Different from the so-called vacuolar apparatus, we have another part of this membrane apparatus, its called mitochondria and the peroxisomes. These two apparatus can make use of our oxygen and produce ATP for all our physiological activities. So. These organelles are suggested to be invaded from outside of eukaryotic system. And some people suggest they origin from the ancient bacteria. And then somehow get into the eukaryotic cells and then, these two part get along very well and then eventually they become a part of our eukaryotic cell. Okay, so the position of this organelles, this organelles are not evenly distributed in everywhere in our cells. Some organelles are not distributed or not localized in the axon. For example ribosomes, rough ER, Golgi, and lysosomes are not in the axon. But recently, there is some evidence show that people find some ribosomes in this distal area of the axon. It's not fully proved. So for now, we put here. The ribosome is not found in the axon. And some organelle can be found all over in the cell. These include mitochondria and smooth ER. Cytoskeleton, in a cell, there are a lot of cytoskeleton. These cytoskeleton can be counted for about one-fourth of the total protein of the neuron. There are several functions of these cytoskeleton. One is to determine the shape of a neuron and the other function is to support the neuron, serve as scaffold of the neuron. And the third function, very important function is the transport to transport materials, proteins, vesicles, cellular organelles inside of the cell. In the neuron there are three major parts of cytoskeleton, microtubules, neurofilaments and actin microfilaments. These are three major components of the cytoskeleton in the neuron. Microtubule is made with several sub units, turning together form this barrel-like structure. Neurofilaments formed with alpha and beta sub units, turn together, twist together, form a thicker filament element. And in this thicker elements can turn together, form this neurofilament. And the actin microfilaments has two sub unit, alpha and beta sub unit. And then, they turn together and form this actin microfilaments. Microtubules. Microtubules consist of alpha and beta tubulin. Microtubules undergo very rapid polymerization and depolymerization, process all the time. So these two process, one is a polymerization, the other one is a depolymerization happen all the time with your microtubules system. They are not stable and they are not there all the time. So, these two process are always happened. The stability is due to the microtubule associated protein called a MAPs and before we mention a MAP2 is a specific marker for dendrites and also MAP3, also called a Tau protein is a marker for axons. These proteins are all microtubule associated protein. They help microtubule to form this stable structure. So, MAP2 is only localized in a dendrites, MAP3 and tau are only in axons. This is a MAP2. Neurofilaments. Neurofilaments is compared to microtubule. Neurofilaments is very stable and it's almost totally polymerized all the time. So, the most abundant fibrillar components of the axon is the neurofilaments. It is three to ten times more neurofilaments than microtubules in an axon. So, it's a major component of the cytoskeleton in the axon. So, in AD we mentioned there is a pathological structure called neurofibrillary tangle. Is composed with hyperphosphorylated tau. So, normally tau is phosphorylated but in the AD, tau is hyperphosphorylated. We call it hyperphosphorylated. And these hyperphosphorylated tau can aggregate together and form these so-called neurofibrillary tangles. . And this thing is toxic to the cell, so this neurofibrillary tangle will kill the cell, eventually. So inside of the cell, we see this neurofibrillary tangle congested in the cell and then this neurofibrillary tangle forms with hyperphosphorylated tau protein. Microfilaments. Microfilaments is consist with actin. Actin is perhaps the most abundant animal protein in the nature. So, normally we use that as a load and control for our western blot because it's very easy to detect. It is highly conserved from a human even to a protozoa. Actin filaments is the short form of a polymer. Compared to the microtubule and the neurofilaments, actin filaments are much shorter. The acting filaments concentrated at a cell junctions and just underneath the plasma membrane. And the function of these microfilaments is associated with the movement of growth cones, , filopodia, and the generation of the microdomains. What is a microdomain like? We just mentioned the spine, the dendritic spine. The growth or generation of the dendritic spine and the formation of synapses are highly associated with the function of these microfilaments. The formation of the pre and the postsynaptic specialization.
