Point Mutations

Introduction

• Point mutations are a specific type of genetic mutation that involves the substitution of a single nucleotide within a DNA sequence.
• These mutations result in changes to the codons within a gene, which can have various effects on the protein produced.

Types of Point Mutations

1. Missense Mutations

• Missense mutations occur when a single nucleotide substitution changes the codon, leading to the incorporation of a different amino acid into the protein.
• Effects of missense mutations:
  • Altered protein structure: The change in amino acid may alter the protein's shape and affect its function.
  • Variable impact: Some changes may have no significant effect on protein function.

2. Nonsense Mutations

• Nonsense mutations involve a nucleotide substitution that changes a codon coding for an amino acid into a stop codon.
• Effects of nonsense mutations:
  • Shortened protein: The resulting protein is typically shorter than the original and often non-functional.
• Premature termination: The mutation causes premature termination of protein synthesis.

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Point Mutations

3. Splice-Site Mutations

• Splice-site mutations affect the boundaries between exons (coding regions) and introns (non-coding regions) in a gene.
• These mutations can prevent proper splicing during post-transcriptional processing.
• Effects of splice-site mutations:
  • Altered gene splicing: Introns may be included, or exons may be removed, leading to a different protein product.
  • Diverse protein structure: Splice-site mutations can result in a wide range of protein variants.

Causes of Point Mutations

• Point mutations can arise from various sources, including:
  • Spontaneous mutations: Errors during DNA replication or repair.
  • Induced mutations: Exposure to mutagenic agents like radiation or chemicals.
  • Inherited mutations: Passed down from one generation to the next.

Impact of Point Mutations

• The consequences of point mutations depend on their type and location within a gene.
• Missense mutations may affect protein structure and function.
• Nonsense mutations lead to truncated, often non-functional proteins.
• Splice-site mutations can result in diverse protein products with altered functions.

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Point Mutations

Summary

Point mutations involve the substitution of a single nucleotide within a DNA sequence, leading to changes in codons and, subsequently, the protein produced. These mutations can be missense, nonsense, or splice-site mutations, each with its specific effects on protein structure and function. The impact of point mutations varies depending on their type and location within a gene.