Genetic Mutations

Genetic Mutations

Learning Objectives

• Identify the types of change in DNA related to:
  • Point Mutation
  • Deletion Mutation
  • Insertion Mutation

Overview of Mutations

• A mutation is defined as:
  • A change in the nucleotide sequence of DNA.
  • It may lead to changes in the sequence of amino acids, affecting the structure and function of cells.
  • Generates from external factors known as mutagens, e.g., radiation, chemicals, and some viruses.
  • Severe mutations affecting proteins/enzyme function
  • May lead to cell death or various diseases stemming from genetic defects.

Normal DNA Functioning

• Normal DNA sequence leads to the production of mRNA, which instructs the correct series of amino acids in proteins.

Types of Genetic Mutations

1. Point Mutation

   • Definition: Replacement of one base in the DNA template strand with another.
   • Consequence: May result in a different amino acid being inserted into the polypeptide chain.
   • Silent Mutation: A type of point mutation where the amino acid remains unchanged despite the DNA change.

2. Deletion Mutation

   • Definition: A base is removed from the normal nucleotide sequence in the DNA template strand.
   • Consequence: This change alters all subsequent codons, resulting in a different amino acid sequence from that point onward.

3. Insertion Mutation

   • Definition: A base is added to the normal nucleotide sequence in the DNA template strand.
   • Consequence: Similar to deletion, it changes all the following codons and amino acid sequences after the point of insertion.

Illustrative Example of Deletion Mutation

• Example:
  • Normal Template Strand: TACTTCAACCGATT
  • After Mutation: Potentially changes the entire mRNA sequence, leading to drastic shifts in amino acids, e.g.,
  • mRNA Output: AUGAAGUUGGCUAA (Illustrates a different sequence post-deletion)

Effects of Genetic Mutations

• Not all mutations lead to dramatic changes in the primary structure of proteins. However:
  • Severe changes in the amino acid sequence
  • Can result in loss of biological activity in proteins.
  • Some proteins, particularly enzymes, may fail to catalyze reactions, leading to toxic accumulations of substances within cells.

Practice Identifications of Mutation Types

1. Cytidine (C) enters the DNA sequence. → (I): Insertion Mutation
2. One adenosine is removed from the DNA sequence. → (D): Deletion Mutation
3. A base sequence of TGA in DNA changes to TAA. → (P): Point Mutation