text
stringlengths 3
503
| title
stringlengths 10
73
|
|---|---|
So in this particular case, this is our DNA template that the RNA polymerase molecule is actually using. | RNA Polymerase .txt |
So this is the three end and this is the five end. | RNA Polymerase .txt |
Now, what our RNA polymerase does is it binds onto that DNA molecule and it reads the DNA template from the three to the five end and that means it builds it from the five to three end. | RNA Polymerase .txt |
So this is the RNA chain that the RNA polymerase already built. | RNA Polymerase .txt |
So let's imagine that inside this chain we have N number of nucleotides and this is the N plus one nucleotide that is being added onto that growing RNA chain. | RNA Polymerase .txt |
So what the RNA polymerase does is it essentially hovers around this section and it brings that complementary ribonucleocide triphosphate which is complementary to this base that is found on the DNA template. | RNA Polymerase .txt |
Now, how do we know when it's complementary? | RNA Polymerase .txt |
Well, basically when the bonding is just perfect, this molecule will stay in this location for long enough for this bond to actually take place. | RNA Polymerase .txt |
So it will stay long enough for the bond to form. | RNA Polymerase .txt |
And the way that the bond forms is so we can label these carbon atoms as carbon atom one, carbon atom two, carbon atom three, carbon atom four, and carbon atom five on this sugar molecule. | RNA Polymerase .txt |
And we have the three prime hydroxyl group acts as a nucleophile and attacks this innermost phosphorus atom of this incoming nucleuside triphosphate. | RNA Polymerase .txt |
And it forms a covalent bond between the oxygen and this phosphorus. | RNA Polymerase .txt |
Now eventually this H atom is removed and this Pyrophosphate molecule is kicked off. | RNA Polymerase .txt |
And so in the process when we form the phosphodieester bond and we form this polynucleotide chain, we essentially release a single pyrophosphate molecule and as we'll see in a future lecture the hydrolysis of the pyrophosphate molecule essentially drives this reaction forward. | RNA Polymerase .txt |
So RNA polymerase catalyzes the formation of phosphodiasta bond. | RNA Polymerase .txt |
It brings the complementary nucleotide triphosphate this nucleotide that is complementary to this base into the mixture and then our RNA polymerase holds this in place and it catalyzes the formation of this bond as shown in the following diagram and the pyrophosphate is released as a result. | RNA Polymerase .txt |
Now, as I mentioned before the RNA polymerase reads the DNA template from the three to five end but it synthesizes that polynucleotide chain in the five to three end and this is the same exact method that DNA polymerase uses. | RNA Polymerase .txt |
Remember, DNA polymerase also reads that DNA template from the three to five end and it synthesizes that DNA molecule from the five to three in the same way that RNA polymerase does. | RNA Polymerase .txt |
Now, the difference between RNA polymerase and DNA polymerase is in RNA polymerase. | RNA Polymerase .txt |
Notice we do not need a primer sequence to actually initiate the process. | RNA Polymerase .txt |
So in DNA polymerase we said that DNA polymerase requires that primer sequence but RNA polymerase does not. | RNA Polymerase .txt |
Now, unlike DNA polymerase which has the endonuclease activity has the ability to essentially correct the mistakes it makes. | RNA Polymerase .txt |
RNA polymerase cannot correct the mistakes it makes. | RNA Polymerase .txt |
So if it incorrectly pairs up two bases it will not be able to correct that mistake. | RNA Polymerase .txt |
And that means RNA polymerase makes many more mistakes as compared to DNA polymerase which makes less mistakes. | RNA Polymerase .txt |
So this is the RNA polymerase molecule that essentially is involved in forming that RNA molecule during the process of transcription when we essentially copied the code found in the DNA and form these RNA molecules. | RNA Polymerase .txt |
For example transfer RNA molecules, messenger RNA molecules and ribosomal RNA molecules. | RNA Polymerase .txt |
Now, the last thing I'd like to mention is in E. Coli cells so in prokaryotic cells, for example, bacterial cells a single RNA polymerase forms all the different types of RNA molecules the mRNA tRNA and RNA. | RNA Polymerase .txt |
But in our own cells, in the human cells we have three different we have three different RNA polymerases as we'll discuss in a future lecture. | RNA Polymerase .txt |
And each one of these RNA polymerases actually synthesizes a specific type of RNA molecule. | RNA Polymerase .txt |
Carbon atoms. | Fatty Acid Synthesis Part II .txt |
So 1234. | Fatty Acid Synthesis Part II .txt |
So two of those carbon atoms basically came from these this acetyl coenzyme A molecule and the other two came from this acetyl coenzyme A molecule. | Fatty Acid Synthesis Part II .txt |
Now, what happens next? | Fatty Acid Synthesis Part II .txt |
Because ultimately we said that fatty acid synthase can generate a 16 carbon fatty acid molecule. | Fatty Acid Synthesis Part II .txt |
So what happens next is is this cycle basically takes place six more times. | Fatty Acid Synthesis Part II .txt |
And when it takes place six more times, it generates a 16 carbon palmitate a 16 carbon palmitate fatty acid molecule. | Fatty Acid Synthesis Part II .txt |
So quickly, let's talk about how that actually takes place. | Fatty Acid Synthesis Part II .txt |
So in the next step, once we generate this, what will happen is this entire group here, this four carbon group will be moved onto this cysteine in the same way that we move this group onto this holding 16 molecules shown here. | Fatty Acid Synthesis Part II .txt |
So in the next step, we're going to use another Malcolm coenzyme A to attach it onto the ACP that now does not contain this. | Fatty Acid Synthesis Part II .txt |
And now we're going to continue via these steps. | Fatty Acid Synthesis Part II .txt |
We have a condensation reduction dehydration and a second reduction step. | Fatty Acid Synthesis Part II .txt |
And now we'll generate a six carbon intermediate and this will take place five more times until we generate that 16 carbon palmatoil intermediate molecule. | Fatty Acid Synthesis Part II .txt |
And once we generate that palmatoil intermediate molecule, an enzyme known as Thio esterase will cleave that bond that will release that 16 carbon palmitate fatty acid molecule. | Fatty Acid Synthesis Part II .txt |
And that pretty much completes that fatty acid elongation step. | Fatty Acid Synthesis Part II .txt |
So these are the steps involved in synthesizing fatty acid molecules. | Fatty Acid Synthesis Part II .txt |
Again, the first elongation step involves steps one through step seven. | Fatty Acid Synthesis Part II .txt |
But then these steps from two and onward have to take place six more times to actually help is generate that 16 carbon fatty acid molecule that does not contain any double bond. | Fatty Acid Synthesis Part II .txt |
So it's a fully saturated 16 carbon fatty acid molecule. | Fatty Acid Synthesis Part II .txt |
So far in our discussion on on channels, we focused on two types of on channels. | Gap Junctions.txt |
We discussed voltage gated on channels and ligand gated on channels. | Gap Junctions.txt |
Now, we move on to a slightly different category, vine channels we call gap junctions. | Gap Junctions.txt |
Now, gap junctions are also known as cell to cell channels, and we'll see why in just a moment. | Gap Junctions.txt |
Now, although gap junctions are in fact on channels, they have very different properties from the properties of voltage gated and ligand gated on channels. | Gap Junctions.txt |
And there are five important things that differentiate gap junctions from voltage gated and ligand gated on channels. | Gap Junctions.txt |
So let's begin by comparing and contrasting these different types of on channels. | Gap Junctions.txt |
So voltage gated channels and ligand gated channels are actually closed when that membrane is the rest, and they're only open when that membrane is excited by some type of stimulus. | Gap Junctions.txt |
Now, when they do open, they're only open for a very short period of time, about a milliseconds or so, and then they're quickly closed off or they're inactivated. | Gap Junctions.txt |
And the size of the pore inside these channels is actually very small. | Gap Junctions.txt |
And that's why only small inorganic ions can pass across. | Gap Junctions.txt |
And finally, these ion channels are usually very specific to the type of ions they allow across that membrane. | Gap Junctions.txt |
Now, what about gap junctions? | Gap Junctions.txt |
Well, unlike voltage gated and ligand gate on channels, these gap junctions actually have relatively large pore sizes, so the diameter is about 20 angstroms. | Gap Junctions.txt |
On top of that, they also allowed the movement of not only inorganic ions, so ions like calcium, sodium, potassium, chloride ions across that particular channel, but they also allow the movement of organic substances such as glucose molecules, amino acids, as well as nucleotides. | Gap Junctions.txt |
So we see, unlike the voltage gated and ligangate on channels, which are usually specific and can only move these inorganic ions, gap junctions are non specific. | Gap Junctions.txt |
They allow any molecule to move across or any ion to move across, as long as it's not too large. | Gap Junctions.txt |
So large substances such as proteins and polynucleotides and polysaccharides, these molecules cannot pass across gap junctions. | Gap Junctions.txt |
Now, unlike these voltage gated and ligand gate on channels, which are only open for about a millisecond before being closed or inactivated, these gap junctions can be open anywhere from seconds to minutes. | Gap Junctions.txt |
Now, voltage gated and ligand gate on channels connect the cytoplasm of a cell to the outside extracellular environment. | Gap Junctions.txt |
But we see that these gap junctions actually connect two adjacent cells. | Gap Junctions.txt |
And more specific, they transverse the membrane of these two adjacent cells and they connect the cytoplasm of one cell to the cytoplasm of that contiguous adjacent cell. | Gap Junctions.txt |
So gap junctions transverse two membranes of contiguous cells. | Gap Junctions.txt |
That simply means the cells are very close in proximity, closely packed to one another, and they connect the cytoplasm of one cell to the cytoplasm of the adjacent cell. | Gap Junctions.txt |
And this can be seen in the following diagram. | Gap Junctions.txt |
So this entire structure that transverses the membrane of one cell and the membrane of the adjacent cell, and also transverses this into cellular space. | Gap Junctions.txt |
This is a single gap junction. | Gap Junctions.txt |
So this is the cytoplasm of one cell and this is the cytoplasm of that adjacent cell. | Gap Junctions.txt |
And the length of this gap junction is about 35 angstroms. | Gap Junctions.txt |
And the final aspect, the final difference between the voltage gated and ligan gate channels and the gap junctions is that these iron channels are produced by single type of cell, but gap junctions are actually produced by two cells. | Gap Junctions.txt |
And we'll see why in just a moment. | Gap Junctions.txt |
So let's move on to actually discuss what the structure of this gap junction is. | Gap Junctions.txt |
So notice we have these two individual structures which are connected end to end inside that intercellular space. | Gap Junctions.txt |
So each of these structures is known as a hemichannel or a connection. | Gap Junctions.txt |
And we see that a single gap junction consists of these two hemichannels, also known as connections that are connected end to end to basically form this single gap junction. | Gap Junctions.txt |
Now, if we examine each one of these hemichannels, each one of these hemichannels actually consist of six individual polypeptide chains we call connections. | Gap Junctions.txt |
And these connections are basically formed to form a hexamer, which basically means we have six individual units within that hemichannel. | Gap Junctions.txt |
Now, cell number one produces hemichannel number one, and cell number two produces hemichannel number two, and then they connect them to form that gap junction. | Gap Junctions.txt |
And so that's the final difference between these voltage gated and ligandgate on channels and gap junctions. | Gap Junctions.txt |
Now, what exactly? | Gap Junctions.txt |
Well, actually, before we examine the functionality of these gap junctions, let's discuss how these gap junctions are actually regulated by ourselves. | Gap Junctions.txt |
Because just like voltage gated and ligan gate on channels have to be regulated for the proper functionality of the cells, these gap junctions too have to be regulated. | Gap Junctions.txt |
And there are four methods by which we can actually close off these gap junctions. | Gap Junctions.txt |
So we can close off these gap junctions by either increasing the concentration of the calcium, increasing the concentration of the h plus ions. | Gap Junctions.txt |
So the same thing as saying lowering the PH number three is there are special hormones that can basically induce the process of phosphorylation of these gap junctions. | Gap Junctions.txt |
And that too can close off the gap junction. | Gap Junctions.txt |
And number four is in some cases, changing the voltage difference can also actually close off these gap junctions. | Gap Junctions.txt |
Now, why would we want to actually close off a gap junction? | Gap Junctions.txt |
Well, let's suppose we have two cells which are connected by these gap junctions, and one of the cells is damaged in some way and ends up dying. | Gap Junctions.txt |
So to basically prevent a second nearby healthy cell from being damaged, that dying cell will want to close off these gap junctions. | Gap Junctions.txt |
And that's exactly where these different processes come into play to close off that gap junction. | Gap Junctions.txt |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.