Exercise:
You have a relayed 6864 base pair of large plasmid that you treat with gyrase until the plasmid has received 40 negative supercoils. Assume that B form DNA has 10.4 bp / gain.
a. What is the linking number of the plasmid before treatment with gyrase.
b. What is the linking number of the plasmid after treatment with gyrase.
c. What is the change in the linking number (Δ L) after the treatment with gyrase
d. Explain what is meant by superhelic density (σ). Calculate the superhelic density (σ) after treatment with gyrase.
The plasmid's DNA helix opens ("unwinder") at 0.01 ° / bp for each degree the Celius temperature is raised.
e. Calculate Δ Lk, ΔWr, and ΔTw when the temperature is raised by 21 ° C.
The linking number is the number of times a strand of DNA is wound in the right-handed direction around the helix axis when the axis is in plane.
a) This equals 6864/10.4 = 660
b) Gyrase uses ATP to increase negative supercoiling., 40 is the linking number after gyrase treatment
c) change = -640
d)superhelic density is the quantitative measure of the degree of supercoiling; change in linking number /original linking number, -640/660=-0.969
Exercise: You have a relayed 6864 base pair of large plasmid that you treat with gyrase...