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