Eukaryopolis – The City of Animal Cells: Crash Course Biology #4

Eukaryopolis – The City of Animal Cells: Crash Course Biology #4

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This is an animal. This is also an animal. Animal. Animal. Animal carcass. Animal. Animal.
Animal carcass again. Animal. The thing that all of these other things have
in common is that they’re made out of the same basic building block: the animal cell. Animals are made up of your run-of-the-mill eukaryotic
cells. These are called eukaryotic because they have a “true kernel,” in the Greek.
A “good nucleus”. And that contains the DNA and calls the shots
for the rest of the cell also containing a bunch of organelles. A bunch of different kinds of organelles and
they all have very specific functions. And all this is surrounded by the cell membrane. Of course, plants have eukaryotic cells too,
but theirs are set up a little bit differently, of course they have organelles that allow
them to make their own food which is super nice.  We don’t have those. And also their cell membrane is actually a
cell wall that’s made of cellulose. It’s rigid, which is why plants can’t dance. If you want to know all about plant cells,
we did a whole video on it and you can click on it here if it’s online yet. It might not
be. Though a lot of the stuff in this video is
going to apply to all eukaryotic cells, which includes plants, fungi and protists.   Now, rigid cells walls are cool and all, but
one of the reasons animals have been so successful is that their flexible membrane, in addition
to allowing them the ability to dance, gives animals the flexibility to create a bunch
of different cell types and organs types and tissue types that could never be possible
in a plant. The cell walls that protect plants and give them structure prevent them from
evolving complicated nerve structures and muscle cells, that allow animals to be such
a powerful force for eating plants. Animals can move around, find shelter and
food, find things to mate with all that good stuff.  In fact, the ability
to move oneself around using specialized muscle tissue has been 100% trademarked by kingdom
Animalia.>>OFF CAMERA: Ah! What about protozoans? Excellent point! What about protozoans? They don’t have specialized muscle tissue.
 They move around with cillia and flagella and that kind of thing. So, way back in 1665, British scientist Robert
Hooke discovered cells with his kinda crude, beta version microscope. He called them “cells”
because hey looked like bare, spartan monks’ bedrooms with not much going on inside. Hooke was a smart guy and everything, but
he could not have been more wrong about what was going on inside of a cell.  There is
a whole lot going on inside of a eukaryotic cell. It’s more like a city than a monk’s
cell.  In fact, let’s go with that a cell is like a city. It has defined geographical limits, a ruling
government, power plants, roads, waste treatment plants, a police force, industry…all the
things a booming metropolis needs to run smoothly.  But this city does not have one of those
hippie governments where everybody votes on stuff and talks things out at town hall meetings
and crap like that.  Nope.  Think fascist Italy circa 1938.  Think Kim Jong Il’s- I mean, think Kim Jong-Un’s North Korea, and
you might be getting a closer idea of how eukaryotic cells do their business.
  Let’s start out with city limits. So, as you approach the city of Eukaryopolis
there’s a chance that you will notice something that a traditional city never has, which is either
cilia or flagella.  Some eukaryotic cells have either one or the other of these structures–cilia
being a bunch of little tiny arms that wiggle around and flagella being one long whip-like
tail.  Some cells have neither. Sperm cells, for instance, have flagella, and our lungs
and throat cells have cilia that push mucus up and out of our lungs.  Cilia and flagella
are made of long protein fibers called microtubules, and they both have the same basic structure:
9 pairs of microtubules forming a ring around 2 central microtubules. This is often called
the 9+2 structure. Anyway, just so you know–when you’re approaching city, watch out for the
cilia and flagella! If you make it past the cilia, you’ll encounter
what’s called a cell membrane, which is kind of squishy, not rigid, plant cell wall,
which totally encloses the city and all its contents.  It’s also in charge of monitoring
what comes in and out of the cell–kinda like the fascist border police. The cell membrane
has selective permeability, meaning that it can choose what molecules come in and out
of the cells, for the most part.   And I did an entire video on this, which you
can check out right here. Now the landscape of Eukaryopolis, it’s important
to note, is kind of wet and squishy. It’s a bit of a swampland. Each eukaryotic cell is filled with a solution
of water and nutrients called cytoplasm.  And inside this cytoplasm is a sort of scaffolding
called the cytoskeleton, it’s basically just a bunch of protein strands that reinforce
the cell.  Centrosomes are a special part of this reinforcement; they assemble long
microtubules out of proteins that act like steel girders that hold all the city’s buildings
together. The cytoplasm provides the infrastructure
necessary for all the organelles to do all of their awesome, amazing business, with the
notable exception of the nucleus, which has its own special cytoplasm called “nucleoplasm”
which is a more luxurious, premium environment befitting the cell’s Beloved Leader. But
we’ll get to that in a minute.   First, let’s talk about the cell’s highway
system, the endoplasmic reticulum, or just ER, are organelles that create a network of
membranes that carry stuff around the cell. These membranes are phospholipid bilayers.
The same as in the cell membrane. There are two types of ER: there’s the rough
and the smooth. They are fairly similar, but slightly different shapes and slightly different
functions. The rough ER looks bumpy because it has ribosomes attached to it, and the smooth
ER doesn’t, so it’s a smooth network of tubes. Smooth ER acts as a kind of factory-warehouse
in the cell city. It contains enzymes that help with the creation of important lipids,
which you’ll recall from our talk about biological molecules — i.e. phosopholipids
and steroids that turn out to be sex hormones. Other enzymes in the smooth ER specialize
in detoxifying substances, like the noxious stuff derived from drugs and alcohol, which
they do by adding a carboxyl group to them, making them soluble in water. Finally, the smooth ER also stores ions in
solutions that the cell may need later on, especially sodium ions, which are used for
energy in muscle cells.   So the smooth ER helps make lipids, while
the rough ER helps in the synthesis and packaging of proteins. And the proteins are created by another typer
of organelle called the ribosome. Ribosomes can float freely throughout the cytoplasm
or be attached to the nuclear envelope, which is where they’re spat out from, and their
job is to assemble amino acids into polypeptides. As the ribosome builds an amino acid chain,
the chain is pushed into the ER. When the protein chain is complete, the ER pinches
it off and sends it to the Golgi apparatus. In the city that is a cell, the Golgi is the
post office, processing proteins and packaging them up before sending them wherever they
need to go. Calling it an apparatus makes it sound like a bit of complicated machinery,
which it kind of is, because it’s made up of these stacks of membranous layers that
are sometimes called Golgi bodies. The Golgi bodies can cut up large proteins into smaller
hormones and can combine proteins with carbohydrates to make various molecules, like, for instance,
snot.   The bodies package these little goodies into
sacs called vesicles, which have phosopholipid walls just like the main cell membrane, then
ships them out, either to other parts of the cell or outside the cell wall. We learn more
about how vesicles do this in the next episode of Crash Course. The Golgi bodies also put the finishing touches
on the lysosomes. Lysosomes are basically the waste treatment plants and recycling centers
of the city. These organelles are basically sacks full of enzymes that break down cellular
waste and debris from outside of the cell and turn it into simple compounds, which are
transferred into the cytoplasm as new cell-building materials. Now, finally, let us talk about the nucleus,
the Beloved Leader.  The nucleus is a highly specialized organelle that lives in its own
double-membraned, high-security compound with its buddy the nucleolus.  And within the
cell, the nucleus is in charge in a major way.  Because it stores the cell’s DNA, it
has all the information the cell needs to do its job. So the nucleus makes the laws for the city and orders the other organelles around, telling
them how and when to grow, what to metabolize, what proteins to synthesize, how and when
to divide. The nucleus does all this by using the information blueprinted in its DNA to
build proteins that will facilitate a specific job getting done.  For instance, on January
1st, 2012, lets say a liver cell needs to help break down an entire bottle of champagne.
The nucleus in that liver cell would start telling the cell to make alcohol dehydrogenase,
which is the enzyme that makes alcohol not-alcohol anymore. This protein synthesis business is
complicated, so lucky for you, we will have or may already have an entire video about
how it happens. The nucleus holds its precious DNA, along
with some proteins, in a weblike substance called chromatin. When it comes time for the
cell to split, the chromatin gathers into rod-shaped chromosomes, each of which holds
DNA molecules. Different species of animals have different numbers of chromosomes. We
humans have 46. Fruit flies have 8. Hedgehogs, which are adorable, are less complex than
humans and have 90 Now the nucleolus, which lives inside the
nucleus, is the only organelle that’s not enveloped by its own membrane–it’s just
a gooey splotch of stuff within the nucleus. Its main job is creating ribosomal RNA, or
rRNA, which it then combines with some proteins to form the basic units of ribosomes. Once
these units are done, the nucleolus spits them out of the nuclear envelope, where they
are fully assembled into ribosomes. The nucleus then sends orders in the form of messenger
RNA, or mRNA, to those ribosomes, which are the henchmen that carry out the orders in
the rest of the cell. How exactly the ribosomes do this is immensely
complex and awesome, so awesome, in fact, that we’re going to give it the full Crash
Course treatment in an entire episode. And now for what is, totally objectively speaking
of course, the coolest part of an animal cell: its power plants!  The mitochondria are these
smooth, oblong organelles where the amazing and super-important process of respiration
takes place. This is where energy is derived from carbohydrates, fats and other fuels and
is converted into adenosine triphosphate or ATP, which is like the main currency that
drives life in Eukaryopolis. You can learn more about ATP and respiration in an episode
that we did on that. Now of course, some cells, like muscle cells
or neuron cells need a lot more power than the average cell in the body, so those cells
have a lot more mitochondria per cell.   But maybe the coolest thing about mitochondria
is that long ago animal cells didn’t have them, but they existed as their own sort of
bacterial cell. One day, one of these things ended up inside
of an animal cell, probably because the animal cell was trying to eat it, but instead of
eating it, it realized that this thing was really super smart and good at turning food
into energy and it just kept it. It stayed around. And to this day they sort of act like their
own, separate organisms, like they do their own thing within the cell, they replicate
themselves, and they even contain a small amount of DNA. What may be even more awesome — if that’s
possible — is that mitochondria are in the egg cell when an egg gets fertilized, and
those mitochondria have DNA. But because mitochondria replicate themselves in a separate fashion,
it doesn’t get mixed with the DNA of the father, it’s just the mother’s mitochondrial DNA.
That means that your and my mitochondrial DNA is exactly the same as the mitochondrial
DNA of our mothers. And because this special DNA is isolated in this way, scientists can
actually track back and back and back and back to a single “Mitochondrial Eve” who lived
about 200,000 years ago in Africa.   All of that complication and mystery and beauty
in one of the cells of your body. It’s complicated, yes. But worth understanding. Review time! Another somewhat complicated
episode of Crash Course Biology. If you want to go back and watch any of the stuff we talked
about to reinforce it in your brain or if you didn’t quite get it, just click on the
links and it’ll take you back in time to when I was talking about that mere minutes ago. Thank you for watching. If you have questions
for us please ask below in the comments, or on Twitter, or on Facebook. And we will do
our best to make things more clear for you. We’ll see you next time.

100 thoughts on “Eukaryopolis – The City of Animal Cells: Crash Course Biology #4

  • Mohamed Lehachi Post author

    thank you for this

  • Cassidy Varg Post author

    fortunately, my biology professor is awesome and knows how to describe things in an easy to understand way however, there's only so much you can teach in 45min

  • yahirfortniteking Post author

    Bruh Im in 7th grade why am I learning this

  • Andrew Caddel Post author

    bruh moment

  • Roger Snow Post author

    How does the Golgi app. know how to fold molecules of protein into specific shaped molecules? I mean, how does it know what it is doing? How does it know what shape proteins it needs, how does it know how to fold those shapes? How does it fold those shapes? How does it know what it is doing, is there a brain inside the Golgi? How does it know what it needs to do? It just seems so complex, how can something that is not even its own cell, know how and when to do all these things?

  • Jacob MtCastle Post author

    Thank the good lord I found this I have an exam tomorrow and my Biology professor sucks

  • Emmanuel Abraham Post author

    Learning new things about cell it's very fun.
    Mabey a little bit.🤔

  • Daniel Culver Post author

    he looks like dwight shrute

  • RAMY Post author

    The comment section is getting a bit repetitive… we get it your biology teacher sucks. Mine is actually quite good but I like to see other people teach it Incase she missed anything.

  • J McG Post author

    Hank, what's written on your hand? Lol i think it's really cool that one of my idols has to write things on his hand to remember them just like I do.

  • Sara Mammedova Post author

    Hello l want have a doctor becouse l like this job an this job its fantactic amazinnng👏💛😅

  • ashwini ranade Post author

    Every sentence he utters has a whole episode explaining that sentence..

  • blob fish Post author

    my ancestors fought for there life’s and where the best of there generations, and yet i’m here just watching a video and doing nothing in my life, does it get better?

  • Savannah Rudolph Post author


  • Dragon Pearl Post author

    Ah yes. This has aged well.

  • wtf Post author

    picture of burger
    Hank: animal carcass
    Me: gags

    idk why but that changed my opinion on burgers omg

  • the rush 27 Post author

    Me watching this for a test tommorow 😰

  • *cough* It's BTS Post author

    Watch at 0.75 speed to be able to process information.
    You’re welcome

  • Natalie Mak Post author

    So technically are mitochondrial DNA the same in all humans if they came from one single mother Eve?

  • AS Post author

    Is this for A level new spec?

  • Diane None Post author

    So does this mean that the first signs of life was Africa! You did mention mitochondria was found long ago in Africa? Soooo we know what this means!! Yes first signs of life was in "Africa". Yeah! 🙂

  • Roker Sunny Post author

    you are very smart like a cow

  • CalignousAurora : Post author

    Who is watching this cuz they got a test tommorow and they are not confident

  • i Think Post author

    Who create all that beautiful and complicated cells ?

  • Jacob Bermudez Post author

    List that biology teacher that doesn’t teach you anything down below

  • Kristin Aker Post author

    Got a 90 on my bio test. Thanks, Hank

  • Novalize Post author

    Mitochondria is like the dad that isn't your real dad, but sticks around anyway.

  • Poop? Poop? Post author

    science is useless

  • squishy and hork Post author

    When the teacher cant teach

  • Jack Molloy Post author

    When he talks about the mitochondria, is he talking about the endosymbiotic theory

  • Julia dixon Post author

    Need more videos like this!! 😁

  • Kyle Sensenig Post author

    Why are the border police fascist?

  • Lachy Mengersen Post author

    So the nucleus is like the brain of the cell

  • Liban Sheikh Post author

    Here at 9.99 million subs!!

  • PrincessPandaTube Post author

    8:27 So, Sonic is less complex?!

  • Soham Panigrahi Post author

    When you have to study for a test and you're teacher is too slow….

  • Random Guy Post author

    Hi it’s me Isaac

  • poppy rose Post author

    He must be Christian

  • SqiffyMarlin Post author

    When you can’t afford your own teacher

  • Scott Happy Post author

    My bio teacher assigned a test this morning. For the next day. Well this darn helps

  • Dani Nino Post author

    Watches the video:…
    Me during the test: PLANTS CANT DANCE🌱

  • Charles Brown Post author

    crashcourse biology science education teach learn animal cells cell membrane eukaryote eukaryotic organelle organ tissue muscle nerve animalia robert hooke cilia flagella microtubules cytoplasm ctyoskeleton centrosome nucleus nucleoplasm nucleolus endoplasmic reticulum ribosome amino acid polypeptide golgi apparatus golgi lysosomes DNA chromatin rRNA mRNA mitochondria tags

  • Carlton Allen Post author

    im depressed

  • Marquis Smith Post author

    nice one man

  • Jaylin Jackson Post author

    no no no

  • evilqueen 9099 Post author

    I A'sed my test just by rewatching a few times. I dont even play attention in class

  • Sanika Chitre Post author

    crash course is very helpful as i am a struggling student in science

  • Jade Tamplin Post author

    When your watching this hoping and praying it will allow you to pass your upcoming NZQA Level 2 biology paper at 9:30am tomorrow… yeaa. Anyone else in the same boat?

  • Shairy Jimenez Post author


  • elias gurule Post author

    Plant cells have cell membranes and cell walls

  • Life of an Aussie Kid Post author

    this guy needs to set his links up

  • Zeke Steed Post author

    Nucleolus is The Godfather of the cell.

  • Jagdish Barot Post author

    Very strongly I recommend Gene Machine by Dr Venki Ramakrishnan, the Nobel Laureate 2009.

  • Joanne Lee Post author

    Do cilia and flagella do something to stop stuff from getting into the cell? Why do we have to watch out for them?

  • Daniel Hamilton Post author

    What's the key to animal's? A: Haemitology, life it's all in the blood baby(Gen. 9:4-6).  We see this is my favorite red dye from where we get red cherries, which is made from "beetlejuice".  Unlike these beetles, humans should only give blood about every 60 days.

  • Salma Shawky Post author

    my biology teacher can teach very well but I want to be ahead

  • Chadthe38yearoldman Post author

    i want YOU to eat more bacon

  • سید حسین آرامی Post author


  • Max Tanner Post author


  • Katerina Williams Post author

    When you're watching this because you don't want to read your ugly handwritten notes

  • Clarah Zonda Post author

    Does the human cell fall under the animal cell. Please help

  • swest88041 Post author

    so in Eukaryopolis dictatorships like Kim Jun Moon =GOOD, fashism with border patrols like USA=BAD. great!!! long live N. Korea.

  • NCERT BIOLOGY Vaidya Academy Class 11th and 12th Post author

    Nicely explain

  • Binge Watch Post author

    You should've said "Animal" when the camera switched to you, because Human's are animals, not in the slur form, but biologically, we are animals. There is no such thing as a third Kingdom, there is no Human Kingdom alongside the Plant Kingdom and Animal Kingdom. We shouldn't differentiate ourselves from that bucket of KFC that you just got done eating. That's why I get so heated when people argue that we're different.

  • Rees Freeman Post author

    0:58 "Plants can't Dance" …I AM GROOT!!!

  • Rees Freeman Post author

    Stop comparing the cell to fascism! You could equally compare the nucleus to a strong central government such of the United States, and likewise the cell membrane to selectively permeable borders of any non-fascist state. Arbitrarily claiming the most basic unit of life, the cell is like a fascist state in a metaphor of body politic, only serves to literally naturalize fascism! You should learn from the more historically wise John Green, at Crash Course history, and remember that this machine kills fascists…

  • Life of Kaay & Jay Post author

    I am not ready for biology bro 🤨🤨🤨

  • J Pope Post author

    Im here because my science teacher said that if we watched this video we would get 30 points in extra credit which I need since I have a C in science 🤒

  • Bean Beanington Post author

    my bio final is tomorrow, you're my only hope

  • Alex Kenobi Post author

    its 2 am and i have a college-level biology exam tomorrow. thank you hank

  • Adam Smith Post author

    What about the Mitochondrial eve's mother?

  • eric de jesus Post author


  • dheeraj pimoli Post author

    How mitochondrial dna pass down from a single female.why mitochondrial dna of other female didn't pass who were living at that same time?

  • itz_Starr_btw Post author

    maze bean

  • Yanyan Zl Post author

    When Your mum is making you memorise this 🙁

  • Yenthe Vandeputte Post author


  • Yenthe Vandeputte Post author


  • travis scott Post author


  • Athena Goddess of War Post author

    If I may, I suggest doing a course on Forensic Anthropology. The topic is something that I am very passionate about and is extremely interesting. Having your videos on the subject would be very helpful to the full understanding of Forensic Anthropology.

    Thank you,
    ~ Tiger

  • Arina Filatova! Post author


  • linh jin Post author

    exams next week kinda cramming 💁‍♀️

  • Idontknow myguy Post author

    This vid is good. Even 8 years later

  • Pablo Garcia Seminara Post author

    That moment when Crash Course explains the plot of Parasite Eve.

  • Mike Or Post author

    "Midi-chlorians are a microscopic organism that resides within all living cells." -Qui-Gon Jinn.
    According to George Lucas, midi-chlorians are the same as mitochondria.

  • madeline schwartz Post author

    what is written on his left arm?

  • cutecoot batkat Post author

    I love the memes but have always hated "the mitochondria is the powerhouse of the cell" because it never taught me anything. Teachers loved saying it without elaborating why it is a powerhouse, so I never understood its importance until now. Thanks so much!

  • Lacye Hepler Post author

    If i was an instructor, I would play crash course before I lectured to give them a visual. lolol

  • Srikar Bala Post author

    What's written on ur hand, Hank?

  • Alyssa Fajardo Post author

    what grade are yall watching this in
    Mine 7th

  • Rayan Zouai Post author

    Who’s here during the wuhan coronavirus outbreak 💋

  • 「spicy」 Post author

    I’ve got an A-Level mock exam coming up tomorrow so this is saving my life.

  • Another Day With Natalia Post author

    cell membrance
    endoplasmic reticulum
    transport vesicle

  • Another Day With Natalia Post author


    Animal cell

    Eukaryotic cells, with membrane ,organelles and nucleus containing DNA that calls the shots

    Animal, plants, fungi and protist

    Flexible and squishy membranes as oppose to plants, allowing the creation of cell, organs and tissue types

    Cell is like a city:

    On the surface:

    Microtubials: made of long protein fibers: Cillia (tiny arms like in lungs and throat pushing the mucus up) and Flagella (whip-like tail like in sperms), Protozoans, move with Microtubials instead of muscle tissue

    Membrane: Selective permeability: monitoring coming in and out like boarders


    Cytoplasm: water+nutrients

    Cytoskeleton: scaffolding made of protein strands, Centrosomes: infrastructures

    Endoplasmic Reticulum (ER): network of membranes like a highway system

    The smoother parts of ER are like factories:

    containing enzymes (proteins) producing lipids,

    detoxifying substances by adding carboxyl to make them soluble in water,

    storing ions like Sodium used for energy

    The rougher parts of ER have Ribosomes attached to them:

    Synthesis and packaging of proteins

    Ribosomes: float freely, assemble amino acids into Polypeptides pushing the protein chain into ER where it's bitten off and sent to Golgi Aparatus

    Golgi Aparatus: made of membranous layers: the post office for packaging proteins, cutting them into hormones, combining them with Carbs to make molecules

    Vessicles: the packages with Phospholipid walls

    Lysosome: waste treatment and recycling, sacks containing enzymes breaking down cell waste into building material

    Mitochondria: the power plant where respiration takes place, fuels converted to Adenosine Triphosphate (ATP) which is the currency

    They were separate bacteria that animal cells absorbed and kept, and they still act as their own organisms with their own DNA, they exist in the egg and doesn't mix with sperms DNA during fertilization


    The leader

    Contains DNA and has all the information and instructions

    Has a double membrane

    Nucleoplasm (is like Cytoplasm)

    Nucleolus at the center: creates Ribosomal RNA+proteins=Ribosomes

    Messenger RNA: carry the orders to Ribosomes

    Chromatin: web-like substance that holds DNA molecules, upon cell division they gather into rod-shaped chromosome, humans have 46

  • Keri F. Post author

    My bio teacher said "the powerhouse of the cell" isn't
    a good answer for explaining its function xD

    it's good to understand that sentence, but
    it's better to be more descriptive when writing an
    organelles' function.

  • Nate MITCHELL Post author

    hello there

  • Alana Post author

    Who’s here because they have a test on it tomorrow?

  • Anii_ _Squ11d Post author

    Hank: the Golgi bodies can cut up large proteins into smaller hormones and combine proteins with carbohydrates to make various molecules, for instance snot.
    Me: *blowing my nose* Eh WhAt!?

  • DanFan :D Post author

    Class lectures are so long, boring, and useless. Crash course teaches you so fast, that you have to pause in between.

  • Mouser613 Post author

    How does the nucleus communicate with the rest of the cell?

  • CoUrtney Clarke Post author

    Thank you for helping me understand this as part of my pharmaceutical science diploma!

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