Lecture Notes: Mutations

Introduction

• Definition of mutation: Change in DNA base sequence.
  • Example: Change from C to G in DNA code.
• Mutations occur spontaneously during cell division (mitosis).
• Risk factors increasing mutations:
  • Carcinogens in cigarette smoke.
  • Certain types of radiation (e.g., x-rays, gamma rays).
  • Note: These factors increase risk, but don't always cause mutations.

How DNA Works

• Genes are DNA sections coding for proteins.
• DNA structure:
  • Sequence of bases organized into triplets or codons.
  • Each codon codes for one of 20 different amino acids.
  • Example: ACC codes for amino acid 7, CTA for amino acid 18.
• Proteins are formed by linking amino acids in sequence.
• Mutations can alter amino acids, affecting protein shape/function.
  • Example: Altered enzyme active site affects substrate binding.

Effects of Mutations

• Minor effects: Slight protein changes, no significant functional impact.
• Non-coding DNA:
  • Most mutations occur here, usually inactive but some regulate gene expression.
  • Example: Nerve cells switch off hemoglobin genes as it's not needed.

Types of Mutations

1. Substitution Mutations

   • One base is replaced by another (e.g., C to T, G to A).
   • Changes codon and possibly amino acid it codes for.

2. Insertion Mutations

   • An extra base is added to the sequence.
   • Causes a shift in the reading frame, altering subsequent codons.
   • More severe than substitution due to altering entire sequence post-insertion.

3. Deletion Mutations

   • A base is removed from the sequence.
   • Like insertion, it shifts the reading frame and alters subsequent codons.

Conclusion

• Understanding mutations is key to grasping genetic variation and potential impacts on protein function.
• Non-coding DNA plays a significant role in gene expression regulation.

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