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Flashcards

DNA and RNA

Anahita Sehgal English 59 cards

Cards in this deck (59)

  1. 1Expand the acronym 'RNA'Ribonucleic acid
  2. 2True or False: DNA comprises disulfide bonds.False. DNA doesn't have thiol groups to create these covalent crosslinks.
  3. 3What do we mean by a 'self encoding' character? Which two cellular processes is this property necessary for?Complimentary base paring between the two anti-parallel strands gives DNA its self encoding character - one strand can serve as a template for the other strand.
    This is needed in replication and transcription.
  4. 4Which part of DNA is rich in chemical information such as specific amino acid sequences?Major Groove
  5. 5How can we denature DNA?Using heat. Since DNA doesn't have disulphide bonds, we don't need an external reducing agent.
  6. 6Describe the relationship of melting point and salt conc. for DNA molecules. Briefly explain why this relationship exists.DNA molecules in a high salt concentration have higher meting points. This is because DNA has a poly-anionic backbone, and higher salt concentrations shield the negative charges on the phosphate group. When these charges are not shielded, repulsion caused by the interaction of like charges makes it more energetically favourable to separate the two strands.
  7. 7True or False: As GC content increases, AT content increasesFalse. As GC content increases, AT content decreases.
  8. 8Describe the relationship of GC content and melting point within DNA molecules.Higher the GC content , higher the melting point.
  9. 9Describe the relationship of AT content and melting point within DNA molecules.As the AT content increases, melting point reduces.
  10. 10True or False: Once we start melting the double stranded molecules, the segments to melt first are high in GC content.False.
    They are high in AT content.
  11. 11Which base pairs are the origin of replication and transcription start sites rich in?A-T
  12. 12How did the concept of an RNA molecule arise?There existed a physical barrier between the site of chromosomal DNA (in the nucleus) and the site of protein synthesis (in the cytoplasm).
    Genetic information needed to be transported with some molecule, which was thought to be RNA.
  13. 13Describe the basic structure of RNA.Poly -nucleotide sequence joined by phospho-diester bonds.
  14. 14What are the three major differences between RNA and DNA?1) DNA is double stranded and RNA is single stranded.
    2) DNA is missing a hydroxyl group at the 2' position - that's why its called 'deoxyribose'. RNA has that hydroxyl group.
    3) Since Thymine is missing a methyl group in RNA, it is called Uracil but still binds to Adenine.
  15. 15Briefly explain the Pulse-Chase experiment.1) Radioactively labeled nucleotides are introduced in a culture of eukaryotic cells over a short period of time (15 mins) --- called a pulse. Within the pulse, the RNA molecules are given a chance to synthesised.
    2) These radioactively labelled RNA molecules are then observed for their path i.e. the CHASE.
  16. 16Why was rRNA assumed as the 'template molecule'?Ribosomes comprise 85% of RNA
  17. 17Why was rRNA finally NOT accepted as the template molecule?1) A large quantity of rRNA exists because so many ribosomes exist.
    2) rRNA has very low variability - its nucleotide composition is relatively constant compared to DNA which has a highly variable concentration.
  18. 18What is the role of mRNA, tTRNA and rRNA?rRNA:
    1) Passive site for the production of proteins.
    2) catalyses peptide bond synthesis!!
    3) low variability
    4) 85% of cellular DNA
    mRNA:
    1) Carries genetic material from DNA onto ribosomes.
    2) highly variable
    3) ~ few % of total cellular RNA
    tRNA:
    1) encodes genetic information and helps in the synthesis of polypeptide sequence.
    2) low variability
    3) ~10% cellular RNA
  19. 19Why can RNA never be classified as the 'molecule of heredity'?RNA has the hydroxyl group at the 2' position which is absent in DNA. In alkali conditions when the H is pulled away from the hydroxyl group, it turns into a nucleophile and attacks the phosphate group. This results in a cleaved phospho-diester bond, and gives RNA its self-hydrolysing character.
    RNA is thus too unstable to be the molecule of heredity.
  20. 20True or False: Molecules will always try and adopt a structure that maximises weak interactions such as Van der Waals and minimize unfavourable interactions such as polar-non polar interactions.True!!
  21. 21DNA has ______________ base pairing whereas RNA has ______________ base pairing.interstrand, intrastrand.
  22. 22What do we mean by 'self- complementarity' in RNA?Self complementarity means that RNA forms base pairs within the single strand.
  23. 23What is a Hair Pin Loop? Why is it seen on a RNA molecule?In order to achieve a structure that maximises weak interactions, the single stranded RNA molecule folds itself and one of the structures formed as a result is the hairpin loop. It comprises an 'inverted repeat' wherein the complementary sequence of a particular sequence is present but in an inverted direction.
  24. 24In a RNA molecule, what happens when: 1) a single unpaired nucleotide is present on one side? 2) two unpaired nucleotides are present on each side?1) The RNA molecule folds into a bulge.
    2) The RNA molecule forms a hairpin loop.
  25. 25Describe briefly the secondary and tertiary structure of RNA?1) Secondary structure -- maps out the folding of RNA (hairpin loops, bulges etc)
    2) Tertiary structure -- RNA takes the A-form helix. Its right handed (dehydrated form of DNA).
  26. 26Why can't RNA form a B-form helix?RNA has the presence of the 2' hydroxyl group (missing in DNA) which doesn't allow it to form the B form helix.
  27. 27What is the consequence of not being able to form the B-form helix?The roles of the major and minor groove get switched. The Major groove, which is rich in unique chemical patterns helpful for proteins to recognize, becomes inaccessible for those proteins. It becomes narrow and shallow.
    The minor groove instead becomes wide and deep.
  28. 28True or False: RNA doesn't participate in base stacking for stability.FALSE. RNA also participates in base stacking for stability.
  29. 29True or False: RNA has the constraint to form long helical structure.False; it doesn't have any constraint.
  30. 30RNA single stranded molecule has a lot of ______________ freedom.rotational
  31. 31List 4 stable structures the RNA tertiary structure comprises of.1) Non Watson and Crick Base Pairs: Any possible base pair arrangement can occur because of the free folding ability of the RNA single strand.
    2) Base triples may also exist: gives RNA enhanced self-complementarity.
    3 ) base- backbone interactions- the bases do interact with the backbone unlike DNA where the point away from the backbone.
    4) Metal Ions: they interact with the poly-anionic backbone and neutralise the (-) charges. This allows the structure to become more compact and the (-) charges don't repel.
  32. 32Central DogmaDNA --> RNA --> Protein.
  33. 33DNA molecule is a ___________ helical structure.double stranded.
  34. 34The DNA molecule strands run ____________ to each other and undergo __________________________.antiparallel, complimentary base pairing.
  35. 35What does the DNA backbone comprise of?Repeating units of sugar-phosphate molecules joined by phosphodiester bonds.
  36. 36How many H bonds exist between: 1) A-T 2) G-C1) 2
    2) 3
  37. 37What are purines and pyrimidines? Give examples of each.Purines are double ring structures.
    Example - Adenine and Guanine
    Pyrimidines are single ring structures.
    Example- Cytosine and Thymine.
  38. 38Mention the Chargaff's rule.AT= GC
  39. 39True or False: Number of Purines = Number of PyrimidinesTrue:
    A+G = C+ T
  40. 40Briefly explain Base-Stacking.Due to the hydrophobic effect, the DNA base pairs align themselves in the center of the molecule (away from the polar surrounding). These base pairs comprise a ring structure which gives them resonance. Resonance results in the planarity of the base pairs, allowing them to stack upon one another towards the center of the molecule.
  41. 41When was the discovery of the DNA molecule made?In 1953 by Watson and Crick.
  42. 42The DNA structure is _____________.Uniform
  43. 43What does a nucleotide comprise?A phosphate group, a pentose sugar and a nitrogenous base.
  44. 44__________________ bond exist between the base and the sugar.Glycosidic
  45. 45___________________ bond exists between two nucleotides.Phosphodiester.
  46. 46Complete the following: 1) The 1' base of the sugar is attached to -- 2) The 3' base of the sugar is attached to -- 3) The 5' base of the sugar is attached to --1) The base is connected here.
    2) used to form phosphodiester bonds
    3) where the phosphate group is attached.
  47. 47The (-) charge of DNA exists because of ___________ group.phosphate
  48. 48_________________ without a phosphate group and _________________ with a phosphate group.Nucleoside, Nucleotide
  49. 49Every phosphate group is bonded to how many sugar molecules?2. One within the nucleotide and the other on the joined nucleotide.
  50. 50________________ determines the unique part of DNA.Order of bases.
  51. 51True or False: DNA has a polarity. It lies from the 3' to the 5' terminal.False. DNA DOES have a polarity but it lies on the 5' to 3' terminal.
  52. 52DNA is a ________ handed helix.right
  53. 53self encoding characterA will always bind to T and G will always bind to C.
  54. 54TautomeresAlternate forms of the common base pairs. Changes the H bonding patterns which affects the base pairing preferences.
  55. 55Briefly describe the Z-form Helix1) Is a left-handed helix.
    2) alternating between purines and pyrimidines.
  56. 56What factors help in denaturing DNA?1) Low salt concentrations
    2) High temperatures
  57. 57Describe the Hyper-chromic Effect?Describes the decrease in UV absorbance of a double stranded DNA molecule compared to its single-stranded counterpart. This is because in a double stranded molecule, due to base pairing and base stacking, the base pairs are less able to absorb UV light.
  58. 581) Single stranded DNA molecules absorb _______% more UV light. 2) DNA has maximum UV absorption at _____ nm.1) 40
    2) 260
  59. 59True or False. Hybridisation is often uncommon because the DNA source takes precedence over complimentary base pairing ability.False.
    Hybridisation DOES NOT care about the source. The sequence available should have base pairs complementary to the base pairs on the target sequence, and that's enough to hybridise.

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Flashcards on DNA and RNA , created by Anahita Sehgal on 01/02/2018.
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Anahita Sehgal
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