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Types of DNA and RNA and their importance

  1. 1. A Presentation on Types of DNA and RNA and their importance Course title: Principle of Genetics (GP501) Submitted to: Dr. N.V.Soni, Submitted by: Gami Pankajkumar B. M.Sc.(Agri.)GPB 1st sem, 1
  2. 2. Introduction: Deoxyribonucleic acid (DNA) J.D. Watson and F.H.C. Crick showed in 1953 that DNA has a double helical structure with two polynucleotide chains connected by hydrogen bonds and running in opposite directions. When DNA samples are analysed from different organs of body of the same individual or from different individuals belonging to the same species, no differences in the relative composition of different bases were observed.
  3. 3. The following generalizations could also be made : (1) Number of adenine molecules always equal to number of thymine molecules. (2) Number of cytosine molecules always equal to number of guanine molecules. (3) Number of adenine molecules did not necessarily equal that of guanine and similar relationship was observed between cytosine and thymine. Although A = T and C ≡ G, there is no restriction on the ratio (A + T)/(C + G); nor is there any restriction on sequence of bases in one polynucleotide chain.
  4. 4. But, since A is always linked to T and C to G as determined from the above evidences, sequence of bases in one polynucleotide should determine the sequence of bases in the other polynucleotide of the double helix.  Studied by X-ray crystallography by Frederick demonstrated that DNA was a helical structure with a diameter of 20 Å and a pitch (one round) of about 34 Å.  On the basis of these studies of chemical analysis and X-ray crystallography , following features of the DNA molecule are now known :
  5. 5. (1) DNA consists of a double helix, in which two polynucleotide chains are coiled about the same axis in such a fashion that they can separate from one another only by uncoiling and that lateral separation would not be possible. (2) Bases are set in a plane at right angle to the long axis. (3) Two polynucleotide chains which run in opposite directions have complementary base sequence. (4) Distance between two base pairs is 3.4 Å and there are 10 base pairs in each turn. Choice of base pairing is understandable because of a constant diameter of 20 Å in the molecule; two purines would need too much space and two pyrimidines would occupy too little space to pair. When a pyrimidine always pairs with a purine, space could remain constant.
  6. 6. Alternative forms of DNA double helices:  The well known structure of DNA described by Watson and Crick (1953). Helical coiling of this DNA assumed to be right handed and this form of has been called B-form. It has been shown that DNA may also exist in other alternative forms of double helical structures.  These alternative forms are differ in features like I. number of residues per turn ('n') or II. the spacing of residues along the helical axis ('h'). III. Diameter IV. Sugar phosphate backborne V. Major Groove VI. Minor Groove
  7. 7. The various types of conformations that the DNA can adopt depend on different factors such as: Hydration level Salt concentration Quantity and direction of super-coiling Presence of chemically modified bases Different types of metal ions and its concentrations Presence of polyamines in solution.
  8. 8. Why?? The existence of DNA as double helix has also been confirmed by experiments used to measure the number of base pairs per turn and it has been shown that this is 10.4 instead of 10.0 shown in classical B –form. This will lead to modification of the twist angle (rotation) between two pairs from 36 to 34.60 (360/10.4).  This figure of 10.4 base pairs per turn is an average and according to conditions, this may shift in either direction. It is thus obvious that there may be several families of structures of DNA, each of a characteristic type showing variation in the values of 'n‘ and ‘h. Three structural forms, namely A, B and C are known for a long time and transitions between them can occur.
  9. 9. B-DNA: This is the most common and predominant form of DNA. It is observed when humidity is 92% and salt concentration is high. The coiling is in the right direction. The number of base is 10 per turn of helix. The pitch is 33.2 Å. The sugar phosphate linkage is normal. The helix is narrower and more elongated than A form. The major groove is wide which is easily accessible to proteins. The minor groove is narrow. The base pairing is nearly perpendicular to helix axis. The sugar puckering is C2'-endo.
  10. 10. Z- Form: The existance of this DNA was discovered by Andrews wang and Alexander Rich. The helix has left hand coiling pattern. Due to syn position of the purine while the B DNA has a anti position. The number of bases is 12 per turn of helix The pitch is 45 Å The sugar phosphate linkage is zig-zag. The major "groove" is not really a groove. The minor groove is narrow. The helix is narrower and more elongated than A or B form.
  11. 11. The base pairing is nearly perpendicular to helix axis. The conformaion is favored by high salt concentrations. Z-DNA is one of the biologically active forms of DNA found in vivo in the cells. The exact biological function of Z-DNA is not clear but the Z-DNA is usually located upstream of the start site of a gene and thus it may have some role in the regulation of gene expression.
  12. 12. Differences between Z-DNA and B- DNA (1) Z-DNA has left-handed helical sense as against right handed helical sense of B-DNA. (2) Due to a different arrangement of molecules within Z-DNA polymer, phosphate backbone follows a zig-zag course, while in B-DNA it is regular. (3) In Z-DNA, sugar residues have alternating orientation so that repeating unit is a dinucleotide as against B-DNA where repeating unit is a mononucleotide and the orientation of sugar molecules is not alternating.
  13. 13. (4) In Z-DNA, one completc helix i.e. a twist through 3600, has twelve base pairs or six repeating dinucliotidc units (12 base pairs), while in B-DNA, one complete helix has only ten base pairs or ten repeating units. (5) One complete helix is 45 Å in Z-DNA while it is 34 Å in B-DNA. (6) Since bases get more length to spread out in Z-DNA and they are closer to the axis and hence the diameter of Z- DNA molecule is 18 Å, whereas it is 20 Å in B-DNA.
  14. 14. A-form:  A DNA conformation is rare in nature and it adopted under dehydration condition. This form is observed at the humidity of the sample is 75%. The coiling is in the right direction. The number of bases is 10.7 per turn of helix. The pitch is 2.8 nm. The sugar phosphate linkage is normal. The major groove is deep and narrow which is not easily accessible to proteins. The minor groove is wide and shallow which is accessible to proteins. The helix is shorter and wider than B form. The sugar puckering is C3'-endo.
  15. 15. C-DNA C-DNA formed at 66% relative humidity (low)in presence of Li+ or Mg2+. Right handed ,with axial rise of 3.32A° per base pair . 9.33 base pairs per turn. Helical pitch 3.32A°×9.33°A=30.97A°. Base pair rotation=38.58°. Has diameter of 19A°,smaller than that of A- &B- DNA. The tilt of base is 7.8°
  16. 16. D-DNA • Extremely rare variant with only 8base pairs per helical turn . • This forms of DNA found in some DNA molecules devoid of guanine. • Axial rise of 3.03A°per base pairs .Tilt is 16.7° from axis of helix. • Actually 2 different forms of D-DNA 1. D(A):Takes part in D-A-B transition. 2. D(B):Associated with D-B change of confirmation. • 2 DNA structure have same helical parameters.
  17. 17. E-DNA • Cytosine methylation or bromination of DNA sequence d(GGCGCC)2 is to induce a novel extended &eccentric double helix, which we call E- DNA. • E-DNA has a long helical axis rise and base perpendicular to the helical axis. • Deep major groove and shallow minor groove. • E-DNA allowed to crystallize for a longer period time, the methylated sequence forms standard A- DNA.
  18. 18. • E-DNA is the intermediate in the transition to A- DNA.
  19. 19. A B Z HELIX RIGHT HANDED RIGHT HANDED LEFT HANDED Base Pairs Per Turn 11 10 12 Diameter 26A° 20A° 18A° Sugar phosphate backborne Regular Regular Zig-Zig Major Groove Narrow& Deep Wide &Deep Flat Minor Groove Wide & Shallow Narrow&Deep Narrow&Deep
  20. 20. There are 3 basic types of DNA tested by ancestry DNA tests now-a-days: Paternal DNA (Y-DNA) Maternal DNA (mtDNA) and, Autosomal DNA (atDNA) Y-DNA: paternal lineage This is the test you go for if you want to research your father’s side of the family. Since only males have the Y-chromosome which is passed on almost unchanged from father to son, you can trace a direct line between male members on your paternal side. The Y-DNA test can only be taken by males. Women who want to trace their paternal side have to ask their brother, father, paternal uncle, paternal grandfather or paternal cousin to take the test for them. With a Y-DNA test, it’s possible to go thousands of years back through your ancestry timeline.
  21. 21. mtDNA: Maternal lineage Mitochondria are small internal cellular structures that serve as the body’s energy factories, and they have their own DNA called mitochondrial DNA or mtDNA. Only mothers can pass mtDNA to her children. mtDNA in sperm is destroyed either in the male genital tract or by the fertilized egg. As a result, only female mtDNA survives inheritance. Because a mother passes mtDNA to both male and female children, both men and women can get value from this test. By comparing your mtDNA to that of other people, you have a chance of finding a relative from your maternal side. As with Y-DNA, mtDNA has several limitations. The biggest one is the limited set of ancestors it can trace. You can only trace someone with a direct maternal line to your mother. So it’ll go from your mother to your mom’s mom to her mom’s mom and so on.
  22. 22. Autosomal DNA (atDNA): long-term ancestry and recent lineage An autosome refers to the remaining 22 numbered chromosomes except for your 23rd, sex chromosome (X-Y). Unlike Y-DNA and mtDNA, autosomal DNA is inherited from both parents. So you can use it to trace either side of your family. The major DNA testing providers rely mostly on autosomal DNA testing. But the timescale is limited with this test – you can use this test to find relatives up to the second cousin level. Beyond that, you’ll need to use a family tree or other types of DNA testing. Autosomal DNA testing also tells you a lot about location and migration patterns of your ancestors.
  23. 23. Types of RNA Genetic RNA Non genetic RNA m-RNA t-RNA r-RNA
  24. 24. TWO TYPES OF RNA: 1) GENETIC RNA:  RNA which act as genetic material like DNA is called Genetic RNA.  Genetic RNA may be single stranded or double stranded.  Genetic RNA has self replication property .  Example:RNA is found as genetic material in: Plant viruses: TMV Bacteriophages: MS2
  25. 25. 2)NON GENETIC RNA: • RNA which does not act as genetic material is known as non-genetic RNA. • This is found in higher where DNA act as genetic material. • such RNA is usually single stranded. • The organisms having DNA along with RNA. • In such organisms ,RNA has no genetic role ,but carries the orders of DNA. • All non genetic RNA have DNA Dependent replication they does not have self replication property.
  26. 26. TYPES OF NON GENETIC RNA • In all prokaryotic and eukaryotic organisms, three main classes of RNA molecules exist- 1) Messenger RNA(m RNA) 2) Transfer RNA (t RNA) 3) Ribosomal RNA (r RNA) • The other are –  small nuclear RNA (snRNA)  micro RNA(mi RNA)  small interfering RNA(Si RNA)  heterogeneous nuclear RNA (hnRNA)  Signal-recognition particle(SRP) RNA  Monocistronic RNA & Polycistronic RNA
  27. 27. 1. Messenger RNA or mRNA • Jacob and Monod (1961) proposed the name messenger RNA for the RNA carrying information for protein Synthesis from the DNA (genes) to the sites of protein formation(ribosomes) cytoplasm. • It consists of only 5 to 10% of the total cellular RNA.
  28. 28. Size of Messenger RNA • The molecular weight of an average sized mRNA molecule is varies from 20,00,000 to 5,00,000, and its sedimentation coefficient is 8S. • It should be noted however, that mRNA varies greatly in length and molecular weight.
  29. 29. Stability of Messenger RNA • The cell does not contain large quantities of mRNA. This is because mRNA, unlike other RNAs is constantly undergoing breakdown. • It is broken down to its constituent ribonucleotides by ribonucleases.
  30. 30. Structure of Messenger RNA • It is a kind of single stand RNA molecule which is complementary to sense strand of DNA molecule. • Produced by transcription of structural genes in the DNA Sequence. • mRNA carries the genetic message from the chromosome to the site of protein synthesis i.e. Ribosome. • mRNA molecule corresponds to each gene that is expressed. Function: The main function of mRNA is protein synthesis in ribosomes in the cytoplasm.
  31. 31. 2. Transfer RNA or tRNA • After rRNA the second most common RNA in the cell is transfer RNA. • It is also called soluble RNA because it is too small to be precipitated by ultracentrifugation at 10,000 g. It constitutes about 10-20% of the total RNA of the cell. • Transfer RNA is a relatively small RNA having a molecular weight of about 25,000Da to 30,000Da and the sedimentation coefficient of mature eukaryote tRNA is 3.8S.
  32. 32. • tRNAs are RNA molecules that provide the means of translating the genetic code. • One end of the tRNA contains a three nucleotide sequence called the anticodon loop that is complementary to the codon of the mRNA. • The other end of the tRNA is covalently attached to a specific amino acid. • They carry the activated aminoacids to the ribosome for protein synthesis. • There is a specific tRNA for each of the twenty aminoacids. • Transfer RNAs (tRNAs), the smallest of the three major species of RNA molecules .
  33. 33. • tRNAs species make up about 15% of the total RNA in the cell. • tRNA contains many unusual bases between 7 and 15 per molecule. • The 5‘ end of tRNA have poly G and it is phosphorilated. • tRNA is folded into a clover leaf pattern. It has five following special region as follows.
  34. 34. Structure of t- RNA • The carboxyl group of amino acid is attached to 3’OH group of Adenine nucleotide of the acceptor arm. The anticodon arm base pairs with the codon present on the m- RNA
  35. 35. i. CCA end: The base sequence in 3’ end of all tRNA is CCA. The activated amino acid is attached to 3’ hydroxyl group of the terminal adenosine.The amino acid is accepted this point only. ii. TΨC arm: Involved in the binding of the tRNA to ribosome iii. Anticodon loop: It consists of sevenbases with following sequences. • Anticodon (codon Recognition site) • Codon recognition site is complementary to codons of mRNA. iv. DHU arm: It is the site for the recognition of amino acid activated enzymes
  36. 36. Function: The main function of tRNA is to carry various types of amino acids and attach them to mRNA template for protein synthesis. *For further reading :Genetics by P.K.Gupta ( chepter:31 )
  37. 37. 3. Ribosomal RNA or rRNA • It is a kind of RNA molecule serving as a major component of ribosomes. • rRNA is a type of RNA that is a component of ribosomes and plays a role in the process of translation (making protein from nucleic acid sequence). • E.Coli has three kind of rRNA i.e., 23s, 16s, 5s. • Ribosomal RNA (rRNAs) are found in association with several proteins as components of the ribosomes-the complex structures that serve as the sites for protein synthesis.
  38. 38. • rRNAs species make up 80% of the total RNA in the cell. Function: The function of ribosomal RNA binding of mRNA and tRNA to ribosomes in the cytoplasm.
  39. 39. small nuclear RNA(sn RNA) • Play structural and catalytic roles in spliceosomes, the complexes of protein and RNA that splice pre- mRNA in the eukaryotic nucleus. small interfering RNA • Affects gene expression; used by scientists to knock out a gene being studied. Micro RNA • Affects gene expression; importance in growth and development.
  40. 40. SRP RNA • Is a component of the signal-recognition particle(SRP),the protein-RNA complex that recognizes the signal peptides of polypeptides targeted to the ER. Monocistronic RNA • The mRNA which is coded by one cistron (gene). Polycistronic RNA • The mRNA which is coded by several cistrons (genes).
  41. 41. SR NO. Particulars DNA RNA 1 Location Nuclear and cytoplasm Chromosomes & Ribosomes 2 Replication Self replication Self replication rare 3 Types Sevaral Three: mRNA, tRNA& rRNA 4 Strands Usually two, rarely one Usually one, rarely Two 5 Bases A,G,C&T A,G,C&U 6 Base pairing AT & GC AU & GC 7 Sugar Deoxyribose Ribosome 8 Size Upto 4.3 million nucleotides Upto 12,000 nucleotides 9 Function Genetic Role Protein synthesis; genetic in some viruses.
  42. 42. REFERENCES: 1. Genetics by B. D. Singh 2. Biotechnology : Expanding horizons by B. D. Singh 3. Genetics by P. K. Gupta 4. 5.
  43. 43. Than ks

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  • Chargaff’s rules