Raster mutation: definition, example, consequences & types

Your genome, or more precisely your DNA, is transcribed many times a day and translated into proteins. Errors, the so-called mutations, occur during this process. On average, there is one mutation in 10,000 cells per day, but since you have almost 4 quadrillion cells, the mutation rate increases to 4 x 109 mutations per day. Many of these mutations are completely harmless and do not affect your life, but a few can cause significant damage.

One type of these gene mutations is the raster mutationin which a mutation in the DNA sequence results in a shift in the reading frame.

Raster mutation definition

One raster mutationalso known as a reading frame mutation or in English as frame shift mutation is a type of gene mutation that results in a frameshift by insertion (insertion) or Delete (deletion) comes from base pairs in DNA.

The consequence of inserting or deleting base pairs is that the raster of the gene and thus the resulting mRNA is not only distorted at one point, but the entire subsequent base sequence is shifted.

Raster mutation simply explained

Your DNA is made up of many individual nucleotides, which in turn consists of a base and a sugar phosphate residue. These bases pair with an opposite base. In order for the information on the DNA to be usable, it has to go to a mRNA be written off.

If you need a refresher on your basic knowledge of DNA and mRNA, then you are welcome to check out the relevant explanations on .

the mRNA (messengerRNA) is also described as messenger RNA and, like DNA, is a nucleic acid. As a form of transport, it contains the blueprint for protein biosynthesis.

This mRNA is then translation codon read for codon and translated into amino acids.

A codon are three consecutive nucleotides that are read together. All codons together form the reading frame.

the translation is a biological process in which proteins are synthesized through the activity of ribosomes.

The following illustration should help you to understand the principle and the process of the protein biosynthesis to understand better.

Figure 1: Principle of protein biosynthesis

Through different mutagens, i.e. substances that change the DNA, it can now happen that one or more bases are inserted or deleted. As a result, the reading frame is shifted and either other amino acids are translated during translation or translation stops because a stop codon arises. Not only mutagens can trigger mutations, but also errors that occur, for example, during replication and are not repaired.

Examples of such mutagens are ionizing radiation, UV rays or chemical substances.

The stop codon is the codon that gives the signal to stop translation.

Types of raster mutation

Grid mutations can point mutations be, that is, only a single base has been added or removed.

One point mutation is a gene mutation in which only one base in the DNA sequence is added, removed, or swapped.

However, multiple bases can also be inserted or removed. The addition of one or more bases is called insertionwhile removing deletion.

insertion

If one or two single nucleotides are inserted, this results in a so-called reading frameshift. This means that either incorrect amino acids are created during translation or a stop codon is created and translation comes to a standstill. This type of mutation will out of frame mutation called because the entire reading frame behind the mutation is shifted.

One in-frame mutation occurs when the number of inserted nucleotides is three or a multiple of three. Thus, the reading frame is not shifted, but rather the amino acids are lengthened by the number of codons inserted.

Figure 2: Example of a out of frame and one in frame mutation

deletion

As with the insertion, the number of lost bases plays a role here: If three or a multiple of three bases are removed, the rest of the grid remains intact. That’s also called in frame deletionwhile removing a different number of bases than out-of frame deletion referred to as.

Consequences and effects of a raster mutation

As with the point mutation, a distinction is also made between the raster mutation and the silent mutationthe missense mutation and the nonsense-Mutation. However, these types of mutations can only occur when only one or two nucleotides have been swapped.

Silent mutation

One silent mutationn is a gene mutation that does not result in a change in the amino acid sequence.

You speak of a silent mutation when the mutation occurs in a region that does not contain important amino acid coding information. Another possibility is that the mutation occurs at the third base of a triplet and due to the redundancy of the genetic code, the intended amino acid is encoded. This means that different codons code for the same amino acid.

A vivid example is the formation of the amino acid proline:

There are four different codons that code for the amino acid proline. The first two positions in the codon are fixed, only the last position is flexible. Thus, the codons CCG, CCA, CCC and CCU all code for proline. If the last base of the triplet is replaced by a mutation, there is a high probability that proline will be synthesized anyway.

If you need a refresher on your knowledge of the genetic code, then feel free to check out the «genetic code» explanation on .

missense mutation

At a missense mutation (English: false sense mutation), a different codon is created by a gene mutation, which encodes a wrong amino acid.

The consequence of a missense mutation is the incorporation of a completely different amino acid in a protein, as a result of which the function of the protein can also be disrupted. Often one can missense mutation be compensated for by the body so that no damage occurs.

Nonsense mutation

At a nonsense mutation (German: nonsense mutation) a premature stop codon is created by a point mutation.

This type of mutation creates a codon that does not code for the intended amino acid, but for a stop codon. The stop codon then causes protein synthesis to halt. The protein cannot be completed and is therefore not functional.

Figure 3: Example of a deletion leading to translation stop (nonsense mutation)

Examples of diseases caused by raster mutation

Duchenne muscular dystrophy is a rare and life-threatening genetic disorder. The lack of the protein dystrophin leads to muscle atrophy at an early age. Even in their early teens, those affected need a wheelchair to get around.

The disease is triggered by a mutation in the gene for the protein dystrophin, which is needed for muscle synthesis. It is often a deletion or a point mutation that results in a shift in the reading frame. This then leads to a premature stop in translation and the dystrophin cannot be synthesized.

Undo raster mutation

In general, all gene mutations are permanent and cannot be reversed. However, they can be counterbalanced by opposite mutations. For example, a previous insertion, in which a base was inserted into the DNA sequence, can be compensated for by a later deletion, i.e. removing a base.

Imagine you have the following DNA sequences:

Original:

ATG TCC AGC TAA CAT

1. mutation (insertion):

ATG TCA CAG CTA ACA T

2. mutation (deletion):

ATG TCA CAC TAA CAT

Here you can see that the mutation has balanced out again. A base was inserted first, causing the reading frame to shift. A deletion then took place so that the reading frame shifted back to the previous position.

Raster mutation – the most important thing

  • A framemutation is a gene mutation that results in a shift in the reading frame by the insertion or deletion of one or more bases.

  • There are different types of frame mutation, in which either bases are inserted or deleted.

    • During insertion, one or more nucleotides are inserted into the DNA.

      • This mutation can be out of frame if the entire reading frame has been shifted. This is the case when one or two bases are mutated.

      • In an in-frame mutation, 3 or a multiple of 3 bases are exchanged, after which the reading frame is extended by only one or more codons.

    • A deletion occurs when one or more bases are removed from the DNA sequence.

  • A frame mutation can be offset if the opposite mutation occurs after a previous mutation.

  • Effects of a frame mutation can be the silent mutation, the missense mutation, or the nonsense mutation.

  • An example of a disease caused by a frameshift is Duchenne muscular dystrophy.

proof

  1. David Sadava et al. (2019). Purve’s biology. jumper.
  2. Jochen Graw (2015). Genetics. jumper.