5. Consider a covalently closed, circular DNA molecule of length 10,500 base pai

Question

5. Consider a covalently closed, circular DNA molecule of length 10,500 base pairs and Lk 950. Under physiological condition, assume that there is 10.5 bp per each helical turn. (10 pt) A. Calculate Tw and Wr B. What is the effect of the binding of 110 molecules of ethidium on Lk, Tw, and Wr? [Hint: Ethidium is a large, flat, multiringed cation. Ethidium intercalates between stacked base pairs of DNA, so it decreases the twist of DNA. Assume that there will be a decrease of about 8 turns of the DNA with 110 bound molecules of ethidium] Use your knowledge of X-ray diffraction to match the letter below with its corresponding diffraction pattern. Assume that the diffraction pattern is based on a repeating pattern of that letter. Which of the following is the correct order? (5 pt) A. E-N-A-Z 6. B. Z-A-E-N C. N-A-E-Z D. Z-A-N-E A E N Z

Explanation / Answer

Answer:

A) given= 10500bp

Lk=950

Twist= total base bp/no. of bp per turn

=10500/10.5=1000

Lk=tw+Wr

950=1000+Wr

Wr=-50

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