Without the genetic code, no living being could exist. It is indispensable for the production of proteins in the body. The genetic code specifies the scheme according to which the bases of the DNA (=DNA) are translated into amino acids in protein biosynthesis.
The genome of all organisms is encoded with the genetic code and the decoding leads to the production of the proteins.
The well-known abbreviation DNA comes from the English and stands for deoxyribonucleic acid and is often used as a synonym for the German abbreviation DNS, deoxyribonucleic acid. It represents the heritage.
Definition and structure of the genetic code
Of the genetic code consists of specific, consecutive bases (nucleotides) in the DNA. There are the bases thymine (T), arginine (A), guanine (G) and cytosine (C).
The complementary base of guanine is cytosine. The complementary base of arginine is thymine. Thymine is only found in DNA. The mRNA does not contain thymine, but a similar base, the uracil (U).
The mRNA is a transcript of the DNA. It is formed during transcription by an RNA polymerase reading the codogenic DNA strand and forming a complementary mRNA. Unlike DNA, mRNA is one single stranded nucleic acid and can be transported from the cell nucleus to the ribosomes. There it is translated codon by codon into an amino acid sequence. This process is called translation.
You can find an overview of the process of protein biosynthesis here:
Figure 1: Simplified representation of the pathway of protein biosynthesis
In the following you will get to know the structure and the different types of codons on the mRNA.
The structure of the codon
How is a codon structured and what kind of codons are there?
A codon consists three nucleotidesso-called triplets. These are usually, but not always, translated into amino acids. This triplet code is also called Triplet raster code designated.
codons for amino acids
An amino acid is replaced by a base sequence determined with three bases. This triplet of bases is called a codon. There are 64 possible combinations of base triplets, but only 20 different amino acids. These are covered by 61 codons. Thus, most amino acids can be generated by different codons.
start and stop codons
A codon that normally encodes an amino acid also doubles as a start codon. This is the triplet AUG, which is also responsible for coding the amino acid methionine. The start codon is needed to start reading the mRNA.
The other three base triplets are called stop codons denoted – they represent the point at which the translation is terminated. After that the finished amino acid chain released at the ribosomes.
You can think of DNA like a book. The bases are letters, the codons are words, and the gene sequences are sentences. Together they form an entire novel.
The function of the genetic code
The genetic code contributes to the fact that amino acid production and thus also protein production can take place in the body. This process is also called protein biosynthesis. The order of the amino acids in genes is stored in the DNA.
The DNA is well protected in the cell nucleus of every cell in the body. From there, the genome can be read and translated into proteins with the help of the genetic code.
The proteins are involved in important processes, e.g. B. involved in the development of body parts such as hair, muscle fibers, blood cells or tendons. They also catalyze many biochemical reactions. That is, they accelerate reactions without being consumed themselves by lowering the activation energy of a reaction.
The genetic code specifies the scheme according to which the base sequence of the DNA is translated into amino acids. Through him, both the phenotype of living things, as well as the cellular metabolism controlled by proteins.
Of the phenotype of a living being is defined as its outer appearance. Of the genotype is the Entirety of all heredities. The phenotype is therefore only limited to the genetic information, the expression of which is visible to the outside, while the genotype encompasses all hereditary dispositions.
Deciphering the genetic code
The genetic code is the decoding of the hereditary information, i.e. the DNA. In the first phase of protein biosynthesis, the transcription, a copy is first made of part of the DNA. This copy is called Messenger RNA (mRNA). With their help then the DNA during the Translation, read codon by codon on the ribosomes and through the genetic code decrypted.
In order to translate the codons on the ribosomes, complementary triplets attach to the DNA. These deposit their specific amino acid. The sequence of amino acids becomes one amino acid chain formed, which is also known as the primary structure of proteins.
The specific amino acid sequence forms the required protein in the complex. The process from DNA to protein formation is called protein biosynthesis designated. This is shown in Figure 1.
The code sun
The code sun helps you to read off the corresponding amino acid for a codon. The template you apply the code sun to is the mRNA. One transcription the DNA so it happened before.
Figure 2: The code sun. Source: wikipedia.org
The code sun is from inside to outside had read. You start with the first base (i.e. from the 5′ end to the 3′ end) of your codon and work your way outwards. This will help you find out which amino acid is behind a base triplet.
That 3′ end is the end of the mRNA that bears a carboxyl group. This consists of a carbon atom which forms a double bond with an oxygen molecule and connected to the rest of the mRNA strand. In addition, an OH group is attached to the carbon atom.
The 5′ end has an amino group at its end. This consists of a nitrogen atom to which two hydrogens are attached.
Properties of the genetic code
The genetic code is decoded and read. Special properties are required to enable these processes.
1. The genetic code is universal
The genetic code is the same almost everywhere: Codons from bacteria to humans code for the same amino acids. There are only a few exceptions where this is not the case, e.g. B. in mitochondria. Therefore, the genetic code is called universal.
This property is particularly useful for genetic engineering. There, for example, a section of human DNA that codes for an enzyme can be smuggled into a bacterium. This DNA excerpt is read in the bacterium. As a result, human enzymes are also produced in the bacterium.
2. The genetic code is redundant/degenerate
In general you can always remember: A base triplet always stands for only one amino acid, but an amino acid does not only stand for a base triplet.
This is because there are 64 different combinations of codons, but only 20 amino acids. It is inevitable that different codons form the same amino acid. Therefore, the genetic code is called redundant or degenerate.
This means that, for example, the amino acid valine (Val) can be formed both from the triplet GUG and from the triplet GUU. These are multiple base sequences that nonetheless all have valine as the translated amino acid.
3. The genetic code is unique
A triplet of bases always codes for the same amino acid. It is therefore clear that a certain base sequence of three bases always results in the same amino acid.
4. The genetic code is comma and overlap free
A triplet always stands by itself. The triplets are read codon by codon without overlapping. Only after a codon has been read does the next one come. There is therefore no overlapping and no codon is left out even in the middle of the reading process.
The fault tolerance of the genetic code
The fact that several codons encode the same amino acid is very advantageous. It can happen that mutations have no effect (also called silent mutation).
General is one mutation a change in the genetic material, i.e. the DNA. A mutation can lead to a disease or impairment, but it does not have to. There are also numerous mutations in DNA that go completely unnoticed. It usually depends on how severe the change in the DNA is.
But this is not the only decisive factor. For example, a mutation at a base that becomes a stop codon causes translation to stop. As a result, no functional protein can develop. Such a mutation is called nonsense mutation.
Inconspicuous mutations that result in the same amino acid despite the change are called dumb mutations. Because of them, the genetic code has a relatively high error tolerance. This means that such a mutation does not immediately change the protein or render it non-functional.
A codon that stands for the amino acid isoleucine is AUU. The DNA is mutated and the third base uracil is replaced by arginine. This change in DNA makes no difference, since the combination AUA also encodes isoleucine. This is a silent mutation.
Often only two bases of a triplet need to remain unchanged for the correct amino acid to result.
You can also see this from the code sun, where sometimes all four last bases code for the same amino acid (see valine).
Because even if the changed base does not lead to the same amino acid, an amino acid with similar properties usually results. This can be deduced from the fact that bases at certain positions cause specific properties of the amino acid.
The triplets with the base uracil in the middle (U) are mostly hydrophobic. Triplets with the base adenine in the middle (A) are hydrophilic. From this it can be concluded that the change in the first base is usually the most serious. The first base indicates the type of charge on the amino acid. If the charge is reversed, this has more serious consequences for the function of the protein.
The Genetic Code – The most important
- The genetic code consists of specific, consecutive bases in DNA.
- It is read during protein biosynthesis and provides the building instructions for proteins from amino acids.
- A codon is a combination of three bases. It encodes exactly one amino acid.
- The code sun can be used to decipher the genetic code.
- The genetic code is universal, redundant or degenerate, unique and non-overlapping.
- The error tolerance of the genetic code is high.