Physical and chemical mutagens can damage DNA through ionizing and non-ionizing radiation. Ionizing radiations like alpha rays, beta rays, X-rays, and gamma rays have enough energy to generate free radicals from atoms and cause single or double strand breaks in DNA. Non-ionizing UV light is less harmful but can still induce pyrimidine dimer formation between nucleotides, blocking DNA replication. The document discusses different types of radiation and their effects on damaging DNA structure and causing mutations.

1. Physical and Chemical
Mutagens
Dr. Madhura Mukadam
Associate Professor,
Dept. of Zoology,
Gogate Jogalekar College, Ratnagiri
Dt. 12.10.2017

2. A. Ionizing Radiations
• The energy content of a radiation depends upon its
wavelength. Shorter the wavelength- greater the
energy value.
• DNA is the principle target for biological effects.
• Radiations brings about the excitation of the atom.
(movement of electron pair from an inner orbit to an
outer orbit)
• In excited state the atom is highly reactive and called
as free radical. Radiations which capable of generating
such state is called ionizing radiations.

3. • Radiation produces a DNA damage – nucleotide base, DNA
single strand breaks(SSBs), Double strand breaks(DSBs)
• Alpha Rays: single strand breaks and deletions.
• Beta rays: Beta particles are produced from phosphorus. They
are small and fast moving. Cause serious structural damage to
DNA but less severe than alpha radiations.
• They often cause single point damage. Beta rays cause
mutation by breaking the hydrogen bond between
complementary nucleotide base in DNA.
• X rays and gamma rays: both are high energy
electromagnetic radiation. These are packets of energy
known as photons. They indicates SSBs or DSBs to DNA.

6. B. Non-ionizing radiations
(UV light)
• These are electromagnetic radiations which does
not carry enough photon energy to ionize atoms or
molecules.
• These are less harmful for DNA damage.
• UV radiations induce different types of DNA
damages among which pyrimidine dimers are
formed with the highest frequency.
• It blocks DNA replication

9. Thymine dimer caused by UV light