MCQ for Spectrophotometric determination of nucleic acid concentration

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Question 1: The aromatic rings of the bases found in DNA and RNA absorb ultraviolet light with an absorption maximum at ______.
  • INCORRECT. Please try again.
  • INCORRECT. Please try again.
  • CORRECT! The aromatic rings of the bases found in DNA and RNA absorb ultraviolet light with an absorption maximum at 260nm.
  • INCORRECT. Please try again.
Question 2: Which of the following is the formula for calculating the concentration of double-stranded DNA?
  • INCORRECT! This is the formula for calculating the concentration of single- stranded DNA/RNA.
  • CORRECT!
  • INCORRECT! Please try again.
  • INCORRECT! Please try again.
Question 3: Which of the following statements are true for increasing the absorbance of DNA at 260nm when a DNA solution is heated to 90 oC or above? I. The stacked bases of double-stranded DNA are more able to absorb light than the less constrained bases of single-stranded DNA
II. The stacked bases of double-stranded DNA are less able to absorb light than the less constrained bases of single-stranded DNA
III. The DNA becomes denatured
IV. Double-stranded DNA is separated into single-stranded DNA
  • INCORRECT! One of the statements is wrong.
  • INCORRECT. One more statements should be included.
  • CORRECT! When a DNA solution is heated to 90oC or above, there will be enough kinetic energy to denature the DNA completely, causing it to separate into single strands. The stacked bases of double-stranded DNA are less able to absorb light than the less constrained bases of single-stranded molecules, and so the absorbance of DNA at 260nm increases as the DNA becomes denatured.
  • INCORRECT! One of the statements is wrong.
Question 4: When comparing the UV absorption, for a given amount of nucleotides, dsDNA absorbs _____ than ssRNA, which absorbs ______ than free nucleotides.
  • INCORRECT. Please try again.
  • CORRECT! In a solution of unlinked nucleotides, the bases are more spread out and absorb more radiation. In a DNA double helix, the bases are stacked on top of each other and relatively less UV light is absorbed. In single-stranded RNA (or in single-stranded DNA), the situation is intermediate.
  • INCORRECT. Please try again.
  • INCORRECT. Please try again.
Question 5: UV light is preferentially absorbed by which of the following components of nucleic acids?
I. purine
II. pyrimidine
III. sugar
IV. phosphate
  • CORRECT! UV light is preferentially absorbed by the purine and pyrimidine rings, not the sugar or phosphate components of nucleic acids.
  • INCORRECT! UV light is preferentially absorbed by pyrimidine, but not sugar. Please try again.
  • INCORRECT! Please try again.
  • INCORRECT! Please try again.