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Subcellular Organization

by Richard Mitchell, MD

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    00:00 Hello and welcome. In the next series of topic discussions, we are going to look at cell biology, because like Koch said, and Koh is a famous German pathologist, kind of the godfather of pathology, and he's German, and so therefore, he must know what he's talking about.

    00:18 He said that pathology begins with the cell.

    00:22 And understanding what's going on at a cellular level is going to be really important.

    00:27 So, we're gonna take a nice kind of tour through various aspects of subcellular organization to provide a framework for thinking about things at larger levels, such as tissues and organs and whole organisms.

    00:41 This first one is about the inner phase with the outside world.

    00:45 So, how the inside of a cell kind of interacts with the rest of the universe.

    00:51 We'll start first with the molecular biologist view of the cell.

    00:57 And the molecular biologist views everything of importance, being the nucleus, and the rest of the cell is just an afterthought.

    01:04 And of course, that's not true, but a lot of people will say, "Yeah, genetics, and the rest of the world is just details." The traditional view, the cell is more like this.

    01:15 So, we have a round ball, and in it, kind of scattered throughout like raisins in bread pudding, are various organelles.

    01:24 And in the middle, there's a big raisin. That's the nucleus.

    01:26 And there are all these various structures.

    01:28 We're not gonna go through them right now, but they're kind of a yeah, everything is there, and they do different things.

    01:35 Okay, a cell biologist views it a little bit differently.

    01:39 So, biologists actually say, "You know what? Most cells are not round. They are not oval." In fact, the only ones who are round or oval are gonna be the ones that are in the circulation.

    01:49 Every other cell in the body has a different kind of structure, and it may be flat or squamous.

    01:56 It may be cuboidal, like a little cube. It may be columnar, it may be pyramidal, but it's got a structure. And the surfaces got structure. So, here, shown cilia and microvilli.

    02:06 And now, we're starting to understand too that there are particular numbers of intracellular organelles, such as the endosome and the lysosome and the peroxisome and mitochondria.

    02:16 And those are all in there, and they're -- not only are they in there, but they're not in there randomly.

    02:21 It's not raisins and bread pudding, it's actually organelles that are organized in such a way that the cell is able to function in a coordinated fashion.

    02:33 Now, we're getting into a real reality, although it's only two-dimensional.

    02:38 This is a transmission electron micrograph of a cell.

    02:41 We're looking at that big thing in the middle, is a nucleus.

    02:46 That nucleus actually has dark areas and light areas.

    02:50 That's different amounts of euchromatin in the light area, transcriptionally active chromatin, and heterochromatin or the darker chromatin, which is transcriptionally inactive.

    03:00 And if we could look down in there, we would see in the euchromatin, there are specific genes that are being made.

    03:05 This particular cell happens to be a plasma cell.

    03:08 So, this is a mature end stage B cell that's cranking out tons and tons of antibody.

    03:14 And around that nucleus, we see lots of laminated structures.

    03:18 Little fine lines that look like sedimentary rock.

    03:21 Those fine lines are rough endoplasmic reticulum.

    03:23 So, this cell, which is engineered to crank out immunoglobulin, has got a lot of synthetic machinery, neatly, tightly applied to the nucleus that is synthesizing immunoglobulin.

    03:36 And that immunoglobulin, that antibody, is being packaged up in those dark, black circles.

    03:40 Those are secretory vacuoles.

    03:42 And those will eventually be transported to the cell surface and released to the outside world.

    03:46 Also, in here, because it's a cell and it's alive, there's a mitochondria.

    03:51 There are some other structures.

    03:52 There -- we're starting to get a sense that there really is significant organization to this and it's not just randomness.

    03:59 And then, hard to convey in a static image, but really, the cell is constantly in motion.

    04:05 Things are being synthesized in the rough endoplasmic reticulum next to the nucleus and being transported out along microtubules in vacuoles to the cell surface where they are being released. And you see that release going on here.

    04:19 And then, membrane is being invaginated and parceled up, and then shipped to someplace else.

    04:26 And it is like a French cafe in terms of the franticness of things running around in various different directions.

    04:33 So, if we could make this a movie, you would see that the cell is an incredibly dynamic structure.

    04:39 And not only that, but every structure within there is also constantly turning over.

    04:45 Those long blue lines which are microtubules constantly turning over and making new ones, getting rid of old ones.

    04:51 The membrane, making new ones, getting rid of old ones.

    04:54 The nuclear membrane, changing that all the time.

    04:57 All those vacuoles constantly evolving.

    04:59 So, the cell, to capture your imagination, is wildly frantic activity at all times.

    05:07 And it's also turning over at all times.


    About the Lecture

    The lecture Subcellular Organization by Richard Mitchell, MD is from the course Cellular Housekeeping Functions.


    Included Quiz Questions

    1. It is transcriptionally active.
    2. It is transcriptionally inactive.
    3. It has a condensed chromatin structure.
    4. It is located inside the nucleolus.
    5. It appears as intensely-stained bands when observed under the microscope.
    1. Rough endoplasmic reticulum
    2. Smooth endoplasmic reticulum
    3. Mitochondria
    4. The cell membrane
    5. Lysosomes
    1. The cell is dynamic and constantly in motion.
    2. Most of the cells have a round ball-like shape.
    3. Cells have limited turnover in order to conserve energy.
    4. Organelles swim randomly within the cytosol.
    5. The cytoplasm is highly structured by the cytoskeleton and cilia.

    Author of lecture Subcellular Organization

     Richard Mitchell, MD

    Richard Mitchell, MD


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