Voiceover: So what makes
a cell that’s located inside of your nose responsible for smelling, say, a slice
of pizza look and act differently from a cell
that lines your gut and is responsible for absorbing the nutrients from that pizza? They have the exact same DNA so the differences can’t be
attributed to that fact alone. The answer actually lies in
the expression of that DNA, which genes are actively
transcribed and which ones aren’t and there are several ways
in which gene regulation occurs at the level of
transcription and so we’re going to be talking
about the main ones here. Now let’s draw out a
hypothetical gene here and associated with this
gene is a sequence upstream so towards the three prime
region of the antisense strand, also called the template strand. And this sequence is called the promoter and there is another sequence in between the promoter and the
gene called the operator. The operator is the
sequence of DNA to which a transcription factor protein combined and the promoter is the
sequence of DNA to which the RNA polymerase binds
to start transcription. Now first off in
prokaryotes we have what are called general transcription factors, which are a class of proteins that bind to specific sites on DNA to
activate transcription. General transcription
factors plus RNA polymerase and another protein complex called the mediator multiple protein complex constitute the basic
transcriptional apparatus, which positions RNA
polymerase right at the start of a protein coding sequence or a gene and then releases the
polymerase to transcribe the messenger RNA from that DNA template. Now there’s another type
of DNA binding protein called activators and these
enhance the interaction between RNA polymerase
and a particular promoter, encouraging the expression of the gene and activators can do this
by increasing the attraction of RNA polymerase for the
promoter through interactions with sub units of the RNA polymerase or indirectly by changing
the structure of the DNA. An example of an activator is the catabolite activator protein or CAP and this protein activates transcription of the lac operon in E. coli. In the case of the lac
operaon and E. coli, cyclic adenosine monophosphate or cAMP is produced during glucose starvation and so this cAMP actually binds to the catabolite activator protein or CAP which causes a confirmational change that allows the CAP protein
to bind to a DNA site located adjacent to the promoter
and then this activator, the CAP, then makes a
direct protein to protein interaction with RNA
polymerase that recruits the RNA polymerase to the promoter. Now enhancers are sites on the DNA that are bound to by activators
in order to loop the DNA in a certain way that
brings a specific promoter to the initiation complex
and as the name implies this enhances transcription of the genes in a particular gene cluster. And while enhancers are usually what are called cis-acting,
cis meaning the same or acting on the same chromosome, an enhancer doesn’t necessarily need to be particularly close to
the gene that it acts on and sometimes it’s not even located on the same chromosome. Enhancers don’t act on the
promoter region itself, but are actually bound
by activator proteins and these activator
proteins can interact with that mediator complex I mentioned earlier which recruits RNA polymerase and the general transcription
factors which then can lead to transcription of the genes. So here I’ve drawn a
little schematic of what it might look like to have the enhancer actually change the structure of the DNA so that the DNA is now looping around. Here you still have
your promoter sequence, the operator sequence, the gene sequence, and the enhancer sequence,
and having the DNA looped in such a way
so that you could then recruit RNA polymerase,
the transcription factors, the mediator protein
complex, and then you have transcription begin of this gene here. Now let’s talk about repressors. Repressors are proteins
that bind to the operator, impending RNA polymerase
progress on the strand and thus impeding the
expression of the gene. Now if an inducer, which is a molecule that initiates gene
expression, is present, then it can actually interact
with the repressor protein in such a way that causes it
to detach from the operator and then this frees up
RNA polymerase to then transcribe the gene further
down on the DNA strand. One example of a repressor protein is the repressor protein associated again with the lac operon
operator, which prevents the transcription of genes
used in lactose metabolism unless lactose, which
is the inducer molecule, is present as an
alternative energy source. Now silencers are regions
of DNA that are bound by repressor proteins in order
to silence gene expression and this mechanism is
very similar to that of the enhancer sequences
that I just talked about. And similarly, silencers
can be located several bases upstream or downstream from the actual promoter of the gene and when a repressor protein binds to the silencer region of the DNA, RNA polymerase is prevented from binding to the promoter region. Now a few notes about the differences between prokaryotes and eukaryotes when it comes to
transcriptional regulation. In prokaryotes, the
regulation of transcription is really needed for
the cell to be able to quickly adapt to the ever-changing outer environment that it is sitting in. The presence, the quantity, the type of nutrients actually determines which genes are expressed
and in order to do that, genes must be regulated
in some sort of fashion so a combination of
activators, repressors, and rarely enhancers, at least in the case of prokaryotes, determines
whether a gene is transcribed. In eukaryotes, transcriptional regulation tends to involve a
combination of interactions between several transcription factors which allows for a more
sophisticated response to multiple conditions in the environment. And another major difference between eukaryotes and prokaryotes
is the fact that eukaryotes have a nuclear envelope which prevents the simultaneous transcription and translation of a particular gene and this adds an extra spacial and temporal control of gene expression.

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48 thoughts on “Regulation of transcription | Biomolecules | MCAT | Khan Academy”

  1. thanks for the upload but isn't operator rarely in eukaryotes? And isn't operator to eukaryotes is promoter-proximal element..? 

  2. She speaks way too fast and doesn't write enough, had to pause a thousand times. Also, you she didnt mention that Eukaryotes DO NOT have an operator like prokaryotes do…and didn't mention a LOT of necessary details about transcription. Sal is so much easier to follow…please slow down and take more notes in future videos.

  3. Activators don't bind to the promoter, only the basal transcription factors bind. Activators bind to enhancers, silencers, or promoter-proximal elements.

  4. C'mon give the nice lady a break. No need to compare her with Sal. I think if you're gonna constructively critic her presentation then just do that, but its not nice to compare.

  5. Great video, but i feel you spoke very fast, maybe perhaps you had limited time to make the video. I literally wrote every single word she said a 7min video took me like 35min to cover all the martial, but other then that great video!

  6. Is this for Euks or Proks? This video is not as good as the others, she speaks too quickly and it's not as well-explained.

  7. I think she had some stuff confused…. upstream is 5' and activators don't bind to promoters…. they bind to enhancers and silencers. Operator is also in prokaryotes and not in eukaryotes

  8. had to study this and oncogene but i couldnt get the help from khan academy this time because sal wasnt explaing it for me. i dont want to be rude but i dont think teaching is the thing for you. you make things sound harder than it seems and you cant really make people understand it, you just pour out the information and make people teach themselves like my professor.. i was utterly disappointed and i wish sal comes back to redo this concept.. im sorry but please don’t make any videos from now on. i wish to see sal on them videos, thanks

  9. This was definitely way too fast. I would rather everything be well explained and have the video be twice as long.

  10. Prokaryotic and Eukaryotic transcription shouldn't be amalgamated into one explanation. They are very different in many ways.

  11. you didn't explain enhancers at all. just listed some components and said they loop the DNA "so that you can then recruit RNA polymerase and transcription factors"… which are recruited anyway…?

  12. This is probably the worst video from Khan Academy I’ve ever watched. I’ve been watching loyally for 7 years and she completely messed up the video. Upstream should be 5’ on the TEMPLATE STRAND not coding strand. She switched it around to try to make a point but she got it wrong. Also she’s mixing prokaryotic/eukaryotic dna. Finally, she’s an activator binds to an enhancers….

  13. too many small mistakes regarding the promoter, the enhancer, where they bind, etc. It's obvious that she knows her stuff but a quick review before teaching would not hurt.

  14. Biological life cannot exist without gene regulation. Without gene regulation any type or amount of protein could be synthesized. This would kill the organism. Same with the DNA repair system. Without the DNA repair system, biological life would mutate right out of existence. Gene regulation and the DNA repair system are both extremely sophisticated processes which biological life depends on.

    These processes cannot evolve under any circumstance. They were created by God(Father, Jesus, Holy Spirit) according to the bible.

    This God, who created all things, is completely holy. We humans however are completely sinful and wicked(Romans 3:23). The penalty for sin is Hell(Revelation 21:8). Thankfully the bible ALSO says that God is rich in mercy and grace. That is why He sent Jesus to die on a cross to save us from our sin. We broke God’s law but Jesus paid our fine. Then Jesus rose from the dead, 3 days later, thus defeating death.

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