CHNOPS: The 6 Elements That Make All Life Possible on Earth

The French biochemist and Nobel laureate  Dr. Jacques Monod famously said,   “All that is true for E. coli, is true for  the elephant.” And you might be thinking,   okay, had Monod ever actually seen an  elephant? Which is a totally fair question!

On the surface, we see lots of differences between  the single-celled bacterium and the elephant,   which contains upwards of a quadrillion  cells. But what Monod was getting at is   that on a biochemical level, all living  things are actually shockingly similar.

We can see that unity, which comes from our  shared evolutionary history, in the identical   chemical building blocks that form the DNA and  proteins of E. coli, elephants, and, well, us.  Despite our differences, we can use many of  the same chemical reactions to break down food,  

harnessing energy along the way. Of course,  we need more energy than E. coli needs,   and the elephant needs more than us.  But the rules of the game are the same. And across all forms of life, that game  is played with six key elemental players:  

now taking the field for team life: carbon,   hydrogen, nitrogen, oxygen, phosphorus,  and sulfur. Give it up for team CHNOPS! Hi! I'm Dr. Sammy, your friendly  neighborhood entomologist,  

and this is Crash Course Biology. And this  is some seriously banging theme music. [THEME MUSIC] You’re probably familiar with  the periodic table. As of 2023,  

it lists 118 known elements, and it  isn’t unusual for it to be updated. Heck,   as recently as 2016, scientists added four  new elements to it. Elements are just atoms,   by the way, and they are pretty much  the simplest form of stuff that exists.

An element is a name for a certain type of  atom. When it comes to the team of life,   our atomic captain is carbon. Here on Earth,   carbon is the most common element  in living things, making it our MVP.

Producers, like plants and algae, pull  carbon dioxide from the air or the water   to make carbon-based molecules — or connected  groups of atoms. When consumers — like mice,   or lizards, or you — eat your vegetables,  the molecules can be broken down. Then,  

they get reused to build our own biological  molecules, just like you might break down one   Lego creation to build another – these types of  repeated uses are called biogeochemical cycles. But carbon isn’t just plentiful, it takes a  lot more to be MVP in the game of life. One  

of carbon’s most amazing talents  is its ability to be bound up in   larger molecules. See, to really pull  together as a team to make life work,   our six elements need to make  - and break - chemical bonds.

Carbon wears number six on the periodic table.  And it’s quite the team player — it can form   four links, called covalent bonds, with  other atoms. Think of covalent bonds like   the molecular version of a rodeo. In this case,  carbon is the cowpoke lassoing bucking atoms.

Hydrogen wears atomic number one on the periodic  table. It’s the smallest element, and it can only   form one covalent bond. So if we arrange four  hydrogens around the carbon, and connect them   with lines to represent bonds, we’ve successfully  built methane, the simplest organic molecule.

So, our new chemical, methane, has both carbon  and hydrogen, which makes it an organic compound,   also known as an organic molecule. Forming an  organic compound is one of the top moves in the   team’s playbook because these compounds are the  chemical basis for life. Most components of food,  

for example, are made up of organic compounds,  including proteins, carbohydrates, and fats. And we’re not talking ‘organic’ like the kind  you’d find on a food label at a grocery store,   that just refers to the lack of synthetic  additives. Same name, totally different  

thing. But those labels can be wildly misleading  so we’re not going to get into that here. No   matter how they’re built, organic compounds will  always include carbon in at least some capacity. And the compounds change based on  the number of players involved. If  

we put four carbons in a row and  connect them with covalent bonds,   and then add in enough hydrogens to give each  carbon four bonds, BAM! We get butane! Which   is helpful for all kinds of things, including  using a lighter to kickstart your campfire.

Organic compounds don’t have to be straight chains  of carbon atoms, though. If we rearrange butane,   we can make a branched organic compound  called isobutane. This compound is often   used in gasoline. Butane and isobutane  have the exact same chemical formula,  

with four carbons and ten hydrogens  apiece. This makes them isomers,   compounds with the same chemical  formula, but a different arrangement   of atoms. Molecules can take all kinds of  shapes — and it can get pretty elaborate.

We all know that there is no “I” in team,  and our MVP carbon often needs a little   help from another member of the starting  lineup, wearing atomic number eight,   here comes oxygen. Oxygen is sort of like the team  ball hog, and doesn’t collaborate as much with  

carbon. It’s only going to create two covalent  bonds. Which can make team-ups a little trickier! Take carbon dioxide for example. It has the  chemical formula CO2. So if carbon likes to   make four bonds and oxygen two, what do we do?  We run some special plays. We put double covalent  

bonds between carbon and each oxygen, so the four  bonds are shared between two other atoms. Score! And now, the moment you’ve all been waiting for,   give it up for the last member of our starting  lineup with atomic number seven on its jersey,  

Nitrogen. It makes three bonds. For example, it  teams up with three hydrogens to make ammonia. We'll mention our second-stringers phosphorus and  sulfur a bit later — they’re also essential to   our team! Our starting lineup can’t win the  game all on its own. And winning the game,  

in case you lost track, means sustaining all life  on Earth. So these guys are kind of a big deal. The upshot is that when our team coordinates  their plays, we get the four major classes of   biological molecules that make up nearly  everything in our bodies. And not just  

our bodies. Elephant bodies. Plant bodies. And  every other living thing that you can think of. So, what are these majestic molecules, and  how do they work like complicated Lego kits to   build you and me? The four types of biological  molecules are lipids, carbohydrates, proteins,  

and nucleic acids, and they are made from our  team CHNOPS. And then they, in turn, make us. Lipids are organic molecules that can’t dissolve  in water, like cooking oil or beeswax. They’re   usually made of smaller blocks called fatty  acids, which consist of long chains of carbon  

atoms. Some lipids are chemical messengers,  like the hormones estrogen and testosterone,   which help prepare our bodies for things  like puberty and reproductive processes. Oh,   so that’s what I had to blame for all  those pimples? Thanks a lot, lipids.

Carbohydrates are our second class of  biological molecules. They’re used as   sweeteners, and they’re never-ending  at The Olive Garden. Meaning: they’re   the main components of pasta and those endless  breadsticks – you might know them as “carbs.”

In our bodies, carbs can be used to store  energy for release as needed. Their mini   Lego piece is a monosaccharide, simple  sugars like glucose or fructose. Stick   a bunch of monosaccharides together and  you get complex carbs like those in pasta  

and bread. Our brains are particularly  hungry for glucose — and they should be,   considering that the brain consumes 20  percent of the body’s metabolic fuel. Our third type of biological  molecule, called nucleic acids,  

store and transmit genetic information, which  is basically instructions that we inherit from   our parents that tell our bodies how  to work. DNA stores this information,   and the nucleic acid RNA tells  the body what to do with it.

All of this rests on the mini  Lego piece called a nucleotide,   which is made of a simple carbohydrate,  a phosphate group, and some nitrogen-rich   rings. Did you see that? Phosphorus coming  in for the assist – we love a team player.

Our fourth and final class are proteins, like  the hormone insulin that helps regulate our   blood sugar, or the antibodies that help  our immune system fight off infections.   Some also have structural roles, like  the collagen that makes up much of our  

skin. And while those proteins are tiny,  some huddle together so much that you can   actually see them—like the protein keratin  that makes your hair and your fingernails. Proteins are built from amino acids.  And all amino acids are pretty similar,  

but each one has its own special group that  makes it unique. Like Tryptophan the amino   acid in that turkey leg that used to take the  blame for making you tired. Even though your   sleep hormones are made out of this stuff, eating  it doesn’t mean you’re going to get drowsy. That  

turned out to be a myth—the sleepiness  was just because you were really full. And finally, taking the field we  have sulfur! It’s in some of these   amino acid building blocks giving  us the S in CHNOPS. As you can see,  

these atomic Lego pieces don’t act alone! They  continue to build even bigger teams of molecules. Like, say we need our bodies to  interpret our DNA — which we do   need all the time. The process is kind of  like a text chain full of coded emojis.  

DNA sends the messages that get interpreted  by RNA, a codebreaker extraordinaire. These   messages are not just your average gossip,  they’re instructions for amino acids. So the amino acids join together end to end,  

making a polymer — which is a large molecule  containing many repeating molecules. And the   name for a molecule containing many other  molecules, by the way, is a macromolecule. DNA is the champion of polymerization —  or linking up repeating molecules to make  

macromolecules. In humans, chromosome  one — our largest chromosome — contains   a single polymer made of 498 million  nucleotide blocks – that’s a lot of Legos. It works out to over 16 billion atoms  working together to store the genetic  

information in just one of our 46 chromosomes.  There are more atoms in that single chromosome   of yours than there are humans on  Earth. Now that’s a macromolecule. We also have biological molecules  to thank for the sweeter things  

in life. Some carbohydrates can be made  of just two Lego blocks — like sucrose,   the carb that makes the fruit in your smoothie  taste sweet. Or carbs can be macromolecules,   like polysaccharides, which help plants and  animals get their shape and store their energy.

Let’s check out how our bodies break down  molecules. It works the same way in polymers,   but for simplicity, we’ll look at sucrose. When you sip hot chocolate, proteins in  your digestive system break sucrose into  

the monosaccharides, or simpler sugars,  glucose and fructose. They do this by   adding water to the covalent bond holding  them together. These are called hydrolysis   reactions. With “Hydro” meaning water and  “lysis” meaning to pull apart or loosen.

Hydrolysis is a process that cleaves one big  molecule into two smaller molecules using   water. Hydrolysis lets us reuse the building  blocks from the producers and consumers that   we eat to build up our own macromolecules.  Each amino acid from a plant protein can  

be recycled to make the specific proteins  that we need. And the different proteins   that organisms make contribute to the  uniqueness among all living things. So hydrolysis is how our bodies break  bonds between building blocks. But we  

also need to make new bonds, putting the Lego  pieces back together in new combinations.   For that, there’s the opposite of  hydrolysis: dehydration reactions. Just like the dehydration you might feel on  a hot summer day, this process involves water  

loss. It removes water from the building blocks  to make them stick together. In chemical terms,   a water molecule is squeezed out from two building  blocks, joining them into a bigger molecule. For example, dehydration reactions  occur when three fatty acids team  

up by attaching to a molecule of  glycerol, a type of carbohydrate,   squeezing out water to make what’s called  a triglyceride. This process helps bears   get ready for hibernation, when their bodies  live on fat stored during the summer and fall.

Life can take on a lot of different shapes,  but despite differences in the DNA code,   it’s the same nucleotides  carrying the message that   makes every organism on this planet.  And the similarity doesn’t stop there!

From a tiny amoeba to an enormous blue whale,   we’ll see similar lipids holding stuff inside  cells, DNA and RNA working together to make   proteins, and structural proteins  helping cells keep their shape.

And behind it all, the six-atom team,  CHNOPS, are key players in the game of   life. Chemically speaking, that is. In the next  episode, we’re going to take a deep dive into,   well, water – and how our friend H20 makes  life better for everyone. I’ll see you then.

This series was produced in collaboration with  HHMI BioInteractive. If you’re an educator,   visit BioInteractive.org/CrashCourse  for classroom resources and professional   development related to the  topics covered in this course.

Thanks for watching this episode of Crash Course  Biology which was filmed at our studio here in   Indianapolis, Indiana, and was made with the  help of all these nice people. If you want   to help keep Crash Course free for everyone,  forever, you can join our community on Patreon.