Your body has all sorts of complicated processes going on inside it
and a lot and a lot of these processes are carried on by incredibly powerful and often incredibly large molecules.
Some of these molecules that you're using right now are so big
that they challenge the definition of what a molecule is.
Technically a molecule is the smallest group of atoms that performs a function,
but sometimes there are really complicated groups of atoms that work together.
They're definitely more complex and say molecules of water or carbon dioxide but
they're still just one unit.
Many of your body's most important molecules fall into this category;
biologists refer to these huge life-giving arrangements of atoms as macromolecules.
Some of them you've possibly heard of others you might never have known where that important
but together they are what's keeping you alive.
And aside from water and glucose and other nutrients that you have to ingest to keep going,
these are some of the most important molecules in your body.
And hey, I love and appreciate all of them equally. No playing favorites here.
But if I had to pick five of the most important molecules that keep your body ticking
I have to include these five and we'll start with the first one I mentioned:
Deoxyribonucleic acid or DNA.
It's probably your body's most famous molecule and rightfully so.
It's the one that tells yourselves what proteins to make as well as how and where.
Now, you usually hear people talk about DNA in the context of genetics like
they'll say that their hair color or their allergy to cucumbers or whether
they have wet or dry earwax is because of their DNA and that's true: your DNA
contains your genetic blueprints; the instructions on how to make you you,
but what's important to understand is that your user DNA every single time
your body creates a new cell and it does this two trillion times every day.
It's made up of pairs of interlocking molecules called nucleotides,
building blocks that are arranged in a very particular order and each of your cells
is able to read these sequences of nucleotides as a kind of code,
interpreting different segments which are your genes as instructions of how to
build proteins. And when it comes to your body, proteins are the boss!
If you don't count water they make up seventy five percent of your body weight.
There are more than 100,000 different proteins in you right now,
and your DNA knows how to make them all. That is a lot of instructions!
So it should be no surprise that DNA is by far
the largest molecule you have.
If you stretched out the DNA in just one of your cells, it would be about two meters long.
And this enormous code is readable thanks to another macromolecule
called messenger RNA. It collects the recipe, from whatever
segment of DNA it needs, and delivers it to your cell's protein assembly lines
called ribosomes. So, each of your cells has the instructions to make proteins
but they still need the ingredients to make them.
Those are the amino acids and those hundred thousand different proteins that
you have all are made from different combinations of the same 20 amino acids.
In a pinch, your body can make about half of these amino acids all by itself but nine of them,
the essential amino acids, have to come from food and that's where another one
of your body's most important molecules comes in: Pepsin.
Pepsin is an enzyme and it's a really big complicated macromolecule
that helps digest proteins and food breaking them down into amino acids.
It hunts down the bond between certain amino acids and just mercilessly rips
them apart and pepsin is very good at it's job.
It's so powerful that your stomach cells have to produce it in a special
deactivated form called pepsinogen.
If it didn't, the pepsin would set to work
digesting your stomach's own cells but once the pepsinogen is released into the
stomach it becomes activated by hydrochloric acid in your stomach and
then it's free to wreak havoc. But just how strong is this stuff?
Well, if you've ever had the misfortune of having your stomach contents
come out of you, you felt it. The reason that things like vomiting and acid
reflux are so unpleasant is because they allow pets in to come into contact with
your unprotected tissues, so that burning that you feel is basically pepsin
digesting the cells in your esophagus.
But normally, and thankfully, pepsin limits it's work to your stomach, releasing those
essential amino acids that your cells use to build the proteins that you are made of.
But all this protein building takes energy. And to get energy, you first need oxygen.
You breathe it in, but that oxygen needs to get from your
lungs to the rest of your body, somehow. Enter hemoglobin. Hemoglobin is a protein
found in red blood cells and it's so big that those red blood cells get rid of
most of the other stuff inside them, like the nucleus, to make room for just one
macromolecule of hemoglobin and even then, red blood cells can get so big that
they get stuck in your capillaries which have to dilate to let your hemoglobin-laden
cells pass through.
Hemoglobin's main function is to transport oxygen and carbon dioxide.
Each molecule is made up of four groups called hemes that have one iron atom apiece.
These iron atoms have a positive charge; they're really good bonding with the electrons in oxygen.
And when just one of the iron atoms bonds with an oxygen molecule the whole shape
of the hemoglobin changes so that three more oxygen molecules can just pop right
into the other hemes which are just empty and waiting.
Then the hemoglobin travels through your circulatory system to unload the oxygen
to the cells that need it and once the oxygen is safely delivered the iron
atoms pick up carbon dioxide. The hemoglobin takes that to your lungs and
the whole process starts all over again.
Meanwhile, the cells use this oxygen to crank out another one of your body's
most crucial molecules: ATP. ATP or adenosine triphosphate is your body's fuel.
Your cells manufacture it in organelles that are like power stations,
the mitochondria.
They usually make it with the help of that oxygen that the hemoglobin has supplied.
Of the many important molecules that we're talking about today, ATP is the
only one that's not considered a true macromolecule, just because it's smaller,
but it still has plenty of moving parts. The most useful thing about ATP is that
it has three phosphorus atoms, each of which is surrounded by oxygen atoms.
Cramming these combinations of atoms, called phosphate groups, together forces
those oxygens close to one another which serves to store a lot of energy and
breaking one of the phosphates off releases that energy.
Your body is constantly going through loads of ATP to power everything that requires energy.
That includes big things, like making your muscles contract and small things,
like dilating tiny capillaries so that a single red blood cell can get through.
So, your cells get their instructions from DNA. Some of the ingredients from the
amino acids are kindly provided by pepsin and then the cells use oxygen
delivered by hemoglobin to make ATP for energy. The digestive, respiratory,
circulatory and nervous systems are all working together here, but your body
still needs to know when to do what. That is where your endocrine system comes in
and it owes a lot to cholesterol.
Now hold up. If you've ever seen a commercial for heart medicine or diet
supplements or so-called health food you've probably been subjected to some
pretty negative press about cholesterol.
It has a bad rap as an artery clogger but it's also got a really important job making hormones.
Hormones are chemical messengers that regulate processes that
don't need to happen all the time. When the villain in a movie suddenly pops up
on the screen brandishing a chainsaw,
it's your hormones that tell your blood vessels to constrict and your heart to
start pumping faster, preparing you to fight that monster or run away.
And cholesterol is the first step in making some of these hormones. Even though you hear
people talking about cholesterol in their diet, most of the cholesterol that
your body uses doesn't come from food;
your liver makes up to a gram of the stuff every day. Some of that cholesterol
stays in your liver where it's used to make vitamin D, but the rest is carted
through your bloodstream by molecules called lipoproteins, which are sort of
like their personal chauffeurs. And it's these reckless drivers that have been
giving cholesterol a bad name. When lipoproteins have too much fat in them
and not enough protein, they can get stuck to the walls of arteries and form
plaque that can impede the flow of blood.
That's a big problem, but it's not caused by the cholesterol directly.
It's the fault of its chauffeur. Meanwhile the cholesterol molecules that
have good healthier lipoproteins toting them around have better things to do
than just hang out on the side of your arteries. These cholesterols are
incorporated into cell membranes, keeping them fluid and functioning while others
are turned into steroid hormones like cortisol, estrogen and testosterone.
So cholesterol can be pretty cool. Just like you.
Looking at these five molecules gives a lot of insight into
how awesome the human organism is. If you want to learn more about what's in you
and how it works, head on over to Crash Course where you can take your brain for
a nice long soak in biology, anatomy, and physiology and lots of other disciplines.
But in the meantime, thanks for watching this episode of SciShow. If you'd like to
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