Mutagens alter DNA structure in different ways

The public is concerned for 2 important reasons (440):
1. Mutagenic agents are often involved in development of cancer.
2. Mutations can be harmful for future offspring.
In some cases, non-mutagenic agents can be altered to a mutagenically active form (440).
Certain foods contain antioxidents (440).
Some mutagens act by covalently modifying the structure of bases (440)
- Nitrous oxide replaces amino groups with keto groups, a processes called deamination. This can change cytosine to uracil and adenine to hypoxanthine.
  - When altered DNA replicates, modified bases do not pair w/appropriate bases in newly made strand. Uracil pairs with adenine, hypoxanthine pairs with cytosine.
Other chemical mutagens can disrupt appropriate pairing between nucleotides by alkylating bases within DNA (441).
- Methyl or ethyl groups are covalently attached to the bases.
- Examples include nitrogen mustard and ethyl methanesulfonate.
Some mutagens exert their effects by directly interfering w/the DNA replication process (441).
- Acridine dyes, such as proflavin, contain flat structures that intercalate between adjacent base pairs, thereby distorting helical structure.
- When DNA containing these mutagens is replicated, single-nucleotide additions and/or deletions can be incorporated into newly made daughter strands.
Compounds like 5-bromouracil (5BU) and 2-aminopurine are base analogues that become incorporated into daughter strands during DNA replication (441),
- 5BU is a thymine analogue that can replace thymine in DNA. Thus, it will base-pair with guanine, causing a mutation in which a TA base pair is changed to a 5BU-G base pair.
DNA molecules are sensitive to physical agents like radiation (441).
- Short wavelength radiation and high energy, known as ionizing radiation, can alter DNA structure.
- Ionizing radiation penetrates into biological tissues and creates chemically active molecules known as free radicals.
  - These can cause base deletions, single nicks in DNA strands, cross-linking, and even chromosomal breaks.
Non-ionizing radiation contains less energy, so it penetrates only the surface (441).
- UV light causes the formation of cross-linked thymine dimers, which interfere w/transcription and DNA replication.

	Created by Olivia McRitchie over 8 years ago

NCLEX Biology (Genetics) Note on Ch 16: Gene Mutation and DNA Repair, created by Olivia McRitchie on 02/05/2018.