After cAMP becomes bound to the CAP to form a complex, it goes on to attach to a specific site on the lac operon of the gene called the "CAP site". This enhances the affinity of the gene to the RNA polymerase, which can now attach and transcribe the mRNA much more efficiently.
Although B-galactosidase transcription will not be upregulated, it is true that a very small amount of transcription will occur even in the presence of an active repressor. This is because repressor binding is governed by kinetics describing the probability of binding or falling off the promoter. The bound & unbound states will be in an equilibrium determined by the equilibrium dissociation constant, which favors binding, but allows for low level transcription even with an active repressor.
Just for clarity, does CAP (with cAMP bound to it) bind to the RNA polymerase which then binds to the promoter and starts transcription? or in other words, what exactly does CAP bind to that facilitates transcription?
I know this might be unrelated to the video,but I have a question regarding bio 142. I wonder about lac and trp repressor mutants. When lac operon repressor or trp operon repressor gets mutated, does it mean they those repressors will not be able to bind to the operon? Or does it mean that lactose trp will not be able to bind to the repressors? Or can it mean both?
@crazychic0009 with no lactose and plenty of glucose, B-galactosidase would NOT be produced; it would be unnecessary given that glucose will be used as the primary sugar source. Glucose is a monosaccharide (unlike lactose which is a disaccharide) and therefore does not need to be cleaved by an enzyme like B-galactosidase for it to be used by the cell.
@theauk This is not an entirely true response. Remember that even though the repressor molecule prevents the lac operon from being transcribed, it sometimes "pops" off the operator (in reality the repressor is mostly bound, pops off, rebinds, pops off, rebinds, etc..... it does NOT just stay bound the entire time). During the small amount of time it pops off, RNA polymerase transcribes a small amount of genes- hence there is always a small amount of B-galactosidase and permease in the cell.
I'm not trying to be dense here....But i'm struggling to understand what is happening in thre presence of glucose. I understand that its preferable but it seems like the structural genes are being produced even in its presence....
Regardless of glucose levels, if lactose is not present, the transcription of the structural genes is inhibited by the binding of the repressor to the operator. Assuming lactose is present and the repressor inactive, transcription of structural genes will depend on the presence or absence of glucose. If glucose is present, then cAMP levels are low and therefore CAP remains inactive and RNA polymerase doesn't efficiently bind the promoter, so transcription of the structural genes is low. If glucose is absent, cAMP levels increase, activating CAP and enhancing RNA polymerase binding. This leads to transcription of the structural genes at high levels only if lactose is present and glucose is not.
Some of this CAP stuff is apparently wrong according to my Bio Professor, glucose apparently blocks LacY(the transport protein for lactose) and so lactose is unable to enter the cell. CAP is only part of why lactose is not transcribed in the presence of glucose. Also: remember that basal(very low) levels of the lac operon are being transcribed at all times, even when the repressor is bound to the operator.(lacI)
No, he meant even though lactose is present. The structural genes aren't produced unless lactose is present. But there ALSO needs to be low levels of glucose, which is the whole point of this video. So he's saying yes even though lactose is present, the genes won't be produced BECAUSE there are high levels of glucose (low cAMP) :)
this is easily the best, and most informative, video on the lac operon
😀
Probably the best Lac Operon explanation on youtube. Thank you!
Best explanation out there on lac gene expression. Covers both positive and negative control. Thanks bruh.
best video for students to understand the operation of the lac operon. thank you.
This is the best video explains how Lac Operon operates. Thank you for your work!
nicely presented~
I like the simple animation! It helps to see it in motion!
After cAMP becomes bound to the CAP to form a complex, it goes on to attach to a specific site on the lac operon of the gene called the "CAP site". This enhances the affinity of the gene to the RNA polymerase, which can now attach and transcribe the mRNA much more efficiently.
this really gave me a quick review of lac operon model i surely suggest this one over manyother videos on this topic!! thanx a lot!!
Great detailed explanation with no distractions. Thank you
I'm studying for a test and this video helped me A LOT! THANKS Johnny!
Sigh...videos like this make me so relieved after studying for hours and being hours away from a midterm :o
This is a great video!!! Great for explaining what my genetics teacher can't.
I have an exam in 2 hours and this has probably just saved me!!!
Although B-galactosidase transcription will not be upregulated, it is true that a very small amount of transcription will occur even in the presence of an active repressor. This is because repressor binding is governed by kinetics describing the probability of binding or falling off the promoter. The bound & unbound states will be in an equilibrium determined by the equilibrium dissociation constant, which favors binding, but allows for low level transcription even with an active repressor.
God bless your teaching skills. Saved me from my test. Well, nearly a quarter of it.
Well done Mr. Clore!---especially the positive control of the CAP protein triggered by cAMP when glucose levels are low---i get the picture now:)
Great 👌 information...
Thank you so much for this. You are better than my college professor.
Just for clarity, does CAP (with cAMP bound to it) bind to the RNA polymerase which then binds to the promoter and starts transcription? or in other words, what exactly does CAP bind to that facilitates transcription?
So simplistic to understand. Very well done. Thank you.
that was to the point!! absolutely specific...awesome...it has relived my confusion of a week in jus 4 min..thank you sir..
Bravo! Excellent information! It's not as pretty as other videos, but it has the info others seem to forget(Cap protein and cAMP molecule)!
I know this might be unrelated to the video,but I have a question regarding bio 142.
I wonder about lac and trp repressor mutants. When lac operon repressor or trp operon repressor gets mutated, does it mean they those repressors will not be able to bind to the operon? Or does it mean that lactose trp will not be able to bind to the repressors? Or can it mean both?
Isn't glucose the molecule on the right at 33 seconds?
The 4' spots are reversed for galactose and glucose, right?
Best explanation I heard so far, thank you!
This really clarified a seemingly difficult concept, thank you very much.
Hey can i ask a question?
What's the difference between the lac promoter and the lac operator. Kinda confused about the uses for each of them.
Best video on Lac Operon
THANKYOU SO MUCH. I WAS STRUGGLING FOR HOURS.
Thanks a million!! Perfect summary just before my test!
God bless!
Great video man, it really clears things up. Go ahead, have my thumbs up.
Love this video. It was short and sweet. My kind of video.
this video saved my ASS!! this was the best video on the lac operon!
@crazychic0009 with no lactose and plenty of glucose, B-galactosidase would NOT be produced; it would be unnecessary given that glucose will be used as the primary sugar source. Glucose is a monosaccharide (unlike lactose which is a disaccharide) and therefore does not need to be cleaved by an enzyme like B-galactosidase for it to be used by the cell.
excellent video. TH-cam makes studying so much easier.
I thought i was the only one looking up biochem videos. Biochem is the worst, doctors in training goes through it so fast. Good luck on yours.
Video for transcription nd translation are available
Thank you thank you thank you! Exam today and I forgot to bring my notes for quick revision.
@theauk
This is not an entirely true response. Remember that even though the repressor molecule prevents the lac operon from being transcribed, it sometimes "pops" off the operator (in reality the repressor is mostly bound, pops off, rebinds, pops off, rebinds, etc..... it does NOT just stay bound the entire time). During the small amount of time it pops off, RNA polymerase transcribes a small amount of genes- hence there is always a small amount of B-galactosidase and permease in the cell.
I heard that even without lactose, so with an active repressor, a small transcription occured. Anyone heard of that? Can someone explain? thank you
Great, concise video. Really helped me grasp the topic. Thank you
this is a very good video man, its helped my understanding alot
Thanks
What about when only glucose is present?
just helped me through a chapter of revision :) thanyou so much i actually understand it so much better now!!! :)
May I know what app do you use to make this video?
I'm not trying to be dense here....But i'm struggling to understand what is happening in thre presence of glucose. I understand that its preferable but it seems like the structural genes are being produced even in its presence....
Regardless of glucose levels, if lactose is not present, the transcription of the structural genes is inhibited by the binding of the repressor to the operator. Assuming lactose is present and the repressor inactive, transcription of structural genes will depend on the presence or absence of glucose. If glucose is present, then cAMP levels are low and therefore CAP remains inactive and RNA polymerase doesn't efficiently bind the promoter, so transcription of the structural genes is low. If glucose is absent, cAMP levels increase, activating CAP and enhancing RNA polymerase binding. This leads to transcription of the structural genes at high levels only if lactose is present and glucose is not.
+Johnny Clore y r u here
....like u know every thing...😶
Thank you :) saved me tons of hours in reading!
Thank you so so so so so so so much this was an amazing explanation.
Some of this CAP stuff is apparently wrong according to my Bio Professor, glucose apparently blocks LacY(the transport protein for lactose) and so lactose is unable to enter the cell.
CAP is only part of why lactose is not transcribed in the presence of glucose.
Also: remember that basal(very low) levels of the lac operon are being transcribed at all times, even when the repressor is bound to the operator.(lacI)
thank you! but why dont u make i video about the trip operon
ohhh bt in presence of glucose ,the level of cAMP decreases but u r saying that cAMP level increases in presence of glucose.plz let me sure about it .
I hated lac op topic for the MCAT before, but this video really helped me make sense out of that sucker
Very well explained. Thank you.
Thank you, very well explained and demonstrated!
Champion! thanks so much! very clear and concise :) Much appreciated!
This was sooo helpful. Thank you for the upload!
wow, awesome video man!!!
Great explanation, thank you!
very good job
Awesome animation
RNA polymerase can't even bind the promoter at all when the repressor is attached to the operator due to steric inhibition**
Great video man!
good concept
great video !!! thank you it helped me a lot
Thank you very much!!!! This video helped me lots!
Thank you. This video really helped.
Thank you very much! great video!!
i wish you were my molecular genetics lecturer..
YOU ARE AWESOME ! NOTHING TO ADD
You are the best! That helped a ton!
very helpful video!
*Falls to knees*
IT MAKES SENSE!!! Now I won't fail genetics.
Great appreciated, man. Thank you very much.
No, he meant even though lactose is present. The structural genes aren't produced unless lactose is present. But there ALSO needs to be low levels of glucose, which is the whole point of this video. So he's saying yes even though lactose is present, the genes won't be produced BECAUSE there are high levels of glucose (low cAMP) :)
nice work thanx
God Bless You ..YOU SAVED ME!!
brilliant
Very good thank you
Thanks, very informative
Thank you for this video!!!
شكرا لك :)
Thank you very much sir
THANK YOU
GOD BLESS YOU.
Dudeeeeeeeeeeeeee you are like the best ever!
@marinarina113
Thanks a lot!! I understand how it works now.
=]
thanks!
thank you for the video it helped me a lot
thank u very much,
Thanks so much. Really helpful :)
thank you so much!!!
THANK YOU!
Legend, thank you so much!
thank you very much! this was very helpful! :D
Thank you this helped!!
gud video
ok, i got it now. thanks
thank u thank u thank u.....sooooo much...
THANK YOUUUU!!