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How Genes Express Themselves: Crash Course Biology #36
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MLA Full: | "How Genes Express Themselves: Crash Course Biology #36." YouTube, uploaded by CrashCourse, 28 March 2024, www.youtube.com/watch?v=NeeaP8pp9HI. |
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CrashCourse, "How Genes Express Themselves: Crash Course Biology #36.", March 28, 2024, YouTube, 11:38, https://youtube.com/watch?v=NeeaP8pp9HI. |
If nearly all your cells have the same DNA, why are muscle cells so different from skin cells? In this episode, we’ll learn how gene expression is regulated in eukaryotes, and how methylating DNA, modifying histones, and messing with translation not only leads to different types of cells, but allows cells to adapt to the world around them.
Introduction: A Cellular Cookbook 00:00
Gene Regulation 1:18
Differential Gene Expression 2:36
Gene Regulation Strategies 3:58
Epigenetic Mechanisms 6:13
Review & Credits 9:22
This series was produced in collaboration with HHMI BioInteractive, committed to empowering educators and inspiring students with engaging, accessible, and quality classroom resources. Visit https://BioInteractive.org/CrashCourse for more information.
Check out our Biology playlist here: https://www.youtube.com/playlist?list=PL8dPuuaLjXtPW_ofbxdHNciuLoTRLPMgB
Watch this series in Spanish on our Crash Course en Español channel here: https://www.youtube.com/playlist?list=PLkcbA0DkuFjWQZzjwF6w_gUrE_5_d3vd3
Sources: https://docs.google.com/document/d/1GLDtAXE6ekg4Chk2qN3TYbNt0pJbyaHqTqRd6QY8pd4/edit?usp=sharing
Introduction: A Cellular Cookbook 00:00
Gene Regulation 1:18
Differential Gene Expression 2:36
Gene Regulation Strategies 3:58
Epigenetic Mechanisms 6:13
Review & Credits 9:22
This series was produced in collaboration with HHMI BioInteractive, committed to empowering educators and inspiring students with engaging, accessible, and quality classroom resources. Visit https://BioInteractive.org/CrashCourse for more information.
Check out our Biology playlist here: https://www.youtube.com/playlist?list=PL8dPuuaLjXtPW_ofbxdHNciuLoTRLPMgB
Watch this series in Spanish on our Crash Course en Español channel here: https://www.youtube.com/playlist?list=PLkcbA0DkuFjWQZzjwF6w_gUrE_5_d3vd3
Sources: https://docs.google.com/document/d/1GLDtAXE6ekg4Chk2qN3TYbNt0pJbyaHqTqRd6QY8pd4/edit?usp=sharing
Nearly all of your cells contain an identical copy of your entire genetic code: the full cookbook for how to make every kind of protein that your cells are capable of.
And that’s true for many other forms of complex life as well, including plants and many fungi. The cells in your stomach have all the same instructions as the cells in your heart.
I feel like there’s a good joke in there about the way to a person’s heart being through their stomach but it’s just not translating. Like the joke ribosomes in my brain must be hitting a stop codon. Anyway, don’t worry: your stomach isn’t going to start beating in the same rhythms as your heart.
Despite having the same information, those stomach cells ignore the instructions they don’t need, in the same way that I might ignore all the recipes in a cookbook that contain jalapenos, because heartburn, ugh! In the words of the old African-American proverb: “Ain’t nobody got time for that”! Anyway, cells pull off this spectacular feat by regulating the way that genes get expressed.
Hi! I’m Dr. Sammy, your friendly neighborhood entomologist, and this is Crash Course Biology.
Now where did I put that recipe for the world’s greatest theme music… [THEME MUSIC]
Our cells are amazing. Now, I know what you’re probably thinking, “Dr. Sammy, you say that about all the biology stuff.” Well, yeah, but that’s because it’s true!
In order to do the jobs that they need to do, our cells can selectively use certain genes while /ignoring/ others. It’s called gene regulation, and it’s the process that determines which proteins get made, and when and where they’re created. And proteins are important in just about everything we do.
Like, are you binge-watching more Crash Course after this? Eating a plate of spaghetti? Taking your pet coconut crab out for a walk?
It’s all thanks to your cells making proteins. To make a protein, cells start with a section of DNA called a gene, and then, the information in that gene gets copied, or transcribed, into a piece of messenger RNA, or mRNA. Then, structures called ribosomes translate, or read that mRNA, using it as the instructions to make a chain of amino acids that eventually fold up into a protein.
Okay, so that’s the TLDR, but there’s much more on how proteins get made in episode 35. For today, we’re talking about how that process can be interrupted at nearly any stage. You see, our cells have access to about 20 thousand genes.
That’s a whole grocery store’s worth of ingredients. But like any good chef, our cells know which ones to use. They don’t have to express every gene in their DNA to make a protein.
For instance, there are certain genes in nearly all of your cells that are only expressed in your heart. They allow for the creation of proteins that help your heart muscles – and only your heart muscles – contract in that special heartbeat rhythm. And those same heart cells contain genes that only get expressed in your stomach, helping it digest food.
This variation in how different kinds of cells express themselves based on their unique function is called differential gene expression. And much like how a chef might need to adjust a menu based on the season or available ingredients, our cells have to regulate gene expression based on factors like temperature or availability of nutrients. All of this can affect which proteins a cell needs and, by extension, which genes get expressed.
So gene expression can change from year to year, day to day, or even minute to minute. This allows cells to adapt as the world changes around them. Like, when you get hungry, thirsty, or even when you fall asleep.
There are a lot of ways that gene expression can be changed and regulated. In fact, there are too many for us to fully explain in the episode, but we’ve picked some highlights. One of the main ways that differential gene expression happens is through transcriptional regulation.
That means it regulates the way DNA is copied into mRNA. You see, our DNA is expansive, but less than two percent of the roughly three billion letters actually code for proteins. The rest of it… well, for a long time, scientists didn’t know what the rest of it did.
They called it “junk DNA”. But with more research, we’ve learned that a lot of this non-coding DNA, as it’s now called, is involved in turning genes on or off. Normally, to kickstart transcription and create a piece of mRNA, a protein called a transcription factor has to bind to a section of DNA called a control element - a short snippet of non-coding DNA.
That then tells cells whether or not to begin the protein-making process. Some combinations of control elements tells cells to begin transcription. While others, appropriately called silencers, act like a stop sign.
When transcription factors bind to silencers, transcription is blocked. No mRNA, no gene expression. But, even if an mRNA molecule is produced, that doesn’t mean it’ll necessarily be expressed.
For instance, mRNA can get spliced before it has a chance to get translated, or read. This creates different proteins from the same original molecule. Let’s say an mRNA has sections 1 through 5.
It can be sliced and diced so that the message only codes for a protein with sections 1, 3, and 5 — or just 2, 3, and 4, depending on what the cell needs. Or, the mRNA can have a run-in with that stuff that they used to call junk DNA. Turns out a lot of it gets transcribed into little sections of RNA, like microRNA or small interfering RNA.
And those sections don’t get translated into proteins because they have another job. They bind to mRNA that was on its way to get translated, and break it down before translation happens. And it makes a difference how long mRNA floats around in a cell before it’s broken down.
Think about it: if it takes a long time for an mRNA to break down, it’ll be translated into more and more copies of a protein in the meantime. Now, none of what we’ve just talked about so far is passed on when a cell divides into new cells. Each new cell does its own regulation based on signals it gets from its surroundings.
But there is one category of gene regulation that is heritable, meaning it can be passed on to new cells, and if it happens in a sperm or egg cell, then it can even be passed on to an organism’s offspring’s cells. These are called epigenetic mechanisms, which are heritable modifications to gene expression that don’t directly change the underlying DNA sequence. Instead of changing the sequence of DNA, epigenetic mechanisms modify what part of the DNA is accessible for translation.
And there are a couple of different ways to alter gene expression epigenetically. One involves the way DNA gets packaged. See, DNA isn’t floating around the nucleus all willy-nilly.
That would be like trying to stuff your entire wardrobe into your carry-on bag. Some organisms have literally meters of DNA in each cell, and unless it’s wound up into a compact package, those cellular bags are going to burst at the seams. So, cells keep all this DNA organized with the help of proteins called histones.
They’re like structural beads that DNA wraps around to stay nice and neat. And when it comes to gene expression, how these histones are arranged can also determine whether or not a gene gets turned on. Histone modification works by essentially exposing certain genes for transcription and hiding others so they can’t be copied or read.
Cells can also change expression epigenetically by tagging genes with particular molecules in a process called DNA methylation. This typically can’t turn genes on, but it can turn them off in a couple different ways. For example, the molecules can tell histones to condense and hide certain genes.
Or, they can block transcription factors from binding. Either way, this halts the process before mRNA is produced. These epigenetic mechanisms play a big role in our lives.
Someone’s environment and even their levels of stress can affect how their DNA is methylated, how their bodies behave, and might even get passed on to their children. Doctors have known for years that experiencing persistent discrimination causes forms of stress that are linked to different health risks. But more recent studies have found links between that discrimination and DNA methylation.
This suggests that stress driven by societal inequities could be causing physical changes in DNA. And although it’s too early to say for sure, they’re even beginning to find evidence that these changes may be able to pass from parent to child — even if the child never experiences the same discrimination themselves. But, there is some hope to be had here.
Understanding the damage these stressors cause can help researchers, activists, and community leaders work toward removing those stressors at the source, and better address their impacts. Now, that doesn’t mean that all epigenetic modifications are bad. In fact, many are essential to proper functioning.
Like, male mammals typically have an X and a Y chromosome, while female mammals typically have two X’s. But expressing two of the same chromosomes could potentially cause a lot of issues. So, one of the chromosomes in female mammals is epigenetically silenced, remaining in a stable, inactive state.
That means mammals of all sexes express a single X chromosome. Like I said, your cells have lots of ways of regulating gene expression. These are just a few of the many amazing tricks that your cells have up their sleeves.
Er, membranes. You’ve got transcriptional regulation, including epigenetic ways to guide transcription and non-epigenetic ways like control elements. All of that is just very fancy lingo that really means “if the cell doesn’t make mRNA, it can’t build a protein.” You’ve also got post-transcriptional processes that regulate translation from mRNA to protein.
These include alternative mRNA splicing, interfering mRNAs, and much more. So at every level of gene expression, your cells have ways to regulate whether or not they really need that protein. It’s basically a long sequence of repeatedly asking, “Are you sure about that?” The ability to regulate gene expression is what allows organisms to be so diverse, and complex, and interesting!
It makes your stomach muscles distinct from your heart muscles, and it allows your cells to respond as conditions change around them. But if we’ve learned anything in this episode, it’s that genes don’t get turned on or off in a vacuum. Someone’s environment and even how they’re treated may play a role in how DNA gets methylated — sometimes, for the worse.
Still, if stress can alter gene expression and make someone more likely to develop a disease, that also means a life /without/ those stressors could prevent those changes. In other words, making a more just, equitable world could lead to changes that run deep — all the way down to someone’s DNA. In our next episode, we’re going to spend some time talking about how mutations can emerge in our bodies’ genetic codes.
Peace! 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 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.
And that’s true for many other forms of complex life as well, including plants and many fungi. The cells in your stomach have all the same instructions as the cells in your heart.
I feel like there’s a good joke in there about the way to a person’s heart being through their stomach but it’s just not translating. Like the joke ribosomes in my brain must be hitting a stop codon. Anyway, don’t worry: your stomach isn’t going to start beating in the same rhythms as your heart.
Despite having the same information, those stomach cells ignore the instructions they don’t need, in the same way that I might ignore all the recipes in a cookbook that contain jalapenos, because heartburn, ugh! In the words of the old African-American proverb: “Ain’t nobody got time for that”! Anyway, cells pull off this spectacular feat by regulating the way that genes get expressed.
Hi! I’m Dr. Sammy, your friendly neighborhood entomologist, and this is Crash Course Biology.
Now where did I put that recipe for the world’s greatest theme music… [THEME MUSIC]
Our cells are amazing. Now, I know what you’re probably thinking, “Dr. Sammy, you say that about all the biology stuff.” Well, yeah, but that’s because it’s true!
In order to do the jobs that they need to do, our cells can selectively use certain genes while /ignoring/ others. It’s called gene regulation, and it’s the process that determines which proteins get made, and when and where they’re created. And proteins are important in just about everything we do.
Like, are you binge-watching more Crash Course after this? Eating a plate of spaghetti? Taking your pet coconut crab out for a walk?
It’s all thanks to your cells making proteins. To make a protein, cells start with a section of DNA called a gene, and then, the information in that gene gets copied, or transcribed, into a piece of messenger RNA, or mRNA. Then, structures called ribosomes translate, or read that mRNA, using it as the instructions to make a chain of amino acids that eventually fold up into a protein.
Okay, so that’s the TLDR, but there’s much more on how proteins get made in episode 35. For today, we’re talking about how that process can be interrupted at nearly any stage. You see, our cells have access to about 20 thousand genes.
That’s a whole grocery store’s worth of ingredients. But like any good chef, our cells know which ones to use. They don’t have to express every gene in their DNA to make a protein.
For instance, there are certain genes in nearly all of your cells that are only expressed in your heart. They allow for the creation of proteins that help your heart muscles – and only your heart muscles – contract in that special heartbeat rhythm. And those same heart cells contain genes that only get expressed in your stomach, helping it digest food.
This variation in how different kinds of cells express themselves based on their unique function is called differential gene expression. And much like how a chef might need to adjust a menu based on the season or available ingredients, our cells have to regulate gene expression based on factors like temperature or availability of nutrients. All of this can affect which proteins a cell needs and, by extension, which genes get expressed.
So gene expression can change from year to year, day to day, or even minute to minute. This allows cells to adapt as the world changes around them. Like, when you get hungry, thirsty, or even when you fall asleep.
There are a lot of ways that gene expression can be changed and regulated. In fact, there are too many for us to fully explain in the episode, but we’ve picked some highlights. One of the main ways that differential gene expression happens is through transcriptional regulation.
That means it regulates the way DNA is copied into mRNA. You see, our DNA is expansive, but less than two percent of the roughly three billion letters actually code for proteins. The rest of it… well, for a long time, scientists didn’t know what the rest of it did.
They called it “junk DNA”. But with more research, we’ve learned that a lot of this non-coding DNA, as it’s now called, is involved in turning genes on or off. Normally, to kickstart transcription and create a piece of mRNA, a protein called a transcription factor has to bind to a section of DNA called a control element - a short snippet of non-coding DNA.
That then tells cells whether or not to begin the protein-making process. Some combinations of control elements tells cells to begin transcription. While others, appropriately called silencers, act like a stop sign.
When transcription factors bind to silencers, transcription is blocked. No mRNA, no gene expression. But, even if an mRNA molecule is produced, that doesn’t mean it’ll necessarily be expressed.
For instance, mRNA can get spliced before it has a chance to get translated, or read. This creates different proteins from the same original molecule. Let’s say an mRNA has sections 1 through 5.
It can be sliced and diced so that the message only codes for a protein with sections 1, 3, and 5 — or just 2, 3, and 4, depending on what the cell needs. Or, the mRNA can have a run-in with that stuff that they used to call junk DNA. Turns out a lot of it gets transcribed into little sections of RNA, like microRNA or small interfering RNA.
And those sections don’t get translated into proteins because they have another job. They bind to mRNA that was on its way to get translated, and break it down before translation happens. And it makes a difference how long mRNA floats around in a cell before it’s broken down.
Think about it: if it takes a long time for an mRNA to break down, it’ll be translated into more and more copies of a protein in the meantime. Now, none of what we’ve just talked about so far is passed on when a cell divides into new cells. Each new cell does its own regulation based on signals it gets from its surroundings.
But there is one category of gene regulation that is heritable, meaning it can be passed on to new cells, and if it happens in a sperm or egg cell, then it can even be passed on to an organism’s offspring’s cells. These are called epigenetic mechanisms, which are heritable modifications to gene expression that don’t directly change the underlying DNA sequence. Instead of changing the sequence of DNA, epigenetic mechanisms modify what part of the DNA is accessible for translation.
And there are a couple of different ways to alter gene expression epigenetically. One involves the way DNA gets packaged. See, DNA isn’t floating around the nucleus all willy-nilly.
That would be like trying to stuff your entire wardrobe into your carry-on bag. Some organisms have literally meters of DNA in each cell, and unless it’s wound up into a compact package, those cellular bags are going to burst at the seams. So, cells keep all this DNA organized with the help of proteins called histones.
They’re like structural beads that DNA wraps around to stay nice and neat. And when it comes to gene expression, how these histones are arranged can also determine whether or not a gene gets turned on. Histone modification works by essentially exposing certain genes for transcription and hiding others so they can’t be copied or read.
Cells can also change expression epigenetically by tagging genes with particular molecules in a process called DNA methylation. This typically can’t turn genes on, but it can turn them off in a couple different ways. For example, the molecules can tell histones to condense and hide certain genes.
Or, they can block transcription factors from binding. Either way, this halts the process before mRNA is produced. These epigenetic mechanisms play a big role in our lives.
Someone’s environment and even their levels of stress can affect how their DNA is methylated, how their bodies behave, and might even get passed on to their children. Doctors have known for years that experiencing persistent discrimination causes forms of stress that are linked to different health risks. But more recent studies have found links between that discrimination and DNA methylation.
This suggests that stress driven by societal inequities could be causing physical changes in DNA. And although it’s too early to say for sure, they’re even beginning to find evidence that these changes may be able to pass from parent to child — even if the child never experiences the same discrimination themselves. But, there is some hope to be had here.
Understanding the damage these stressors cause can help researchers, activists, and community leaders work toward removing those stressors at the source, and better address their impacts. Now, that doesn’t mean that all epigenetic modifications are bad. In fact, many are essential to proper functioning.
Like, male mammals typically have an X and a Y chromosome, while female mammals typically have two X’s. But expressing two of the same chromosomes could potentially cause a lot of issues. So, one of the chromosomes in female mammals is epigenetically silenced, remaining in a stable, inactive state.
That means mammals of all sexes express a single X chromosome. Like I said, your cells have lots of ways of regulating gene expression. These are just a few of the many amazing tricks that your cells have up their sleeves.
Er, membranes. You’ve got transcriptional regulation, including epigenetic ways to guide transcription and non-epigenetic ways like control elements. All of that is just very fancy lingo that really means “if the cell doesn’t make mRNA, it can’t build a protein.” You’ve also got post-transcriptional processes that regulate translation from mRNA to protein.
These include alternative mRNA splicing, interfering mRNAs, and much more. So at every level of gene expression, your cells have ways to regulate whether or not they really need that protein. It’s basically a long sequence of repeatedly asking, “Are you sure about that?” The ability to regulate gene expression is what allows organisms to be so diverse, and complex, and interesting!
It makes your stomach muscles distinct from your heart muscles, and it allows your cells to respond as conditions change around them. But if we’ve learned anything in this episode, it’s that genes don’t get turned on or off in a vacuum. Someone’s environment and even how they’re treated may play a role in how DNA gets methylated — sometimes, for the worse.
Still, if stress can alter gene expression and make someone more likely to develop a disease, that also means a life /without/ those stressors could prevent those changes. In other words, making a more just, equitable world could lead to changes that run deep — all the way down to someone’s DNA. In our next episode, we’re going to spend some time talking about how mutations can emerge in our bodies’ genetic codes.
Peace! 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 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.