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Nucleic Acid DNARNA Nucleic Acids are the polymers of nucleotides. Nucleotides are the combination of Nucleosides+ Phosphate Nucleosides = Nitrogenous.

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Presentation on theme: "Nucleic Acid DNARNA Nucleic Acids are the polymers of nucleotides. Nucleotides are the combination of Nucleosides+ Phosphate Nucleosides = Nitrogenous."— Presentation transcript:


2 Nucleic Acid DNARNA Nucleic Acids are the polymers of nucleotides. Nucleotides are the combination of Nucleosides+ Phosphate Nucleosides = Nitrogenous Base + Pentose Sugar

3 Nitrogen Base A GC TU Purines Pyrimidines + Deoxyribose pentose sugar DNA + Ribose Pentose Sugar RNA AT G C A= Adenine G = Guanine T = Thymine C = Cytosine U = Urasil Phosphate + + Phosphate

4 Duplex DNA  H bond– DNA Strand<----- Polymer Nucleotide Nucleoside Phosphate Nitrogen Base A G C T/UT/U Pentose Sugar Deoxyribose Ribose

5 What is Genetic Engineering??? Genetic engineering: The manipulation of genetic makeup of living cells by inserting desired gens through a DNA vector is known as genetic engineering. Genetic Engineering involves: removing a gene (target gene) from one organism inserting target gene into DNA of another organism ‘cut and paste’ process. Gene : Small piece of DNA OR hereditary unit consisting of sequence of DNA

6 Alternative names for genetic engineering: Genetic Manipulation Genetic Modification Recombinant DNA Technology Gene Splicing Gene Cloning

7 Genetically Modified Organism (GMO): is the organism with the altered DNA.


9 This goat contains a human gene that codes for a blood clotting agent. The blood clotting agent can be harvested in the goat’s milk.

10 How It Is Done??? 1.Preparation Of Desired Gene 2.Isolation of DNA vector 3.Construction of Recombinant DNA (rDNA) 4.Introduction of rDNA in to host cells 5.Selection and multiplication of recombinant host cells. 6.Expression of cloned gene.

11 A Bacterial Cell

12 1. Preparation Of Desired Gene Preparation Of Desired Gene Using Restriction Enzymes Using mRNA by Reverse Transcriptase Using m/c DNA Synthesizer

13 2. Isolation of DNA vector Vectors : The extrachromosomal DNA that carries desired gene to the host cell is called gene cloning vector. Eg. Plasmids, viral DNA, Cosmids etc Plamids : Plasmids are small, circular, double stranded extrachrosomal DNA present in bacterial cells.

14 3. Construction of Recombinant DNA (rDNA)

15 DNA 1 DNA 2

16 4.Introduction of rDNA in to host cells 1.Direct Transformation eg. Bacterial Cell intake rDNA 2.Pathological Agent eg. Bacteriophages & agarobacterium. 3.Liposomal Fusion eg. Animal/ Plant cells pick up rDNA in liposomes. 4.Direct Introduction eg. By microinjection or electron gun

17 5. Selection and screening of recombinant host cells Antibiotic resistance Visible Characters Assay of biological activity Colony Hybridization

18 6. Expression of cloned gene. The desired gene expressed in the form of protein. The protein is isolated and tested immunologically.

19 Gene Clonning Gene clonning refers to in-vivo production of multiple copies of desired genes. In-vitro construction of rDNA and amplification of rDNA in bacterium or yeast. Inside the host cell the desired gene replicates along with the vector DNA by using replicative system and form more no of copies. As cell devides rDNA transferred to daughter cells. Thus many identical copies of desired gene are produced from a single rDNA.

20 Enzymes used for genetic engineering Restriction Endonucleases (DNA cutting Enzyme) The enzyme that cut the DNA at a unique sequence is called restriction endonuclease. These are also known as molecular knives, molecular scissors, restriction enzymes or molecular scalpels. Restriction site/ Recognition site.

21 Discovery In 1962, Werner Arber, a Swiss biochemist, provided the first evidence for the existence of "molecular scissors" that could cut DNA. Widespread among prokaryotes He showed that E. coli bacteria have an enzymatic “immune system” that recognizes and destroys foreign DNA, and modifies native DNA to prevent self-destruction.

22 Why don’t bacteria destroy their own DNA with their restriction enzymes? Part I: Restriction Bacteria produce restriction enzymes that digest foreign (viral DNA) Part II: Modification Bacteria methylate their DNA to protect it from digestion Foreign DNAHost DNA

23 Types Of Restriction Enzymes Type I Type II Type III Type I & Type III restriction enzymes recognize specific sequence in duplex DNA but cut the DNA far away from the recognition sites. So they are not useful for genetic engineering.

24 Type II restriction endonucleases recognize specific sites and cut the DNA at the recognized sites. Eg. ECoR I, Hind III etc Molecular Weight – 20,000 to 1,00,000 daltons. Naming….

25 Few Restriction Enzymes EnzymeOrganism from which derived Target sequence (cut at *) 5' -->3' Bam HIBacillus amyloliquefaciensG* G A T C C Eco RIEscherichia coli RY 13G* A A T T C Hind IIIHaemophilus inflenzae RdA* A G C T T Mbo IMoraxella bovis*G A T C Pst IProvidencia stuartiiC T G C A * G Sma ISerratia marcescensC C C * G G G Taq IThermophilus aquaticusT * C G A Xma IXanthamonas malvacearumC * C C G G G

26 Mechanism Of Cutting Restriction Endonuclease scan the length of the DNA, binds to the DNA molecule when it recognizes a specific sequence and makes one cut in each of the sugar phosphate backbones of the double helix – by hydrolyzing the phoshphodiester bond. (5’ Phospahte group and 3’ OH group bonds)


28 – Covalent bonds (within a single strand) – Hydrogen bonds (between strands) as a result of the strands coming apart Hydrogen bond Image taken without permission from Covalent bond What kinds of bonds are broken when restriction enzymes cut?

29 two types Based on the TYPES OF CUTS they make, there are two types of restriction enzymes.  BLUNT ENDS  STICKY ENDS 5’... G A A T T C …3’ 3’... C T T A A G …5’ 5’... G A A T T C …3’ 3’... C T T A A G …5’

30 Blunt Ends

31 Sticky Ends


33 Plane Of Cutting (Palindromic Sequence)(Palindromic Sequence) Type II restriction enzymes recognizes a palindromic sequence to cut DNA.



36 Examples of Type II Restriction Endonucleases Blunt ends Cohesive “sticky” ends

37 Difference Between Type I & II Type I Restriction EndonucleasesType II R.E. Mol wt. 400,000Mol wt. 20,000 to 100,000 daltons The enzyme has both endonuclease and methylase activity. Restriction activity alone The site of cutting is 1000 nucleotides away from the recognition site. The site of cutting is the same recognition site The sequence of cutting is non-specificThe sequence of cutting is specific. The enzymes protect DNAs by methylation.No methylation activity ATP, Mg++ and adenosyl methionine are for activation.Mg++ alone required for activation

38 Uses Restriction enzymes are used to cut a source DNA into small frangments for clonning. Used to cut the unwanted sequence Used to cut the vector DNA Used to cut the larger DNA in to smaller fragments.

39 DNA Ligase DNA ligase is an enzyme that joins the ends of two duplex DNA to make a long DNA. This process is known as ligation. It can’t add any nucleotide to a gap in the DNA. Hydrogen bonds are not strong enough hence phosphodiester bonds are formed. 5’ Phosphate grp and 3’ OH grp forms phosphodiester bond.

40 DNA ligase is isolated from E-coli requires ATP and NAD+ for enzyme activity. However DNA ligase of lambda T4 phase requires ATP alone to catalyze the ligation. This enzyme is called T4 DNA ligase. Mol wt. 68,000 daltons.

41 USES Used to join vector DNA and target DNA to construct rDNA Used to join DNA fragments of different organisms for making vectors. It is used to add linkers and adators sequence to blunt ended vector DNA and target DNA

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