Hi guys there is a question which has been driving me crazy ever since I saw this video(https://youtu.be/az2c6UbEdug). At 4:50 the guy says that when a right-handed circular DNA starts forming a right handed interwounding writhe the DNA must adjust by twisting more(You can see the number goes up to 8 from 5 in the equation) and that when an interwounding writhe is done in the opposite direction it must twist less. To me this doesn't make sense at all. I thought that as you interwound to the right the twisting should lessen and when you interwound to the left the twisting should increase. Can someone explain(or show a very clear diagram/illustration which explains this) please??
It is all explained here in Wikipedia. If you want to make a 3D model of your own, you can use two pieces of tygon tubing (like the rubber hose for a Bunsen burner), that are both circularized and attached with connectors that can be opened and closed--that lets you simulate nicking and re-sealing the strands.