The Most Important Concept in Biology (Chapter 1)

The goal is for you to leave this video with
an intuitive understanding of one of the most important concepts in all of science: The
Central Dogma. This crucial idea provides the basic framework
for understanding how we inherit traits and diseases, why we are different from plants
and other animals, and really it’s the core of understanding how all life inherently works. Now, I will admit that a good number of you
watching this (I’m looking at you, biology students) probably have already heard of the
idea of DNA going to RNA to protein.

However, after many hours of scrolling through
biology forums, I’ve come to realize that although many people have “learned” this
concept before, they don’t completely understand it, and I totally get that. The way that biology is taught unfortunately
often reduces it to just rote memorization, and all the complicated vocab terms often
get in the way of fully appreciating the bigger picture. And I think this trend of biology being toted
as a boring subject is really sad.

I’d argue that biology, out of all the sciences,
is at its most exciting stages right now, with new discoveries being made each year,
which is why I think it’s so important for everyone, not just biology students, to have
a solid grasp of the fundamentals of the subject. And at the core of all biology lies the Central
Dogma. Even the most advanced scientists nowadays
still use the Central Dogma in all the research they do, whether that’s trying to cure cancer
or develop a vaccine for COVID. So I don’t think it’s a stretch when I
say that this is a concept worth learning. But instead of us blindly going through the
steps or throwing out meaningless vocabulary words, we’re actually going to start our
journey from the end and work our way backwards so that you can build an intuition for the
topic. Pay close attention. Linus Pauling, one of the most famous chemists
of the 20th century, once said, “Proteins hold the key to the whole subject of the molecular
basis of biological reactions.” Now, Pauling made this claim back in 1949,
but even today, in 2020, most scientists would agree with his statement.

Out of everything in your body, proteins are
the most important in allowing life to function Think about it… almost everything you do
is in some way because of proteins. Proteins help carry oxygen around your blood. They form the protective layer of your skin. They digest the food in your stomach. They make your muscles contract. The list goes on and on. Thus, that begs the question: from where does
your body get all these proteins? There’s such a diversity of proteins in
your body, all of which play a vital role, but where do they all come from? Some people used to believe that all your
proteins came from your diet. After all, food is known to contain proteins,
so it wouldn’t be a stretch to assume that the proteins in your body come from the food
you eat. However, this hypothesis wasn’t entirely
correct, and the reasoning as to why was pretty straightforward.

There’s simply no way for you to be eating
all of these different types of proteins! Take a look at your fingernails, for example. Your fingernails are made of a relatively
hard protein called keratin, but you never see anyone going around eating hard fingernail
texture-like foods. So that keratin protein had to have come from
somewhere else. So that leaves the other possible answer:
our body makes the proteins itself. It makes sense that there might be some way
for our body, and life in general, to build the proteins from scratch. That way, you wouldn’t have to eat the keratin
protein in order to grow fingernails; your body would just synthesize the keratin protein
itself. This idea makes sense! And after some experiments, scientists determined
that… yes! Our body, and all of life in general, does
synthesize proteins within the body, or “in vivo” So the obvious question is… How? Sure, our body might be able to make these
important proteins, but what’s the actual mechanism, the actual process, of synthesizing
the proteins? And before we can even get to that question,
there’s the other question of how our body makes all these different types of proteins.

How does our body know how to make hemoglobin
protein? Or keratin protein?. Or pepsin protein? There is so much diversity of proteins, and
the body somehow needs to be able to make all of these. Now just take a second and think about it. How can our body possibly know how to make
all of these different types of proteins? It’s a difficult challenge! And yet, as you’ll come to find for most
of biology, the answer is actually quite simple.

Our body simply has a sort of recipe book,
one that contains the instructions and necessary ingredients to make every type of protein. For example, one page in the book might be
dedicated to making the acting protein, another page giving instructions to synthesize the
hemoglobin protein, another page for the keratin protein, etc. There is a unique recipe for every single
protein in this recipe book, and in fact, every single cell in your body has a copy
of this recipe book.

So if any part of your body needs to make,
let’s say collagen protein, then that cell will simply go to the appropriate page of
the recipe book, get the instructions, and make the collagen protein! It’s pretty clever! But obviously, you never hear biologists walking
around talking about this “recipe book,” and that’s because no sane scientist refers
to it as the “recipe book.” Instead, we refer to the recipe book by its
scientific name… DNA.

Yes, DNA, which you’ve all probably heard
of a million times by this point, is in fact the recipe book that all cells refer to in
order to make proteins. Here’s what a segment of DNA might actually
look like, just to give you the sense that DNA does contain the instructions to make
proteins. If you want some numbers, there are over 20,000
different proteins in the human body, so therefore, our DNA contains over 20,000 different recipes
in order to make those proteins. With regards to terminology, scientists call
each protein recipe a “gene,” and they appropriately refer to the entire recipe book
as the “genome.” Take a moment and really make sure that you’ve
understood what you just heard, because the idea of genes being segments of DNA that hold
the instructions to make proteins is the most important concept of all modern biology, no
exaggeration.

Most of the rest of this series will be dependent
on you understanding this logic of genes encoding proteins, so if you need to, I highly encourage
you to pause and make sure you understand. Now, if you truly understand this concept,
then it would make sense to you that if, for some reason, something was wrong with a gene,
then it’s possible that the respective protein would not be formed correctly, potentially
leading to health issues.

This is what scientists refer to as a mutation. And it would also make sense to you that even
though all the cells in your body have the same genome or recipe book, different cells
in your body might need different proteins. So therefore, each cell will use different
genes to make those proteins. The act of a cell using a specific gene to
make a protein is what scientists call “gene expression.” And the act of a cell controlling which genes
to use and which not to use is referred to as “gene regulation.” And one more thing to keep in mind, just some
food for thought.

Scientists used to believe that one gene had
the instructions to make exactly one protein, which they famously made into the motto “One
gene, one protein.” But scientists nowadays know that this isn’t
true. In fact, for reasons we’ll get into later
this series, one gene might be able to encode multiple proteins, but don’t worry about
that for now. Now that you understand the concept of gene
to protein, I want you to consider this. Each cell contains just one recipe book, one
genome. So if something wrong happens to it, let’s
say the instructions get messed up, then that’s bad news for the cell because there’s no
backup. So obviously, your body will do whatever it
can to protect its DNA. And what the cell does is it kind of locks
up the DNA in a special part of the cell that we call the nucleus.

However, this leads to another problem. If the DNA is stuck in the nucleus, then how
is the cell supposed to access it when it needs to make proteins? You can think of this like not taking your
recipe book into the kitchen because if you burn it or spill water on it, your recipes
are gone for good. But at the same time, if you don’t have
your recipe book in the kitchen, then you don’t have the instructions to make anything! So what’s a cell to do?? Well, what would you do if you wanted to make
something from your recipe book but couldn’t bring the entire book with you? Well, you might grab some scratch paper and
copy down your recipe of interest, and take your handwritten recipe with you to the kitchen
instead of the whole recipe book.

That way, your recipe book stays safe and
you still have the necessary instructions, albeit a copied version, with you in the kitchen. In a sense, you could say that what you did–
writing down the recipe yourself onto a piece of paper– was transcribe the message. And this, in fact, is exactly what cells do. Whenever a cell needs to use a specific gene
in order to make a protein, it goes and makes a copy of that gene, a process known as transcription. And just like your handwritten transcript
of the recipe won’t look exactly the same as the original in the recipe book, the cell’s
transcript won’t look exactly the same either. While the original gene is made of DNA, the
transcript is actually composed of RNA, hence the saying that transcription is DNA to RNA.

Specifically, because this RNA provides the
same instructions, the same message, as its respective gene, it is referred to as messenger
RNA, or mRNA for short. And now that the cell has its messenger RNA,
its next step is to make the respective protein that is encoded by the mRNA! So how does this happen? Well, the cell would have to read the recipe,
follow the instructions, and then actually make the protein! One could say that we are going from the written
language of the recipe to the language of action: actually building the protein. Thus the process of mRNA being used to make
protein is commonly called translation, as we’re going from one language to another.

So.. we’re done, right? We’ve completed our Central Dogma, DNA to
RNA to Protein. Well… almost. There’s one more important step of the Central
Dogma that we have still yet to discuss, and for you to understand it, I want you to consider
the following scenario. Most of you know that cells divide. That’s how our bodies grow and how paper
cuts get closed. However, you also know (because I’ve told
you) that each cell contains exactly one copy of the recipe book, only one copy of the genome. So when one cell splits into two daughter
cells, what happens to the DNA? Remember, the original parent cell has only
one copy of the DNA, so… does one daughter cell get all the DNA while the other gets
none? Does each daughter cell get half the DNA,
like we’re cutting the recipe book in half and splitting it evenly amongst the cells? Well, of course not! You know by now that each cell needs an entire
copy of the genome, an entire copy of the DNA, in order to make all its necessary proteins. But how can two daughter cells each get a
full copy of the DNA when the original parent cell only had only one copy in the first place? Think about it! How do you think the cell solves this problem? The answer is simple: right before dividing,
the original cell simply makes a copy of all of its DNA so that it has 2 copies ready,
one for each daughter cell.This process is appropriately called DNA Replication.

Keep in mind that while in transcription,
the cell only copied the specific recipe or gene that it needed, in DNA replication the
cell makes a copy of the entire genome, all its DNA. And with that, that is the final piece of
our Central Dogma. Now obviously, this was a fairly simplified
view of the Central Dogma. We didn’t even touch some of the concepts
that you might learn in an introductory biology class, like DNA Polymerase or Transcription
Factors. But that’s kind of the point of this video. Oftentimes people get overwhelmed and lost
by the miniscule details and complicated terminology that they lose sight of the bigger picture. To sum up, proteins are essential to life,
and in order for cells to make the proteins, it uses instructions encoded by genes in your
DNA. The necessary gene is converted to mRNA through
transcription, and that mRNA is used to actually create the protein through translation. And right before dividing, the cell copies
all of its DNA in a process called DNA replication. It’s important to realize that DNA isn’t
being chemically changed into RNA, nor is RNA being chemically changed into protein.

DNA to RNA to protein is simply a way to express
the direction that the instructions, or the information, flows within life. In the next few videos, we’ll look at all
of these processes in more detail so that we understand exactly how the cell makes the
mRNA transcript or how the mRNA is used to make proteins. To test your understanding, try answering
this question. It’s a tough one! But if you understood this video, then it’s
something that you’re more than capable of answering. If it helps, try to refer back to the analogy
of the recipe book, and go on from there. Leave your answer in the comments below, and
spark a conversation with others! See if your answer lines up with everyone
else’s.

In the next video, we’ll take a look at
DNA structure and how the double helical nature of DNA makes it the perfect molecule to hold
the instructions to make proteins. We’ll also explore some of the experiments
performed to determine DNA’s structure, including X-ray crystallography and Fourier
Transforms. So subscribe and hit the bell to make sure
that you don’t miss out. And as always, keep on appreciating..

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