Dna as Primary Genetic Material

PRESENTED BYYADVEER SINGH

M PHARM 1ST YEARDEPT. OF PHARMACOLOGY

DHARWAD

INTRODUCTION:INTRODUCTION:• DNA is the functional unit of lifeDNA is the functional unit of life• That controls the cellular activity and growthThat controls the cellular activity and growth• Made up of many genesMade up of many genes• As long as molecular structure of gene was As long as molecular structure of gene was

unknown there was no way to think about unknown there was no way to think about gene-protein relationgene-protein relation

• DNA (genes) consist of DNA (genes) consist of Deoxyribonucleic Deoxyribonucleic acidacid

Some discovery in nucleic Some discovery in nucleic acids acids • Investigator Investigator

* Freidrich Miescher(1868) * Freidrich Miescher(1868) * Discovery : Isolated substance from pus celland called it * Discovery : Isolated substance from pus celland called it

nuclein.nuclein. * Altman (1889) : Named the substance nucleic acid.* Altman (1889) : Named the substance nucleic acid. * E. Chargaff (1950) :Discovered the equivalence in base * E. Chargaff (1950) :Discovered the equivalence in base

ratios in DNA. ratios in DNA. * R. Franklin and M.F.H. Wilkins (1952) : Studied x-ray * R. Franklin and M.F.H. Wilkins (1952) : Studied x-ray

diffraction and revealed that DNA has a helical structure.diffraction and revealed that DNA has a helical structure. * J.D.Watson, F.H.C. Crick (1953) : Proposed the double * J.D.Watson, F.H.C. Crick (1953) : Proposed the double

helical model for DNA. helical model for DNA.

DNADNA

It is defined as, long chain of poly nucleotide It is defined as, long chain of poly nucleotide sequence running anti parallel to each sequence running anti parallel to each other, two strands held by weak hydrogen other, two strands held by weak hydrogen bonds, which has capacity to self replication bonds, which has capacity to self replication and expression, which is responsible for the and expression, which is responsible for the trait and hereditary characters. DNA is a trait and hereditary characters. DNA is a macromolecule of a high molecular weight macromolecule of a high molecular weight of the order of millions of daltons. It is the of the order of millions of daltons. It is the mastermolecule of a biological system and mastermolecule of a biological system and forms the genetic material.forms the genetic material.

Location Of DNALocation Of DNA• DNA is sited on chromosomes (genes sitting side DNA is sited on chromosomes (genes sitting side

by side)by side)• Improvement in microscope made possible to see Improvement in microscope made possible to see

genesgenes• Isolation of pure chromosomes is much more Isolation of pure chromosomes is much more

informative about DNAinformative about DNA• DNA occurs in the central region of the spherical DNA occurs in the central region of the spherical

or polyhydral head of the virus or polyhydral head of the virus • In prokaryotes ,it occurs in the nucleoid as their In prokaryotes ,it occurs in the nucleoid as their

chromosome .chromosome .• In eukaryotic plant and animal cells the DNA In eukaryotic plant and animal cells the DNA

occurs in the chromosomes found in the nuclei. occurs in the chromosomes found in the nuclei. • DNA is normally found inside the nuclei of the DNA is normally found inside the nuclei of the

cells.cells.

Two Main Chromosomal Two Main Chromosomal Components Were Almost Components Were Almost Invariably FoundInvariably Found

1.1. A A Deoxyribonucleic acidDeoxyribonucleic acid (DNA) major (DNA) major constituent of nucleus so called nucleic constituent of nucleus so called nucleic acid (1869 by Fredric Miescher) acid (1869 by Fredric Miescher)

2.2. A small class of +vely charged proteins A small class of +vely charged proteins called called histones histones Basic in nature, neutralizes the acidity Basic in nature, neutralizes the acidity of nucleic acidof nucleic acid

• In 1920 DNA specific purple dye is In 1920 DNA specific purple dye is developed by Robert Feulgen ( sited on developed by Robert Feulgen ( sited on chromosome)chromosome)

Cells Contains Both RNA Cells Contains Both RNA As Well As DNAAs Well As DNA• Cells have a second kind of nucleic acid Cells have a second kind of nucleic acid

called RNAcalled RNA• RNA located primarily in the nucleus RNA located primarily in the nucleus

concentrated as a dense granules concentrated as a dense granules (Nucleoli)(Nucleoli)

• Found abundance in cytoplasm alsoFound abundance in cytoplasm also• Both DNA and RNA resemble proteins in Both DNA and RNA resemble proteins in

that they are constructed from many that they are constructed from many smaller building blocks linked end to endsmaller building blocks linked end to end

• Chemistry of DNA:- cemical analysis of DNA Chemistry of DNA:- cemical analysis of DNA has revealed the presence of three different has revealed the presence of three different chemical substances namely pentose sugars, chemical substances namely pentose sugars, phosphate groups and nitrogeneous bases.phosphate groups and nitrogeneous bases.

• Adenine pairs with Thymine with two Adenine pairs with Thymine with two hydrogen bonds (A=T) and Guanine pairs hydrogen bonds (A=T) and Guanine pairs with cytosine with three hydrogen with cytosine with three hydrogen bonds(G=C).This specific base pairing is bonds(G=C).This specific base pairing is called complementary base pairing.called complementary base pairing.

• Each nucleotide contains a phosphate Each nucleotide contains a phosphate group, sugar and purine or pyrimidine group, sugar and purine or pyrimidine basebase

• When nucleotide linked together in When nucleotide linked together in large number then called as large number then called as polynucleotidepolynucleotide

• The sugar for RNA was known to be The sugar for RNA was known to be different from that of DNAdifferent from that of DNA

• Two purines and two pyrimidines Two purines and two pyrimidines are found in both DNA & RNAare found in both DNA & RNA

Diameter of DNADiameter of DNA

• DNA has asymmetrical from its DNA has asymmetrical from its behavior in solutionbehavior in solution

• Direct measurement of DNA is possible Direct measurement of DNA is possible only with electronic microscopeonly with electronic microscope

• Shows many thousand Shows many thousand Å in length & Å in length & 20Å thickness20Å thickness

• All DNA molecules are unbranchedAll DNA molecules are unbranched• Each nucleotide base was just over 3 ÅEach nucleotide base was just over 3 Å

• The helix makes one complete turn at every 34A The helix makes one complete turn at every 34A along its length containing 10 nucleotides. The along its length containing 10 nucleotides. The distance between two nucleotides in a helix is distance between two nucleotides in a helix is 3.4A. The length of the DNA molecule varies from 3.4A. The length of the DNA molecule varies from chromosome to chromosome and species to chromosome to chromosome and species to species . The amount of DNA per nucleus of a species . The amount of DNA per nucleus of a species is measured in terms of picograms ex: in species is measured in terms of picograms ex: in human beings DNA per nucleus is 5.6 pg and total human beings DNA per nucleus is 5.6 pg and total length is 174cm(1 pg=31cm) length is 174cm(1 pg=31cm)

• Nucleosides are the combination of pentose Nucleosides are the combination of pentose sugar (deoxyribose) and base sugar (deoxyribose) and base

• Nucleotides are the combination of a pentose Nucleotides are the combination of a pentose sugar, a nitrogen base and a phosphate group.sugar, a nitrogen base and a phosphate group.

CharacteristicCharacteristic A-A-DNADNA

B-B-DNADNA

Z-Z-DNADNA

diameter (D)diameter (D) 2.6 2.6 nmnm

2.0 2.0 nmnm

1.8 1.8 nmnm

bp/turnbp/turn 1111 10.410.4 1212degrees rotation/bpdegrees rotation/bp +32.7+32.7 +34.6+34.6 -30.0-30.0

axial distance/turnaxial distance/turn 2.8 2.8 nmnm

3.4 3.4 nmnm

4.5 4.5 nmnm

axial distance axial distance between bpbetween bp

0.25 0.25 nmnm

0.33 0.33 nmnm

0.38 0.38 nmnm

DNA & RNA linked by 5’-3’ DNA & RNA linked by 5’-3’ phoshodiester bondsphoshodiester bonds

DNA Has Highly DNA Has Highly Regular ShapeRegular Shape• DNA chains are very regularDNA chains are very regular• Contains repeating nucleotide Contains repeating nucleotide

sequences sequences • 4 different bases can arrange any 4 different bases can arrange any

order along the back bone – order along the back bone – individualityindividuality

• Dry DNA appear irregular white fluffs Dry DNA appear irregular white fluffs of cottonof cotton

• With water becomes tachy and fibersWith water becomes tachy and fibers• x-ray studies of Para-crystalline x-ray studies of Para-crystalline

pattern chows helical configurationpattern chows helical configuration

The Double Helix Is Held By The Double Helix Is Held By H-bondingH-bonding

DNA Self ReplicationDNA Self Replication• makes an exact copy of itself. The copy is called the makes an exact copy of itself. The copy is called the

replica, and the process is called replication . replica, and the process is called replication . Whenever DNA replicates, it produces two daughter Whenever DNA replicates, it produces two daughter molecules which are identical to each other and also molecules which are identical to each other and also to the parent Occur prior to the cell division (S- phase)to the parent Occur prior to the cell division (S- phase)

• The parent strands forms template for the new strand The parent strands forms template for the new strand • Replication is semi-conservativeReplication is semi-conservative• During cell division the DNA molecule molecule.During cell division the DNA molecule molecule.• During replication, the two strands of DNA helix During replication, the two strands of DNA helix

unwind dueto the dissolution of hydrogen bonds at unwind dueto the dissolution of hydrogen bonds at specific sites called ORI (Origin of Replication) sites by specific sites called ORI (Origin of Replication) sites by the action of certain enzymes. The region at which the the action of certain enzymes. The region at which the DNA opens is called the eye or replication fork. DNA opens is called the eye or replication fork.

Replication Of DNAReplication Of DNA• A A topoisomerasetopoisomerase, which introduces , which introduces

negative supercoils negative supercoils • A A helicasehelicase, which unwinds and splits the , which unwinds and splits the

DNA ahead of the fork. Thereafter, single-DNA ahead of the fork. Thereafter, single-strand binding proteins (SSB) swiftly bind to strand binding proteins (SSB) swiftly bind to the separated DNA, the separated DNA,

• A A primaseprimase (in prokaryotes, RNA (in prokaryotes, RNA polymerase II), which generates an RNA polymerase II), which generates an RNA primer to be used in DNA replication. primer to be used in DNA replication.

• A DNA A DNA holoenzyme,holoenzyme, which in reality is a which in reality is a complex of enzymes that together perform complex of enzymes that together perform the "actual" replication, i.e., the the "actual" replication, i.e., the polymerization of nucleotides. polymerization of nucleotides. – DNA DNA polymerase Ipolymerase I

-- DNA -- DNA polymerase III polymerase III

Replication Of DNAReplication Of DNA

Super Coiled DNASuper Coiled DNA

DNA AS PRIMARY GENETIC DNA AS PRIMARY GENETIC MATERIALMATERIALGerm plasm theory proposed by august weisman in Germ plasm theory proposed by august weisman in

1904 states that the reproductive cell or gametes are 1904 states that the reproductive cell or gametes are the germ cell. These germ cell are carried to the the germ cell. These germ cell are carried to the descendents generation after generation. Later it was descendents generation after generation. Later it was belived that chromosomes present in the gametes belived that chromosomes present in the gametes carry and transmit the hereditary characters. carry and transmit the hereditary characters. Chomosomes cocatain nucleic acid and proteins. Chomosomes cocatain nucleic acid and proteins. Molecular biologists have proved that nucleic acids Molecular biologists have proved that nucleic acids located in the chromosomes are the hereditary located in the chromosomes are the hereditary materials and chromosomes are the vehicles of materials and chromosomes are the vehicles of heredity now Now it has been accepted that deoxyribe heredity now Now it has been accepted that deoxyribe nucleeic acid [DNA]is the geneticmaterial and the DNA nucleeic acid [DNA]is the geneticmaterial and the DNA forms genes which control all the activities of micro forms genes which control all the activities of micro organisms as well ashigher organisms.organisms as well ashigher organisms.

CONT…CONT…• The DNA carries the genetic The DNA carries the genetic

information form gereration to information form gereration to generation. This concept may be generation. This concept may be proved by a number of experiments proved by a number of experiments which will form 1.Direct avidences which will form 1.Direct avidences and 2.Indirect evidences.and 2.Indirect evidences.

1.DIRECT EVIDENCES 1.DIRECT EVIDENCES • Experiments on microorganism give Experiments on microorganism give

concrete direct evidence show that DNA concrete direct evidence show that DNA is the genetic material they are the is the genetic material they are the followingfollowing

• 1. Griffith’s bacterial transformation 1. Griffith’s bacterial transformation experiment experiment

• 2.Bacteriophase infection2.Bacteriophase infection• 3. Bacterial conjugation3. Bacterial conjugation• 4. Transduction.4. Transduction.

1.GRIFFITH’S BACTERIAL 1.GRIFFITH’S BACTERIAL TRANSFORMATION TRANSFORMATION EXPERIMENT.EXPERIMENT.Fredrick Griffith [1928] has reported a phenomenon Fredrick Griffith [1928] has reported a phenomenon in a bacteriumin a bacterium

Pneumococcus’ which is now known as genetic Pneumococcus’ which is now known as genetic bacterial transformation. It is a direct evidence to bacterial transformation. It is a direct evidence to show that DNA is the genetic material. There are show that DNA is the genetic material. There are two strains of pneumococcus bacteria.they are [i] two strains of pneumococcus bacteria.they are [i] virulent and [ii] avirulent.virulent and [ii] avirulent.

Virulent strains [pathogenic] have smooth [s] Virulent strains [pathogenic] have smooth [s] glistening polysaccharide capsules and cause glistening polysaccharide capsules and cause pneumonea diseases . The avirulent pneumonea diseases . The avirulent [nonpathogenic] stains of pneumococcus have duli, [nonpathogenic] stains of pneumococcus have duli, rough [R] appearance without capsule and are rough [R] appearance without capsule and are unable to cause pneumonia disease . Smooth and unable to cause pneumonia disease . Smooth and rough stains are genetically determined. Conti…rough stains are genetically determined. Conti…

CONT….CONT….• When the virulent strains are injected into the host. Mice When the virulent strains are injected into the host. Mice

they kill then by causing pncumonia. When avirulent they kill then by causing pncumonia. When avirulent strains are injected into mice, there is no effect and they strains are injected into mice, there is no effect and they do not cause the discase’ Heat killed virulent stain of do not cause the discase’ Heat killed virulent stain of pneumococcus is injected with a mixture of effect and it pneumococcus is injected with a mixture of effect and it does not cause the disease. When mice are injeted with does not cause the disease. When mice are injeted with a mixture of avirulent and heat killed virulent a mixture of avirulent and heat killed virulent pneumococcus bacteria, the mice die due to pneumonia.pneumococcus bacteria, the mice die due to pneumonia.

• BY conducting post mortom of dead mice it was found BY conducting post mortom of dead mice it was found out that, they ware killed because of the virulent out that, they ware killed because of the virulent bacteria from this result it is evedent that heat killed bacteria from this result it is evedent that heat killed virulent bacteria are responrible for the transformation virulent bacteria are responrible for the transformation of avirulent once into virulent once with smooth capsule. of avirulent once into virulent once with smooth capsule. Thenomenon of transformation is no as Griffith,s effect Thenomenon of transformation is no as Griffith,s effect or bacterial transformation.or bacterial transformation.

Griffith effectGriffith effectFig. 2.2: Frederick Griffith’s Transformation Experiment - 1928

“transforming principle” demonstrated with Streptococcus pneumoniae

Griffith hypothesized that the transforming agent was a “IIIS” protein.

Cont…Cont…• O.T. Avery, C.M.MC LEOD and M.MC Carthy [1944] O.T. Avery, C.M.MC LEOD and M.MC Carthy [1944]

identified that this permanent change in viruence identified that this permanent change in viruence is due to the transformation of a chemical is due to the transformation of a chemical substance, cell free extract of heat killed virulent substance, cell free extract of heat killed virulent strains also produces the same effect. When the strains also produces the same effect. When the extract treated with DNA ase, the transformation extract treated with DNA ase, the transformation property was lost. This is because, DNA ase property was lost. This is because, DNA ase enzyme destroys the DNA.The same extract enzyme destroys the DNA.The same extract treated with protease enzyme to remove the treated with protease enzyme to remove the protein, has the transformation ability . Thus it is protein, has the transformation ability . Thus it is proved directly that DNA is the genetic material in proved directly that DNA is the genetic material in pneumococci.pneumococci.

2. BACTERIOPHASE 2. BACTERIOPHASE INFECTION INFECTION • A. Hurshey and M.Chase 1952 by using A. Hurshey and M.Chase 1952 by using

radio active tracars provided a direct radio active tracars provided a direct proof that DNA is the genetic material proof that DNA is the genetic material in a bacteriophase bacteriophase is a in a bacteriophase bacteriophase is a virus infecting bacteria.virus infecting bacteria.T2T2 bacteriophase attacks the bacterium E bacteriophase attacks the bacterium E scherichia coil. scherichia coil.

• Conti…Conti…

Bacteriaophage InfectionBacteriaophage Infection

CONT…CONT…• This expriment based on the fact, expressed by Harriou This expriment based on the fact, expressed by Harriou

[1951], that virus as such never entry the bacteria; only the [1951], that virus as such never entry the bacteria; only the tail contacts the outer memorane of the bacteria.with the tail contacts the outer memorane of the bacteria.with the help of enzyme, the virus forms a hole through which viral help of enzyme, the virus forms a hole through which viral DNA flows into the host bacterial cells. DNA flows into the host bacterial cells.

• A groups of T2 phase was labelled with radioactive isotope A groups of T2 phase was labelled with radioactive isotope sulphur, sulphur, 8835 by growing them on E coli already labelled 35 by growing them on E coli already labelled

with with 8835 sulphur is a component of protein only;35 sulphur is a component of protein only;• Another group of same T2 phase was labelled with P32 by Another group of same T2 phase was labelled with P32 by

growing them on e. coli already labelled with P32 growing them on e. coli already labelled with P32 phosphorusis one of the components of DNA and not of phosphorusis one of the components of DNA and not of protein.protein.

CONT….CONT….• These two groups of labelled phages are allowed to These two groups of labelled phages are allowed to

infect separate cultures of E coli. After obtaining the infect separate cultures of E coli. After obtaining the first progeny in about 20 minutes, the daughter first progeny in about 20 minutes, the daughter phages are tested for radioactivity. Phages labelled phages are tested for radioactivity. Phages labelled with p32 showed radio active p32 in their with p32 showed radio active p32 in their daughter phages also. But phages labelled with s35 daughter phages also. But phages labelled with s35 showed no radioactivity in their daughter phages. showed no radioactivity in their daughter phages. This result indicates that DNA is the genetic material, This result indicates that DNA is the genetic material, which has been transmittedfrom the parent to the which has been transmittedfrom the parent to the daughter generation. But the labelled protein is not daughter generation. But the labelled protein is not passed on to the daughter phages, since protein coat passed on to the daughter phages, since protein coat has never entered the bacterium. has never entered the bacterium.

3. BACTERIAL CONJUGATION 3. BACTERIAL CONJUGATION • Bacterial conjugation gives direct evidence that the Bacterial conjugation gives direct evidence that the

DNA is the genetic material. Conjugation is a DNA is the genetic material. Conjugation is a process of temporary union of two bacteriafor the process of temporary union of two bacteriafor the trasfer of genetic material. Laderberg and Tatum trasfer of genetic material. Laderberg and Tatum [1946] found out that a f+[male] E. coli bacterium [1946] found out that a f+[male] E. coli bacterium conjugate with a F-[female] E.coli. F+ cell has a conjugate with a F-[female] E.coli. F+ cell has a double stranded circular DNA in the cytoplasm double stranded circular DNA in the cytoplasm called the plasmid. F- Cell has no such plasmid. called the plasmid. F- Cell has no such plasmid. After conjugation,through the newly formed After conjugation,through the newly formed conjugation tube one strandof the plasmid [DNA] is conjugation tube one strandof the plasmid [DNA] is trasmitted to the F- cell. This DNA converts the F- trasmitted to the F- cell. This DNA converts the F- cell in to F+ cell. Thus a female bacterium is cell in to F+ cell. Thus a female bacterium is converted in to a male bacterium. This proves that converted in to a male bacterium. This proves that DNA is the genetic material.DNA is the genetic material.

BACTERIAL CONJUGATION BACTERIAL CONJUGATION

4. TRANSDUCTION 4. TRANSDUCTION

Cont…Cont…Transduction is a process by which transfer of Transduction is a process by which transfer of

genetic material takes place from one genetic material takes place from one bacterium to the other. Some bacteria are bacterium to the other. Some bacteria are resistant to antibiotic Streptomycin and resistant to antibiotic Streptomycin and other bacteria are sensitive to this antibiotic. other bacteria are sensitive to this antibiotic. The resistace is due to the presence of The resistace is due to the presence of dominant gene in the chromosomal DNA of dominant gene in the chromosomal DNA of the bacteria. The sensitive bacteria do not the bacteria. The sensitive bacteria do not posses this dominant gege. posses this dominant gege.

Cont…Cont…• When the lysogenic bacteriophages grow on When the lysogenic bacteriophages grow on

streptomycin resistantbacteria, the viral DNA gets streptomycin resistantbacteria, the viral DNA gets a fragments of a bacterchromosomal DNA a fragments of a bacterchromosomal DNA containing the streptomycin resistant gege. When containing the streptomycin resistant gege. When these phages with a bit of bacterial chromosomes these phages with a bit of bacterial chromosomes are injected in to sensitive bacterial cells, the are injected in to sensitive bacterial cells, the sensitive bacteria receive the chromosomal DNA sensitive bacteria receive the chromosomal DNA containing the resistant gege from the phages. containing the resistant gege from the phages. Due to this trasfer of gege, the sensitive bacteria Due to this trasfer of gege, the sensitive bacteria become resistant to streptomycin.become resistant to streptomycin.

• This transmission of resistant is correlated with This transmission of resistant is correlated with the transfer of chromosomalDNA. Hence, DNA is the transfer of chromosomalDNA. Hence, DNA is consideredas the genetic materialconsideredas the genetic material. .

2. Indirect Eviderccs2. Indirect Eviderccs• Bacteria, viruses and other microorganisms Bacteria, viruses and other microorganisms

show direct evidences to prove that DNA is show direct evidences to prove that DNA is the genetic material. But higher organisms the genetic material. But higher organisms show only indirect evidences to support this show only indirect evidences to support this fact DNA is the genetic. The indirect fact DNA is the genetic. The indirect evidences to evidences to

• 1.Localization 4.Effect OF Mutagenes1.Localization 4.Effect OF Mutagenes• 2.Amount of DNA 5.Composition2.Amount of DNA 5.Composition• 3.Stability 6.Integrity 3.Stability 6.Integrity

1.LOCALZATION1.LOCALZATION• ALL Cells of the living organisms ALL Cells of the living organisms

have DNA paticularly located in the have DNA paticularly located in the chromosomos feulgen reaction is an chromosomos feulgen reaction is an evidence to show that major evidence to show that major component of chromosome is DNA component of chromosome is DNA which performs the duty of the which performs the duty of the genetic material.genetic material.

2.Amount of DNA2.Amount of DNA• THE quantity of DNA depnds on the number THE quantity of DNA depnds on the number

of chromosome and the sets of of chromosome and the sets of chromosomes. Sex cells have haploid chromosomes. Sex cells have haploid number of chromosomes.MALE And female number of chromosomes.MALE And female sex cells fuse together and become zygote sex cells fuse together and become zygote with diploid number of chromosomes. In with diploid number of chromosomes. In polyploid cells the amount of DNA increases polyploid cells the amount of DNA increases with the increase in the number of sets of with the increase in the number of sets of chromosomes The effect of extra chromosomes The effect of extra chromosomes such as Klinefelter’s chromosomes such as Klinefelter’s syndromes and 21 trisomy also prove that syndromes and 21 trisomy also prove that DNA is the genetic material.DNA is the genetic material.

3.Stability3.Stability• Studies on chromosomes reveal that Studies on chromosomes reveal that

genes are arranged in a linear manner in genes are arranged in a linear manner in all the chromosomer. Genes are nothing all the chromosomer. Genes are nothing but the series of polynucleotides. Genes but the series of polynucleotides. Genes are stable compounds. Genes are stable are stable compounds. Genes are stable compounds. Genes DNArepicate without compounds. Genes DNArepicate without committing any mistake in each and committing any mistake in each and every cell division. Even then stable every cell division. Even then stable rarely it changes causing mutations.rarely it changes causing mutations.

4.Effect of Mutagens4.Effect of Mutagens• Mutation may occur spontancously or Mutation may occur spontancously or

through the effect of mutagens such as through the effect of mutagens such as radiation, chemicals. Etc. mutations alter radiation, chemicals. Etc. mutations alter the chemical structur of DNA mutations the chemical structur of DNA mutations are inherited by the offspring, which are inherited by the offspring, which show phenotypic variations. These show phenotypic variations. These effects of mutagenes also give evidence effects of mutagenes also give evidence to the fact DNA is the genetic material.to the fact DNA is the genetic material.

5.composition5.composition• Structure of DNA is the same in all Structure of DNA is the same in all

microorganisms and other higher microorganisms and other higher organisms. composition of DNA is organisms. composition of DNA is similar in organisms of the same similar in organisms of the same species and they interbreed. It is species and they interbreed. It is different in organisms belonging to different in organisms belonging to different species and they do not different species and they do not interbreed.interbreed.

6.Integrity6.Integrity• DNA maintains integrity during cell DNA maintains integrity during cell

metabolism and also during embryonic metabolism and also during embryonic development of the organisms but due to development of the organisms but due to crossing over variations have been produced crossing over variations have been produced within the species. Mutation distrupts the within the species. Mutation distrupts the proper functioning of the DNA. The direct proper functioning of the DNA. The direct evidences of microorganisms and indirect evidences of microorganisms and indirect evidences of other higher organisms prove evidences of other higher organisms prove that DNA as the stable genetic material which that DNA as the stable genetic material which will survive in this biosphere with all sorts of will survive in this biosphere with all sorts of environmental hazards.environmental hazards.

FUNCTIONS OF DNAFUNCTIONS OF DNA• 1:DNA controls all the metabolic activities 1:DNA controls all the metabolic activities

of the cell directly or indirectly of the cell directly or indirectly • DNA synthesizes RNA and directs the DNA synthesizes RNA and directs the

synthesis of protein in the cytoplasm.synthesis of protein in the cytoplasm.• DNA can undergo mutation and DNA can undergo mutation and

recombination which are changes at the recombination which are changes at the genetic level.genetic level.

• The synthesis of RNA by DNA is called as The synthesis of RNA by DNA is called as transcription. This is called as the transcription. This is called as the heterocatalytic function .heterocatalytic function .

•