Question

A missense mutation cannot be: a. the code for the sickle-cell gene. b. caused by a frameshift. c. the deletion of a base in a coding sequence. d. the addition of two bases in a coding sequence. e. the same as a silent mutation.

Short answer

A missense mutation cannot be caused by a frameshift, which is option b.

Step-by-step solution

Understand the concept of a missense mutation

A missense mutation is a type of genetic mutation where a single nucleotide base is changed, resulting in the substitution of a different amino acid in the protein produced. This can affect the function of the protein.

Analyze the options

Go through each option and determine whether it can describe a missense mutation. Remember that missense mutations involve the change of a single nucleotide, resulting in a different amino acid.

Identify which options cannot describe a missense mutation

Option b, c, and d do not describe a missense mutation. A frameshift is caused by insertions or deletions of a number of nucleotides in a DNA sequence that is not divisible by three, option c describes a deletion which is a type of frameshift mutation, and option d talks about an addition of two bases which also leads to frameshift, hence altering the entire reading frame of the gene.

Select the correct answer

Based on the definition of a missense mutation, the correct answer is 'b. caused by a frameshift', as this does not lead to a simple amino acid substitution but rather shifts the entire reading frame, potentially altering the entire protein beyond just one amino acid.

Key concepts

Genetic Mutations

Genetic mutations are alterations in the DNA sequence that can affect the structure and function of proteins and may lead to genetic disorders or changes in an organism's traits. These mutations can occur naturally during DNA replication or be induced by environmental factors.

There are various types of genetic mutations, including point mutations (altering a single nucleotide), insertions, deletions, and complex rearrangements. Each type can have different consequences on an organism's genome, from benign effects to causing significant physiological changes.

Understanding how different mutations affect gene expression is crucial for knowing how genetic diseases develop and for creating targeted treatments. For students studying genetics, grasping the concept of these mutations and their implications helps to appreciate the complexity of biological systems and the precision required in DNA replication and repair mechanisms.

Frameshift Mutation

A frameshift mutation occurs when nucleotides are inserted into or deleted from the genetic code in numbers not divisible by three. Since the genetic code is read in triplets, called codons, this type of mutation shifts the grouping of these codons and therefore changes the entire sequence that follows the mutation.

A frameshift mutation can result in a completely different protein, often nonfunctional, because the amino acid sequence after the mutation is altered. It is one of the most severe types of mutations due to the potential to completely change the structure and function of the resulting protein.

Implications for Students

Understanding frameshift mutations is vital for students, as these introduce a fundamental concept that genetic information is read in a specific format. Misalignment in this format can have dramatic effects on protein synthesis, highlighting the precision required in biological systems.

Nucleotide Substitution

Nucleotide substitutions, also known as point mutations, involve the replacement of one nucleotide in the DNA sequence with another. This includes transitions (purine to purine or pyrimidine to pyrimidine) and transversions (purine to pyrimidine or vice versa).

These mutations can have different outcomes depending on their impact on the protein coded by the gene. Possible consequences include silent mutations, which do not change the protein structure, to more significant changes such as missense or nonsense mutations affecting protein function.

Teaching Importance

In an educational context, teaching about nucleotide substitutions offers insight into genetic variability and how single nucleotide changes can lead to various phenotypic outcomes. This knowledge is foundational for students in genetics, molecular biology, and related fields.

Amino Acid Substitution

An amino acid substitution arises from a point mutation where a single nucleotide change results in the incorporation of a different amino acid into the resulting protein. This is a type of missense mutation and is often contrasted with silent mutations, where the nucleotide change does not result in an amino acid change.

The consequences of an amino acid substitution can range from benign to deleterious, depending on the role of the changed amino acid in the protein's structure and function. A classic example of an amino acid substitution leading to disease is sickle-cell anemia, where the missense mutation results in the substitution of valine for glutamic acid in hemoglobin.

Student Focus

For students, understanding the specifics of amino acid substitutions provides a clear example of how even small changes at the genetic level can lead to significant differences in biological functions. It underscores the importance of precise genetic coding and the sophisticated nature of protein structure and function.