Key Points on Mutation

Definition and Importance

• Mutation: A permanent change in the DNA sequence, from a single base change to large chromosomal alterations.
• Impact: Causes protein sequence changes, affecting phenotype and providing genetic variation essential for evolution.

Mutation Based on Occurrence

1. Depurination:

   • Loss of a purine base (adenine or guanine), potentially causing point mutations during replication.

2. Deamination:

   • Removal of an amino group from a nucleotide (e.g., cytosine to uracil), possibly altering C-G to U-A base pairs.

3. Induced Mutation:

   • Caused by environmental factors (UV light, radiation, chemicals).

Types of Induced Mutations

1. Base Analogs:

   • Chemicals mimicking DNA bases; can lead to incorrect base pairing.

2. Base Modifying Agents:

   • Add alkyl groups to bases, altering base pairing properties.

3. Intercalating Agents:

   • Insert between DNA bases, causing frame-shift mutations (insertions or deletions).

Chromosomal Mutation

• Large-Scale Changes: Deletions, duplications, inversions, translocations, aneuploidy.
• Consequences: Potentially cause diseases, developmental issues, and evolutionary changes.

DNA Repair Systems

1. Direct Repair System:

   • Reverses specific types of DNA damage (e.g., UV-induced thymine dimers).

2. Excision Repair System:

   • Base Excision Repair (BER): Removes small base lesions, followed by DNA repair.
   • Nucleotide Excision Repair (NER): Removes large DNA lesions, important for fixing UV damage.