Mutations

Mutations and Their Effects

  • Mutation = change in DNA base sequence.

  • Mutations happen randomly and all the time.

Effects on Proteins

  1. No effect (silent mutation):

    • Different base triplets can code for the same amino acid.

    • Protein shape & function remain unchanged.

  2. Change in amino acid sequence (missense mutation):

    • Mutation → different amino acid added.

    • Alters protein’s shape → may affect function.

    • Examples:

      • Enzyme: active site shape changes → cannot bind to substrate.

      • Structural protein (e.g., collagen): may lose strength.

  3. Severe mutations (nonsense mutation):

    • May cause the protein to be non-functional.

Non-Coding DNA Mutations

  • Chromosomes contain non-coding regions.

  • These switch genes on or off (control when proteins are made).

  • Mutations in non-coding DNA can:

    • Cause a gene to be switched on when it should be off (or vice versa).

    • Lead to proteins being made at the wrong time/place.

    • Possible outcome = uncontrolled mitosis → cancer.

✅ Exam Tip:

  • Be ready to give examples of how mutations affect protein function.

  • Know the difference between coding DNA mutations (change amino acids) and non-coding DNA mutations (gene switching errors).