17. Mutation, Repair, and Recombination

Types of Mutations

17. Mutation, Repair, and Recombination

Types of Mutations

2: minutes

Problem 31f

Textbook Question

Mutations in the IL2RG gene cause approximately 30 percent of severe combined immunodeficiency disorder (SCID) cases in humans. These mutations result in alterations to a protein component of cytokine receptors that are essential for proper development of the immune system. The IL2RG gene is composed of eight exons and contains upstream and downstream sequences that are necessary for proper transcription and translation. Below are some of the mutations observed. For each, explain its likely influence on the IL2RG gene product (assume its length to be 375 amino acids).
Deletion in Exon 2, in frame

Verified step by step guidance

Understand the context: The IL2RG gene encodes a protein that is essential for the immune system. Mutations in this gene can disrupt its function, leading to severe combined immunodeficiency disorder (SCID). The gene consists of eight exons, and mutations in these exons can affect the protein's structure and function.

Identify the mutation: The problem specifies a deletion in Exon 2 that is 'in frame.' An in-frame deletion means that the deletion does not disrupt the reading frame of the gene. This is important because the codons (sets of three nucleotides) downstream of the mutation will still be read correctly.

Determine the effect on the protein: Since the deletion is in-frame, it will remove a specific number of amino acids from the protein sequence without causing a frameshift. This could lead to a shorter protein or one with missing amino acids in a specific region, potentially altering its structure and function.

Consider the role of Exon 2: Exon 2 likely encodes a specific domain or region of the IL2RG protein. The deletion of amino acids in this region could impair the protein's ability to interact with other molecules, such as cytokines or other components of the immune system, depending on the functional importance of the deleted region.

Conclude the likely impact: The deletion in Exon 2 may result in a partially functional or nonfunctional IL2RG protein. This could disrupt cytokine receptor signaling, impairing immune system development and leading to SCID. Further experimental analysis would be needed to confirm the exact functional consequences.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

IL2RG Gene Function

The IL2RG gene encodes a protein that is a critical component of the interleukin-2 receptor, which plays a vital role in the immune system by facilitating communication between immune cells. Mutations in this gene can disrupt the normal signaling pathways necessary for immune cell development and function, leading to severe combined immunodeficiency (SCID). Understanding the gene's role helps in assessing how specific mutations affect immune responses.

Types of Mutations

Mutations can be classified into several types, including deletions, insertions, and substitutions. A deletion in exon 2, particularly if it is in-frame, means that a portion of the coding sequence is removed without altering the reading frame of the gene. This can lead to the loss of one or more amino acids in the resulting protein, potentially affecting its structure and function, which is crucial for understanding the impact on the IL2RG gene product.

Protein Structure and Function

The structure of a protein is directly related to its function, as the specific arrangement of amino acids determines how the protein interacts with other molecules. In the case of the IL2RG gene product, any alteration in the amino acid sequence due to mutations can lead to misfolding or loss of function, which can severely impair immune system development. Analyzing how mutations affect protein structure is essential for predicting their biological consequences.

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Most organisms display a circadian rhythm, a cycling of biological processes that is roughly synchronized with day length (e.g., jet lag occurs in humans when rapid movement between time zones causes established circadian rhythms to be out of synch with daylight hours). In Drosophila, pupae eclose (emerge as adults after metamorphosis) at dawn.

In each case, how would you clone the genes you identified by mutation?

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Textbook Question

Shown here are the amino acid sequences of the wild-type and three mutant forms of a short protein.

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Wild-type: Met-Trp-Tyr-Arg-Gly-Ser-Pro-Thr

Mutant 1: Met-Trp

Mutant 2: Met-Trp-His-Arg-Gly-Ser-Pro-Thr

Mutant 3: Met-Cys-Ile-Val-Val-Val-Gln-His _

Use this information to answer the following questions:

Using the genetic coding dictionary, predict the type of mutation that led to each altered protein.

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Textbook Question

Shown below are two homologous lengths of the alpha and beta chains of human hemoglobin. Consult a genetic code dictionary, and determine how many amino acid substitutions may have occurred as a result of a single nucleotide substitution. For any that cannot occur as a result of a single change, determine the minimal mutational distance.

Alpha: ala val ala his val asp asp met pro

Beta: gly leu ala his leu asp asn leu lys

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Textbook Question

Mutations in the IL2RG gene cause approximately 30 percent of severe combined immunodeficiency disorder (SCID) cases in humans. These mutations result in alterations to a protein component of cytokine receptors that are essential for proper development of the immune system. The IL2RG gene is composed of eight exons and contains upstream and downstream sequences that are necessary for proper transcription and translation. Below are some of the mutations observed. For each, explain its likely influence on the IL2RG gene product (assume its length to be 375 amino acids).

Large deletion covering Exons 2 and 3

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Textbook Question

Deletion in Exon 2, causing frameshift

Missense mutation