A double-stranded DNA strand with radius 1.15 nm is in a salt solution with a co

Question

A double-stranded DNA strand with radius 1.15 nm is in a salt solution with a concentration of 8e + 25 ions/m^3 and at a temperature of 29.6 Celsius. Remember that the persistence length (that is the length of a straight run at physiological temperatures) of DNA is 50 nm and the spacing between base pairs, each of which contains in its structure 2P^- ions, is 0.34 nm. The ions in solution distribute themselves uniformly in the region immediately surrounding the DNA. What is the charge density per unit length on the DNA (in C/m)? For a sphere, V = 4/3 pi r^3, A = 4 pi r^2; For a cylinder, V = pi r^2 L, A = pi (r^2 + 2 L) A. 9.42 times 10^-10 B. 1.37 times 10^-9 C. 1.98 times 10^-9 D. 2.87 times 10^-9 E. 4.17 times 10^-9 Initially, ions are attracted to the DNA. Which of the following statements is correct? A. Na^+ ions will be repelled from the DNA. B. Cl^- ions will be repelled from the DNA. C Cl^- ions will be attracted to the DNA Ultimately, the ions form a shell surrounding the DNA that is lambda_D = 0.76 nm thick, resulting in an electric field, E = 0, outside of the shell. Which of the following statements is correct? A. The number of excess ions surrounding the DNA will equal the number of charges on its surface. B. The number of excess ions surrounding the DNA will be less than the number of charges on its surface. C. The number of excess ions surrounding the DNA will be greater than the number of charges on its surface. A positively charged protein moves to distance of lambda_D/2 from the DNA. The work required to do this is A. zero. B. Negative. C. Positive.

Explanation / Answer

45. What is the charge density per unit length on the DNA:

C. 1.98*10-9

46. Following statement is correct?

B. Cl- ions will be repelled from the DNA

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