Mutation 2
Download as PPTX, PDF6 likes1,094 views
Mutagens are agents that cause mutations and can be physical, chemical, or biological. Physical mutagens include ionizing radiation like X-rays and gamma rays. These high energy radiations can directly damage DNA through ionization, producing reactive ions that cause breaks in DNA strands. Ionizing radiation is especially harmful to rapidly dividing cells. Ultraviolet light is also mutagenic through formation of pyrimidine dimers in DNA, though it does not ionize. The type and amount of radiation exposure determines the mutagenic effect.
Mutation 2
- 1. Mutagens are the agents responsible to cause mutation & are of three types 1. Physical 2. Chemical 3. Biological Physical Radiation was first mutagen reported ( its effect on genes were first time suggested to cause mutation). It was discovered in 1890. Roentgen discovered X ray in 1896 Bacquerel discovered radioactivity in 1896 Marie & Pierre Curie discovered radioactive elements in 1896. These discoveries lead to birth of atomic physics & our understanding of electromagnetic radiations. Atoms are made of -ve charged particles e- orbiting round nucleus. Nucleus contains + charged neutrons & uncharged neutrons. E move from one orbit to another when gets energy jumps to higher energy levels when releases again moves to lower energy level. This energy is release in the form of electromagnetic radiations Visible light UV light, Xray, gamma ray are all electromagnetic radiations
- 2. Radiations break a chromosome by chemical reactions which requires energy. Mutagenic effect of radiation depends upon the type & amount of energy left in tissues Electromagnetic radiations energetic high energy radiations Visible light UV light X & Gamma leaves energy in High energy radiations form of heat & activations not only heat & Leaves energy in leads to chemical change activate but leave form of heat it is Energy in form of Less energetic ionization in cell Ionizing radiations penetrates deeper in cells than visible & UV light Imparting much energy to absorbing tissue to ionize atoms/molecules.
- 3. High energy wave moving at high speed is stopped it releases energy. This energy makes an atom to lose an e- & become charged or ion (process is known as ionization). Free moving electrons causes other atoms to lose electron & become +ly charged ions, two processes generate pairs of +ve & -ve charged ions A large number of ions may cluster together to form an ion track. These ions undergo chemical reactions to neutralize their charges to reach to stable configuration while doing so they produce breaks in chromosomes thus inducing mutations. Free ions may combine with O2 produce highly reactive chemicals which may also react with DNA & cause mutation. Ionizing radiations X ray & Gamma rays are energetic enough &produce reactive ions (charged atoms or molecules) when they react with biological molecules are referred as Ionizing radiations Term also includes corpuscular radiations Stream of atomic & subatomic particles emitted by radioactive elements (alpha & beta former He nuclei 2 protons & 2 neutrons ; later electrons. UV light not ionize but they react with DNA & other biological molecules.
- 5. Biological effects of Radiations Produce range of damage to cells /organisms mainly due to production of free radicles of water (hydroxyl group). These free radicles posses unpaired electrons& chemically very reactive interact with DNA, protein, lipids in cell membranes Xray cause DNA & protein damage –Organelle failure, block cell division & cause cell death rapidly dividing cell types (blood cells forming areas of bone marrow2, gastro- intestinal track lining are mostly affected by ionizing radiations & severity depends on dose received. A lot of information available on accidental exposure o nuclear plant 3 workers & victims of atomic bomb explosion such as those in Nagasaki & Hiroshima. Sub lethal (100-200 rems) ; lethal (350-450 rems); supra lethal (> 650 rems) Ionizing radiations produce a range of effects on DNA through free radicals & breaks in one or two strands (rearrangement or deletion of chromiosome).
- 6. Free e- directly interacts with either e- or OH- can cause DNA following types damage e- P+ H O ss Break H Deletion cross linking DS break Hydroge atom consist of 1e- & 1 H+ e- may interact with water to produce It is ionized OH free radicle which can damage the DNA in same way as e-
- 7. • Zirkle (1930) reported that plants nucleus is more sensitive to ionizing radiations than cytoplasm. Purines are less sensitive than pyrimidines • UV Light UV C UV B UV A (180-290nm) (290-320nm) (320-visible) Germicidal most Major lethal fraction deleterious effect Energetic & lethal mutagenic fraction of creates O2 radicles pro Absorbed by O3 layer sunlight duce few dimers
- 8. E Altenberg first to report that UV can cause mutation Longer WL can not penetrate deeply effect superficial layers DNA has absorption max at 260nm. Results in formation of pyrimidine dimers linked by C=C bonds