of nitrogenous bases.
This modification is also used for X-chromosome inactivation. As a result, Barr bodies are formed.
With increased carcinogenesis, DNA analysis shows that the chain of nucleotides was subject to methylation on many bases. In the observations made, 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.
DNA structure
There are two types of structure in the structure of a molecule. The first type is a linear sequence formed by nucleotides. Their construction is subject to certain laws. The writing of nucleotides on a DNA molecule starts at the 5' end and ends at the 3' end. The second chain, located opposite, is built in the same way, only in the spatial relation 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 adenine of the first chain, and cytosine or uracil can be opposite guanine). Such accuracy is due to the fact that the construction of the second chain occurs on the basis of the first, therefore, there is an exact correspondence between the nitrogenous bases.
Synthesis of the molecule
How does a DNA molecule form?
There are three stages in the cycle of its formation:
- Disconnecting chains.
- Connection of synthesizing units to one of the chains.
- Completion of the second chain according to the principle of complementarity.
At the stage of separation of the molecule, the main role is played by enzymes - DNA gyrases. These enzymes are focused on the destruction of hydrogen bonds between chains.
After the divergence of the chains, the main synthesizing enzyme, DNA polymerase, comes into play. Its attachment is observed in section 5'. Further, this enzyme moves towards the 3'-end, simultaneously attaching the necessary nucleotides to the corresponding nitrogenous bases. Having reached a certain site (terminator) at the 3'-end, the polymerase is disconnected from the original chain.
After the daughter chain is formed, a hydrogen bond is formed 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. At the same time, the hereditary information contained in it is divided between the newly formed cells evenly (clones are formed) or in parts (it is often possible toobserve such a phenomenon during meiosis). The defeat of the nucleus entails a violation of the formation of new tissues, which leads to mutation.
In addition, a special type of hereditary material is found in mitochondria. Their DNA is somewhat different from that in the nucleus (mitochondrial deoxyribonucleic acid has a ring shape and performs slightly different functions).
The molecule itself can be isolated from any cells of the body (for research, a smear from the inside of the cheek or blood is most often used). The genetic material is missing only in the sloughing epithelium and some blood cells (erythrocytes).
Functions
The composition of the DNA molecule determines the performance of its function of transmitting information from generation to generation. This occurs due to the synthesis of certain proteins that cause the manifestation of one or another genotypic (internal) or phenotypic (external - for example, eye or hair color) trait.
The transfer of information is carried out by implementing it from the genetic code. Based on the information encrypted in the genetic code, specific informational, ribosomal and transfer RNAs are produced. Each of them is responsible for a specific action - messenger RNA is used to synthesize proteins, ribosomal RNA is involved in the assembly of protein molecules, and transport RNA forms the corresponding proteins.
Any failure in their work or a change in the structure leads to a violation of the performed function andthe appearance of atypical traits (mutations).
DNA paternity test allows you to determine the presence of related signs between people.
Genetic tests
What can genetic testing currently be used for?
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. These diseases include Down syndrome, autism, Marfan syndrome.
You can also test DNA to determine family ties. The paternity test has long been widely used in many, primarily legal, processes. This study is prescribed when determining the genetic relationship between illegitimate children. Often this test is taken by applicants for inheritance when questions arise from the authorities.
