Suppose a covalently closed circular DNA molecule (one that cannot form crucifor
ID: 51067 • Letter: S
Question
Suppose a covalently closed circular DNA molecule (one that cannot form cruciforms or Z-DNA) has a twist of 500 and 20 right-handed supercoils. Answer the following questions about this molecule.
a. If the supercoils could be removed so that the torsional stress were evenly distributed throughout the molecule), what would be the twist in the resulting molecule? (Write the number.)
b. Would a new topoisomer be formed if the supercoils were removed in this way? (Yes or No)
c. The molecule without the supercoils would be
a. overwound
b. underwound
c. under no torsional stress
d. How many base pairs long would you expect the molecule to be? (Assume 10 bp/turn for relaxed DNA.)
Explanation / Answer
curisiforms are the DNA molecules which are totally inverted repeats which are equidistant and symmetrical. IF the molecule is negatively supercoiled it undertwisting
a. If the supercoils could be removed so that the torsional stress were evenly distributed throughout the molecule), what would be the twist in the resulting molecule? (Write the number.)
Twist represent the local twisting , if we remove the 20 right handed supercoils ,it represent the local spacial relationship .so if we reomovethe number of bases form the supercoils that will give he number
number of base pairs - number of supercoils = twist
500-20 = 480 base pairs
b; Would a new topoisomer be formed if the supercoils were removed in this way? (Yes or No)
yes ,because the supercoiles are removed and gain linked so the linking number changes
c. The molecule without the supercoils would be
overwounded , molecule without the supercoils
d. How many base pairs long would you expect the molecule to be? (Assume 10 bp/turn for relaxed DNA.)
47.6 base pairs long will be the molecule
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