DNA REPLICATION
At first we gone look on Biochemical reaction for Dna Replication.
DNA archetype begins with the "unzipping" of the ancestor atom as the hydrogen bonds amid the abject pairs are broken. Once exposed, the arrangement of bases on anniversary of the afar strands serves as a arrangement to adviser the admittance of a commutual set of bases on the fiber actuality synthesized.The new strands are accumulated from deoxynucleoside triphosphates.Anniversary admission nucleotide is covalently affiliated to the "free" 3' carbon atom on the pentose (figure) as the additional and third phosphates are removed calm as a atom of pyrophosphate (PPi). The nucleotides are accumulated in the adjustment that complements the adjustment of bases on the fiber confined as the template.
Role of Enzymes......
A allocation of the bifold braid is unwound by a helicase. A atom of a DNA polymerase binds to one fiber of the DNA and begins affective forth it in the 3' to 5' direction, application it as a arrangement for accumulating a arch fiber of nucleotides and reforming a bifold helix. In eukaryotes, this atom is alleged DNA polymerase basin (δ). Because DNA amalgam can alone action 5' to 3', a atom of a additional blazon of DNA polymerase (epsilon, ε, in eukaryotes) binds to the added arrangement fiber as the bifold braid opens. This atom charge amalgamate alternate segments of polynucleotides (called Okazaki fragments). Another enzyme, DNA ligase I again stitches these calm into the backward strand.
Dna Replication is semi conservative.
When the archetype action is complete, two DNA molecules — identical to anniversary added and identical to the aboriginal — accept been produced. Anniversary fiber of the aboriginal atom has remained complete as it served as the arrangement for the amalgam of a commutual strand. This approach of archetype is declared as semi-conservative: one-half of anniversary new atom of DNA is old; one-half new. Watson and Crick had appropriate that this was the way the DNA would about-face out to be replicated. Proof of the archetypal came from the abstracts of Meselson and Stahl Follow this link to see the proof...http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/M/Meselson_Stahl.html
Another important point is the SPEED OF REPLICATION.
Among Bacteria
The distinct atom of DNA that is the E. coli genome contains 4.7 x 106 nucleotide pairs. DNA archetype begins at a single, anchored area in this molecule, the archetype origin, gain at about 1000 nucleotides per second, and appropriately is done in no added than 40 minutes. And acknowledgment to the attention of the action (which includes a "proof-reading" function), the job is done with alone about one incorrect nucleotide for every 109 nucleotides inserted. In added words, added generally than not, the E. coli genome (4.7 x 106) is affected after error!
Among Eukaryotes
The boilerplate animal chromosome contains 150 x 106 nucleotide pairs which are affected at about 50 abject pairs per second. The action would booty a ages (rather than the hour it absolutely does) but for the actuality that there are abounding places on the eukaryotic chromosome area archetype can begin. Archetype begins at some archetype origins beforehand in S appearance than at others, but the action is completed for all by the end of S phase. As archetype nears completion, "bubbles" of anew replicated DNA accommodated and fuse, assuredly basic two new molecules.
We now Look on Control of Replication....
With their assorted origins, how does the eukaryotic corpuscle apperceive which origins accept been already replicated and which still anticipate replication?
An observation: When a corpuscle in G2 of the corpuscle aeon is alloyed with a corpuscle in S phase, the DNA of the G2 basis does not activate replicating afresh alike admitting archetype is proceeding commonly in the S-phase nucleus. Not until mitosis is completed, can freshly-synthesized DNA be replicated again.
Two ascendancy mechanisms accept been articular — one absolute and one negative. This back-up apparently reflects the acute accent of absolute archetype to the candor of the genome.
It has two kind of controls a positive and a negative.
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INFORMATION ON DNA
Deoxyribonucleic acid (DNA) is a nucleic acid present in the cells of all living organisms. It is often referred to as the “building blocks of life,” since "DNA" encodes the genetic material which determines what an organism will develop into. In addition to maintaining the genetic blueprints for its parent organism, DNA also performs a number of other functions which are critical to life.
This nucleic acid was first identified in 1889, when researcher Friedrich Miescher found a substance he called “nuclein” in human cells. In the early 20th century, several researchers including Phoebus Levene and William Astbury performed additional research on nuclein, beginning to understand its components, structure, and role in life. A seminal article published in Nature in 1953 by James Watson and Franklin Crick is often cited as the breakthrough moment in DNA research, as it correctly posited the distinct structure of DNA, with significant help from scientist Rosalind Franklin.
- DNA stands for deoxyribonucleic acid.
- DNA is allotment of our analogue of a active organism.
- DNA is begin in all active things.
- DNA was aboriginal abandoned in 1869 by Friedrich Miescher.
- James Watson and Francis Crick ample out the anatomy of DNA.
- DNA is a bifold helix.
- The anatomy of DNA can be likened to a askance ladder.
- The rungs of the ladder are fabricated up of “bases”
- Adenine (A) is a base.
- Thymine (T) is a base.
- Cytosine (C) is a base
- Guanine (G) is a base.
- A consistently pairs with T in DNA.
- C additionally pairs with G in DNA.
- The bulk of A is according to the amoun tof T, aforementioned for C and G.
- A+C = T+G
- Hydrogen bonds authority the bases together.
- The abandon of the DNA ladder is fabricated of sugars and phosphate atoms.
- Bases absorbed to a sugar; this circuitous is alleged a nucleoside.
- Sugar + phosphate + abject = nucleotide.
- The DNA ladder usually twists to the right.
- There are abounding conformations of DNA: A-DNA, B-DNA, and Z-DNA are the alone ones begin in nature.
- About all the beef in our anatomy accept DNA with the barring of red claret cells.
- DNA is the “blueprint” of life.
- Chromosomal or nuclear DNA is DNA begin in the basis of cells.
- Bodies accept 46 chromosomes.
- Autosomal DNA is allotment of chromosomal DNA but does not accommodate the two sex chromsomes – X and Y.
- One chromosome can accept as little as 50 actor abject pairs or as abundant as 250 actor abject pairs.
- Mitochondrial DNA (mtDNA) is begin in the mitochondria.
- mtDNA is alone anesthetized from the mother to the adolescent because alone eggs accept mitochondria, not sperm.
- There’s a archetype of our absolute DNA arrangement in every corpuscle of our anatomy with one exception.
- Our absolute DNA arrangement is alleged a genome.
- There’s an estimated 3 billion DNA bases in our genome.
- One actor bases (called a megabase and abbreviated Mb) of DNA arrangement abstracts is about agnate to 1 megabyte of computer abstracts accumulator space.
- Our absolute DNA arrangement would ample 200 1,000-page New York City blast directories.
- A complete 3 billion abject genome would booty 3 gigabytes of accumulator space.
- If unwound and angry together, the strands of DNA in one corpuscle would amplitude about six anxiety but would be alone 50 trillionths of an inch wide.
- In humans, the DNA atom in a non-sex corpuscle would accept a absolute breadth of 1.7 metres.
- If you bare all the DNA you accept in all your cells, you could ability the moon 6000 times!
- Our sex cells–eggs and sperm–have alone bisected of our absolute DNA.
- Over 99% of our DNA arrangement is the aforementioned as added humans’.
- DNA can self-replicate application cellular accouterment fabricated of proteins.
- Genes are fabricated of DNA.
- Genes are pieces of DNA anesthetized from ancestor to baby that accommodate ancestral information.
- The boilerplate gene is 10,000 to 15,000 bases long.
- The articulation of DNA appointed a gene is fabricated up of exons and introns.
- Exons accept the cipher for authoritative proteins.
- Introns are amid sequences sometimes alleged “junk DNA.”
- Junk DNA’s action or abridgement thereof is a antecedent of debate.
- Allotment of “junk DNA” advice to adapt the genomic activity.
- There are an estimated 20,000 to 25,000 genes in our genome.
- In 2000, a asperous abstract of the animal genome (complete DNA sequence) was completed.
- In 2003, the final abstract of the animal genome was completed.
- The animal genome arrangement generated by the clandestine genomics aggregation Celera was based on DNA samples calm from bristles donors who articular themselves alone by chase and sex.
- If all the DNA in your anatomy was put end to end, it would ability to the sun and aback over 600 times (100 abundance times six anxiety disconnected by 92 actor miles).
- It would booty a being accounting 60 words per minute, eight hours a day, about 50 years to blazon the animal genome.
- scientist 09If all three billion belletrist in the animal genome were ample one millimeter apart, they would ability a acme 7,000 times the acme of the Empire State Building.
- DNA is translated via cellular mechanisms into proteins.
- DNA in sets of 3 bases, alleged a codon, cipher for amino acids, the architecture blocks of protein.
- Changes in the DNA arrangement are alleged mutations.
- Abounding affair can account mutations, including UV betterment from the sun, chemicals like drugs, etc.
- Mutations can be changes in aloof one DNA base.
- Mutations can absorb added than one DNA base.
- Mutations can absorb absolute segments of chromosomes.
- Distinct nucleotide polymorpshisms (SNPs) are distinct abject changes in DNA.
- Abbreviate bike repeats (STRs) are abbreviate sequences of DNA again consecutively.
- Some genitalia of the DNA arrangement do not accomplish proteins.
- Genes accomplish up alone about 2-3% of our genome.
- DNA is afflicted by the environment; ecology factors can about-face genes on and off.
- There are abounding means you can assay your DNA application commercially accessible tests.
- Paternity tests assay segments of DNA amid the abeyant ancestor and child.
- There are added types of accord testing that compares DNA amid siblings, grandparents and grandchild, etc.
- DNA tests can advice you accept your accident of disease.
- A DNA alteration or aberration may be associated with a college accident of a cardinal of diseases, including breast cancer.
- DNA tests can advice you accept your ancestors history aka abiogenetic genealogy.
- DNA tests can advice you accept your indigenous make-up.
- DNA can be extracted from abounding altered types of samples: blood, audacity cells, urine.
- DNA can be stored either as beef on a affection swab, buccal brush, or arctic claret or in extracted form.
- In forensics, DNA assay usually looks at 13 specific DNA markers (segments of DNA).
- The allowance that two individuals will accept the aforementioned 13-loci DNA contour is about one in one billion.
- A DNA fingerprint is a set of DNA markers that is different for anniversary alone except identical twins.
- Identical twins allotment 100% of their genes.
- Ancestors allotment 50% of their genes.
- A ancestor and adolescent allotment 50% of their genes.
- You can abstract DNA at home from bake-apple and alike your own audacity cells.
- DNA is acclimated to actuate the full-blooded for livestock or pets.
- DNA is acclimated in wildlife forensics to assay endangered breed and bodies who coursing them (poachers).
- DNA is acclimated in assay victims of accidents or crime.
- DNA is acclimated to absolve innocent bodies who’ve been abominably convicted.
- Abounding countries, including the US and UK, advance a DNA database of bedevilled criminals.
- The CODIS databank (COmbined DNA Index System) is maintained by the BI and has DNA profiles of bedevilled criminals.
- Polymerase alternation acknowledgment (PCR) is acclimated to amplify a sample of DNA so that there are added copies to analyze.
- We eat DNA every day.
- DNA testing is acclimated to accredit aliment like caviar and accomplished wine.
- DNA is acclimated to actuate the abstention of crops.
- Genetically adapted crops accept DNA from addition animal amid to accord the crops backdrop like annoyance resistance.
- Dolly the cloned sheep had the aforementioned nuclear DNA as its donor mom but its mitochondrial DNA came from from the egg mom. (Does that accomplish any sense?)
- Bodies like to allocution about DNA alike if it bears no affiliation to science or reality.
- A accumulation of bloggers who address consistently about DNA and analysis accept affiliated to gether to anatomy The DNA Network.
- Lists about DNA can get a little boring.
Messenger RNA Synthesis
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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DNA GENE DECODING SITES
While these adaptation sites accommodate the befalling for DNA Acceptance Networking, that seems to be a by-product of their capital function, which is to break your DNA. For the acceptance world, casework like this accept amazing implications, including:
(i) In the majority of adoptions in the world, there is little or no advice about the bearing father. This includes calm adoptions, as able-bodied as adoptions from added genitalia of the world. Adaptation your child's DNA will accommodate you with cogent advice about the bearing ancestor and the bearing mother. The websites affirmation they acquiesce you to attending 20 or 40 years into the approaching at cogent DNA markers that will affect your child's bloom (such as pre-disposition to assertive diseases).
(ii) Once registered with some sites, you will be automatically brash over the abutting 10, 20 or 30 years, as medical science makes new discoveries and advances.
(iii) In some situations DNA adaptation may become accessible as allotment of pre-adoption medical and amusing advice about the child. Currently, parents accept bound medical information, photographs, and sometimes a video. Perhaps in the approaching a DNA besom will become allotment of this pre-adoption advice package.
(iv) As countries become added careful about whom may accept their accouchement (such as China) will they demand DNA tests of the adopting parents? Adopting Parents already accept to accumulation medical and lab letters as allotment of a abstracts for all-embracing adoption. Are DNA letters next?
These websites will accompany abundant opportunities, but additionally abundant quandaries. We will no best accept the botheration of not knowing, but instead accept the accountability of whether we demand to apperceive in the aboriginal place. We will apperceive whether our accouchement are agreeable to assertive ancestry or talents, athletics, music or languages, and we'll animate them to accompany assertive paths. I accept afresh declared these websites to clients, accompany and relatives. It is absorbing how abounding bodies accept said, "But do you absolutely demand to apperceive this information?". Clearly, some bodies would rather not apperceive and aloof let the approaching unfold.
This is a web-based account that helps you accept your DNA. Send in a sample of your child's saliva and see how the decoded genes announce your child's future. This armpit is partly adjourned by Google. The amount for a DNA assay is $999, and you will accept a address allegory about 600,000 DNA checkpoints.
At this time their account is alone accessible in the USA, Europe and Canada, although it will aggrandize in the approaching to added countries. In acknowledgment to my catechism to this armpit as to whether adopting parents could use it to accept the DNA decoded for a adolescent proposed to them for adoption, the acknowledgment was "Our account is not advised to be acclimated for abiogenetic screening purposes."
Doug Chalke
Executive Director
Sunrise Family Services Society
Vancouver, February, 2008
www.SunriseAdoption.com
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WHAT IS PROTEIN SYNTHESIS ????
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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CANCER DUE TO RADIATION EFFECTS ON DNA
Large doses of radiation to ample numbers of bodies are bare in adjustment to account assessable increases in the cardinal of cancers and appropriately actuate the differences in the acuteness of altered organs to radiation. Because the cancers can action anytime in the apparent person's lifetime, these studies can booty seventy years or added to complete. For example, the better and scientifically best admired epidemiologic abstraction of radiation furnishings has been the advancing abstraction of the Japanese diminutive bomb survivors. Added important studies accommodate studies of ample groups apparent to radiation as a aftereffect of their activity (such as uranium miners) or as a aftereffect of medical treatment. These types of studies are discussed in greater detail in the area blue-blooded "How Do Scientists Actuate the Long-Term Risks from Radiation?"
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HOW LONG DOES RADIATION AFFECTS THE DNA????
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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RADIATION EFFECTS ON DNA DUE TO EFFECT OF IONIZING RADIATION AND CADMIUM
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.
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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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