Anatomy-Lexicon

Deoxyribonucleic Acid - DNA

Synonyms

Hereditary material, genes, genetic fingerprint

English: Deoxyribonucleic acid (DNS)

definition

The DNA is the building instruction for the body of every living being (mammals, bacteria, Mushrooms Etc.). In its entirety, it corresponds to our genes and is responsible for the general characteristics of a living being, such as the number of legs and arms, as well as for individual characteristics such as hair color.
Similar to our fingerprint, the DNA of every person is different and depends on the DNA of our parents. Identical twins are the exception here: They have identical DNA.

Rough structure of the DNA

In humans, there is DNA in every cell of the body Cell nucleus (nucleus) contain. In living beings that do not have a cell nucleus, such as bacteria or Mushrooms, the DNA is exposed in the cell space (CytoplasmThe cell nucleus, which is only approx. 5-15 µm that is how it measures heart of our cells. It houses our genes in the form of DNA in 46 chromosomes. Around the approx. 2m long DNA Packing it into the tiny cell nucleus is about stabilizing it Proteins and enzymes compressed in spirals, loops and coils.

Thus, multiple genes on one strand of DNA make one of 46 X-shaped chromosomes. Half of the 46 chromosomes are made up of chromosomes from the mother and half from the father's chromosomes. However, the activation of the genes is far more complicated, so the child's characteristics are not accurate too 50% can be traced back to each parent.

Apart from the DNA in the form of Chromosomes in the cell nucleus, there is more circular DNA in the "Energy power plants“Of cells den Mitochondria.
This DNA circle is only passed on from mother to child.

Illustration of a DNA

Structure of DNA, DNA
Deoxyribonucleic acid
Deoxyribonucleic acid
Double strand (helix)

Cytosine
Thymine
Adenine
Guanine
phosphate
sugar
Hydrogen bond
Base pairs
Nucleotide
a - pyrimidine bases
b - purine bases
A - T: 2H bridges
G - C: 3H bridges

You can find an overview of all Dr-Gumpert images at: medical illustrations

Detailed structure of the DNA

One can imagine the DNA as a double strand, which is built up like a spiral staircase. This double helix is somewhat uneven, so that there is always a larger and smaller distance between the steps of the spiral staircase (large and small furrows).

The handrail of this ladder alternately forms:

a sugar residue (Deoxyribose) and
a phosphate residue.

The handrails have one of four possible bases. Thus, two bases form a step. The bases themselves are connected to one another via hydrogen bonds.

This structure explains the name DNA: deoxyribose (= sugar) + Nucleic (= from the Cell nucleus) + Acid / acid (= total charge of the sugar-phosphate backbone).

Bases are ring-shaped, different chemical structures with correspondingly different chemical bonding functions. There are only four different bases in DNA.

Cytosine and thymine (replaced by uracil in the RNA) are so-called pyrimidine bases and have a ring in their structure.
Purine bases, on the other hand, have two rings in their structure. In the DNA these are called adenine and guanine.

There is only one possibility of combining the two bases, which together form a step.

There is always a purine base linked to a pyrimidine base. Due to the chemical structure, cytosine always forms complementary base pairs with guanine and adenine with thymine.

You can read more detailed information on this topic under: Telomeres - Anatomy, Function & Diseases

DNA bases

Come in DNA 4 different bases in front.
These include the pyrimidine-derived bases with only one ring (cytosine and thymine) and the purine-derived bases with two rings (adenine and guanine).

These bases are each with a sugar and a Phosphate molecule linked and are then also referred to as adenine nucleotide or cytosine nucleotide. This coupling to the sugar and to the phosphate is necessary so that the individual bases can be connected to form a long strand of DNA. This is because sugar and alternate in the DNA strand phosphate they form the side elements of the DNA ladder. The ladder steps of DNA are formed by the four different bases that point inwards.
Adenine and thymine, respectively. Guanine and cytosine form a so-called complementary base pairing.
The DNA bases are linked by so-called hydrogen bonds. The adenine-thymine pair has two, and the guanine-cytosine pair three of these bonds.

DNA polymerase

The DNA polymerase is a enzymethat can connect the nucleotides together and thus produce a new strand of DNA.
The DNA polymerase can only work if a so-called enzyme (another DNA polymerase) is activated by another enzyme "Primer", i.e. a starter molecule for the actual DNA polymerase was produced.
The DNA polymerase then attaches to the free end of a sugar molecule within one nucleotide and links this sugar to the phosphate of the next nucleotide.
The DNA polymerase represents in the context of DNA replication (Duplication of DNA in the process of cell division) produces new DNA molecules by reading the existing DNA strand and synthesizing the corresponding opposite daughter strand. In order for the DNA polymerase to reach the “parent strand”, the actually double-stranded DNA has to go through preparatory DNA replication Enzymes to be unwound.

In addition to the DNA polymerases, which are involved in the replication of DNA, there are also DNA polymerases that can repair broken or incorrectly copied areas.

DNA as a material and its products

In order to ensure the growth and development of our body, the inheritance of our genes and the production of the necessary cells and proteins, cell division (meiosis, mitosis) must take place. The necessary processes, which our DNA has to go through, are shown in an overview:

Replication:

The aim of replication is the duplication of our genetic material (DNA) in the cell nucleus, before the cells divide. The chromosomes are unwound piece by piece so that enzymes can attach themselves to the DNA.
The opposing DNA double strand is opened so that the two bases are no longer connected to one another. Each side of the handrail or the base is now read by various enzymes and supplemented by the complementary base including the handrail. This creates two identical double strands of DNA that are distributed between the two daughter cells.

Transcription:

Just like replication, transcription also takes place in the nucleus. The aim is to rewrite the base code of the DNA in an mRNA (messenger ribonucleic acid). Thymine is replaced by uracil and parts of the DNA that do not code for proteins, similar to a space, are cut out. As a result, the mRNA, which is now transported out of the cell nucleus, is considerably shorter than the DNA and only has a single strand.

Translation:

If the mRNA has now arrived in the cell space, the key is read from bases. This process takes place on ribosomes. Three bases (Base triplet) result in the code for an amino acid. A total of 20 different amino acids are used. Once the mRNA has been read, the strand of amino acids results in a protein that is either used in the cell itself or sent to the target organ.

Mutations:

When multiplying and reading the DNA, more or less serious errors can occur. In a cell there is around 10,000 to 1,000,000 damage per day, which can usually be repaired by repair enzymes, so that the errors have no effect on the cell.

If the product, i.e. the protein, is unchanged despite the mutation, then there is a silent mutation. However, if the protein is changed, disease often develops. For example, UV radiation (sunlight) means that damage to a thymine base cannot be repaired. The result can be skin cancer.
However, mutations do not necessarily have to be associated with a disease. You can also modify the organism to its advantage. Mutations are a large part of evolution because organisms can only adapt to their environment in the long term through mutations.

There are various types of mutations that can occur spontaneously during different phases of the cell cycle. For example, if a gene is defective, it is called a gene mutation. However, if the error affects certain chromosomes or chromosome parts, then it is a chromosome mutation. If the chromosome number is affected, it then leads to a genome mutation.

Read more about this under: Chromosome aberration - what does it mean?

DNA replication

The aim the DNA replication is the Duplication of the existing DNA.
During cell division will the Cell DNA exactly doubled and then distributed to both daughter cells.

The doubling of the DNA takes place after the so-called semi-conservative principle instead, that is, that after the initial Unwinding the DNA the original strand of DNA through a Enzyme (helicase) is separated and each of these two "original strands" serves as a template for a new DNA strand.

The DNA polymerase is the enzyme that is responsible for the Synthesis of the new strand responsible is. Since the opposing bases of a DNA strand are complementary to each other, the DNA polymerase can use the existing “original strand” to arrange the free bases in the cell in the correct order and thus form a new DNA double strand.

After this exact doubling of the DNA, the two daughter strandswhich now contain the same genetic information, on the two cellsthat arose during cell division, divided up. So are two identical daughter cells emerged from it.

History of DNA

For a long time it was unclear which structures in the body are responsible for the transmission of our genetic material. Thanks to the Swiss Friedrich Miescher, the focus of research in 1869 was on the content of the cell nucleus.

In 1919 the Lithuanian Phoebus Levene discovered the bases, the sugar and the phosphate residues as building materials of our genes. The Canadian Oswald Avery was able to prove that DNA and not proteins are actually responsible for the transfer of genes in 1943 with bacterial experiments.
The American James Watson and the British Francis Crick put an end to the research marathon, which had spread across many nations, in 1953. They were the first, with the help of Rosalind Franklin's (British) DNA X-rays, a model of the DNA double helix including purine and pyrimidine bases, sugar and phosphate residues. Rosalind Franklin's x-rays, however, were not released for research by herself, but by her colleague Maurice Wilkins. Wilkins received the Nobel Prize in Medicine in 1962, along with Watson and Crick. Franklin had already passed away at this point and could therefore no longer be nominated.

This topic may also be of interest to you: Chromatin

The significance of the discovery of DNA today

Some blood on the scene can convict the perpetrator.

Criminology:

Will suspicious material like

Blood,
Semen or
hair

Found at a crime scene or on a victim, DNA can be extracted from it. Aside from the genes, DNA contains more sections that consist of frequent repetitions of bases that do not code for a gene. These cutscenes serve as a genetic fingerprint because they are highly variable. The genes, however, are almost identical in all humans.

If you cut up the DNA obtained with the help of enzymes, many small pieces of DNA, also called microsatellites, are formed. If one compares the characteristic pattern of the microsatellites (DNA fragments) of a suspect (e.g. from a saliva sample) with that of the existing material, there is a high probability that the perpetrator will be identified if they match. The principle is similar to that of the fingerprint.

Paternity test:

Here, too, the length of the child's microsatellites is compared with that of the possible father. If they match, paternity is very likely (see also: Criminology).

Human Genome Project (HGP):

In 1990 the human genome project was launched. With the aim of deciphering the entire code of DNA, James Watson initially headed the project. Since April 2003, the human genome has been considered completely deciphered. Approximately 21,000 genes could be assigned to 3.2 billion base pairs. The sum of all genes, the genome, is in turn responsible for several hundred thousand proteins.

DNA sequencing

In DNA sequencing, biochemical methods are used to determine the order of the nucleotides (DNA base molecule with sugar and phosphate) in a DNA molecule.

The most common method is that Sanger chain termination method.
Since DNA is made up of four different bases, four different approaches are made. In each approach there is the DNA to be sequenced, a Primer (Starter molecule for sequencing), DNA polymerase (enzyme that extends the DNA) and a mixture of all four required nucleotides. However, in each of these four approaches a different base is chemically modified in such a way that it can be incorporated, but does not offer a point of attack for the DNA polymerase. So then it comes to Chain termination.
This method creates DNA fragments of different lengths, which are then separated by the so-called Gel electrophoresis are chemically separated according to their length. The resulting sorting can be translated into the sequence of the nucleotides in the sequenced DNA segment by marking each base with a different fluorescent color.

DNA hybridization

DNA hybridization is a molecular genetic methodwhich is used to create the Detect similarity between two single strands of DNA of different origin.

This method makes use of the fact that a DNA double strand is always made up of two complementary single strands.
The more similar both single strands are to each other, the more bases form a solid connection (hydrogen bonds) with the opposite base or the more more base pairings arise.

There will be no base pairing between sections on the two strands of DNA that have a different base sequence.

The relative number of connections can now through the Determination of the melting point, in which the newly created DNA double strand is separated.
The higher the melting point lies, the more complementary bases have formed hydrogen bonds to each other and the more similar are the two single strands.

This procedure can also be used for Detection of a specific base sequence in a DNA mixture be used. You can do this artificially formed DNA pieces marked with (fluorescent) dye become. These then serve to identify the corresponding base sequence and can thus make it visible.

Research goals

After completing the Human genome project The researchers are now trying to assign the individual genes to their importance for the human body.
On the one hand, they try to draw conclusions Disease emergence and therapy On the other hand, by comparing human DNA with the DNA of other living beings, there is hope of being able to better represent the evolutionary mechanisms.