Mutagens and carcinogens | Khan Academy

Central Dogma of Molecular Biology

• Genetic information is stored in DNA, which is transcribed to RNA and translated to proteins.

• Nucleotides in DNA are complementary to those in RNA, forming codons that code for amino acids.

• Mutations in DNA affect RNA sequences and protein production, leading to abnormal proteins.

Mutagens

• Definition: Chemical substances or physical events causing genetic mutations.

• Types:

  • Endogenous Mutagens: Originating from within the organism (e.g., reactive oxygen species).

  • Exogenous Mutagens: From external sources (e.g., UV light, certain chemicals).

Endogenous Mutagens - Reactive Oxygen Species (ROS)

• Produced during oxidative phosphorylation in mitochondria.

• Examples include superoxide (O2•-) and hydrogen peroxide.

• Effects:

  • Can cause double-strand breaks in DNA, leading to significant structural damage.

  • Can cause base modifications, resulting in point mutations.

• High levels of ROS can lead to oxidative stress, which can overwhelm the cell's defenses.

• Role of Antioxidants: Help mitigate ROS damage to DNA.

Exogenous Mutagens

• Example 1: Intercalators

  • Ethidium bromide intercalates between DNA strands, deforming the structure.

• Example 2: Base Analogs

  • 5-bromouracil (5-BU) mimics uracil but can shift forms, leading to mispairing during DNA replication.

Carcinogens

• Definition: Substances that can lead to cancer (uncontrolled cell division and tumor formation).

• Relationship with Mutagens: Some carcinogens are mutagens, but not all mutagens are carcinogens.

• Examples: Tobacco, asbestos, UV radiation.

Summary

• Mutagens increase the likelihood of genetic mutations.

• Carcinogens cause cancer and can act by inducing mutations or increasing cell division rates.