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What type of mutation occurs when a stop codon replaces an amino acid codon?
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A point mutation that changes a codon specifying an amino acid into a stop codon is called a?
nonsense mutation
Is it possible for mutations to go unnoticed in mRNA?
Yes it is. There are more triplet codons than there are [biologically active] amino acids that need to be represented in the Cell, so that there is some duplication of codon/amino acid 'alignment'. This occurs only in the third base position of the triplet codon - the 'wobble base' position - so if a mutation occurred in the wobble (third) position and the codon was one of the few that was not alone in its amino acid specificity this mutation would go unnoticed.
Why does mrna mutation affect the amino acid sequence?
The codon UGU codes for the amino acid Cysteine. The codon UGG codes for the amino acid Tryptophan. Therefore the mutation will cause the amino acid Cysteine to be replaced with Tryptophan. These amino acids are quite different, and the final shape of the protein could be changed as a result. This could affect the function of the protein.
What type of mutation is likely to have the least effect on an organism?
A silent mutation has the least effect on an organism. It is when the codon is changed to the same amino acid.
How is it possible for gene with a mutation in coding region to encode a polypeptide with the same amino acid sequence as the nonmutant gene?
If the mutant codon still codes for the same amino acid (a silent mutation). For example: GUU, GUC, GUA and GUG all code for the amino acid Valine. So if the mutation changed the codon from GUU to GUA - Valine would still be produced and therefore the polypeptide will be identical.
A point mutation that changes a codon specifying an amino acid into a stop codon is called a?
nonsense mutation
What amino acid is coded for by this sequence before mutation?
The neutral mutation does not change the amino acid coded for by the codon. A good example is the RNA codon that could be the CCA, CCC or the CCG.
What amino acid is coded for by this sequence before the mutation?
The neutral mutation does not change the amino acid coded for by the codon. A good example is the RNA codon that could be the CCA, CCC or the CCG.
When would a mutation in DNA not cause a change in how the gene is expressed or in which proteins are made?
If a point mutation occurs in a location that is not critical to the structure and function of the protein, it will not change the way the gene is expressed. Also, since most amino acids have more than one codon, if the point mutation resulted in a codon for the same amino acid without the mutation, it will not change the way the gene is expressed.
A genetic mutation that causes a codon that should code for a specific amino acid to be changed into a stop codon results in a shortened protein product and is known as?
a nonsense mutation
Is it possible for mutations to go unnoticed in mRNA?
Yes it is. There are more triplet codons than there are [biologically active] amino acids that need to be represented in the Cell, so that there is some duplication of codon/amino acid 'alignment'. This occurs only in the third base position of the triplet codon - the 'wobble base' position - so if a mutation occurred in the wobble (third) position and the codon was one of the few that was not alone in its amino acid specificity this mutation would go unnoticed.
Why does mrna mutation affect the amino acid sequence?
The codon UGU codes for the amino acid Cysteine. The codon UGG codes for the amino acid Tryptophan. Therefore the mutation will cause the amino acid Cysteine to be replaced with Tryptophan. These amino acids are quite different, and the final shape of the protein could be changed as a result. This could affect the function of the protein.
What type of mutation is likely to have the least effect on an organism?
A silent mutation has the least effect on an organism. It is when the codon is changed to the same amino acid.
When is a single base substitution mutation least likely to be deleterious?
when the single base change results in a codon that specifies the same amino acid as the original codon
What produces a nonsense mutation?
A nonsense mutation is a genetic mutation in a DNA sequence that leads to the appearance of a stop codon where previously there was a codon specifying an amino acid. DNA is a chain of many smaller molecules called nucleotides. During protein formation, DNA (or RNA) nucleotide sequences are read three nucleotides at a time in units called codons, and each codon corresponds to a specific amino acid or stop codon, which is also called nonsense codon because it does not code for an amino acid and instead signals the end of protein synthesis. Therefore, nonsense mutations occur when a premature nonsense or stop codon is introduced in the DNA sequence. When the mutated sequence is translated into a protein, this premature stop codon results in the production of a shortened, and likely nonfunctional, protein.
How is it possible for gene with a mutation in coding region to encode a polypeptide with the same amino acid sequence as the nonmutant gene?
If the mutant codon still codes for the same amino acid (a silent mutation). For example: GUU, GUC, GUA and GUG all code for the amino acid Valine. So if the mutation changed the codon from GUU to GUA - Valine would still be produced and therefore the polypeptide will be identical.
What happens if you change a single base in codon?
If one base in a codon was changed, this would be a point mutation. This may not cause any change in the structure of the protein, or it could be severely damaging. Since most amino acids have more than one codon, it's possible that the mutation would result in one of the other codons for that amino acid. In that case, there would be no change in the sequence of amino acids, and no change in the structure or function of the protein. A point mutation might also result in a codon that codes for a totally different amino acid, which can cause a genetic disorder. One example of a genetic disorder caused by a point mutation is sickle cell anemia. It's also possible that the point mutation could cause the codon to code for a stop signal. Please read the article in the related links for more information.
