Chapter 14: Problem 10
Why are frameshift mutations likely to be more detrimental than point mutations, in which a single pyrimidine or purine has been substituted?
Short Answer
Expert verified
Frameshift mutations are more likely to be detrimental than single purine or pyrimidine substitutions because they cause a shift in the reading frame for translation, leading to significant alterations in the amino acid sequence of the synthesized protein and a higher likelihood of protein dysfunction. This can result in nonfunctional or malfunctioning proteins, which may cause severe problems for the organism. In contrast, point mutations involving single purine or pyrimidine substitutions often have more localized effects, with some not even causing changes in the amino acid sequence, making them less likely to disrupt protein function.
Step by step solution
01
Define Frameshift Mutations and Point Mutations
Frameshift mutations are genetic mutations caused by the insertion or deletion of nucleotides in a DNA sequence, which shifts the reading frame for translation. This can result in a completely different sequence of amino acids in the synthesized protein, often leading to a nonfunctional or malfunctioning protein.
On the other hand, point mutations are changes in a single nucleotide in the DNA sequence, either through substitution, insertion, or deletion. In this case, the question specifically refers to substitutions of single purines or pyrimidines. This type of mutation has a more localized effect on the gene, potentially changing a single amino acid or having no effect at all due to redundancy in the genetic code.
02
Consequences of Frameshift Mutations
Due to the reading frame shift in frameshift mutations, a completely different set of amino acids might be translated from the mutated gene. This might lead to a complete loss of protein function or even the formation of a harmful protein. These mutations often result in truncated proteins, meaning that the premature introduction of a stop codon cuts the protein synthesis short. Truncated proteins are usually nonfunctional and can lead to severe dysfunction in some cases.
03
Consequences of Point Mutations
Point mutations involving single purine or pyrimidine substitutions may have mild, severe, or no impact on the encoded protein. Cases where the mutation leads to an amino acid with similar properties might not significantly impact protein function. Due to the degenerate nature of the genetic code, some point mutations do not even result in an amino acid change, as multiple codons can code for the same amino acid.
In some instances, a point mutation may result in the substitution of an amino acid with significantly different properties, which might affect the protein function. In extreme cases, a point mutation could introduce a premature stop codon, leading to a similar truncation as seen in frameshift mutations. However, the overall probability of these severe outcomes is low compared to frameshift mutations.
04
Compare the Effects of Frameshift and Point Mutations
While both frameshift and point mutations have the potential to be detrimental to protein function, frameshift mutations are more likely to have severe consequences due to the drastic changes in the amino acid sequence and potential truncation of the protein. In comparison, point mutations are usually limited to changing a single amino acid at most, with some not even having an effect on the amino acid sequence.
05
Conclusion
Frameshift mutations are likely to be more detrimental than point mutations because they drastically change the reading frame for translation, causing significant alterations to the resulting protein sequence and a higher likelihood of protein dysfunction. In contrast, point mutations involving single purine or pyrimidine substitutions often have localized effects, which may or may not cause amino acid changes and are less likely to result in major disruptions to protein function.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Point Mutations
Point mutations are small changes in the genetic sequence where a single nucleotide base is altered. This change can be categorized as a substitution, insertion, or deletion of a base. In this context, we talk about the substitution of purines or pyrimidines - the building blocks of DNA.
Depending on the location and nature of the change, point mutations can have different effects on the resulting protein. Because the genetic code is degenerate, some point mutations might not lead to a change in the amino acid sequence at all.
Depending on the location and nature of the change, point mutations can have different effects on the resulting protein. Because the genetic code is degenerate, some point mutations might not lead to a change in the amino acid sequence at all.
- If the new and old codons code for the same amino acid, it’s called a silent mutation. These have no effect on protein function.
- If the mutation changes one amino acid to another with similar properties, the change might not impact the protein significantly.
- However, if the mutation alters an amino acid with a noteworthy difference in properties, it can affect the protein’s function or stability.
- In rare cases, a point mutation introduces a stop codon prematurely, which can truncate the protein. But overall, point mutations are generally less disruptive than frameshift mutations.
Genetic Code
The genetic code is the set of rules by which information encoded in genetic material (DNA or RNA sequences) is translated into proteins by living cells. It is nearly universal and shared among almost all organisms.
This code consists of sequences of three nucleotides, called codons, each of which corresponds to a specific amino acid or stop signal. There are 64 possible codons, but only 20 amino acids, meaning the code is redundant (or degenerate).
This redundancy allows for a certain level of buffering against mutations. Many amino acids are encoded by more than one codon.
This code consists of sequences of three nucleotides, called codons, each of which corresponds to a specific amino acid or stop signal. There are 64 possible codons, but only 20 amino acids, meaning the code is redundant (or degenerate).
This redundancy allows for a certain level of buffering against mutations. Many amino acids are encoded by more than one codon.
- This redundancy means that some point mutations do not change the amino acid, which is why not all mutations result in an altered protein.
- In contrast, frameshift mutations alter the entire downstream sequence of codons, usually leading to a completely different, often nonfunctional protein.
Protein Function
Proteins are vital molecules that perform numerous functions within organisms, including catalyzing metabolic reactions, replicating DNA, responding to stimuli, and transporting molecules.
The function of a protein is determined by its three-dimensional shape, which is, in turn, a result of its amino acid sequence. Any alteration in this sequence can potentially change the protein's structure and function.
Specifically:
The function of a protein is determined by its three-dimensional shape, which is, in turn, a result of its amino acid sequence. Any alteration in this sequence can potentially change the protein's structure and function.
Specifically:
- Point mutations might have minimal effect, especially if they result in a conservative amino acid substitution.
- Frameshift mutations, however, generally disrupt the entire sequence of amino acids following the mutation site.
- Such mutations often result in nonfunctional proteins that might be truncated, leading to loss or malfunctioning of protein function.
Amino Acid Sequence
The amino acid sequence, often referred to as the primary structure of a protein, is crucial for determining how a protein will fold and function. This sequence is dictated by the order of codons in the genetic code.
Mutations that alter the amino acid sequence can have various outcomes.
Mutations that alter the amino acid sequence can have various outcomes.
- Point mutations might result in a single amino acid being changed, sometimes with little to no impact on the protein's ability to function. This limited impact is largely due to the redundancy in the genetic code.
- Frameshift mutations, on the other hand, disrupt the reading frame of the sequence, causing a large-scale change in the amino acid sequence from the point of mutation onward.
- This disruption can lead to a significantly altered protein, usually resulting in a loss of functionality or complete inactivity.