Page 201 - MNU microbiology theoritical 2025

General Microbiology & Immunology (PM 401) Second level Semester 4 2024/2025

1- Mutagens that modify DNA bases.

a- Alkylating agents:

add alkyl groups onto purines and pyrimidines, altering their hydrogen-

bonding properties

* For example:

- Ethyl methane sulfonate.

- Nitrosoguanidine.

The modified guanine base can mis-pair
with thymine instead of cytosine

b- Deaminating agents:
It converts amino group (NH2) into keto group (-C=O).

* For example: - Nitrous acid.

Ex: converting cytosine to uracil, which pairs with adenine rather than guanine.

2- Intercalating agents

For example: - Ethidium bromide.

• They are planar (flat) molecules of about the same size as a pair of

nucleotides in DNA

• They do not alter H-bonding properties,

General Microbiology & Immunology (PM 401) theoretical handbook Page 190