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Carbon as a building block of life

AP.BIO:
ENE‑1 (EU)
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ENE‑1.A (LO)

Video transcript

you're probably already familiar with some forms of carbon for example this graphite right over here this is one form carbon takes very important when you're writing with a pencil otherwise you would not see any writing if you just have the graphite get scraping on to you're scraping on to your paper which you and your paper is also it's not pure carbon but it has a lot of carbon in it this right over here is a raw diamond another form that carbon can take under intense after a long period of time under intense pressure but what you may or may not realize is that carbon is actually essential for life in fact life as we know it is carbon-based so carbon-based based life when we look for signs of life or at least life as we know it on other planets we're looking for signs of carbon-based life and there might be other forms other other elements that form the backbone of life but carbon is the only one that we have been able to observe now why is carbon so valuable for life why does it form the backbone of the molecules that make life possible well it all comes down to where it sits in the periodic table and how many and it's atomic number and how it tends to bond with things so this is why chemistry is important so carbon we hover we see over here has an atomic number of six which by definition means it has six protons so if I were to draw its nucleus it would have one two three four five six protons and the most common isotope of carbon on earth is carbon-12 which also has six neutrons so let me draw that in this nucleus one two three four five six neutrons and then neutral carbon is going to have six electrons and so two of them are going to be in their innermost in the first shell so that's two of them right over there these are the these are the inner shell I guess you could say or the so that's the first two electrons and then you have four remaining in its outermost shell and these four considered valence electrons these are the electrons that actually do their reacting and if any of this seems unfamiliar to you I encourage you to watch the videos on Khan Academy on things like valence electrons but this is a little bit of a review right over here Carbon has four valence electrons and valence electrons are the ones that do or that tend to do their reacting and so I could if I wanted to simplify this drawing over here I could say okay carbon and if I were to just draw its valence electrons which is a typical thing to do I could say its carbon has one two three four valence electrons now you might remember the octet rule that that atoms tend to be more stable when they least pretend like they went that they're sharing or that they have eight electrons in their outermost shell and so carbon can do that by forming four covalent bonds for example it could do that with hydrogen's this hydrogen over here has one valence electron it actually only has one electron now the hydrogen feels good it feels like it's sharing two electrons filling its in it's its first shell hydrogens just trying to fill out the first shell feel a little bit more like helium and now this carbon says oh now I get to share this electron and then carbon can do it again with another hydrogen and can do it in again with a another hydrogen and it can do it again with another hydrogen so now carbon can feel like hey I'm sharing eight electrons and that each of the hydrogen's feel like oh look you know I I'm sharing two electrons everyone seems to be happy everyone seems to be stable and this molecule right over here this is methane this is methane and by definition because it involves carbon it is considered an organic molecule it is considered an organic molecule in fact the whole the whole field of organic chemistry is all about studying organic molecules which are molecules that have carbon now because this only has carbon and hydrogen in it it is also considered to be a hydrocarbon hydrocarbon hydrocarbon and you might be familiar with things like like gasoline being considered a hydrocarbon and it is indeed a hydrocarbon in fact gasoline gasoline and actually even even methane could be used as fuel right over here but and typically you could see these long chains of hydrocarbons for example you could have eight carbons form octane you might be familiar with things like high-octane fuel so let's see carbon 2 3 4 six seven eight this is a hydrocarbon it's octane because as eight carbons acht octane and ever all the other bonds remember carbon forms four bonds or typically forms four bonds so now that carbon has four bonds now this carbon has four bonds so now this carbon two of them two hydrogen two of them two carbon two two hydrogen two two carbon hopefully this starts to give you an appreciation why carbon is so useful as a building block because it can form so many bonds with so many different structures and these hydrocarbons they can be chains or they can even form they can even form rings they can form cycles and in things like graphite and in diamond carbons can form these lattice structures where you know carbon is formed as bonding carbon is forming is bonding to more than two carbons in these three-dimensional shapes in these three in these three-dimensional shapes and the shape because it's forming three bonds that that carbon typically forms bonds and these are called tetrahedral shapes or tetrahedral bonding and when someone says tetrahedron if someone says tetrahedron they're talking about they're talking about a there let me just in a different color so a tetrahedron is a three-dimensional a three-dimensional shape that has four sides each of which are triangles each or which are triangles and so it would look like this you could view it as a pyramid with a triangular base a pyramid with a triangular base and when carbon forms bonds let's say in the case of this methane right over here I'll draw the carbon in the middle as this as this as this yellow circle then each of the hydrogen's over here are going to be at the corners or I guess you say the vertices of the tetrahedron and so this is the tetrahedral shape that carbon is actually forming and of course you have these covalent bonds right over here let me do this in a different color you have these covalent bonds over here and we could draw it like this we could draw these covalent bonds like this that's one of them maybe that's this one over here this one over here right over here these electrons are all just buzzing around and then then you have one over here and then you have one over here so you might see methane sometimes just drawn like this you might just see it drawn you might just see it drawn like this but it's really forming it's really forming a tetrahedral a tetrahedral shape so let me finish drawing it so hydrogen hydrogen hydrogen hydrogen where each of these lines represents a pair of electrons so you have eight electrons being shared and aggregate but the actual shape is closer to this now I'm claiming to you that it's the backbone of life or life as we know it and it's it's even the backbone of life as as you are life in the form of you we've already talked about you being a majority water and that's why if you look at the average human being is the average human being is going to be roughly and depends on how much how hot well hydrated you are and your stage of development the average human being is going to be 65 percent oxygen by mass so oxido you're two-thirds oxygen and that's because of all of the water water is h2o and oxygen forms the bulk of the mass of the water molecule but in second place comes carbon in second place comes carbon carbon is approximately 18% of your body's mass and this is because if you think about the non the non fluid part the non liquid part of your body there's a lot of carbon going on there this right over here is a DNA molecule and so this little these little grey areas this is all carbon this right over here this right over here is heck so kinase I'm not going to go into the details about what it does but hexo kinase is a protein EXO kinase and the teal color that you see there that is all carbon that's all carbon this right over here is glucose it's very sweet it's an important way to regulate your body's energy and the teal color that is carbon this is ATP often considered to be the the molecular currency of energy in your body and all the teal there this is carbon this is why as a lot of especially the non are part of your body is carbon so hopefully this gives you a better appreciation for carbon it's not just useful for pencils and diamonds but even if you're just looking at your hand you're looking at a lot of carbon
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