During transcription, RNA polymerase makes a copy of a gene from the DNA to mRNA as needed. This process is similar in eukaryotes and prokaryotes. One notable difference, however, is that prokaryotic RNA polymerase associates with mRNA processing enzymes during transcription so that processing can proceed quickly after the start of transcription. The short-lived, unprocessed or partially processed, product is termed pre-mRNA; once completely processed, it is termed mature mRNA.
Messenger ribonucleic acid, commonly called messenger RNA or mRNA, is an RNA molecule that encodes a chemical "blueprint" for the synthesis of a protein. Messenger RNA contains a copy of the genetic data contained on a strand of DNA. Ribosomal ribonucleic acid (ribosomal RNA or rRNA) helps to form the ribosome itself.
Same like messenger RNA (mRNA), ribosomal RNA does not transmit genetic information. Instead of this it combines with proteins to create a structure that systematically transforms mRNA into proteins.

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Hi This is all about protein synthesis.........

Protein amalgam is the action by which alone beef assemble proteins. Both deoxyribonucleic acerbic (DNA) and all types of ribonucleic acerbic (RNA) are complex in this process. Enzymes in the cell's basis activate the action of protein amalgam by unwinding the bare breadth of DNA, so that RNA can be made. The RNA forms as a archetype of one ancillary of the DNA strand, and is beatific to added areas of the corpuscle to aid in the bringing calm of altered amino acids that anatomy proteins. Protein amalgam is so alleged because proteins are "synthesized" through automated and actinic processes in the cell.

Once the fiber of RNA has been fabricated in the nucleus, it is alleged agent RNA (mRNA). The mRNA exits the basis through tiny openings alleged nuclear pores, and moves into the beyond breadth of the cell, accepted as the cytoplasm. Once it exits the nucleus, the mRNA is fatigued against a anatomy accepted as a ribosome, which serves as the cell's assignment base for protein synthesis. At this point, alone one sub-unit of the ribosome is present.

As the mRNA binds to the ribosome sub-unit, it triggers the access of addition fiber of RNA, alleged alteration RNA (tRNA). The tRNA fiber looks for the able abode to bind to the mRNA, and back it finds it, it attaches to the mRNA, while captivation an amino acerbic on one end. Back this occurs, the added sub-unit of the ribosome arrives to anatomy a complete structure. As the ribosome surrounds the strands of RNA, addition fiber of tRNA approaches. This fiber is accustomed addition amino acid, and is altered from the first. Again, the tRNA looks for the able abode to bind to the mRNA.

When the additional fiber of tRNA is in abode with its amino acid, the two amino acids bind calm with advice from the ribosome, as able-bodied as cellular activity in the anatomy of adenosine triphosphate (ATP). This arrangement repeats itself, and the alternation of amino acids grows longer. Back the amino acids accept all been placed in the actual sequence, the alternation folds into a three-dimensional shape. Back this has occurred, the protein is complete.

Once the protein has been auspiciously made, the two sub-units of the ribosome separate, to be abutting afresh for after use. The action of protein amalgam takes abode in abundant ribosomes throughout the cell. A corpuscle which is operating calmly can amalgamate hundreds of proteins every second.

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HI....TO THIS WE KNOW THAT FOR HOW LONG THE RADIATION HAVE ITS EFFECTS ON DNA.

The aftereffect of the radiation may not be to annihilate the cell, but to adapt its DNA cipher in a way that leaves the corpuscle animate but with an absurdity in the DNA blueprint. The aftereffect of this alteration will depend on the attributes of the absurdity and back it is read. Since this is a accidental process, such furnishings are now alleged stochastic.[100] Two important academic furnishings of radiation are cancer, which after-effects from mutations in nongerm beef (termed actual cells), and ancestral changes, which aftereffect from mutations in antibody beef (eggs and sperm).

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Ionizing radiation, by definition, "ionizes," that is, it pushes an electron out of its apogee about an diminutive nucleus, causing the accumulation of electrical accuse on atoms or molecules. If this electron comes from the DNA itself or from a adjoining atom and anon strikes and disrupts the DNA molecule, the aftereffect is alleged absolute action. This antecedent ionization takes abode actual quickly, in about 0.000000000000001 of a second. However, today it is estimated that about two-thirds of the accident acquired by x application is due to aberrant action. This occurs back the absolved electron does not anon bang the DNA, but instead strikes an accustomed baptize molecule. This ionizes the baptize molecule, eventually bearing what is accepted as a chargeless radical. A chargeless abolitionist reacts actual acerb with added molecules as it seeks to restore a abiding agreement of electrons. A chargeless abolitionist may alluvion about up to 10,000,000,000 times best than the time bare for the antecedent ionization (this is still a actual abbreviate time, about 0.00001 of a second), accretion the adventitious of it abolition the acute DNA molecule. This additionally increases the achievability that added substances could be alien that would abrogate chargeless radicals afore they do damage.

Neutrons act absolutely differently. A fast neutron will bypass orbiting electrons and occasionally blast anon into an diminutive nucleus, animadversion out ample particles such as alpha particles, protons, or beyond bits of the nucleus. The best accepted collisions are with carbon or oxygen nuclei. The particles created will themselves again set about ionizing adjacent electrons. A apathetic neutron will not accept the activity to beating out ample particles back it strikes a nucleus. Instead, the neutron and the basis will animation off anniversary other, like billiard balls. In so doing, the neutron will apathetic down, and the basis will accretion speed. The best accepted blow is with a hydrogen nucleus, a proton that can accelerate or ionize electrons in adjacent atoms.

Effect of cadmium administration (3 mg CdCl2/kg body weight i.p.) and/or whole-body

irradiation (3 Gy of gamma rays) on the rat brain was studied in the course of 21 d after

treatment. The effect was studied on the basis of quantitative analyses of DNA and RNA. It was

found that the changes of nucleic acids in the brain hemispheres were very slight and they lay in

a temporal decrease in DNA content on the 7th – 14th d after the irradiation alone and in

combination with cadmium (CdCl2 administered 30 min before irradiation). In the cerebellum,

the changes of nucleic acids were more profound than in the hemispheres. The decrease in DNA

content in the cerebellum was also only temporal and it occurred on the 1st d after the irradiation

alone. The most interesting finding seems to be the increase in DNA content in the cerebellum in

a later period after the irradiation alone and in combination with cadmium without concomitant

increase in RNA content. This finding suggests increasing number of cells with high

nucleoplasmic ratio (mainly glial elements) in the rat cerebellum in a later period after

irradiation. In general, effect of cadmium administration on the rat brain was less expressed than

effect of irradiation and combination of the two treatments did not induce any summation effect.

Key words: rat, brain, cadmium, gamma radiation, DNA, RNA.

Cadmium is a highly toxic heavy metal with half-life time of about 10 years in

human beings. It accumulates predominantly in the kidneys as well as in liver, which

are the critical target organs (2, 19). Biological role of cadmium in an animal organism

is unknown (9). It is designated as a carcinogen in humans and rodents (20, 23).

However, the concentrations of Cd required to induce overt DNA damage are usually

very high (4, 5, 16). The damage of nucleic acids is due to direct or indirect effects of

cadmium (7). Cadmium induces, for example, an oxidative DNA damage leading to

DNA strand-breaks, DNA-protein cross-linking and inhibition of DNA repair.

128

The effects of ionizing radiation on DNA have been studied in detail for many

years (3, 6, 10, 15, 18, 11, 24). A lot of physical-chemical changes of DNA (e.g.

chemical changes of bases, breaks of phosphodiester bonds in one or both chains of

DNA) were found. Similarly to cadmium, these changes were caused by a direct or

indirect (mediated by reactive free radicals) effects of radiation. In the proliferatively

active tissues, such as haemopoietic and lymphoid tissues and regenerating liver, the

most striking effects of ionizing irradiation include inhibition of DNA synthesis and

mitosis and increase in the number of chromosome abnormalities. Due to the lack of

literature data concerning the influence of cadmium and ionizing radiation on nonproliferating

mammalian tissues, the cytotoxic effects of cadmium and gamma

radiation (alone or in combination) on the rat brain were studied in this model

experiment. The effects were evaluated on the basis of quantitative changes of DNA

and RNA because they can serve as an integral index of damage and recovery of cells

after the insults.

Material and Methods

The experiments were performed on 80 male rats of the SD strain (Anlab

Praha, Czech Republic). The animals were 6 weeks old at the beginning of the

experiments. They were kept under standard vivarium conditions (temperature 22 -

24°C, natural light rhythm), and had access to food and water ad libitum. The animals

were divided into four groups:

- non-treated control rats (C)

- rats treated with cadmium (Cd)

- rats irradiated with gamma rays (Ir)

- rats treated with cadmium 30 min before irradiation (Cd+Ir).

In this experiment, all animals survived. In the previous experiments, by the

use of the same doses of cadmium and ionizing radiation, but realised on younger rats

and in another year season, mortality of 5-10 % of animals was recorded.

Cadmium administration. Cadmium (CdCl2, Lachema Brno, Czech

Republic) was administered i. p. in the dose of 3 mg/kg alone or 30 min before

irradiation (groups Cd and Cd+Ir, respectively).

Irradiation. Animals were whole-body irradiated with the dose of 3 Gy by

gamma rays from a 60Co source (Chisostat Chirana, Czech Republic) at a dose rate of

0.150 Gy.min-1 (groups Ir and Ir+Cd). Doses of cadmium and gamma radiation were

chosen from the wide range of doses on the basis of the results of preliminary

experiments. They appeared to be the highest tolerable doses (as to the survival of rats)

inducing clearly demonstrable biochemical changes in the rat brain.

Determination of RNA and DNA. The animals (6 in each group) were

sacrificed 1, 7, 14 and 21 d after treatment. The brain was immediately excised in toto

and weighed. It was divided into the hemispheres and cerebellum (without truncus

cerebri), because distinct findings were expected due to some differences in structure

and function of these main parts of the brain. RNA and DNA determinations were

carried out according to the method of Tsanev and Markov (22). Tissue samples (in

duplicates) were homogenized in 5% trichloracetic acid solution and then deproteinized

and purified by washing with methanol, chloroform-methanol, benzene and ether. The

separation of RNA and DNA was carried out by consecutive hydrolyses in alkaline

129

(1 M KOH) and acid (0.2 M HClO4) solutions, respectively. The concentration of RNA

and DNA in the hydrolysates was determined by spectrophotometric measurements

(Hitachi, Tokio, Japan) at two wavelengths (RNA at 260 and 286 nm and DNA at 268

and 284 nm).

Statistical analysis. The experimental data were statistically evaluated by

Peritz´ F-test (12) at P≤ 0.05 and P ≤ 0.01 level of significance and they are given as

mean ± S.E.M .

Results

Hemispheres. No significant changes in RNA concentration and total content

were found in the hemispheres of rats exposed to cadmium and/or radiation comparing

to the control rats (Fig. 1). The decrease in DNA concentration in experimental rats

was not statistically significant (Fig. 2). The mean values of total DNA content

decreased after gamma irradiation (Ir) on the 7th d and after combined treatment with

cadmium and gamma irradiation (Cd+Ir) also on the 14th d of the treatment. Changes in

concentration and total content of DNA in experimental rats (Ir and Cd+Ir) were timedependent.

The application of cadmium alone did not cause any significant changes in

DNA in the rat hemispheres. As presented in Table 1, after cadmium administration or

irradiation alone (Cd, Ir) there was a tendency to some increase in the weight of rat

hemispheres. The effect of combined cadmium and radiation treatment (Cd+Ir) on the

weight of hemispheres was rather opposite.

Cerebellum. Cadmium and radiation alone or in the combination (Cd, Ir and

Cd+Ir) induced marked changes in the concentration of RNA in the cerebellum of rats.

As it follows from Fig. 3, statistically significant decrease in RNA concentration in

comparison to control rats was observed after 21 d of treatment. However, decrease in

RNA concentration was not accompanied by adequate decrease in total RNA content in

the organ. The concentration and content of DNA in the cerebellum (Fig. 4)

significantly decreased only 1 d after irradiation (Ir). Later, however, increase in DNA

concentration and especially in DNA content was found in the cerebellum of irradiated

rats of the groups Ir and Cd+Ir. After all treatments (Cd, Ir and Cd+Ir), marked

enhancement of the cerebellum weight was observed mainly in later stages of the

examination

Discussion

The results of the present study indicated that the quantitative changes of RNA

in the brain hemispheres and cerebellum of cadmium treated and/or gamma-irradiated

rats were less expressed than changes of DNA.

In the hemispheres, no quantitative changes of RNA occurred; changes of

DNA manifested themselves in a temporary decrease in total content of DNA in

irradiated rats of the groups Ir and Cd+Ir. We suppose that in both groups, the decrease

in DNA content on the 7th d was caused mainly by irradiation; additional cadmium

administration (Cd+Ir) resulted in extension of the decrease till the 14th d. The DNA

content is considered to be the best biochemical index of cellularity (1), hence, these

results indicate some loss of cells due to apoptosis. Apoptosis of cells is connected with

fragmentation of DNA and following loss of DNA. It seems, therefore, that effects of

irradiation alone and in combination with cadmium imitate process of cell senescence

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