Learning Objectives The effect of a mutation will depend upon the function of the DNA sequence. Mutations in non-protein coding regions could occur in regulatory regions that affect genes or have no effect on a cell or organism. When mutations occur in coding sequences, we can predict the effect on the primary structure of the protein using the codon table.
 Figure \(\PageIndex{1}\): Mutations can lead to changes in the protein sequence encoded by the DNA. (OSC_Microbio_11_05_EffMut.jpg "Mutations" by OpenStax, LibreTexts is licensed under CC BY.) Multiples of three Adding or removing bases in multiples of three, will not cause a frameshift mutation. Why not? Would mutations like this affect the protein? What additional information would you need to make a prediction about such a mutation? Do mutations affect protein function?Both frameshift and nonsense mutations are likely to affect protein function by producing a shortened or extremely altered peptide that is unlikely to retain enough structure to perform the intended function. However, a frameshift or nonsense mutation that occurs near the 3' end of the gene might allow the protein to retain the ability to function. Silent mutations are least likely to affect protein function. Missense mutations are often difficult to predict. If the change is to a similar amino acid or in a non-critical amino acid, the mutation protein may continue to function. However, if the amino acid is changed to a different type of amino acid or removes a critical amino acid (in terms of structure or activity), then the mutant protein may change in activity. Mutations that reduce the function of a gene product are called loss-of-function. If the gene product is completely non-functional, the allele is termed a null allele. Loss-of-function and null alleles are usually (but not always) recessive in diploid organisms, because one functional allele can usually supply enough protein product. Some mutations actually make proteins more active, for example, by altering an inhibitory domain; these mutations are called gain-of-function. Gain-of-function alleles are often dominant alleles because their new function or activity is produced independently of the other allele.
DefinitionA nonsense mutation occurs in DNA when a sequence change gives rise to a stop codon rather than a codon specifying an amino acid. The presence of the new stop codon results in the production of a shortened protein that is likely non-functional.
NarrationA nonsense mutation, or its synonym, a stop mutation, is a change in DNA that causes a protein to terminate or end its translation earlier than expected. This is a common form of mutation in humans and in other animals that causes a shortened or nonfunctional protein to be expressed. SearchThe DNA sequence of a gene can be altered in a number of ways. Gene variants (also known as mutations) can have varying effects on health, depending on where they occur and whether they alter the function of essential proteins. Variant types include the following: Substitution This type of variant replaces one DNA building block (nucleotide) with another. Substitution variants can be further classified by the effect they have on the production of protein from the altered gene.
Insertion An insertion Deletion A deletion Deletion-Insertion This variant occurs when a deletion and insertion happen at the same time in the same location in the gene. In a deletion-insertion variant, at least one nucleotide is removed and at least one nucleotide is inserted. However, the change must be complex enough to differ from a simple substitution. The resulting protein may not function properly. A deletion-insertion (delins) variant may also be known as an insertion-deletion (indel) variant. Duplication A duplication Inversion An inversion changes more than one nucleotide in a gene by replacing the original sequence with the same sequence in reverse order. Frameshift A reading frame consists of groups of three nucleotides that each code for one amino acid Repeat expansion Some regions of DNA contain short sequences of nucleotides that are repeated a number of times in a row. For example, a trinucleotide repeat is made up of sequences of three nucleotides, and a tetranucleotide repeat is made up of sequences of four nucleotides. A repeat expansion What type of mutation causes a nonfunctional protein?Nonsense Mutation
A nonsense mutation occurs in DNA when a sequence change gives rise to a stop codon rather than a codon specifying an amino acid. The presence of the new stop codon results in the production of a shortened protein that is likely non-functional.
Which type of mutation is most likely to render a protein non functional?Nonsense mutations can cause premature truncation of a protein, a potentially disastrous effect, often leading to production of a nonfunctional protein.
What type of mutation is most likely to result in a functional protein?At the level of translation, when RNA copied from DNA is converted into a string of amino acids during protein synthesis, point mutations often manifest as functional changes in the final protein product.
What kind of gene mutation is more likely to result in a non functional protein a frameshift resulting from an insertion or deletion or a substitution point mutation?A frameshift mutation is a mutation that is more expected to result in a nonfunctional protein than a point mutation. A frameshift mutation leads to the insertion and deletion of nucleotide bases, modifying the base sequence in codons which results in changing the AA (amino acid) sequence and the following proteins.
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Which of the following mutations is most likely to result in a non functional protein?
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