- 1. When were alternative non-helical models of DNA briefly considered?
A) Mid 1990s
B) Late 1980s
C) Early 1950s
D) Late 1970s
- 2. Which experimental technique helped set aside non-helical models in favor of the double-helical model?
A) Electron diffraction
B) X-ray crystallography
C) Gas chromatography
D) Nuclear magnetic resonance
E) Mass spectrometry
- 3. What discovery contributed to the acceptance of the double-helical model over non-helical ones?
A) Ribosomes
B) Topoisomerases
C) Mitochondria
D) Golgi apparatus
- 4. How is DNA typically modeled as a polymer?
A) Worm-like chain
B) Completely random coil
C) Perfectly straight rod
D) Rigid crystalline lattice
- 5. Which of these is a significant degree of freedom for DNA?
A) Bending
B) Ionization
C) Denaturation
D) Transmutation
- 6. What is important for the circularization of DNA and orientation of bound proteins?
A) Electrical conductivity
B) Mass density
C) Twisting-torsional stiffness
D) Compression-extension
- 7. Which type of stiffness is important for DNA wrapping and protein interactions?
A) Torsional drag
B) Thermal stiffness
C) Bending-axial stiffness
D) Magnetic stiffness
- 8. Which degree of freedom is considered relatively unimportant in the absence of high tension?
A) Twisting
B) Circularization
C) Compression-extension
D) Bending
- 9. What causes DNA to continually change conformation in solution?
A) DNA replication enzymes
B) Changes in pH
C) Thermal vibration and collisions
D) Magnetic field fluctuations
- 10. How is the bending stiffness of DNA measured?
A) Melting temperature
B) Tensile strength
C) Molecular weight
D) Persistence length
- 11. What tool is used to directly image DNA molecules to measure persistence length?
A) X-ray diffractometer
B) Scanning electron microscope
C) Atomic force microscope
D) Light microscope
- 12. What is the average persistence length of DNA in an aqueous solution?
A) 10 nm
B) 100 nm
C) 200 nm
D) 50 nm
- 13. Approximately how many base pairs correspond to the average persistence length of DNA?
A) 150 base pairs
B) 50 base pairs
C) 300 base pairs
D) 500 base pairs
- 14. What is the diameter of DNA?
A) 10 nm
B) 2 nm
C) 5 nm
D) 1 nm
- 15. What is the approximate range of the persistence length of DNA in base pairs?
A) 50–100 base pairs
B) 400–500 base pairs
C) 132–176 base pairs
D) 200–300 base pairs
- 16. What is a primary factor that causes significant variation in the persistence length of a section of DNA?
A) Light intensity
B) Sequence
C) Age of the sample
D) Air pressure
- 17. What contributes to the variation in persistence length regarding base interactions?
A) Phosphate backbone width
B) Nucleotide sequence length
C) Base stacking energies
D) Hydrogen bond length
- 18. The persistence length is defined as the length below which a polymer behaves like a what?
A) Brittle crystal
B) Circular loop
C) Flexible string
D) Rigid rod
- 19. Which form of DNA is believed to be the most predominant in cells?
A) A-DNA
B) Z-DNA
C) B-DNA
D) P-DNA
- 20. What is the width of B-DNA?
A) 22 Å
B) 23.7 Å
C) 12 Å
D) 34 Å
- 21. How many base pairs constitute one complete turn of B-DNA in solution?
A) 12
B) 10.4–10.5
C) 23.7
D) 10
- 22. Which DNA form is known to have a left-hand twist compared to A and B?
A) C-DNA
B) A-DNA
C) P-DNA
D) Z-DNA
- 23. What is the width of the major groove in DNA?
A) 22 Å
B) 34 Å
C) 23.7 Å
D) 12 Å
- 24. What is the width of the minor groove in DNA?
A) 34 Å
B) 12 Å
C) 23.7 Å
D) 22 Å
- 25. Why do proteins usually bind to the major groove?
A) It is positively charged
B) Bases are more accessible
C) It is always on the outside
D) It is the smaller groove
- 26. Which of the following is a non-helical DNA structure mentioned in the text?
A) i-motif
B) B-DNA
C) Z-DNA
D) A-DNA
- 27. Which letter is NOT among those available to name new DNA structures in the future?
A) Q
B) B
C) F
D) Y
- 28. What was previously thought about the occurrence of A-DNA?
A) Only in dehydrated laboratory samples
B) Only in protein-DNA complexes
C) Only in RNA hybrids
D) Only in methylated DNA
- 29. What happens to the helical pitch of B-DNA every 10 base pairs?
A) It extends 34 Å
B) It extends 12 Å
C) It extends 22 Å
D) It extends 23.7 Å
- 30. Which of the following forms is a quadruplex structure?
A) Z-DNA
B) L-DNA
C) A-DNA
D) G-quadruplex
- 31. Are the major and minor grooves equal in size?
A) Only in Z-DNA
B) Only in A-DNA
C) No, they are unequal
D) Yes, they are equal
- 32. How many coordinates are used to characterize the geometry of a base or base pair step?
A) 6
B) 4
C) 8
D) 12
- 33. Which coordinate represents the rotation of one base with respect to the other in the same base pair?
A) Twist
B) Propeller
C) Tilt
D) Roll
- 34. What is the definition of pitch in a nucleic acid double helix?
A) The height per complete turn of the helix
B) The rotation angle of the helix
C) The diameter of the helix
D) The distance between two bases
- 35. Which displacement is directed from the minor to the major groove?
A) Slide
B) Rise
C) Shift
D) Stagger
- 36. Which coordinate is defined as the rotation around the slide axis?
A) Roll
B) Twist
C) Propeller
D) Tilt
- 37. Which coordinate is defined as the rotation around the shift axis?
A) Tilt
B) Roll
C) Twist
D) Opening
- 38. What does the term 'inclination' refer to in helix-based coordinates?
A) The rotation around the rise axis
B) The distance between strands
C) The displacement along the helix axis
D) The deviation of the inter-strand base-pair axis from perpendicularity to the helix axis
- 39. What is the displacement along the helix axis called?
A) Stagger
B) Rise
C) Slide
D) Shift
- 40. How are roll and tilt typically described in terms of their magnitude?
A) Typically large
B) Always zero
C) Substantial in all DNA
D) Typically small
- 41. What is the rotation around the rise axis called?
A) Twist
B) Propeller
C) Roll
D) Tilt
- 42. Which groove in B-DNA is wider?
A) The phosphate groove
B) Minor groove
C) The grooves are equal in width
D) Major groove
- 43. Who published the book 'The Double Helix: A Personal Account of the Discovery of the Structure of DNA' in 1968?
A) Francis Crick
B) James Watson
C) Rosalind Franklin
D) Maurice Wilkins
- 44. What was the name of the crucial X-ray diffraction image of DNA taken by Rosalind Franklin and Raymond Gosling?
A) The Helix Image
B) Photo 51
C) Structure 1953
D) Photo 52
- 45. In what year was the double-helix model of DNA first published in the journal Nature?
A) 1953
B) 1952
C) 1962
D) 1968
- 46. Whose work on base-pairing chemical and biochemical information contributed to the double-helix discovery?
A) Robert Corey
B) Linus Pauling
C) Alexander Stokes
D) Erwin Chargaff
- 47. What conformation did Linus Pauling incorrectly propose for DNA?
A) Quadruple-stranded
B) Spherical
C) Single-stranded
D) Triple-stranded
- 48. What process involves complementary base pairs binding to form a double helix?
A) Melting
B) Replication
C) Hybridization
D) Transcription
- 49. What is the term for the process of separating the two nucleic acid strands of a double helix?
A) Annealing
B) Hybridization
C) Melting
D) Transcription
- 50. Which sequences are often found at the start of genes to assist RNA polymerase in melting?
A) TGTG
B) GCGC
C) TATA
D) ATCG
- 51. At sub-piconewton forces, what physical law describes DNA bending?
A) Coulomb's law
B) Newton's second law
C) Hooke's law
D) Boyle's law
- 52. Where is tight DNA bending frequently observed?
A) Ribosomal RNA complexes
B) Nucleosome particles
C) Single-stranded DNA viruses
D) Mitochondrial membrane surfaces
- 53. Where was intrinsic bending first observed?
A) Trypanosomatid kinetoplast DNA
B) Viral capsid DNA
C) Human chromosome 21
D) Bacterial plasmid DNA
- 54. If a nick is present in a circularizing DNA molecule, where does bending localize?
A) At the GC-rich segments
B) At the nick site
C) At the AT-rich segments
D) At the center of the molecule
- 55. In whose honor was P-form DNA named?
A) Linus Pauling
B) Francis Crick
C) James Watson
D) Rosalind Franklin
- 56. Which DNA motifs show a sequence preference for the Σ-DNA structure?
A) ATAT motifs
B) GNC motifs
C) TATA motifs
D) CCCC motifs
- 57. What instrument is used to study the entropic stretching of DNA?
A) Centrifuge
B) Electron microscope
C) Optical tweezers
D) X-ray crystallograph
- 58. How many degrees does the B form of the DNA helix twist per 10.4-10.5 base pairs in the absence of torsional strain?
A) 720°
B) 360°
C) 180°
D) 90°
- 59. What is DNA with excess helical twisting called?
A) Negatively supercoiled
B) Positively supercoiled
C) Denatured
D) Relaxed
- 60. What is DNA with insufficient helical twisting called?
A) Negatively supercoiled
B) Positively supercoiled
C) Linearized
D) Intercalated
- 61. Who was one of the first to propose the importance of linking numbers in DNA supercoils?
A) Rosalind Franklin
B) James Watson
C) Francis Crick
D) Francis Collins
- 62. In the equation L = T + W, what does L represent?
A) Left-handedness
B) Linking number
C) Loop
D) Length
- 63. In the equation L = T + W, what does W represent?
A) Writhe
B) Wave
C) Width
D) Weight
- 64. What happens if the twist of a circular DNA molecule is increased or decreased by supercoiling?
A) The linking number becomes zero
B) The writhe is altered
C) The DNA becomes linear
D) The base pairing sequence changes
- 65. What was the topological puzzle regarding residual supercoiling in eukaryotic genomes called?
A) The histone puzzle
B) The linking number paradox
C) The chromatin knot
D) The supercoiling mystery
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