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  • If you had to think about the most exciting day you ever had in a science classroom, which

  • day would that be?

  • Looking back through the years---we have a few.

  • The time we participated in an earthworm dissection.

  • The time we took apart an owl pellet.

  • The osmosis eggs.

  • All of the fruit flies in genetic experiments.

  • Oh, I could go on, but I will never forget one day in my 9th grade science class.

  • My teacher brought in pond water.

  • And I put one drop of pond water on a microscope slide and saw the most amazing thing ever…I

  • saw, an amoeba.

  • A single celled amoeba on that microscope slide, and

  • I was forever stuck on science from that point on.

  • Because I could not believe this little cell was there, alive on this slide, still eating

  • because that’s what amoebas do a lot.

  • To imagine that every person is actually made of billions of cells---of course not amoeba

  • cells but animals cells--- billions of animal cells, is fascinating.

  • In fact, it really makes you reflect on some of the incredible statements of the modern

  • cell theory.

  • The modern cell theory includes the following: 1st that the cell is the smallest living unit

  • in all organisms.

  • 2nd that all living things are made of cells.

  • One or more cells.

  • The amoeba I observed was a single-celled organism, so unicellular.

  • Humans are made of many cells, so multicellular.

  • And 3rd, all cells come from other, pre-existing cells.

  • Cells have their own little world inside them.

  • They carry genetic information!

  • They can divide!

  • Many have functions and processes that their organelles, structures inside them, can take

  • care of.

  • On our planet, we can divide cells into two major groups.

  • As a cell, youre either a prokaryote or an eukaryote.

  • Bacteria and Arachae are prokaryotes.

  • Everything else---plants, animals, fungi, protists----are eukaryotes.

  • Both prokaryotes and eukaryotes have genetic material.

  • Both have cytoplasm.

  • Both have ribosomes, which are small organelles that make proteins.

  • Both have cell membranes which control what goes in and out of the cell.

  • But what makes them different is a big deal.

  • Prokaryote---pro rhymes with no---they have no nucleus which holds the genetic material

  • and controls the cell’s activities.

  • Prokaryotes have no membrane bound organelles.

  • Membrane bound organelles are fancy organelles like the nucleus and mitochondria and golgi

  • apparatus.

  • Eukaryotes---eu rhymes with do----they do have membrane bound organelles.

  • So now you may be wondering what do the organelles do---what are their functions?

  • Well you know our style---we love our science with a side of comics.

  • So we want to take you on a tour of the ride of your life---into the inside of a cell!

  • To start our trip, were first going to have to get through this cell membrane, also

  • called a plasma membrane.

  • It’s selectively permeable which means that it only lets certain select materials in and

  • out.

  • By doing so, it keeps things in the cell stable---also known as keeping homeostasis.

  • We have an entire video on just the membrane

  • itself---which is found in all cells, but for now, were just going to have to squeeze

  • through this protein in the membrane.

  • Inside the cell, we find ourselves in this jelly like material called cytoplasm.

  • It surrounds all of these internal cell structures, and youll find it inside both prokaryotes

  • and eukaryotes.

  • Now organelles that are just floating around in the cytoplasm can have more support than

  • you might think.

  • Cells contain a cytoskeleton which is a collection of fibers that will provide support for the

  • cell and its organelles.

  • The cytoskeleton can even play a major role in movement.

  • The cytoskeleton actually deserves its own video though because it is very complex---and

  • its organization varies depending on what kind of cell youre looking at.

  • Moving through this cytoplasm, let’s start with ribosomes.

  • They are NOT membrane bound organelles and they are going to be in both prokaryotes and

  • eukaryotes.

  • And they make protein.

  • Which is really important because that’s what so much of genetic material---DNA codes

  • for---protein.

  • Ribosomes can be free in the cytoplasm.

  • They can be attached to another organelle too, which well talk about a bit later.

  • We are now going to focus on eukaryote organelles, which means, organelles that will be membrane

  • bound.

  • So this takes our travel to the big boss, the nucleus.

  • In eukaryotes, it holds the genetic material.

  • Genetic material as in DNA for example.

  • All cells have DNA but if youre an eukaryote, you have a nucleus to put it in.

  • The nucleus controls the cell activities.

  • Inside it, it has a nucleolus, which is where ribosomes can be produced.

  • Attached to the membrane of the nucleus, or nuclear membrane, you can find the endoplasmic

  • reticulum.

  • ER for short.

  • It does a lot of processing of molecules for the cell---like protein folding----and it

  • also is highly involved in actually transporting those molecules around.

  • Like a highway!

  • There is rough ER which has ribosomes attached to it, making it---as you can imagine---rough.

  • And them smooth ER which doesn’t have the ribosomes.

  • Rough ER specifically tends to be involved with protein producing and transporting, because

  • remember that ribosomes make protein.

  • Molecules that leave the ER can be sent away in vesicles that actually pinch off of the

  • ER themselves.

  • Smooth ER has many additional roles including detoxification, which is one reason why your

  • liver cells tend to have a lot of smooth ER.

  • Another additional role of smooth ER is that it can make some types of lipids.

  • Next the Golgi apparatus.

  • It’s the ultimate packaging center.

  • It can receive items from the transport vesicles that pinched off of the ER.

  • It has enzymes that can modify molecules it may receive and it sorts the materials it

  • receives as well.

  • It can determine where to send those molecules---including some that may eventually be sent to the membrane

  • so they can be secreted, which means, items that can sent out of the cell.

  • So with all that’s going on in here, you might start to wonderwhat’s powering

  • this thing?

  • The mighty mitochondria.

  • Or mitochondrion, if just talking about 1.

  • Like a power plant!

  • This thing makes ATP energy in a process called cellular respiration.

  • It’s not a type of power plant that you would think ofit runs on glucose, which

  • is a sugar, and needs the presence of oxygen to efficiently make ATP energy.

  • Now at this point, we need to mention that eukaryotes are not a one size fits all. Animal cells can have differences from plant cells.

  • We have a…fork in the road here.

  • For example, plant cells not only have mitochondria, but they also can have these awesome organelles

  • called chloroplasts.

  • Chloroplasts actually make glucose by using light energy in a process known as photosynthesis.

  • They tend to have a green look to them because they have a pigment that captures light energy

  • and reflects green light.

  • Both plant and animal cells can have vacuoles---now vacuoles can have a lot of different functions

  • but many types act as storage of materials.

  • Plant cells can have one large vacuole called a central vacuole while animal cells can have

  • several smaller vacuoles.

  • Remember how we already said that all cells have membranes?

  • Plant cells additionally have a cell wall which is a layer that offers additional protection

  • and shape maintenance that animal cells do not.

  • Hmm now how to get out of this animal cell weve been in?

  • Wellwe could get out like a protein would.

  • So if we were a protein, we would only be made because of instructions from DNA and

  • remember that in Eukaryotes, DNA is found in the nucleus.

  • We would be made by a ribosome.

  • The ribosomes could be attached to the Rough ER.

  • The Rough ER highway would provide a vesicle to send us to the Golgi apparatus where the

  • sorting can take place.

  • Andif were tagged for being secreted...were sent off thru a vesicle from the Golgi to

  • the membrane.

  • Andout we go!

  • Just keep in mind that in our quick tour, there are still so many more awesome organelles

  • found in different types of eukaryote cells to continue exploring so to the Google for

  • more!

  • Well that’s it for the Amoeba Sisters and we remind you to stay curious!

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B2 中上級

細胞入門。グランドセルツアー (Introduction to Cells: The Grand Cell Tour)

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    VoiceTube に公開 2021 年 01 月 14 日
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