Heredity, genes, genetic fingerprint
Definition
DNA is the building instruction for the body of every living being (mammals, bacteria, fungi, etc.) It corresponds in its entirety 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 is different in every person and depends on the DNA of our parents. Identical twins are the exception: they have identical DNA.
Rough structure of the DNA
In humans, DNA is contained in every cell of the body with a nucleus. In living beings that do not have a cell nucleus, such as bacteria or fungi, the DNA lies freely in the cell space (cytoplasm). The cell nucleus, which measures only approx.
5-15 μm, is in this way seen the heart of our cells. In it, our genes in the form of DNA are located in 46 chromosomes. In order to pack the DNA, which is about 2m long in total, into the tiny cell nucleus, it is compressed into spirals, loops and coils via stabilizing proteins and enzymes.
Thus several genes on one DNA strand result in one of 46 X-shaped chromosomes. Half of the 46 chromosomes are made up of chromosomes from the mother and half of chromosomes from the father. However, the activation of the genes is much more complicated, so that the characteristics of the child cannot be traced back exactly 50% to each parent. Apart from the DNA in the form of chromosomes in the cell nucleus, there is other circular DNA in the cells’ “energy power plants”, the mitochondria. This DNA circle is inherited exclusively from the mother to the child.
Detailed structure of the DNA
One can imagine the DNA as a double strand, which is constructed like a spiral staircase. This double helix is somewhat uneven, so that there is always an alternating larger and smaller distance between the steps of the spiral staircase (large and small furrows). The handrail of this ladder is formed alternately: one of four possible bases starts from each of the handrails.
Thus two bases form one step. The bases themselves are connected by 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 unequal chemical binding functions. Only four different bases are found in DNA. There is only one way to combine the two bases, which together form a step.
There is always a purine base linked to a pyrimidine base. Due to the chemical structures, cytosine with guanine and adenine with thymine always form complementary base pairs.
- A sugar residue (deoxyribose) and
- A phosphate residue.
- Cytosine and thymine (in the RNA replaced by uracil) 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.
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