DNA structure – all about it

DNA is the central element of genetics and therefore of outstanding importance in biology. It is a very complex part of the cell, consisting of four chemical bases. In addition, DNA plays an important role in gene expression. In order to understand how they work and how they work, it is important to know how DNA is constructed.

DNA

deoxyribonucleic acid or short DNA is a double-stranded molecule in the shape of a double helixthe the genetic information of a living being wears. Each strand is to its counterpart antiparallel and consists of chained nucleotides. Both strands are connected to each other via the nucleobases (adenine, guanine, thymine, cytosine) of the nucleotides.

The abbreviation DNA stands for the English term deoxyribonucleic acid. In German one speaks of deoxyribonucleic acid, abbreviated DNS. So DNS and DNA mean the same thing, just in different languages. Since the common term is DNA, this term will be used in this article.

DNA construction

DNA consists of different components:

In the following, you will learn more about the tasks these components perform and how the DNA is composed of them.

nucleotide

First, it is important to look at the three components together. Sugar, phosphate and the bases together form the nucleotide.

The nucleotide is a specific part of DNA composed of a nucleoside, one of the four bases and a phosphate group. Nucleotides act as messengers and play an important role in the formation of new cells.

A molecule made up of a nucleobase and a simple sugar is called a nucleoside. It is similar in structure to the nucleotide, but does not have a phosphate residue attached to it.

phosphate

The phosphate has a fixed, continuous place in the structure of the DNA. It docks to the 5th C atom. You can also see this in Figure 1. Phosphate is the attachment point for the ribose of the next nucleotide in the chain of a DNA strand. It is also called the phosphate backbone in the DNA constellation.

But what exactly is phosphate? Of the minerals Along with calcium, it is one of the most important building blocks of the skeleton and also plays an important role for the teeth. In addition, it plays an important role in energy metabolism of the cells.

If you are interested in learning more about phosphates and phosphoric acid, check out the Phosphoric Acid Statement!

pentose

the pentose is represented by the pentagon in Figure 1. The word pentose can come from the ancient Greek word pente be derived, which means something like five. A pentose consists of deoxyribose, which is sugar, and five carbon atoms. The atoms are numbered and arranged clockwise. The pentose offers the stable binding possibility for bases and phosphate in the nucleotide and is therefore essential for the formation of the single strand and the double strand.

Figure 3: Structural formula of ribose with numbered carbon atoms

Here it is essential that you do not confuse deoxyribose with ribose. While deoxyribose is the sugar building block of DNA, ribose is part of RNA. If you want to know the differences between the two parts of the genome, check out the article on RNA!

bases

the bases are the third component of the nucleotide. They are connected to the nucleotide at the first carbon atom of the deoxyribose.

There are four organic bases. You can find them listed here:

BasesBase GroupStructureSymbolAdeninePurine

thyminepyrimidine

guanine purine

cytosine pyrimidine

The bases are divided into two different basic bodies: pyrimidine bases and purine bases. The pyrimidine bases include cytosine, thymine and uracil found in RNA. Meanwhile, adenine and guanine form the purine bases.

RNA also has bases that make up its strand. These include adenine, uracil, guanine and cytosine. Here the second base thymine is replaced by uracil.

You can find out why thymine is being replaced by uracil in the explanation on uracil.

tasks of the bases

Any two nucleotides connect via hydrogen bonds between the bases with each other. In each case, the two complementary bases combine with one another, which means that a purine base binds to a pyrimidine base. Due to their specific sequence (base sequence), the main task of the bases is the formation of the genetic code and thus the storage of the blueprints for proteins and the entire organism.

DNA single strand

By linking several nucleotides, one ultimately forms DNA strand. You can also see this in Figure 4. The C3 atom (3′) of the upper pentose always connects to the phosphate group of the lower nucleotide. Both strands of DNA run antiparallel, i.e. in opposite directions. This means that the 5′ end of one strand is opposite the 3′ end of the complementary strand. They correspond to the respective carbon atom of the ribose.

DNA structure of the double helix

DNA consists of many nucleotides linked together. You will now find out how these nucleotides are linked together and what the primary, secondary and tertiary structure of DNA is all about.

Primary structure of the DNA double helix

The phosphate residue of one nucleotide is linked to the C3 atom (3′) of another nucleotide. This creates a long chain of linked nucleotides. This chain is also known as polynucleotide strand. The two ends of a polynucleotide strand are never identical. A phosphate residue is always only at one end of the chain. This results in the so-called polarity, the «direction» of the chain (here 5′ –> 3′).

The polynucleotide strand is the so-called primary structure the DNA.

Secondary structure of the DNA double helix

DNA consists of two polynucleotide strands running in opposite directions, which are connected to one another by bonds between the bases. One of the four bases already mentioned (adenine, guanine, cytosine, thymine) is bound to the C1 atom (1′) of the sugar of each nucleotide. So-called hydrogen bonds form between the bases of the nucleotides of two strands, which connect the base pairs and thus both strands of the DNA to one another.

This is where another term comes into play that you should know: complementary base pairing. Hydrogen bonds cannot form arbitrarily between the four bases, but only between the pairs Adenine – Thymine and Guanine – Cytosine. These bonding conditions inevitably result in the so-called anti-parallelism, the opposite polarity of the two chains of the DNA double strand (5′ → 3′ and 3′ → 5′).

Polynucleotide strands running in opposite directions, connected by hydrogen bonds between complementary bases, are called secondary structure the DNA.

Tertiary structure of the DNA double helix

In reality, the DNA structure looks a little different than in the diagram: The spatial structure of DNA is a spirally wound double strand, the so-called double helix. This term and the illustration of tertiary structure of DNA you have certainly come across them before.

As already mentioned, the structure of RNA (ribonucleic acid) is very similar to that of DNA. Instead of deoxyribose, the sugar in RNA is ribose. Instead of the base thymine, the RNA contains uracil, which also pairs with adenine. If you want to learn more about RNA, check out the article!

DNA structure – the most important thing

  • DNA means deoxyribonucleic acid
  • The DNA strand consists of strings of nucleotides
  • The nucleotide consists of three parts:
  • The bases are complementary to each other

  • The double helix is ​​made up of three levels: