Cesium Chloride Density Gradient Centrifugation
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- เผยแพร่เมื่อ 12 ก.ย. 2024
- This is the technique used in the Meselson and Stahl experiment, which tested hypotheses about DNA replication. I explain how the cesium chloride density gradient forms, and where DNA goes in the gradient during centrifugation.
Note that the key to forming the density gradient is that you need an ion that is so massive that centrifugation partially overcomes the attraction between the ion and water molecules. The attraction to water keeps the ions dispersed evenly; the force of centrifugation pushes the ions down, but that effect is only noticeable IF the ion is really massive. That's why the Cl ions stay evenly distributed. So no, Na won't work -- it's not massive enough.
What about uranium?
Thank u so much sir. I was struggling so much with the exact use of CsCl centrifugation in Meselson and Stahl experiment. But after watching your video, it is crystal clear.
After struggling to understand it after surfing a lot of webpages with no result, I finally understand it here.
Wow, that was so clear. Thank you for such depth and clarity!! Praise God.
This is a great explanation.. Many thanks! :) English is not my mother tongue so I do not fully get your explanation, but you explain (and write) in such a way that I get the most of it, anyway.
There's only one thing I'm not sure about. I know that DNA density should be around 1.66 - 1.69 g/cm^3. If Cs+ maximum density were 1.6, DNA should fall all the way down.
I thought that Cs density on the bottom were about 1.9 g/cm^3, in order to make the DNA lay "suspended" in the middle of the vial.
i've looked up so many explanations and this is the only one that made me understand it thank you 👍
Very nice and accurate explanation. Greetings from Greece!
i audibly laughed in an empty room when you said duck, thank you for that
I've added a note on the video making this correction at the appropriate point. Good catch, thanks.
Such a beautiful explanation !!! Thank you so much!
I am happy to see you just promoting odia culture.
Hey Asheemita, is it your page. Monika from IIT DELHI
by the way, there is a serious small error in this video: Mr. Gathman claims that only the Cs+ will move down the tube but Cl- will stay equally distributed in the solution. This cannot be right, as this would mean a charge separation. Coulomb forces are very strong, much stronger than the small gravity differences due to the density gradient in solution. Therefore also the Cl- has to follow the Cs+ in order to keep the charge equilibrium in solution.
TheMountblanc I think you’re not taking into account the fact that the charges of both cesium and chloride ions are neutralized by the water molecules surrounding them, so there would be no potential difference between them
Very informative Sir! thank you. Also i laughed when you said ' think about what floats: 'a duck' (7.57). Clear and relatable example.
Such a wonderful explanation, Respect.
One of the best Explanation!
you should upload more videos like this really helpful
thank you..............
Thank you sir your explaination is really conceptual
awesome explanation thank you so much , hope you're safe and healthy
Glad you found it useful. I'm happily retired for 4 years now, and I and my family are all healthy (and vaccinated)!
Thank You, Sir Allen! It's a massive help for me 🙏
Thank you very much! very good explanation
wow, he is very clear and knowledgeable about his explanations!!!! awesome!
Really, well explained sir. I am actually going through Plasmid Purification, so there we use EtBr CsCl density gradient centrifugATION, I got to know real concept of how CsCl creates density. Thanks, @Allen Gathman
@lmarcze11 -- In the gradients that Meselson and Stahl ran, there would have been little protein there in the first place, as they were purifying the DNA before putting it in the gradient. Proteins should do the same thing that DNA or any other molecule does in the gradient, though. They would move to the place in the gradient where their density equals the density of the solution.
Excellent video
This video turned me into a newt.
Thankyou 😊😊
your answer is so good and convincing ... Once again thanks a lot :)
Thank you sir
God bless you
Hmm.. Good point. I bet you're right about that.
@Jonway9 - Who are you who are so wise in the ways of science?
superb best and understandable video thanks alot.........
thank you i hope u still well
I'm fine, thanks, although somewhat grayer. I've been retired for two years now, and am loving it.
@agathman Oh I wasn't implying the explanation was flawed in any way. I was merely referencing Monty Python because your "even small rocks" comment reminded me of the duck scene.
THAT WAS GREAT!! than you for the clear explanation!
Great explanation!
Thank you so much you saved me
thnks a lot fr this video .... I've got some doubts.... instead of CsCl if u proceed the centrifugation wit any salt like NaCl ..wil there b any gradient formation? if so y cant we proceed wit it? can anybody help me?
Because Na ions are smaller than Cs ions..they won't form a gradient..we needed something larger .. that's why
Hi, great video! could you tell me if CsCl could be replaced with anything else that is perhaps cheaper? Thank you.
Another (silly) question: we know that we may use NaCl to shield phosphate negative charges in order to make ss-DNAs re-annealing easier.
According to a purely theoretical point of view, shouldn't CsCl mime the same "salting" effect as NaCl?
I guess that while helping reannealing, we do not use centrifuge: yet, Cs+ should be way heavier than Na+ and tend to precipitate much more easily.
Is it right?
@Jonway9 I know -- you didn't notice my response was also a quote?
Clear explanation, keep it up
So, if she weighs the same as a duck, then she's made of wood. And therefore... A WITCH!
haha lol I missed that. You are too subtle for me :) I need to have a Monty Python marathon.
Thanks a Trillion
Thanku it is very helpful
Great video thankyou!
Great video :)
Excellent!
awesome, Thank you so much!!
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I still can't understand what is the use of chloride here when the experiment depends on the concentration gradient of only cesium?
If you were to put pure metallic cesium in the water, you'd have a violent reaction! What you need is cesium ions in solution. You can't have the cesium ions without another, negative ion for them to form a salt with, so CsCl is the handiest. I suppose it could be done with some other ionic cesium compound, but CsCl is readily available.
Oh. Thank You Allen.
Sir I didn't understand why cs ions will not form pellet at the end of the tube...?
They’re positively charged and repel each other, and they are attracted to polar water molecules that keep them suspended.
@@hammeredgrannies7821 thank you..!!!
nice video thanks Sir!!
fantastic vid
Thank you. It's nice :)
that was awesome
thank you sir
This is absolutely wrong. The centrifuge cannot separate the Cs+ and Cl- ions from each other! That would violate charge balance. It is true that the gradient forms but it is a gradient of Cs+ AND Cl- ions.
Neocles Leontis
CsCl dissociates in any polar solvent. what made you think that the centrifuge would do that.
Hey bro,centtifuge didn't separate them..they just dissociated in water as the Cs & Cl together made CsCl by ionic interactions, just like NaCl(bt sodium ion is much smaller than Cs), so they simply separated in their constituent ions in a polar solvent..hope could help you understand better Neocles
But ducks don't float....they swim😂
ur voice is not much clear