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MOLECULAR GENETICS

MOLECULAR GENETICS. Watson and Crick.

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MOLECULAR GENETICS

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  1. MOLECULAR GENETICS

  2. Watson and Crick • The structure of DNAwas described by British Scientists Watson and Crick as long double helix shaped with its sugar phosphate backbone on the outside and its bases on inside;the two strand of helix run in opposite direction and are anti-parallel to each other. The DNA double helix is stabilized by hydrogen bonds between the bases.

  3. Watson and Crick discovers DNA Feb 28th 1953

  4. DNA A purine always links with a pyrimidine base to maintain the structure of DNA. Adenine ( A ) binds to Thymine ( T ), with two hydrogen bonds between them. Guanine ( G ) binds to Cytosine ( C ), with three hydrogen bonds between them.

  5. Nucleic acid probe • Nucleic acid fragment, labelled by a radioisotope, biotin, etc., that is complementary to a sequence in another nucleic acid (fragment) and that will, by hydrogen binding to the latter, locate or identify it and be detected; a diagnostic technique based on the fact that every species of microbe possesses some unique nucleic acid sequences which differentiate it from all others, and can be used as identifying markers or "fingerprints."

  6. Nucleic acid probe • Nucleic acid fragment, labelled by a radioisotope, biotin, etc., that is complementary to a sequence in another nucleic acid (fragment) and that will, by hydrogen binding to the latter, locate or identify it and be detected; a diagnostic technique based on the fact that every species of microbe possesses some unique nucleic acid sequences which differentiate it from all others, and can be used as identifying markers or "fingerprints."

  7. Hybridization probe • Hybridization probe is a fragment of DNA or RNA of variable length (usually 100-1000 bases long), which is used to detect in DNA or RNA samples the presence of nucleotide sequences (the DNA target) that are complementary to the sequence in the probe. The probe thereby hybridizes to single-stranded nucleic acid (DNA or RNA) whose base sequence allows probe-target base pairing due to complementarily between the probe and target. Dr.T.V.Rao MD

  8. Nucleic Acid Probes Accu probes from Gene probe, which contains a chemiluminescentlabel and target the rRNA of the microorganisms of interest. • It reads events in vivo or during the multiplication of organism.

  9. DNA is Endless structure • The rungs of the ladder can occur in any order (as long as the base-pair rule is followed) • Those 4 bases have endless combinations just like the letters of the alphabet can combine to make different words.

  10. DNA Replication • DNA replication is semi-conservative. That means that when it makes a copy, one half of the old strand is always kept in the new strand. This helps reduce the number of copy errors. • So we remained what we were ?

  11. So we remained what we wereBecause of Our Genetic Materials

  12. DNA to RNA • DNA remains in the nucleus, but in order for it to get its instructions translated into proteins, it must send its message to the ribosome's, where proteins are made. The chemical used to carry this message is Messenger RNA

  13. TYPES OF BLOTTING TECHNIQUES

  14. Nucleic Acid Hybridizations • The hybridization of a radioactive probe to filter bound DNA or RNA is one of the most informative experiments that is performed in molecular genetics. Two basic types of hybridizations are possible. • Southern hybridization - hybridization of a probe to filter bound DNA; the DNA is typically transferred to the filter from a gel • Northern hybridization - hybridization of a probe to filter bound RNA; the RNA is typically transferred to the filter from a gel

  15. Western blotting • Western blotting is an Immunoblotting technique which rely on the specificity of binding between a molecule of interest and a probe to allow detection of the molecule of interest in a mixture of many other similar molecules. • In Western blotting, the molecule of interest is a protein and the probe is typically an antibody raised against that particular protein. • The SDS PAGE technique is a prerequisite for Western blotting .

  16. Western Blotting

  17. Restriction fragment length polymorphism • Sir Alec Jeffreys developed restriction fragment length polymorphism (RFLP), which quickly became the standard technique for DNA testing throughout the 1980s. RFLP provided the world with the first form of genetic testing based on DNA, the body's genetic material

  18. Restriction Fragment Length Polymorphism (RFLP) • Restriction Fragment Length Polymorphism (RFLP) is a technique in which organisms may be differentiated by analysis of patterns derived from cleavage of their DNA.

  19. RFLP • The resulting DNA fragments are then separated by length through a process known as agarose gel electrophoresis, and transferred to a membrane via the Southern blot procedure.

  20. Spoligotyping • Spoligotyping, a new method for simultaneous detection and typing of M. tuberculosis complex bacteria, has been recently developed. This method is based on polymerase chain reaction (PCR) amplification of a highly polymorphic direct repeat locus in the M. tuberculosis genome.

  21. Spoligotyping in Tuberculosis • The well-conserved 36-bp direct repeats are interspersed with unique spacer sequences varying from 35 to 41 bp in size. Clinical isolates of MTC bacteria can be differentiated by the presence or absence of one or more spacers.

  22. Results analyzed by Computer

  23. DNA finger printing • Every one of our DNA is equal except for only about 0.10 %. • DNA finger printing lies in uniqueness of those regions of DNA that do differ from person to person. • Only 5 % of our DNA code rest do not code called in past as Junk DNA and contain repeated sequences of base pairs • Called as Variable number of tandem repeats contain 20 to 100 base pairs and the same sequence is repeated one to 3 times in a row

  24. Documentation of Finger printing for Records • Finger print means translating all the variable number of tandem repeats to visible records • All VNTR is tested for restriction length polymorphism which differ from species to species. • All the obtained material is blotted to Nylon or Nitrocellulose membrane ( Southern Blotting )

  25. RLFP to PCR • Isolation of sufficient DNA for RFLP analysis is time-consuming and labour intensive. However, PCR can be used to amplify very small amounts of DNA, usually in 2-3 hours, to the levels required for RFLP analysis. Therefore, more samples can be analysed in a shorter time.

  26. Molecular diagnostics – how it works • Every organism contains some unique, species specific DNA sequences • Molecular diagnostics makes the species specific DNA visible

  27. PCR methods are rapid and sensitive • PCR, as a specific, sensitive and rapid technique in the identification of the pathogen in the clinical specimen has been developed extensively over the past decade. Its value as a clinical tool is being increasingly recognized

  28. Polymerase Chain Reaction Methodology A Mile stone in Medical History • He had the idea to use a pair of primers to bracket the desired DNA sequence and to copy it using DNA polymerase, a technique which would allow a small strand of DNA to be copied almost an infinite number of times.

  29. Dr. Kary Mullis, wins Nobel Prizein 1993 • Kary received a Nobel Prize in chemistry in 1993, for his invention of the polymerase chain reaction (PCR). The process, which Kary Mullis conceptualized in 1983, is hailed as one of the monumental scientific techniques of the twentieth century.

  30. PCR Liberates a Innocent Prisoner • KirkBloods worth case • A Waterman • Imprisoned for 9 years on wrong evidences of Rape • Unmatched DNA by PCR makes a freeman

  31. Locates Genes for Color Blindness • Color Blind British John Dalton died in 1844 • Request his eyes to be preserved • And to be investigated why he confused scarlet with green, and pink with blue • Recent PCR studies prove Dalton lacked a gene for making one of the three photo pigments essential for normal color vision.

  32. Color Blindness is x linked • The genes for our red and green colour receptors are located on the X-chromosome, giving women a redundant set of receptor genes. • This is why men are far more prone to colour-blindness than women.

  33. DNA – RNA - DNA • In Molecular biology, the polymerase chain reaction (PCR) is a technique to amplify a single or few copies of a piece of DNA across several orders of magnitude, generating millions or more copies of a particular DNA sequence.

  34. Common Tools of Molecular Biology • Nucleic acid fractionation • Polymerase chain reaction • Probes, Hybridization • Vector, Molecular cloning • Nucleic acid enzymes • Microarray • DNA sequencing • Electrophoretic separation of nucleic acid • Detection of genes: *DNA:Southern blotting; inSitu hybridization; FISH Technique *RNA:Northern blotting *Protein:Western blotting, immunohistochemistry

  35. Current Uses of molecular Biology The most recent applied technologies, genetic engineering, DNA finger-printing in the social and forensic science, pre and postnatal diagnosis of inherited disease, gene therapy and drug Design. Molecular biology allows the laboratory to be predictive in nature, it gives information that the patients may be at risk for disease (future). Major tool in Diagnosis of Infectious

  36. Restriction Endonulease • If two organisms differ in the distance between sites of cleavage of a particular restriction endonuclease, the length of the fragments produced will differ when the DNA is digested with a restriction enzyme. The similarity of the patterns generated can be used to differentiate species (and even strains) from one another.

  37. Restriction Endonulease • Restriction endonucleases are enzymes that cleave DNA molecules at specific nucleotide sequences depending on the particular enzyme used. Enzyme recognition sites are usually 4 to 6 base pairs in length. • The recognition sequences are randomly distributed through the DNA and recognizes different nucleotide sequences, and snips through DNA molecule.

  38. Taq polymerase • Taq polymerase is a thermos table DNA polymerase named after the thermophilic bacterium Thermusaquaticus from which it was originally isolated by Thomas D. Brock in 1965. It is often abbreviated to "TaqPol" (or simply "Taq"), and is frequently used in polymerase chain reaction (PCR), methods for greatly amplifying short segments of DNA

  39. Disadvantages of Taq Pol • Taqmis-incorporates 1 base in 104. • A 400 bp target will contain an error in 33% of molecules after 20 cycles. • Error distribution will be random.

  40. Thermo cycler is Back bone of PCR methodology • The method relies on thermal cycling, consisting of cycles of repeated heating and cooling of the reaction for DNA melting and enzymatic replication of the DNA

  41. PCR - Three basic Steps • Cut Paste Amplify

  42. PCR Primers TTAACGGCCTTAA . . . TTTAAACCGGTT AATTGCCGGAATT . . . . . . . . . .> and <. . . . . . . . . . AAATTTGGCCAA TTAACGGCCTTAA . . . TTTAAACCGGTT

  43. Cutting, pasting and amplifying is the basis of Reaction

  44. 3’ 5’ 5’ 3’ 5’ 3’ 3’ 5’ Denaturing Template Heat causes DNA strands to separate Denature DNA strands 94oC

  45. 5’ 3’ 5’ 3’ 5’ 3’ Annealing Primers • Primers bind to the template sequence • Taq Polymerase recognizes double-stranded substrate 3’ 5’ Primers anneal 64oC 5’ 3’ 5’ 3’

  46. 3’ 5’ 5’ 3’ 5’ 5’ 3’ 3’ Taq Polymerase Extends • Taq Polymerase extends primer • DNA is replicated 5’ 3’ 5’ 3’ Extend 72oC 5’ 3’ 5’ 3’ Repeat denaturing, annealing, and extending 30 cycles

  47. Molecular diagnostics is a set of methods to study primary structure (sequence) of DNA • Hybridization with complementary sequences -A-A-T-T-C-G-C-G-A-T-G- - T-T-A-A-G-C-G-C-T-A-C- • Amplification (synthesis) of species specific sequences • PCR – polymerase chain reaction -A-A-T-T-C-G-C-G-A-T-G- -A-A-T-T-C-G-C-G-A-T-G- -A-A-T-T-C-G-C-G-A-T-G- -A-A-T-T-C-G-C-G-A-T-G- -A-A-T-T-C-G-C-G-A-T-G- The 7th Baltic Congress in Laboratory Medicine, Pärnu 11.09.2004

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