This video really helped me understand how DNA supercoils and how the different topoisomerase reduce or increase supercoiling of DNA. Thank you very much!!
I know im randomly asking but does someone know a trick to log back into an Instagram account? I stupidly forgot my login password. I appreciate any help you can give me.
@Thomas Reyansh Thanks for your reply. I got to the site on google and im in the hacking process atm. Seems to take quite some time so I will get back to you later when my account password hopefully is recovered.
I am confused about the activity of topoisomerase I, specifically in relation to the image displayed at 7 minutes. If I consider its activity using the equation L=T+W then it makes sense. You reduce the number of loops (decrease T) and this is balanced by reducing the amount of negative supercoiling (increase W). However, I can't make sense of it theoretically. If negative supercoiling is the result of under winding, then if you produce even less loops then shouldn't that contribute to negative supercoiling? Sorry for the long question, but I appreciate any help.
This is indeed a confusing subject -- no matter how carefully it's presented -- so I understand why you have questions! Instead of thinking of underwinding as the cause and negative supercoiling the effect -- reverse those concepts. First of all the + and - supercoiling simply refers to the direction of the supercoiling. Our DNA double helix is a right-handed helix. If we supercoil in the opposite direction (left-handed) -- this is referred to as positive supercoiling. Because of the topology of the DNA -- the RESULT is that the molecule is overwound -- i.e. there is MORE tension on the molecule -- this makes it harder to unwind. The only organisms we know that do this are archaea -- those that live in extreme environments where the double helix is likely to denature (unravel). If instead the DNA is supercoiled in the same direction as the coiling -- right-handed -- we call those negative supercoils. This results in a DNA molecule that is slightly underwound -- i.e. there is less tension on the molecule. This makes it easier to separate the two strands for purposes of replication and for transcription. Hope that helps! Dr. G
Hi Dr. G, That makes a lot of sense. Its definitely easier to think of supercoiling as the cause, and the subsequent twist change as the effect. However, even using this mentality I still can't make sense of that diagram at 7 minutes. Are you able to explain it with context to the diagram? I think I am getting more confused when we start to introduce topoisomerase which has an effect on the linking number. Because looking at that diagram without considering topoisomerase it seems contradictory to what you've explained. When the supercoiling is reduced (from 5 to 4) you think it would cause an overall tightening of the helix to keep the linking number. However, the number of twists reduces as well. I'm assuming this contradictory result is stemming from the introduction of topoisomerase. The only way I can rationalize it is that topoisomerase reduces the number of twists in the double helix, but in vivo our double helix wants to be at a specific twist number. So, the linking number decreases, but our twist must return to the natural double helix and so the supercoiling adjusts for this. I hope you can understand my question, and I really appreciate all the help you have provided. GB
gspb4 Hi GB, I think I get your question -- so here goes. First, you are right that the linking number, L, does not change for covalently closed DNA -- no matter how it may be distorted. However, the value of L can change if 1 strand is broken and the other strand unwound, then the broken strand resealed. It's in the process of breaking the strand that the twist and linking number is altered. Hope that helps! Dr. G
Wow its too much simple to understand love this
Thank you! this was a great video to study with
Loved this video!!! The photos were very helpful!
Thank you so much
This video really helped me understand how DNA supercoils and how the different topoisomerase reduce or increase supercoiling of DNA. Thank you very much!!
I know im randomly asking but does someone know a trick to log back into an Instagram account?
I stupidly forgot my login password. I appreciate any help you can give me.
@Brett Aryan Instablaster =)
@Thomas Reyansh Thanks for your reply. I got to the site on google and im in the hacking process atm.
Seems to take quite some time so I will get back to you later when my account password hopefully is recovered.
@Thomas Reyansh it did the trick and I finally got access to my account again. I am so happy!
Thanks so much you really help me out !
@Brett Aryan Glad I could help :)
Very nice and good book for information thanx for telling .
thanks great teaching :)
very helpful
What do you think is the importance of the DNA to have a negative and a postive supercoiling?
Awesome
does anyone know why plasmid dna is negatively supercoiled to begin with?
thanx, it helped me alot
Super! Glad I could help!
helpful
I am confused about the activity of topoisomerase I, specifically in relation to the image displayed at 7 minutes. If I consider its activity using the equation L=T+W then it makes sense. You reduce the number of loops (decrease T) and this is balanced by reducing the amount of negative supercoiling (increase W). However, I can't make sense of it theoretically. If negative supercoiling is the result of under winding, then if you produce even less loops then shouldn't that contribute to negative supercoiling?
Sorry for the long question, but I appreciate any help.
This is indeed a confusing subject -- no matter how carefully it's presented -- so I understand why you have questions! Instead of thinking of underwinding as the cause and negative supercoiling the effect -- reverse those concepts. First of all the + and - supercoiling simply refers to the direction of the supercoiling. Our DNA double helix is a right-handed helix. If we supercoil in the opposite direction (left-handed) -- this is referred to as positive supercoiling. Because of the topology of the DNA -- the RESULT is that the molecule is overwound -- i.e. there is MORE tension on the molecule -- this makes it harder to unwind. The only organisms we know that do this are archaea -- those that live in extreme environments where the double helix is likely to denature (unravel). If instead the DNA is supercoiled in the same direction as the coiling -- right-handed -- we call those negative supercoils. This results in a DNA molecule that is slightly underwound -- i.e. there is less tension on the molecule. This makes it easier to separate the two strands for purposes of replication and for transcription. Hope that helps!
Dr. G
Hi Dr. G,
That makes a lot of sense. Its definitely easier to think of supercoiling as the cause, and the subsequent twist change as the effect. However, even using this mentality I still can't make sense of that diagram at 7 minutes. Are you able to explain it with context to the diagram? I think I am getting more confused when we start to introduce topoisomerase which has an effect on the linking number. Because looking at that diagram without considering topoisomerase it seems contradictory to what you've explained. When the supercoiling is reduced (from 5 to 4) you think it would cause an overall tightening of the helix to keep the linking number. However, the number of twists reduces as well.
I'm assuming this contradictory result is stemming from the introduction of topoisomerase. The only way I can rationalize it is that topoisomerase reduces the number of twists in the double helix, but in vivo our double helix wants to be at a specific twist number. So, the linking number decreases, but our twist must return to the natural double helix and so the supercoiling adjusts for this.
I hope you can understand my question, and I really appreciate all the help you have provided.
GB
gspb4
Hi GB,
I think I get your question -- so here goes. First, you are right that the linking number, L, does not change for covalently closed DNA -- no matter how it may be distorted. However, the value of L can change if 1 strand is broken and the other strand unwound, then the broken strand resealed. It's in the process of breaking the strand that the twist and linking number is altered. Hope that helps!
Dr. G
Positive Supercoiling occurs in a right handed direction and vice versa for the Negative Supercoiling, please rectify this
can you share this ppt
It is a nice video, but Sulfolobus thrive in a lower PH between 2-3.5
Positive supercoiling occurs in a right handed direction, please correct it.
4:33 wrong! Positive supercoil is right-handed.