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Nucleic Acid

DNA. RNA. Nucleic Acids are the polymers of nucleotides. Nucleotides are the combination of Nucleosides+ Phosphate Nucleosides = Nitrogenous Base + Pentose Sugar. Nucleic Acid. A. T. G C. Nitrogen Base. A= Adenine G = Guanine T = Thymine C = Cytosine U = Urasil.

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Nucleic Acid

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  1. DNA RNA Nucleic Acids are the polymers of nucleotides. Nucleotides are the combination of Nucleosides+ Phosphate Nucleosides = Nitrogenous Base + Pentose Sugar Nucleic Acid

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

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

  4. 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

  5. Alternative names for genetic engineering: • Genetic Manipulation • Genetic Modification • Recombinant DNA Technology • Gene Splicing • Gene Cloning

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

  7. 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.

  8. How It Is Done??? • Preparation Of Desired Gene • Isolation of DNA vector • Construction of Recombinant DNA (rDNA) • Introduction of rDNA in to host cells • Selection and multiplication of recombinant host cells. • Expression of cloned gene.

  9. A Bacterial Cell

  10. 1. Preparation Of Desired Gene

  11. 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.

  12. 3. Construction of Recombinant DNA (rDNA)

  13. DNA 2 DNA 1

  14. 4.Introduction of rDNA in to host cells • Direct Transformationeg. Bacterial Cell intake rDNA • Pathological Agent eg. Bacteriophages & agarobacterium. • Liposomal Fusion eg. Animal/ Plant cells pick up rDNA in liposomes. • Direct Introductioneg. By microinjection or electron gun

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

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

  17. 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 devidesrDNA transferred to daughter cells. • Thus many identical copies of desired gene are produced from a single rDNA.

  18. 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.

  19. 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.

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

  21. 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.

  22. Type II restriction endonucleasesrecognize 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….

  23. 0 Few Restriction Enzymes

  24. Mechanism Of Cutting • Restriction Endonucleasescan 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)

  25. Hydrogen bond Covalent bond What kinds of bonds are broken when restriction enzymes cut? • Covalent bonds (within a single strand) • Hydrogen bonds (between strands) as a result of the strands coming apart Image taken without permission from http://www.bioteach.ubc.ca/MolecularBiology/RestrictionEndonucleases/endonuclease%202.gif

  26. 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’

  27. Blunt Ends

  28. Sticky Ends

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

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

  31. Difference Between Type I & II

  32. 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.

  33. 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.

  34. 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.

  35. 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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