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Now, finally, let's move on to the functionality of gap junction. | Gap Junctions.txt |
So there are three important functions that we're going to take a look at function number one, intercellular communication. | Gap Junctions.txt |
Function number two, cell nourishment. | Gap Junctions.txt |
And function number three, embryological development. | Gap Junctions.txt |
So let's focus on function number one, intercellular communication. | Gap Junctions.txt |
This simply means communication between adjacent cells. | Gap Junctions.txt |
So let's take a look at example number one. | Gap Junctions.txt |
Let's take a look at our heart. | Gap Junctions.txt |
So in our heart, we have these specialized muscle cells we call cardiac myocides, or simply cardiac muscle cells. | Gap Junctions.txt |
And these cardiac muscle cells are closely packed, so they are contiguous in nature. | Gap Junctions.txt |
And because of that, many of these cardiac muscle cells are connected by these gap junctions. | Gap Junctions.txt |
So what's the function of these gap junctions? | Gap Junctions.txt |
Well, basically, when one cell receives an action potential as a result of these gap junctions, the action potential can actually propagate into nearby cardiac myosytes. | Gap Junctions.txt |
And what that does is it allows the creation of a continuous and a forceful contraction of the entire heart. | Gap Junctions.txt |
And that allows the heart to pump all the blood throughout the cardiovascular system. | Gap Junctions.txt |
Now, another example of these intercellular communications via gap junctions is in the muscle cells of the uterus. | Gap Junctions.txt |
So if a woman is about to give birth, so that uterus must contract. | Gap Junctions.txt |
And it's these gap junctions that allows the contraction of that uterus muscle. | Gap Junctions.txt |
Now, another area that uses gap junctions to basically communicate between nearby cells is inside the brain. | Gap Junctions.txt |
So inside the brain, certain types of nerve cells don't actually use neurotransmitters to send action potential from one cell to another. | Gap Junctions.txt |
Instead of using your transmitters, they actually use gap junctions. | Gap Junctions.txt |
So on the presynaptic cell and the post synaptic cell, they're connected by these gap junctions. | Gap Junctions.txt |
And that allows the quick movement of the action potential from one cell, the presynaptic neuron, to the other cell that postsynaptic neuron. | Gap Junctions.txt |
Now let's move on to function number two, cell nourishment. | Gap Junctions.txt |
So every single cell in our body needs things like glucose, amino, amino acids, nucleotides, to actually survive and function correctly. | Gap Junctions.txt |
Now, not all of these cells actually are found next to capillaries. | Gap Junctions.txt |
And that means not all cells in our body can actually directly obtain the nutrients they need from the body. | Gap Junctions.txt |
And that's where these gap, from the capillaries and that's where these gap junctions actually come into play. | Gap Junctions.txt |
Certain cells which are found far away from capillaries to cells in our bone and cells in our eye, for instance, basically depend on gap junctions to receive the proper nutrients such as glucose and nucleotides and amino acids in order to actually survive and function correctly. | Gap Junctions.txt |
And the final function is embryological development. | Gap Junctions.txt |
So things like differentiation and setting up the polarity of cells basically depends on the presence of gap junctions. | Gap Junctions.txt |
And if we block the function of gap junctions, that embryo will not be able to develop into that adult individual. | Gap Junctions.txt |
And so we see that these gap junctions, although they are a category of on channels, they're very different than the voltage gated and ligand gated on channels that we focused on previously. | Gap Junctions.txt |
So let's summarize the process of glycogenesis. | Overview of Gluconeogenesis .txt |
glycogenesis is the synthesis of glycogen molecules from glucose precursors. | Overview of Gluconeogenesis .txt |
So let's suppose we just ingested a meal that is rich in sugar molecules. | Overview of Gluconeogenesis .txt |
And so what that means is inside our blood plasma there will be an increase in the glucose levels. | Overview of Gluconeogenesis .txt |
Now, our liver is responsible for maintaining the proper glucose levels of our of blood. | Overview of Gluconeogenesis .txt |
And so what the liver cells do is they begin to uptake some of that glucose into the cytoplasm of that cell. | Overview of Gluconeogenesis .txt |
Now, once the glucose is inside the cell, the liver cell will want to trap that glucose inside the cell and prevent it from actually escaping back into the blood plasma. | Overview of Gluconeogenesis .txt |
And so what the liver cells actually do is they phosphorylate the glucose on the 6th position and they use an enzyme known as hexacinase. | Overview of Gluconeogenesis .txt |
So hexaginase takes a phosphoryl group from ATP and places it onto carbon six of glucose and that creates glucose six phosphate. | Overview of Gluconeogenesis .txt |
Now, once glucose actually once glucose six phosphate is created, glucose phosphate then undergoes a reaction in which there is a transfer of the phosphoryl group from the six position to the first position of that glucose and we form glucose one phosphate. | Overview of Gluconeogenesis .txt |
Now, the enzyme that catalyze this step is known as phosphorglucomutase. | Overview of Gluconeogenesis .txt |
And what this enzyme does is the following. | Overview of Gluconeogenesis .txt |
Inside the active side of this enzyme is a phosphorylated serine residue. | Overview of Gluconeogenesis .txt |
And that phosphoryl group on that serene residue is initially placed onto carbon one. | Overview of Gluconeogenesis .txt |
And what that generates is an intermediate molecule known as glucose one six bisphosphate. | Overview of Gluconeogenesis .txt |
In the second step that is not shown here, this blue phosphoryl group is transferred back onto that Serene residue and that regenerates the catalytic enzyme, the phosphoglucomutase. | Overview of Gluconeogenesis .txt |
And it also generates the final product, glucose one phosphate. | Overview of Gluconeogenesis .txt |
And so this phosphoryl group that's attached onto carbon one of the glucose ultimately comes from this enzyme and the enzyme picks up this phosphoryl group shown in blue. | Overview of Gluconeogenesis .txt |
Now, once we form glucose one phosphate, in the next step, the glucose one phosphate needs to be activated because by itself, glucose one phosphate cannot simply be added onto the growing glycogen chain because it's not active enough. | Overview of Gluconeogenesis .txt |
So we have to make it much more reactive and higher in energy. | Overview of Gluconeogenesis .txt |
And what we do is we essentially attach a phosphoryl group as well as a uridine molecule onto this section to form the UDP glucose. | Overview of Gluconeogenesis .txt |
So that takes place in this step three. | Overview of Gluconeogenesis .txt |
So we take the glucose one phosphate shown here and then we basically reacted with a urine triphosphate in the presence of the enzyme known as UDP glucose pyrophosphorylase. | Overview of Gluconeogenesis .txt |
And what this enzyme basically does is it attaches the phosphoryl group and the urine onto this region. | Overview of Gluconeogenesis .txt |
So we generate the following molecules. | Overview of Gluconeogenesis .txt |
So this entire purple region came from the urine triphosphate and the pyrophosphate, the remaining Pyrophosphate was essentially kicked off. | Overview of Gluconeogenesis .txt |
So this is the Pyrophosphate that was kicked off from the urine triphosphate. | Overview of Gluconeogenesis .txt |
And the remaining portion of that urine triphosphate basically was attached onto this molecule to form the uriidine diphosphate UDP glucose. | Overview of Gluconeogenesis .txt |
Now, the purpose of this was to create this high energy bond that is very reactive because as we'll see in just a moment, this is able to actually undergo the reaction which we attach it onto that growing glycogen chain. | Overview of Gluconeogenesis .txt |
Now, the pyrophosphate that is formed in the presence of water, which is basically found in the cytoplasma baristalis, will undergo a hydrolysis reaction in which this bond will be cleaved and will form two orthophosphate molecules. | Overview of Gluconeogenesis .txt |
Now, this is the reaction that actually drives the formation of UDP glucose. | Overview of Gluconeogenesis .txt |
It's because of this reaction, because this is continually being depleted, that this reaction actually takes place in the product favor direction. | Overview of Gluconeogenesis .txt |
So this is an important reaction because it ensures that we continually produce the UDP glucose molecules. | Overview of Gluconeogenesis .txt |
Now, once we produce the UDP glucose molecules, the next step is to basically generate a primer molecule. | Overview of Gluconeogenesis .txt |
So remember that a primer molecule is basically a short sequence of glucose nucleotides which are connected by alpha one four glycocytic bonds. | Overview of Gluconeogenesis .txt |
So why do we need a primer molecule? | Overview of Gluconeogenesis .txt |
Because the enzyme that elongates that glycogen chain, known as glycogen synthase, needs a primer to actually initiate that elongation process. | Overview of Gluconeogenesis .txt |
It simply cannot begin from scratch. | Overview of Gluconeogenesis .txt |
And the enzyme that generates that primer is known as glycogenin. | Overview of Gluconeogenesis .txt |
So it is not shown in the diagram, but basically an enzyme known as glycogenin creates this primer. | Overview of Gluconeogenesis .txt |
And so this is the primer that we have here. | Overview of Gluconeogenesis .txt |
So let's say this primer consists of N number of glucose molecules which are all connected by alpha one four glycocitic bonds. | Overview of Gluconeogenesis .txt |
So we have not yet created any branching points. | Overview of Gluconeogenesis .txt |
And so this is a linear unbranched polymer. | Overview of Gluconeogenesis .txt |
So in the next step, once we generate that primer by using the UDP glucose molecules and the enzyme we call glycogenin. | Overview of Gluconeogenesis .txt |
Now, glycogen synthase takes the primer and takes the UDP glucose shown here and basically catalyze the formation of that alpha one four glycocytic bond between this glucose here and the terminal glucose molecule of this primer. | Overview of Gluconeogenesis .txt |
And we basically form and extend it. | Overview of Gluconeogenesis .txt |
So we extend that primer by one and we also form the UDP, which is basically shown here. | Overview of Gluconeogenesis .txt |
So UDP is urine diphosphate, it contains the uridine and two phosphate groups. | Overview of Gluconeogenesis .txt |
And we're going to use the UDP in the last step, as we'll see in just a moment. | Overview of Gluconeogenesis .txt |
Now, once we form that glycogen, that linear unbranched glycogen, we want to actually begin branching that glycogen. | Overview of Gluconeogenesis .txt |
Because remember, branching actually increases the solubility of glycogen within the cytoplasm and it also increases the number of terminal positions on the glycogen. | Overview of Gluconeogenesis .txt |
And that in turn increases the rate by which we can break down and synthesize glycogen molecules. | Overview of Gluconeogenesis .txt |
So in the next step, step six, we have an enzyme we call the glycogen branching enzyme that basically catalyzes the cleavage of alpha one four glycocitic bond and the formation of Alpha one six glycocitic bond. | Overview of Gluconeogenesis .txt |
So let's suppose we have the following hypothetical glycogen molecules. | Overview of Gluconeogenesis .txt |
So let's suppose this molecule here is this molecule that we have right over here. | Overview of Gluconeogenesis .txt |
So what the glycogen branching enzyme does is it basically takes a region of seven glucose residues that contain a terminal position shown here. | Overview of Gluconeogenesis .txt |
So we have 123-4567. | Overview of Gluconeogenesis .txt |
So it cleaves the alpha one four glycocytic bond and then it forms an alpha one six glycocity bond. | Overview of Gluconeogenesis .txt |
And so we create this branching point. | Overview of Gluconeogenesis .txt |
And notice, as we discussed in a previous lecture, this section has to have at least eleven glucose residues. | Overview of Gluconeogenesis .txt |
So we have 1234-5678, 910, eleven. | Overview of Gluconeogenesis .txt |
So this is how glycogen is actually branched. | Overview of Gluconeogenesis .txt |
And once we undergo this entire process, for this process to actually continue taking place, we have to regenerate the UTP molecules, the urine triphosphate that we use up in this particular step, because glycogen will essentially stop taking place if we don't have enough UTP, because we need the UTP to actually generate the UDP glucose, the active form of glucose. | Overview of Gluconeogenesis .txt |
And so in the final step, what our cells actually do is they use an ATP molecule, transfer the phosphoral group from ATP onto the UDP that we basically formed in this step here. | Overview of Gluconeogenesis .txt |
So we take the UDP, we take an ATP and we transfer that phosphorus loop onto this to basically reform the UTP that now can be used in this step to continually produce the UDP glucose molecules needed to generate that glycogen. | Overview of Gluconeogenesis .txt |
And the enzyme that catalyzed this step is nucleocide difosphokinase. | Overview of Gluconeogenesis .txt |