Biological Molecules – You Are What You Eat: Crash Course Biology #3

Hello, and welcome to the kitchen. I wanted
to invite you here today because last week we started off in my bathroom and kinda feel
bad about that. And also because as I’m making lunch today I wanted to sort
of use it as a lab. During this time in my kitchen I’m going to talk to you about three
different things: 1) the three most important molecules on the
Earth 2) possibly the grossest sandwich I’m ever
going to eat 3) an obscure scientist who taught us almost
everything we know about urine. So far we’ve talked about carbon and we’ve
talked about water, and now we’re going to talk about the molecules that make up every
living thing and every living thing in every living thing.
I don’t care if you’re a bacterium or a blue whale or if you’re Lady Gaga, of if
you’re a mite living on the Queen of England’s eyelashes. They’re called biological molecules. These
aren’t just building blocks, these are the molecules necessary for every living thing
on Earth to survive. They are essential sources of energy. They are the means of storing that
energy. They are also the instructions that all organisms use to be born and grow and
to ultimately pass those same instructions on to their future generations. They are the ingredients for life. And we call them: the carbohydrates, the lipids,
the proteins, and the nucleic acids. Today we’re going to be talking about the
first three. It’s no coincidence that we classify them in the same way that we classify
food, because they’re food. [Hank so smart!] And for this classification, we have to thank
a little-known English physician who hundreds of years ago dedicated his life to the study
of human pee. Oh, my goodness… I’m back in the- That must mean that it’s time for the most
awkwardly named segment here on crash course: Biolo-graphy. His name was William Prout. In the early 1800s,
he became fascinated with human digestion especially our urine. That’s because
he thought the best way to understand the human body was through chemistry, and the
best way to understand body’s chemistry was to understand what it does with food. By day
he was a practicing physician, but every morning before breakfast he did research in his home
laboratory in London. And there he did many great things. Like, being the first to discover
that our stomachs contained hydrochloric acid. And writing a breakthrough book about kidney
stones called An Inquiry Into the Nature and Treatment of
Gravel, Calculus, and Other Diseases Connected with a Deranged Operation of the Urinary Organs. And he was, of course, the first person to
discover the chemical composition of pure urea, the main component of urine. For the record, here it is: CO(NH2)2. And
in the presence of water, urea gives off ammonia, which is why your pee smells. Through his years of studying urine, Prout
came to the conclusion that all “foodstuffs” fell into three categories: the saccharinous
(carbohydrates), oleaginous (fats), and albuminous (proteins). Indeed, he went so far as to say
that in order to be healthy, you needed to eat all three of these things and not just
sheep kidneys and gin, which is what most of London was living on at the time. But like many great minds, Prout was overlooked
in his own lifetime, because while he was studying actual science, everyone else was
walking around believing that the color of your urine was determined by your personality. This guy looks like a total jerk to me! And if you can tell that much by color I wonder
what you could tell by taste. Now he isn’t understand that there were biological
molecules He didn’t understand what these things were,
but he did understand that there were three ingredients necessary for life. And it turns
out that all organisms either need to synthesize or ingest those ingredients in order to live. We’re going to start out with the most basic
of these ingredients for life: Carbohydrates. You’ve no doubt heard of them. You may,
in fact, be avoiding them like the plague. But fact is that nothing, and no one, can
avoid carbohydrates, because they are the source of all energy that we have available
to us. Carbohydrates are made up of sugars, and the
simplest of them are monosaccharides. Mono for one, and saccharides for the actual root
of the word sugar. The star of the show here is glucose, because it’s truly fundamental,
by which I mean like Number One on the global food chain. Because it comes from the sun. All biological energy is originally captured
from the sun by plants as glucose through photosynthesis. And every cell that needs
energy uses glucose to get that energy through a process called respiration. In addition to glucose there are other monosaccharides,
like fructose, which has the same molecular formula (C6H12O6), but arranged differently.
These subtle chemical difference do matter. Fructose, for example, is significantly sweeter
than glucose. It’s also processed by our bodies in different ways. And then there are disaccharides which — like
the name says — are just two monosaccharides put together. The most famous of these is
sucrose, which is simply a glucose molecule and a fructose molecule joined by a covalent
bond. Mono- and disaccharides are pretty much little
niblets of energy that are really easy for our body to process, but when these carbohydrates
start to form into longer and longer chains, their function and their roles change as well.
Instead of being sources for instant energy, they become storehouses of energy or structural
compounds. These are the polysaccharides. Instead of
being just two or three monosaccharides put together, polysaccharides can contain thousands
of simple sugar units. And because they’re so big and burly, they’re
great for building with. In plants, cellulose is the most common structural compound. It’s
just a bunch of glucose molecules bound together and it is the most common organic compound
on the planet. Unfortunately, it’s very difficult to digest.
Cows can do it, but humans certainly cannot, which is why you don’t enjoy eating grass. Polysaccharides are also really good for storing
energy and not just structurally but just as an energy store. And that’s where we get
bread. Now, really interesting thing here: Bread is made up of starch, the most simple
of which is called amylose. Amylose and cellulose looks almost exactly identical, but one is
grass and the other is bread. Like, chemistry! [Well said.] Plants store glucose in the form of starch,
and it comes in lots and lots of different forms, from roots and tubers to the sweet
flesh of fruits, to the starchy seeds of the wheat plant that end up being milled into
flour. Ground-up grain is the main ingredient in
the bread, of course, most of the calories, or energy content, comes from carbohydrates.
When I eat this — and I am going to eat the hell out of it — I’m going to be eating
all of the chemical energy that this wheat plant got from the sun in order to feed it’s
next generation of seeds that we then stole for our own use. Now we, as human beings, can’t grow fruits
or tubers, so we have to store our energy in a couple of different ways. The way that
we tend to store carbohydrate energy is in glycogen, which is very similar to amylose
or starch, but has more branches and is more complicated. It’s basically made up of the
glucose we have left over after we eat and it sits in our muscles where it’s ready to
be used and it’s also stored in our livers. It’s generally a pretty short term store.
If we don’t eat for a day pretty much all of our glycogen gets depleted. But over the longer term, the way we store
energy is through Fat! All of our mom’s worst enemies: the fat.
Which turn out to be really important and are the most familiar sort of a very important
biological molecule: lipids. Lipids are smaller and simpler than complex
carbohydrates, and they’re grouped together because they share an inability to dissolve
in water. This is because their chemical bonds are mostly nonpolar, and since water, as we
learned in the previous episode despises non polar molecules, the two do not mix. It’s
like oil and water. In fact, it’s EXACTLY like oil and water! And if you’ve ever read a nutrition label
or seen this thing called the television, you’re probably pretty conversant in the
way we classify fats. But then 99% of us have no idea what those classifications actually
mean. Fats are made up mainly of two chemical ingredients:
glycerol, which is a kind of alcohol, and fatty acids, which are long carbon-hydrogen
chains that end in a carboxyl group. When you get three fatty acid molecules together
and connect them to a glycerol, that’s a triglyceride — they feature prominently in
things like butter, peanut butter, oils, and the white parts of meat. These triglycerides can either be saturated
or unsaturated. And I know that when we put the word “fat” and “saturated”  into
the same sentence it sounds like an evening at KFC, but here we’re talking about being
saturated with hydrogen. As you hopefully remember from our first lesson:
Carbon is very nimble in how it uses its four electrons. It can form single, double or triple
bonds. This means that if the carbon atoms in a fatty
acid are connected to each other with single bonds, all of the carbon atoms end up connected
to at least 2 hydrogen atoms. And of them even picks up a third. So the fatty acid is
saturated with hydrogen. But when some of the carbons atoms are connected
to each other with double bonds all of those carbons’ electrons are spoken for, so they’re
not able to pick up those hydrogen atoms. This means that they’re not saturated with
hydrogen and they are unsaturated fatty acids. To demonstrate, may I direct your attention
to this jar of peanut butter? Here you can kind of see both kinds of fats.
The liquid stuff you see at the top here: that is the unsaturated fat, which we generally
think of as oils. The pasty stuff down here also contains lots of unsaturated fat but
also contains saturated fat, which doesn’t have any double bonds and so it can pack more
tightly and form solids at room temperature. And there are also other fat classifications
that you’ve heard of. Trans fats, which everyone tells you NEVER
to eat. They’re right, don’t eat them! They don’t exist in nature and are basically unsaturated
fatty acids that instead of kinking go straight across and so they’re super bad for you. Don’t
eat them. Omega-3 fatty acids are unsaturated at the
3 position, which is like, right there [where?]. And that’s the only difference, but the reason
that these are important is because we can’t synthesize them ourselves. They’re essential
fatty acids meaning that we need to eat them in order to get them. All this is starting to make me pretty hungry,
but before we get to more food stuff there are some unappetizing sort of lipids that
we also need to talk about. So remember that triglycerides are three fatty
acid chains connected to a glycerol? Swap one of those fatty acids for a phosphate group
and you have a phospholipid. These make up cell membrane walls. Since that phosphate
group gives that end polarity, it’s attracted to water. And the other end is nonpolar and
it avoids water. So if you were to scatter a bunch of phospholipids into some water,
they would automatically arrange themselves like this with hydrophobic ends facing each
other, and hydrophilic ends sticking out to face the water. Every cell in your body uses
this natural structure to form its cell membrane in order to keep the bad stuff out and the
good stuff in. Another class of lipids is the steroids. Steroids
have a backbone of four interconnected carbon rings, which can be used to form hundreds
of variations. The most fundamental of them is cholesterol, which binds with phospholipids
to help form cell walls. But they can also be activated to turn into different lipid
hormones. And so now we approach the most complicated,
powerful, polymorphously awesome chemicals in our body: the protein. And by complicated I mean that they are probably
the most complicated chemical compounds on the planet. In fact, they are so amazing that
we’re going to so a separate episode on them, and how they’re created by DNA. But right
now, in you, there are tens of thousands of proteins doing everything they can to keep
you alive. There are enzymes regulating chemical processes,
helping you digest food. There are antibodies connecting themselves to invaders like bacterium
and viruses so that your immune system can get them. There are protein endorphins that
mess around with your brain and make you feel emotions [Gross!] But they’re everywhere, they do EVERYTHING! And proteins do all of this stuff using only
20 different ingredients. And these are the amino acids. Just like fatty acids, amino acids have a
carboxyl group on one end. On the other end they have an amino group. Amino acid! Now hey, I don’t know if you’ve noticed
this, but this is the first time nitrogen has shown up in our food. This is super important,
because despite the fact that nitrogen is everywhere — it’s like 80% of the air — we
can’t just pull it out of the air and put it into our bodies. We have to get nitrogen
from food. And so we have to eat foods that are high in protein like this egg, which by
it’s very virtue, because all the white part is protein, it contains a goodly amount of
nitrogen. Now in the middle of the amino and the acid
group is a carbon. It shares one of its electrons with good ol’ hydrogen, and the other electron
is free to be shared with “R” Which is just a kind of fill in the blank.
We call it “The R group” It can also be called a side chain, and there
are 20 different kinds of side chains. Whatever fits in that blank will determine the shape,
and the function, of that amino acid. So if you put this in there, you get valine,
an amino acid that does a lot of stuff, like protecting and building muscle tissue. If
you put this in there, you get tryptophan, which may be best known for its role in helping
you regulate mood and energy levels. Amino acids form long chains called polypeptides.
Proteins are formed when these polypeptides not only connect but elaborate and frankly
really elegant structures. They fold. They coil. They twist. If they were sculptures,
I would go the museum every day just to look at them. And I’d walk straight past the nudes without
even looking. But protein synthesis is only possible if
you have all of the amino acids necessary, and there are nine of them, that we can’t
make ourselves. Histidine, isoleucine, leucine Lysine, methionine, phenylalanine Threonine, tryptophan, and valine. By eating foods that are high in protein,
we can digest them down into their base particles and then use these essential amino acids in
building up our own protein. Some foods, especially ones that contain animal
protein, have all of the essential amino acids including this egg And that concludes this triple-decker sandwich
of biological awesomeness, which is all we need to be happy, healthy people. And I’m sure, because of that, it’s going
to be delicious. Nope. Thank you for watching this episode of Crash
Course. I will be discussing something else very interesting next week. I don’t even know
what it is. Don’t forget. Go back and reinforce what you’ve
learned today by going back and watching bits that you feel like you may not have got completely. We’ll also, of course, be available on Facebook
and twitter if you would like to ask us questions or give us suggestions there. [BURP]


  1. his burp lol

  2. it's a fun to learn with you . I'm a 13 years old girl, studying in 9th grade…
    and you what, your way is very fascinating and pretty easy to understand too. ..😊

  3. Is it safe to drink ur pee

  4. Great video, but just a reminder, animal cells don't have cell walls. They have cell membranes. Plant cells have walls.

  5. Great video very helpful!

  6. I have a group quiz bee tomorrow 🙁

  7. tbh these kinds of educational videos should get more million views from the world

  8. I thought human(animal) cells do not have cell walls. Please explain.

  9. Homie slow down you talk so fast😣😣

  10. I’m gonna eat the hell out of it

  11. Who else have a terrible biology teacher????? Well, I have.

  12. 3:28 I know it’s apple juice or whatever but I still almost threw up 😂

  13. all the 10th graders watching this im in 7th whyyyyyyyyyy

  14. The burp at the last though🤣🤣🤣

  15. His "NOPE" has me LOLing

  16. Ha! Didn’t like the sandwich

  17. Uuuuhhhhh I have to do this in class🤯

  18. Isn't he adorable with his little apron? and i almost died on 2:46

  19. My grandma s apron 👵👵👵

  20. Text books? (Drake saying no)
    Hank green (drake nodding yes)
    *what a dank may may

  21. Anyone here prepping for the 2019 ap bio exam?

  22. Did he really drank urine??????….. please anyone tell me

  23. Great video! Love it. But don't you mean cell membrane when you say 'cell wall'? 🙂

  24. That’s apple juice

  25. ok ??????? i watch this video for a school procject and the teacer watch it to and she dont like it to much i give you my and teachers dislike

  26. Thank you!!!!!!!! YOURE AMAZING

  27. I have my biology cape unit one exam tomorrow and your videos have been a hugeee help 😭🔥

  28. oh god, poor william prout studying pee. what a legacy

  29. great video, but between 10:18 to 10:24, you said cell 'wall' for cells in the body, when it's the plasma membrane

  30. Watching these to help with keystones 🙄😂

  31. "One is grass and the other is bread. Like…chemistry!"

  32. 13:20 who tf cuts an egg like that?

  33. Watching this with no background knowledge was the most confusing thing. The only things I remember are the guy who studied pee and the peanut butter that had unsaturated and saturated fats. And the eggs that have all the essential amino acids.

  34. 14:02

  35. after this how can you possibly forget what proteins are 11:05. 'They are everywhere they do everything'
    And fat is your moms worst nightmare cause she eats and the extra energy is stored in her as fast 6:34
    carbohydrates well who doesn't know that 3:47

  36. I love these videos but im jumping in between these videos and chemistry to try and keep up. Is there a certain order i should follow, or dvds i should get?

  37. 3:48 tentatively points at bread

  38. as someone with adhd and audio sensitivity i had a heart attack every single time the video dinged is all good though thank you for the biology hank i owe u my life

  39. 5:51 let's get this bread


  41. These close up face shots are makin me very uncomfortable.. Cant fullscreen at all on this one, nope.

  42. please tell us a clear picture of how cells uses atoms.bcoz many students think that atoms and cells are totally different and they don't meet each other 🙄

  43. Trying to test out of bio 101 so I can eventually get my third degree: NURSING (thanx Hank)
    Along with that here is what I quickly typed down as a sort of SUMMARY, feel free to fix:

     William Prout discovered our stomachs have hydrochloric acid and discovered chemical composition of urea. Also discovered food is divided into carbs, fats, and proteins

     Carbohydrates are the source of all energy

     Carbs are made of sugars with the simplest being monosaccharides

     Glucose, a monosaccharide, number 1 sugar that comes from the sun

     Fructose, same chemical as glucose, but arranged differently, and is sweeter

     Disaccharides are two monosaccharides put together

     Sucrose, fructose and glucose connected, is a disaccharide joined by a covalent bond

     Polysaccharides are thousands of simple sugar units

     Cellulose is a bunch of glucose molecules

     Bread is made of starch and amylase

     Our bodies store carbs in form of glycogen in our muscle until we need to use them

     We store our energy long term through fat aka lipids

     Lipids are non polar and can’t dissolve in water

     Fats are made of glycerol and fatty acids

     Saturated fats don’t have double bonds, while unsaturated fats do

     Trans fat do not exist in nature and are unsaturated and bad for the body

     Omega 3 fats, unsaturated, are essential but we need to eat them in order to get them

     Phospholipids form cell membrane walls to keep bad stuff out and good stuff in

     Phospholipids are one end polar and one end non polar

     Steroids, a phospholipid made of 4 carbon rings, are used to make cholesterol

     Proteins of made of 20 amino acids which do everything for the body

     Nitrogen can only be gotten into our bodies from food, via foods high in protein

     Polypeptides are formed by long chains of amino acids

     The 9 essential amino acids, which are bodies can’t make on their own, are histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine

  44. You are amazing, thank you so much for your help . I ‘m doing well in school because of you . Keep making videos your work is important.

  45. So cellulose and starch are made up of the same stuff, but the glucose just goes in different directions in the cellulose? Does that actual substance become any different that way? How else are they different?

  46. "It's going to be absolutely delicious…… NOPE"

  47. Hank's face @ 3:29 lol XD

  48. What is the importance of leafy greens? Can I get by without them??

  49. I am studying for the DAT and this is gold! thanks!!

  50. he's like the younger version of bozeman science

  51. Thanks Hank for a great session on Bio-molecules, Please make us a video on micro and macro molecules (maybe "Biological molecules part-2) It would be of great help. Crash course is the only way i can learn biology as my biology teacher at school sucks!

  52. thank you. you're doing the most important work. this is a life changing lesson, if people allow themselves to truly embrace this truth. eating is science, life is science.. lol it could all be so simple.

  53. 07.22.19 now

  54. Please don’t tell me he actually drank pea.😑😳

  55. The yellow background makes it ever so gross
    Ps omg this was 7 years ago is anyone else watching this in 2019? No? Just me? Ohhh ok

  56. Such a lovely dress you're wearing, Hank!

  57. According to the documentary "What the health" on Netflix, eating eggs isn't only unnecessary but also harmful for our health, any comment about it?

  58. Was that glass full of pee or apple juice

  59. slowed playback speed down to .75 and I swear I think the speed up hank talking after the record it originally because .75 seems much more realistic.

  60. Speak slowly please

  61. This is a lot to learn. 🦄

  62. Notes:

    Indigence for life: Biological molecules: sources of energy, storage of energy, instruction (to born, grow and pass on)

    Food: synthesized or ingested

    Carbohydrates, Lipids, Protein, nucleic acids


    made of sugars: chains with different lengths

    simplest: monosaccharides (one-sugar): like glucose and fructose

    Glucose: energy of the sun captured by plants through photosynthesis

    Respiration: cells getting energy from glucose

    Disaccharides (two-sugars): like sucrose: made of glucose and fructose

    Polysaccharides (long chains): structural compounds that store energy: cellulose, indigestible

    Starch: plants way of storing glucose: like amylose (is like cellulose)

    Humans way of storing energy:

    Glycogen: short term storage, for a day without eating, made of left over glucose, stored in muscles and liver

    Long term storage…


    Non polar, don't mix with water

    Made of: glycerol (kind of alcohol) and fatty acids (carbon-hydrogen chains)

    Triglyceride: 3 fatty acid chains stuck to a glycerol

    Saturated (solid) and non-saturated (like oils) with hydrogen (straight structures allow more hydrogen bonds, non-saturated if there are more carbon bonds)

    Trans fats: unnatural and dangerous, unsaturated with straight carbon bonds instead of bent ones

    Omega 3: unsaturated fatty acids

    Phospho-lipid: Cell membrane walls are made of : 2 fatty acids and a phosphate connected a glyceral , one side hydrophilic (polar side) and the other hydrophobic (non-polar side) so when in water, their hydrophobic ends face each other, that's how cell walls are made

    Steroids like cholestrol: with carbon backbone, also in cell walls, they can be activated to turn into lipid hormons

    Protein (made of amino acids: carboxyl group NH2 and amino group COOH on both ends and H and and an arbitrary R group in the middle):

    Complicated chemical compound, elaborate and elegant structures

    Enzymes: regulating chemical processes and digestion

    Antibodies: connecting themselves to invading bacterium and viruses

    Endorphins: in brain, emotions

    Nitrogen (80% of the air), needs to be in our food

    R group is the side chain of amino acids that determines the function (20 known types)

    Valine: protecting and building muscle tissue

    Tryptophan: mood and energy regulation

    Protein sythesis requires the 9 necessary amino acids: Lysine, Histidine, Threonine, Methionine, Valine, Isoleucine, Leucine, Phenylalanine, Tryptophan (, arginine)

  63. was that apple juice or is it p…

  64. sooo amazing the structural formulas shown are also sooo easy to comprehend in such colorful way

  65. I won’t lie. I have to watch these videos a lot to understand them. I’m so dumb…. 😐

  66. today i shall be 4 beers half a kebab a fruit salad with single cream and some marlboro reds

  67. Hank sir
    You are greatest
    Iam indian so I cannot meet but I want to talk with you.
    I am your fan

  68. When everyone is here for AP Bio, and I'm like iGCSEs? Anyone?

  69. If you have bio100 at mcc and have to watch this video for a discussion here is a little tip. Disaccarides are at 4:50. Unsaturate peanut butter is at 9:00. Omega 3 is at 9:39. And 3 types of proteins are at 11:12

  70. I’m taking Biology(a high school class) for my 8th grade year, I have to take notes on this. I don’t know where to start..🥺

  71. Y'all the real MVPs…

  72. 4:18

  73. why do i have to watch this as a 28 year old…..why….why is this for a COLLEGE class

  74. this guy is great

  75. the way he taught better than any biology teacher.

  76. did anybody else have to use this for a school assignment🤦🏻‍♂️🤦🏻‍♂️

  77. Hey Hank, can you please do an episode on Nucleic Acids? Thanks for reading!

  78. Biology is stupid

  79. It's no coincidence that we classify them in the same way that we classify food, because…………………..they're food

  80. It's been years since I took bio. When I opened up my new textbook, I felt overwhelmed. I like these videos. They're fun and Hank is funny. So, with my studies I watch Crash Course Bio and Chem because though I may think I am starting to get it, Crash Course is very helpful.

  81. Why am I watching these for fun Uni doesn't even start for a week

  82. "You are what you eat."

    I eat low fat american cheese…

    Its not working

  83. Phospholipids make up the cell membrane, not the cell wall 10:25 you contradicted yourself.

  84. Crash course out here helping me get my degree

  85. fire my teacher! ! ! !

  86. I lost my attention to listen to my biology class cuz I only understood little bit of it, but I understand the whole lesson in this video. Salute to this channel 😊

  87. Can you do food and the brain

  88. Omg he drank his urine? 😂😂😂

  89. So starch is actually amylose?

  90. 6:34 he is the most productive crackhead I’ve ever seen

  91. If David Mitchell did biology

  92. 3:23 Me to myself, “ it’s apple juice it’s apple juice it’s apple juice it’s apple juice”

  93. This taught me more than my gr11 bio class

  94. oga we be africans abeg talk SLOWLYYYYYY, thanks

  95. 13:48 rewinds to 0:01

  96. payaso

  97. Teachers should try doing this kind of stuff to avoid long boring hours that made students lose their interest in learning

  98. If you disliked this video then you are just NaCl

  99. What about nucleic acids?

  100. 'I don't care if you're a bacterium or if you're a blue whale or if you're Lady Gaga, or a mite living on the Queen of England's eyelashes' im deceased

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