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Are STOP codons impacted by base insertion or deletion mutation?

Are STOP codons impacted by base insertion or deletion mutation?


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I am learning about base insertion and deletion mutations. An example in my textbook is given below.

GUU CCA CAU AUC.

So if there is an insertion (of guanine):

GUU GCC ACA UAU C_ _ (there will be a detrimental effect on the protein created).

I'm a bit confused about how the stop codon will be read. If we have a new example with a stop codon:

GUU CCA CAU AUC UAG

When the mutation occurs (insertion of guanine) will it become:

1) GUU GCC ACA UAU CUA G

OR

2) GUU GCC ACA UAU C_ _ UAG

If mutation 1) occurs, there would be no stop codon, but mutation 2) looks strange to me. So which is the right one?

Thanks


Yes. Mutations can affect STOP codons and they do relatively commonly. These are important because they can lead to significant changes in the resulting peptide and are likely to affect protein functions or phenotype.

For a point mutation (a single base substitution), there are several possible effects:

  • silent mutation is a synonymous base substitution which does not change the encoded amino acids (this is neutral variation).

  • missense mutation is a non-synonymous bass substitution which changes only one amino acid in the protein (these can affect protein functions but do not always).

  • nonsense mutation is a change in a coding codon to a STOP codon (this truncates the encoded amino acid sequence prematurely resulting in a shorter peptide).

  • nonstop mutation is a change from a STOP codon to a coding codon (this means the amino acid sequence will continue to the next STOP codon resulting in a longer peptide).

Insertions and Deletions in DNA sequence (InDels) are important because they change all codons that follow it (not just the base substituted):

  • frameshift mutation adds or removes a base which resulting in a change in the reading frame: all bases following will result in new codons, including STOP codons (this commonly results in entirely new protein domains and proteins of different lengths as STOP codons will also be changed. They are encoded in the reading frame like all other codons.

As you can see, mutations which affect STOP codons are very important as they drastically change the protein sequence. This usually disrupts the protein function and causes diseases or inviable embryos. Most of these are removed from populations long-term by natural selection. However, it can rarely lead to entirely new proteins beneficial to the organism and evolutionary changes. This is more likely with duplicated genes where one can change while the other retains the original function.

As such, mutations involving STOP codons are among the most biologically important. Another important case is splice functions. Point mutations and frameshifts can also affect intron-exon boundaries, resulting in new splice variants, skipped exons, and reading further into introns (which may contain splice junctions or STOP codons).


Let's start with your example:

Wild-type gene looks like:

GUU CCA CAU AUC UAG*

After G insertion, you end up with

GUU GCC ACA UAU CUA G

There are 3 stop codons: UAG*, UAA*, UGA*

You don't see those in your mutated gene, because you truncated sequence. Let's imagine that gene actually goes like this:

WT: GUU CCA CAU AUC UAG* GCG UCU AAA ACG CUA

Mut: GUU GCC ACA UAU CUA GGC GUC UAA* AAC GCU A…

In mutant you got now new stop codon created

Gene, transcribed into mRNA doesn't stop at stop codon, there is whole bunch of sequence after it too (3'-UTR and poly-A tail for Eukaryotas)


Difference Between Substitution Insertion and Deletion Mutations

The key difference between substitution insertion and deletion mutations is their cause. Substitution mutations occur due to a substitution of a base pair from a different base pair, while insertion mutations occur due to the addition of extra nucleotides into a DNA sequence and deletion mutations occur due to the removing of one or more nucleotides from a DNA sequence.

A mutation is an alteration of the nucleotide sequence of DNA. A gene has a specific nucleotide sequence. Gene mutations can alter the genetic information hidden within its nucleotide sequence. The size of the mutation may vary from a single base change to a large fragment of a chromosome that contains multiple genes. Mutations occur due to various reasons. Some of the major reasons are mistakes occurring during the DNA copying in cell division, exposure to ionizing radiation, exposure to chemicals called mutagens and viral infections. Mutations are necessary for evolutions. Most mutations are harmless. Some mutations are heritable, affecting further descendants, while some mutations affect only the individual that carries them.

CONTENTS


CLASSIFICATION OF MUTATION BY THEIR EFFECTS ON THE DNA MOLECULE

Based on their effects on the structural integrity of the DNA molecule, mutations can be classified as substitution, insertion, deletion, inversion, reciprocal translocation and chromosomal rearrangements. This classification of mutation is based on the effect of mutation on the genetic material (DNA) of the cell.

SUBSTITUTION (BASE-PAIR SUBSTITUTION)

Substitution literally means the act of replacing one thing with another. When base substitution as a type of mutation occurs during DNA replication, a single base at one point in the DNA replication process is replaced by one of the other three bases. This type of mutation can also be called point mutation. There are various types of base substitution including silent mutation, missense mutation, and frameshift mutation. Base substitution during DNA replication causes silent, missense, nonsense mutation and frameshift mutational effects (Figure 1). It is also noteworthy that the consequences of base-pair substitution mutations in protein coding regions of a DNA or gene depend on the type of substitution and the location where it occurred.

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Figure 1. Illustration of base-pair substitutions. Base-pair substitutions are example of point mutations. Ala=Alanine, Gly=Glycine, Pro=Proline, Asp=Aspartic acid, Arg=Arginine Photo courtesy: https://www.microbiologyclass.com

Silent mutation is a type of mutation that does not affect the phenotype of the cell undergoing it. It usually occurs outside of the gene. Though they occur outside of a gene and may not produce a mutant phenotype, silent mutations can also be observed within the gene of a cell. Silent mutation also occurs within the coding region (exon) of a gene as aforementioned. For example, arginine (ARG) is an amino acid with two different codons viz: AGA and AGG and thus a substitution in an AGA codon to AGG would have no effect on the amino acid (arginine) since both codons (AGA and AGG) code for the same amino acid (which is arginine).

Exons are the portions of a gene’s DNA or RNA that codes for a particular protein sequence. They are generally the coding region a gene. Introns are portions of a gene’s DNA or RNA that does not code for protein sequence. They are non-coding sequence of a gene. They are removed by RNA splicing during protein synthesis. Introns are usually transcribed into precursor mRNA (pre-mRNA), and they are usually removed by editing (RNA splicing) of the pre-mRNA transcript into a mature mRNA molecule that is translated for the synthesis of a particular protein molecule.

In general, a base-pair substitution can occur either inside the gene or outside the gene. And a base substitution that occurs within the protein-coding region of a gene will often result in the miscoding of an amino acid residue and this will result in the synthesis of a mutant protein molecule. Such mutant protein molecules may have a partial loss of its normal biological function and/or an occasional increase in its biological activity. If a point mutation such as base-pair substitution occurs within the coding region of a gene that encodes a particular polypeptide, any change can result in a change in the amino acid sequence of the polypeptide molecule. Such mutational changes have little or no effect on the phenotype of the cell since not all mutations in the base sequence encoding a polypeptide will change the polypeptide.

Silent mutation does not change an amino acid. But in some scenarios, silent mutations can still produce a phenotypic effect on the protein synthesis process either by speeding up or slowing down protein synthesis or by effecting gene splicing. Gene splicing is defined as the molecular biology technique that is used to cut out part of the DNA in a gene and adding new DNA in its place. It is used in genetic engineering to edit a part of a gene (DNA) by cutting it, and in some cases replacing the existing genes with genes taken from another plant, microbe or animal. Gene splicing is done using chemical scissors known as restriction enzymes (endonucleases) which are known to cut (nick) gene sequences at specific sites. The function f the sliced gene changes once a new gene is in place. Gene splicing technique can be applied in gene therapy techniques to replace an abnormal gene with a functional (normal) gene in order to remedy and restore the biological activity of a defective gene.

Missense mutation is a mutation in which a base substitution could result in an amino acid substitution. Unlike in silent mutations in which there is no novel amino acid in the protein sequence as a result of the genetic modification, the production of a new amino acid molecule usually accompanies missense mutations. Missense mutations have tremendous biological consequences. It is a single base change that results in the change of an amino acid within a given polypeptide molecule. For example, the codon CTC in the DNA sense strand (and GAG in mRNA) specifies a glutamate residue in the protein molecule. But when this codon (i.e. CTC or GAG) is altered in the DNA sense strand and mRNA strand to CAC and GUG respectively, a different amino acid molecule (in this case valine) is produced. In missense mutations, there is usually the addition or insertion of the wrong amino acid molecule.

Sickle cell anaemia is a typical example of a genetic disease or disorder due to missense mutation. Sickle cell anaemia is a blood borne genetic/hereditary disease in which the sufferers have a dysfunctional type of red blood cells that resembles a sickle. Missense mutation changes an amino acid to a different amino acid molecule. Depending on the biological function of the affected amino acid molecule, missense mutation may affect the protein function which those affected amino molecules encodes. Nonsense mutation is a type of mutation in which a prematurely type of shortened protein molecule is formed. In nonsense mutation, the protein formed is usually truncated and an incomplete protein molecule is formed. Nonsense mutations generally result in the production of a STOP CODON. This type of mutation changes an amino acid to a STOP CODON so that the protein synthesis process will automatically stop. Nonsense mutation as shown in Figure 3.1 result in the premature termination of translation (which is a vital process involved in protein synthesis).

Stop codons (termination codons) are nucleotide triplets found within mRNA, and which signal the termination of translation into protein molecules. Examples of STOP CODONS are UAG, UAA and UGA (for RNA) and TAG, TAA and TGA (for DNA). Mutations in which STOP CODONS are formed are generally known as nonsense mutations. Nonsense mutation creates a STOP CODON in the middle of a gene, and this leads to the formation of an incomplete protein molecule. Frameshift mutation is a type of mutation that occurs within the protein coding region of a gene. Such mutagenesis or mutations usually arise from the addition or deletion of one or few bases that are not multiples of three. Frameshift mutations include deletions, insertion and gene duplication that usually occur during DNA replication.

Codons are normally in the groups of three nucleotides. This implies that codons are made of three nucleotide bases. When this pattern is not followed, there will be an alteration in the reading frame of the gene. This type of mutation that occurs in the translational reading frame of a gene is known as a frameshift mutation. There are only three possible reading frames for each gene since codons are groups of three nucleotides. A codon is a group of three successive nucleotides found in the mRNA. They base-pair with the anticodon of an individual tRNA that carries a specific amino acid molecule. A deletion or insertion (i.e. frameshift mutation) of a number of bases that is not a multiple of three usually introduces premature STOP codons that inhibit the protein synthesis process in addition to other genetic alterations associated with frameshift mutations.

Reading frames other than the correct translational reading frames often contain STOP codons which will truncate the mutant protein prematurely. Frameshift mutations completely render mutant protein molecules nonfunctional. The removal of a base (as underlined in Figure 2) results in a change in the coding of the adjacent bases sequences, and this produces a highly altered (mutant) protein molecule (Figure 2). Frameshift mutations almost always cause long stretches of altered amino acids resulting in the production of inactive protein molecules. This type of mutation is generally known to delete or insert one or a few nucleotide bases in the translational reading frame of an mRNA molecule.

Figure 2. Illustration of frameshift mutation. Thr=Threonine, Ser=Serine, Arg=Arginine, Pro=Proline, Val=Valine. Photo courtesy: https://www.microbiologyclass.com

A reading frame refers to one of three possible ways of reading a nucleotide sequence. It is a way of dividing the sequence of nucleotides in a nucleic acid molecule (DNA or RNA) into a set of consecutive, non-overlapping triplets general known as codons. There are three reading frames that can be read in the 5’→3′ direction of DNA synthesis and each of these begins from a different nucleotide in a triplet known as a codon. The reading frame affects protein molecule made during translation.

If for example we have a 15 DNA base pairs as illustrated below:

ACTTAGCCGGGACTA

  1. We can start reading or translating the DNA from the first letter, ‘A,’. This first alphabet would be referred to as the first reading frame of the translation process.
  2. We can also start to translate the DNA from the second letter, ‘C,’ and this would be referred to as the second reading frame.
  3. And we can also start reading or translating from the third letter, ‘T,’ and this would be referred to as the third reading frame.

In all, there are actually six reading frames. Three of the reading frames are on the positive strand of the DNA while three of the reading frame (which is read in the reverse direction) is found on the negative strand. It is noteworthy that the first three reading frames as aforementioned are read in the forward direction and not in the reverse direction.

Insertion is a type of mutation that occurs when there is a gain of nucleotide base pairs. It occurs when there is an addition of one or more nucleotide bases into a DNA sequence. When insertions occur in the amino acid coding region of a gene (i.e. the exon), it can cause genetic alterations that will hazardously affect the resulting phenotype. Insertions and the subsequent frameshift mutation that occur in the reading frame will cause the active translation of the gene to encounter a premature STOP codon. This will result in an end to translation and the production of a truncated protein molecule.

Deletion is a type of mutation that results in the loss of nucleotide base pairs. Deletion mutation is a type of mutagenesis in which a part of a chromosome or a sequence of DNA is lost during DNA replication. Deletions that do not occur in multiples of three bases can cause a frameshift mutation by changing the 3-nucleotide protein reading frame of the genetic sequence. Deletion of a number of pairs that is not evenly divisible by three will lead to a frameshift mutation, causing all of the codons occurring after the deletion to be read incorrectly during translation, producing a severely altered and potentially nonfunctional protein molecule. Small deletions are usually less likely to be fatal but large deletions are usually fatal, and may cause several genetic disorders in the host. Deletion mutation removes the segment of a DNA molecule and this development can result in the loss of substantial segments of the chromosome.

Inversion mutation is a type of mutation or gene rearrangement that occur when the normal order of a gene sequence is flipped in such a way that the chromosomal segment are placed in the opposite orientation with respect to other chromosomes. Inversions are chromosome rearrangements in which a segment of a DNA molecule is reversed end to end. For example, a given chromosome segment depicted as: “abcdefgh” can be inverted or rearranged to be: “ab-edc-fg-h”. Inversions usually do not cause any abnormalities in carriers as long as the rearrangement is balanced with no extra or missing DNA.

Chromosomal rearrangements involve gene deletions, inversions, duplications and translocations. And they usually arise from breakages that occur in the DNA. When there is a break in the DNA structure, a rejoining of the broken DNA can result in the production of a novel chromosomal arrangement of genes that are quite different from the normal order of the gene before the breakage occurred.

Studying mutations in living organisms inclusive of microorganisms is important because changes that affect the entire chromosome or some segments of the chromosomes can cause significant problems associated with the organism’s growth, development and other body functions. Our understanding of mutations in living systems and how cells can be genetically manipulated and/or mutated or transformed will help us to understand more complex biological processes that occur in living cells such as carcinogenesis.

Mutations can also be classified based on their effect on the encoded protein since mutations outside the coding sequence of the gene can also impact on the outcome of gene expression. The DNA or gene encodes the genetic information for the production of a particular protein molecule in the cell of a living organism. Any alteration in the nucleotide base sequence(s) of the gene will ultimately affect the outcome of the protein to be synthesized by the cell. There could be complete loss of function or gain of function when the mutation impact on the protein functions.

Further reading

Cooper G.M and Hausman R.E (2004). The cell: A Molecular Approach. Third edition. ASM Press.

Das H.K (2010). Textbook of Biotechnology. Fourth edition. Wiley edition. Wiley India Pvt, Ltd, New Delhi, India.

Davis J.M (2002). Basic Cell Culture, A Practical Approach. Oxford University Press, Oxford, UK.

Mather J and Barnes D (1998). Animal cell culture methods, Methods in cell biology. 2 rd eds, Academic press, San Diego.

Noguchi P (2003). Risks and benefits of gene therapy. N Engl J Med, 348:193-194.

Sambrook, J., Russell, D.W. (2001). Molecular Cloning: a Laboratory Manual, 3rd edn. Cold Spring Harbor Laboratory Press, New York.

Tamarin Robert H (2002). Principles of Genetics. Seventh edition. Tata McGraw-Hill Publishing Co Ltd, Delhi.


What type of mutation is caused by an insertion or deletion of a base and results in a change of the entire sequence after the point of insertion or deletion?

Three base pairs (codon) in RNA code for one specific amino acid. There is also a specific start codon (AUG) and three specific stop codons (UAA, UAG and UGA) so the cells knows where a gene/protein starts and where it ends.

With this information you can imagine that deleting a base pair changes the entire code / reading frame, this is called a frameshift mutation . This can have several effects:

The wildtype is the RNA/ protein as it should be. When you delete one base pair, the reading frame shifts and suddenly it codes for completely different amino acids, this is called a missense mutation. It is also possible that the deletion causes a nonsense mutation, this happens when the mutated RNA codes for a stop codon.


When considering the damage or advantages caused by point mutations, it is essential to evaluate the different types of point mutations that can occur. Whether you’re considering genetic experiments, or looking to understand how mutations occur naturally or as a result of environmental changes, looking at possible types of mutations can help a great deal. It will not only help evaluate the way certain organisms respond to external stimulation, but also shed some light on what the most damaging mutations are.

How Do Point Mutation Types Work?

When DNA is transcribed by messenger RNA, it’s on its way to generating proteins, the building blocks of life. As the DNA is “read” by the RNA three bases at a time, it also matches its complementary bases to it to create what is known as codons. Each codon codes for a different amino acid, and chains of these amino acids generate proteins. Now, should the DNA be affected by different types of point mutations, the information read by the RNA is no longer the same. As a result, understanding the specific type of mutation that happens is extremely essential, if we want to know exactly how the protein was affected and what the repercussions might be.

Substitution Mutations

One of the main types of point mutations that are possible are substitution mutations. These can involve one of three varieties of mutations that have to do with one base pair being substituted with another. An example would be when a nucleotide that contains cytosine is substituted by accident with one containing guanine. The most common type of substitution mutation is the missense mutation, in which the substitution leads to a different codon being formed than the original. If the amino acid formed has similar properties to the original, then we’re talking about a conservative mutation. Otherwise, the mutation is non-conservative, and can lead to severe destabilization in the chain of codons. Silent and nonsense mutations can also occur, but these are more specific and, therefore, less common types of substitution mutations. They lead to either a stop codon (nonsense mutation) or a near identical codon to the original being formed.

Insertion vs. Deletion Mutations

If an extra base pair is added to a sequence of base pairs, then the mutation that occurs is an insertion mutation. Deletion mutations, on the other hand, are opposite types of point mutations. They involve the removal of a base pair. Both of these mutations lead to the creation of the most dangerous type of point mutations of them all: the frameshift mutation.

Why It’s Important to Understand Types of Mutations

Knowing which types of mutations have occurred in an organism can account for the various disorders or adaptations that have happened since the change. In some cases, these changes are benign or beneficial, however, they can also be negative or only temporarily neutral. Figuring out which types of point mutations you are dealing with can determine the next course of action to help fend off certain genetic unbalances, repair the protein encoding and even prevent the onset of a certain disease before it even happens.

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Are STOP codons impacted by base insertion or deletion mutation? - Biology

Medicine is transforming rapidly. During this era of human history, scientists are forever changing lives, because for the first time humans are not powerless against their genes! We now have the power to not only predict, but also alter our very future. The Genetic Revolution is here!

With the power of gene therapy, scientists now have a new tool that enables them to change a patient's DNA. Medical treatments usually counteract the symptoms of a disease. But with gene therapy, doctors can cure diseases. Click to learn more

The concepts described in this website might be a review for some people, or it might be a new learning experience. Click in order to learn or review the basics of biology and genetics.

Medicine is transforming rapidly. During this era of human history, scientists are forever changing lives, because for the first time humans are not powerless against their genes! We now have the power to not only predict, but also alter our very future. The Genetic Revolution is here!

Although mutations sound negative, they are a fundamental part of natural evolution. Mutations allowed humans to evolve, and is also a large factor in making each human different.

Mutations create genetic diversity, but they can also be problematic. Some mutations are small, therefore making them not as life threatening, but others can cause great harm.

A mutation is technically defined as any changes or alterations in the sequence of nucleotides in DNA.

One of the most common type of genetic mutations, point mutation, otherwise known as a base-pair substitution, alters a single nucleotide base pair.

There are three types of point mutations:

Silent Mutations: In a silent mutation, there is a change in the DNA sequence, but the mutation does not affects the produced proteins. There are multiple genetic codons (group of three) that codes for the same amino acid. If one of the three nucleotide is changed, depending on the location of the nucleotide, the same amino acid could still be produced.

Missense Mutation: In this mutation, the altered nucleotide sequence will create a different amino acid. Sometimes the change is little, and have no great effect on the individual, other times it could be very dangerous.

Nonsense Mutation: In a nucleotide sequence, there are always codons that signal the end of the translation process, which will stop the protein production. These codons are called "stop codons". In a nonsense mutation, the alteration of the nucleotide sequence will create a stop codon, instead of an amino acid. When this happen, the amino acid sequence is shortened considerably, resulting in a most likely nonfunctioning protein.


METHODS

Ranking genes in cancer of each tissue and ranking cancer tissues for each gene

Histograms showing the frequency of occurrence of each of the 12 possible base changes at pos1, pos2 and pos3 of codons in: ( a ) synonymous ( b ) missense and ( c ) nonsense substitutions. In each histogram, base changes are indicated along the x -axis, the number of times that each base change is observed (frequency) is indicated along the y -axis and the frequencies of base changes at pos1, pos2 and pos3 of codons are shown as separate series.

Histograms showing the frequency of occurrence of each of the 12 possible base changes at pos1, pos2 and pos3 of codons in: ( a ) synonymous ( b ) missense and ( c ) nonsense substitutions. In each histogram, base changes are indicated along the x -axis, the number of times that each base change is observed (frequency) is indicated along the y -axis and the frequencies of base changes at pos1, pos2 and pos3 of codons are shown as separate series.

Analyses of substitution, deletion and insertion mutations

A single mutation may be observed many times. The 1633G > A, E545K substitution in the PIK3CA gene, in breast tissue, for example, occurs 165 times. This is because a large number of breast PIK3CA samples have been studied and the mutation occurs frequently in them. Unless otherwise specified, a mutation occurring multiple times in a tissue has been considered only once (i.e. only unique mutations in a tissue have been considered), in order to avoid biases due to differing sample sizes. The same mutation occurring in multiple tissues, however, has been considered once in each tissue.

Substitution mutations

Single-base substitutions were sorted into synonymous, missense and nonsense ones, and each set was analysed separately [ Supplementary Methods (i)a ]. Multiple-base substitutions were also analysed. WT and mutant codons from all single-base substitutions, and from multiple-base ones in which 2 or 3 bases in a single codon were substituted, were used to generate a 64 × 64 WT codon—mutant codon pair frequency matrix ( Supplementary Table S2 ).

Deletion and insertion mutations

Deletions and insertions were separated into I-F and FS ones, and each set was analysed separately [ Supplementary Methods (i)b ]. Results are given in Supplementary Tables S3 and Supplementary Data , respectively.


Are STOP codons impacted by base insertion or deletion mutation? - Biology

Given the different numbers of “letters” in the mRNA and protein “alphabets,” scientists theorized that combinations of nucleotides corresponded to single amino acids. Nucleotide doublets would not be sufficient to specify every amino acid because there are only 16 possible two-nucleotide combinations (42). In contrast, there are 64 possible nucleotide triplets (43), which is far more than the number of amino acids. Scientists theorized that amino acids were encoded by nucleotide triplets and that the genetic code was degenerate. In other words, a given amino acid could be encoded by more than one nucleotide triplet. This was later confirmed experimentally Francis Crick and Sydney Brenner used the chemical mutagen proflavin to insert one, two, or three nucleotides into the gene of a virus. When one or two nucleotides were inserted, protein synthesis was completely abolished. When three nucleotides were inserted, the protein was synthesized and functional. This demonstrated that three nucleotides specify each amino acid. These nucleotide triplets are called codons. The insertion of one or two nucleotides completely changed the triplet reading frame, thereby altering the message for every subsequent amino acid (Figure 1). Though insertion of three nucleotides caused an extra amino acid to be inserted during translation, the integrity of the rest of the protein was maintained.

Figure 1. The deletion of two nucleotides shifts the reading frame of an mRNA and changes the entire protein message, creating a nonfunctional protein or terminating protein synthesis altogether.

Scientists painstakingly solved the genetic code by translating synthetic mRNAs in vitro and sequencing the proteins they specified (Figure 2).

Figure 2. This figure shows the genetic code for translating each nucleotide triplet in mRNA into an amino acid or a termination signal in a nascent protein. (credit: modification of work by NIH)

In addition to instructing the addition of a specific amino acid to a polypeptide chain, three of the 64 codons terminate protein synthesis and release the polypeptide from the translation machinery. These triplets are called nonsense codons, or stop codons. Another codon, AUG, also has a special function. In addition to specifying the amino acid methionine, it also serves as the start codon to initiate translation. The reading frame for translation is set by the AUG start codon near the 5′ end of the mRNA.

The genetic code is universal. With a few exceptions, virtually all species use the same genetic code for protein synthesis. Conservation of codons means that a purified mRNA encoding the globin protein in horses could be transferred to a tulip cell, and the tulip would synthesize horse globin. That there is only one genetic code is powerful evidence that all of life on Earth shares a common origin, especially considering that there are about 1084 possible combinations of 20 amino acids and 64 triplet codons.

Transcribe a gene and translate it to protein using complementary pairing and the genetic code at this site.

Degeneracy is believed to be a cellular mechanism to reduce the negative impact of random mutations. Codons that specify the same amino acid typically only differ by one nucleotide. In addition, amino acids with chemically similar side chains are encoded by similar codons. This nuance of the genetic code ensures that a single-nucleotide substitution mutation might either specify the same amino acid but have no effect or specify a similar amino acid, preventing the protein from being rendered completely nonfunctional.


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It is normally formed using the “codons” found in the mRNA, since the mRNA is the messenger that transports information from the DNA to the site of protein synthesis.

Everything in our cells is finally built based on the genetic code . Our hereditary information, that is, the information transmitted from parents to children, is stored in the form of DNA.

That DNA is used to build RNA, proteins and finally cells, tissues and organs.

Like the binary code, DNA uses a chemical language with only a few letters to store information in a very efficient way. While the binary uses only ones and zeros, the DNA has four letters that are the four nucleotides:

Thymine and uracil are very similar to each other, except that “thymine” is a little more stable and is used in DNA. Uracil is used in RNA and has all the same properties as thymine, except that it is a little more prone to mutate.

This does not matter in RNA, since new copies of RNA can be produced from DNA at any time, and most RNA molecules are intentionally destroyed by the cell shortly after production so that the cell does not waste resources producing unnecessary proteins from old RNA molecules.

Together, these four letters of A, C, G and T / U are used to “spell out” coded instructions for each amino acid, as well as other instructions such as “start transcription” and “stop transcription”.

The instructions to “start”, “stop” or for a given amino acid are “read” by the cell in blocks of three letters called “codons”.

When we speak of “codons”, we usually refer to codons in mRNA: the “messenger RNA” that is made by copying the information in the DNA.

For that reason, we talk about codons made of RNA, which uses uracil, instead of the original DNA code that uses thymine.

Each amino acid is represented in our genetic instructions by one or more codons .

One of the most remarkable evidences of the common ancestor of all life on earth of a single ancestor is the fact that all organisms use the same genetic code to translate DNA into amino acids.

There are some small exceptions that are found, but the genetic code is sufficiently similar in all organisms that when a gene from a plant or jellyfish is injected into a mammalian cell, for example, the mammalian cell will read the same gene way and build the same product as the original plant or jellyfish!

Function of the genetic code

The genetic code allows cells to contain a huge amount of information.

Consider this: a microscopically fertilized egg, following the instructions contained in its genetic code, can produce a human being that even has a personality and behaviors similar to those of their parents. There’s a lot of information there!

The development of the genetic code was vital because it allowed living beings to reliably produce the products necessary for their survival, and passed instructions on how to do the same to the next generation.

When a cell tries to reproduce, one of the first things it does is make a copy of its DNA. This is the “S” phase of the cell cycle, which means “Synthesis” of a new copy of the cell’s DNA.

The information encoded in the DNA is conserved by specific pairing of the DNA bases with each other. Adenine will only join with Timina, Citosina, Guanina, etc.

That means that when a cell wants to copy its DNA, all it has to do is separate the two strands of the double helix and align the nucleotides with which the existing DNA bases “want” to pair.

This specific base pairing ensures that the new partner’s strand will contain the same sequence of base pairs, the same “code”, as the previous one. Each resulting double helix contains an old DNA strand paired with a new strand of DNA.

These new double helices will be inherited by two daughter cells. When the time comes for these daughter cells to reproduce, each strand of these new double helixes acts as templates for a new double helix.

When the time comes when a cell “reads” the instructions contained in its DNA, it uses the same principle of peer-specific linking. RNA is very similar to DNA, and each RNA base binds specifically to a DNA base. Uracil binds to adenine, cytosine to guanine, etc.

This means that, like DNA replication, the information in the DNA is transferred precisely to the RNA provided that the resulting RNA chain is composed of the bases that bind specifically to the bases in the DNA.

Sometimes, the RNA chain itself can be the final product. The structures made of RNA play important functions in ourselves, such as the assembly of proteins, the regulation of gene expression and the catalysis of protein formation.

In fact, some scientists think that the first life on earth could have been composed mostly of RNA.

This is because RNA can store information in its base pairs like DNA, but it can also perform some enzymatic and regulatory functions.

In most cases, however, the RNA becomes transcribed into a protein. Using the amino acid “building blocks of life”, our cells can build almost protein machines for almost any purpose, from muscle fibers to neurotransmitters and digestive enzymes.

In protein transcription, the codons of RNA that were transcribed from the DNA are “read” by a ribosome.

The ribosome finds the appropriate transfer RNA (tRNA) with “anti-codons” that are complementary to the codons in the messenger RNA (mRNA) that has been transcribed from the DNA.

Ribosomes catalyze the formation of peptide bonds between amino acids as they “read” each codon in the mRNA. At the end of the process, it has a chain of amino acids specified by the DNA, that is, a protein

Other building blocks of life, such as sugars and lipids, in turn are created by proteins. In this way, the information contained in the DNA is transformed into all the materials of life, using the genetic code!

Types of genetic mutations

Because the genetic code contains information for life, errors in the DNA of an organism can have catastrophic consequences.

Errors can occur during DNA replication if the wrong base pair is added to a DNA strand, if a base is omitted, or if an additional base is added.

In rare cases, these errors can be useful: the “wrong” version of DNA can work better than the original or have a completely new function! In that case, the new version may be more successful, and your provider may outperform the operators of the previous version in the population.

This extension of new features in an entire population is the way evolution works.

Silent mutations and redundant coding

In some cases, genetic mutations may have no effect on the final product of a protein. This is because, as seen in the previous table, most amino acids are connected to more than one codon.

Glycine, for example, is encoded by the codons GGA, GGC, GGG and GGU. A mutation that results in the wrong nucleotide being used for the last letter of the glycine codon, then, would not matter.

A codon that starts at “GG” will still encode glycine, regardless of which letter was last used.

It is believed that the use of multiple codons for the same amino acid is a mechanism that evolved over time to minimize the possibility of a small mutation causing problems for an organism.

Mutation without meaning

In a nonsense mutation, substituting a base pair for an incorrect base pair during DNA replication results in the use of the wrong amino acid in a protein.

This can have a small effect on an organism, or a large one, depending on how important the amino acid is for the function of its protein and in which it is made.

This can be thought of as furniture construction. How bad would it be if you used the wrong piece to screw the leg of a chair into place?

If you used a screw instead of a nail, the two are probably similar enough so that the leg of the chair stays lit, but if you try to use, for example, a cushion to attach the leg to the chair, your chair will not It will work very well.

A nonsense mutation can result in an enzyme almost as good as the normal version, or an enzyme that does not work at all.

A nonsense mutation occurs when the incorrect base pair is used during DNA replication, but when the resulting codon does not encode an incorrect amino acid.

Instead, this error creates a stop codon or other information that is indecipherable for the cell. As a result, the ribosome stops functioning in that protein and all subsequent codons are not transcribed.

The nonsense mutations lead to incomplete proteins, which can work very badly or not work at all. Imagine if you stopped building a chair in half!

Suppression

In a deletion mutation, one or more DNA bases are not copied during DNA replication. Elimination mutations come in a variety of sizes: a single pair of bases may be missing, or a large piece of a chromosome may be missing!

The smallest mutations are not always less harmful. The loss of only one or two bases can result in a mutation of the reading frame that damages a crucial gene.

Conversely, larger deletion mutations can be fatal, or they can result in a disability, as in DiGeorge syndrome and other conditions that result from the removal of part of a chromosome.

The reason for this is that the DNA looks a lot like the source code of the computer, a piece of code can be crucial for the system to turn on, while other parts of the code could ensure that a website looks good or loads quickly.

Depending on the function of the code fragment that is deleted or modified, a small change can have catastrophic consequences, or a seemingly large alteration of the code one can result in a system that is a bit imprecise.

Insertion

An insertion mutation occurs when one or more nucleotides are mistakenly added to a growing DNA strand during DNA replication. Rarely, long stretches of DNA can be added incorrectly in the middle of a gene.

Like a nonsense mutation, the impact of this may vary. The addition of an unnecessary amino acid in a protein can make the protein only slightly less efficient or it can paralyze it.

Consider what would happen to your chair if you added a random piece of wood that the instructions did not require. The results can vary greatly depending on the size, shape and location of the extra piece!

Duplication

A duplication mutation occurs when a segment of DNA is accidentally replicated two or more times. Like the other mutations listed above, these may have mild effects, or they may be catastrophic.

Imagine that your chair has two backs, two seats or eight legs. A small duplication and the chair can still be usable, although a bit strange or uncomfortable. But if the chair had, for example, six seats joined together, it could quickly become useless for its intended purpose!

Mutation with scrolling reading pattern

A mutation of the reading frame is a subtype of insertion, deletion and duplication mutations.

In a mutation of the reading frame, one or two amino acids are deleted or inserted, resulting in a displacement of the “frame” used by the ribosome to indicate where a codon stops and the next begins.

This type of error can be especially dangerous because it causes all the codons that occur after the error to be misinterpreted. Typically, each amino acid added to the protein after the mutation of the reading frame is incorrect.

Imagine if you were reading a book, but at some point during the writing, an error occurred, so that each subsequent letter changed one letter later in the alphabet.

A word that was supposed to read “letter” would suddenly become “mfuuft”. This is approximately what happens in a mutation of the reading frame.


Watch the video: Transcription DNA to mRNA (May 2022).


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