The impact of Gamma Ray on DNA molecule

The aim of this review is to provide an overview concerning the effect of one type of ionization radiation (e.g. gamma ray) on DNA considering three axes. The fi rst one considers defi ning gamma ray, sources of gamma ray and interaction of gamma ray with matters. The second axis focuses on the DNA in term of , while the third one clarify the health effects of the gamma ray with different doses on DNA of human cells. Focusing on the DAN molecule in this review because its importance in two sides. First, the DNA of the human cell is responsible of the function of the specifi c type of that cell of a given organ. Second, it is responsible of the transferring the gigantic information across new generations.


Introduction
Ionizing radiations, in general, can lead to a similar effect at the cellular level. However, due to that alpha and beta particles are relatively classifi ed as non-penetrating radiations, the external exposure to such kind of radiation can results in only localized damage to include radiation burns to the skin as an example [1]. By contrast, the gamma radiation and neutrons are most penetrating when compared with alpha and beta radiations, then causing a diffuse damage in the body. The types of damage include radiation sickness, damage of DNA, cell death resulting from the damaged DNA, cancer incidence rather than burns only. In this regards, distinguishing the external exposure from that of internal exposure to radiation is necessary. This is due to the ingested or inhaled radioactive substances depending on the chemical nature of substances that can produce both diffuse and localized internal damage [2,3]. Tissue cancer has received the most scientifi c attention among those effects that the radiation might cause. In this regards, it is well established that radiation, especially the ionizing ones, can destroy the DNA, hence causing cancer and genetic mutations. However, it should be noted that when an individual has induced cancer following a radiation exposure, this depends on the types of damage that the DNA experienced, and also on what portion within the DNA has damaged. Furthermore, it should be considered that the cell line can replicate or not, and the damage is fully fi xed, the cell accomplishes the transformations that has the ability to produce the malignancy, how fast the latent cancer improves, in uterus, humans that exposed to high levels of background radiation, nuclear workers, patients exposed to radiation from therapeutic or diagnostic radiations, and also people exposed to radiation from nuclear weapons [3]. The radiation effects on the biomolecules and the DNA in specifi c can be classifi ed into two categories. The fi rst one is the direct effect and then the second one is the indirect effect. The direct one is resulted from the interaction of radiation itsef directly with the biomolecule. But, the indirect effect can be caused from the interaction of radiation with water molecules existed around the DNA. This would lead to what is known by water hydrolysis. This hydrolysis can yield different types of chemical products. Some of these are known by free radicals while the others which are very toxic such hydrogen peroxide (H 2 O 2 ). The free radical are very dangerous due their very high reactivity with the surrounding molecules and therefore change their biological and chemical functions [4,5]

Gamma-ray
The gamma ray can be defi ned as an electromagnetic radiation with an extremely high frequency and therefore of high energy. Generally, it is an ionizing radiation; hence it is a biologically hazardous radiation. Gramm ray are produced, classically, via the decay of unstable nuclei of atoms as they are experiencing a transition from the high energy to a lower energy state that known as gamma ray disintegration/decay. However, gamma ray may also be produced through other processes. The emission of a particle from the nucleus with excited state, gamma ray is emitted. The gamma rays are carrying the excess energy of the partially excited nucleus after a disintegration event occurs. These rays are with a discrete energy and this is characteristic to the specifi c nuclide considered. So, the corresponding energies can be used for purposes of elements characterization. The gamma-rays are charge less; this means that they do not interact with electrostatic forces as in that of charged particles, which lead to ionization of atoms directly along their path of travel [6,7].

Human DNA
The DNA or Deoxyribonucleic acid is a biological molecule that comprises the required guidelines for any creature to emerge, grow, live and proliferate. The aforementioned instructions are exist within every cell, and these are handed down from the fathers and mothers to their children [8].
The DNA is generally consisted of certain molecules that known by nucleotides. Every nucleotide comprises a phosphate body, a sugar group together with a nitrogen base. The nitrogen bases are broken down into four types as follows: adenine (A), thymine (T), guanine (G) and cytosine (C) (Figure 1). These bases are built in such order that determines instructions of the DNA, or what is known by the genetic code. The shape of nitrogen structures in a DNA sequence forms genes is resemble to the order of alphabetical letters which can be used to create a word. The latter can be considered as the language of the cell in which it informs the cells how to produce proteins. In this regards, other genre of nucleic acid, which is the ribonucleic acid, or what is known by 'RNA'? The role of it is to transmit the genetic information from DNA into proteins [9].

Characteristics of DNA damage by radiation exposure
As is was mentioned earlier in this review, the ionizing radiations can directly impact the cellular components or indirectly which impacts the water molecules fi rst. This consequently can cause water-derived free radicals. The

Conclusion
Ionizing radiation such that of gamma rays is absolutely hazardous to human beings specifi cally for those who are in direct contact may be due to their jobs or their health status. This of course due to the high penetration power the gamma ray had. The cell contain a very sensitive biomolecule which the DNA. This DNA is a very critical molecule then efforts must be placed to protect it from being exposed to unnecessary radiation to avoid cancer incidence as one consequences of that exposure.