VIDEO: Understanding DNA, Genes, and Chromosomes

We've gone ahead and reviewed the structure of DNA and talked about how it's packaged. I want to talk about how much DNA organisms have and what parts of that DNA actually code for proteins. So let's start first with this concept of the genome. Like we said kind of at the tail end of the last video, most organisms have so much DNA that it's not packaged onto just one chromosome structure. They have multiple chromosomes that's needed to package all of the DNA across. The number of chromosomes, the total number that encompasses all of the DNA, that is the organism's genome. So you can think of kind of in shorthand that the genome is all the DNA that any given organism has, and specifically the total number of chromosomes that that DNA is packaged across. Now within the genome, there's generally two different categories of chromosomes. And I'll start with the second one first, the sex chromosomes. Many organisms just have one pair of sex chromosomes, although the number can vary. And these are essentially chromosomes that carry genetic information that dictate biological sex. So these would be the chromosomes that would dictate whether the individual was biologically male or biologically female. The other classification of chromosomes are autosomes or somatic chromosomes. We can kind of use those terms interchangeably. And essentially, they are all the chromosomes excluding the sex chromosomes. So they possess all kinds of information. They simply carry the information that isn't directly connected to determining biological sex. Now, like we said, many organisms have multiple chromosomes. And sort of the rule of thumb is this. Organisms within the same species will have the same number of chromosomes, barring some sort of genetic anomaly. and we'll talk about what genetic anomalies might make the exception in chapter eight, but the number of chromosomes does not stay constant from one species to the next. So for instance, we have two different types of organisms down here. We have houseflies. The genome of a housefly has eight chromosomes in it, whereas the genome of some dogs, it can differ slightly from one breed to the next, have 78 chromosomes in total. Okay, now all house flies, barring a genetic anomaly, should have eight, and all dogs of the same breed should have 78. But clearly, between species, that's not constant. Now, we're going to focus mostly on humans in genetics going forward, since we are humans, and humans have in their genome a total of 46 chromosomes for humans, or sometimes we say 23 pairs. And we'll talk about why we talk about them in pairs in a later video, okay? And actually what I have off here to the right is a picture of a human's genome. And this is a karyotype. So a karyotype is just a picture of an organism's genome. And it shows all of the chromosomes that that organism possesses. So this is a karyotype of a human genome. And if we look at it, we can kind of classify the categories. You can see that they are shown in pairs. So for instance, this is one chromosome, this is another chromosome, but these two are paired together. So that's one pair. And if we look, we can see that they are numbered all the way up to 22 pairs. So let me draw like my little circle here. And then the last pair isn't numbered. And the reason why is that the first 22 pairs within the human genome are the somatic or autosomal chromosomes. So this one right here. And then the last pair, so the 23rd pair, I'll pick a different color here. This will show up, yeah. So 23rd pair. Those are the sex chromosomes that indicate biological sex. This person has an X and a Y. That makes them biologically male. If it was two X chromosomes, that would make them biologically female. And we'll talk a little bit more about gender determination in Chapter 8. All right, so moving on. The chromosome holds a whole bunch of DNA. So the chromosome is a highly compacted structure. with some fraction of the total DNA wound up inside of it. Now, on one chromosome, there are multiple sets of instructions for different proteins. And the word that we use for these sets of instructions is we call them genes. So a gene is a portion of the DNA that codes for a specific protein. And that specific protein that it codes for is then going to have some specific job or function within the living organism. So the gene is a fraction of a DNA that's compiled into a chromosome. Sorry. And I like this image off here to the right because it kind of puts these things in context of one another, right? We have the genome. The genome is all of the DNA condensed into all of the chromosomes, right? So a genome will usually have multiple chromosomes. Each chromosome contains a lot of DNA compacted into it, and segments of that DNA are going to contain different genes that code for different proteins. So a given chromosome is going to have multiple genes on it. Each gene, so here's one gene, each gene is going to have the genetic instructions for producing one protein. Now there's another set of terms that we're going to see, and that's the word locus or loci. And really all this refers to is the location on a chromosome. If you want to talk about where a gene is located in a chromosome, the word we use is the loci. So the loci refers to the location of the gene on a specific chromosome. And in terms of location, organisms of the same species have their genes in the same location. Okay, so let's go back for a moment to the last slide so we can look at the human genome, just to kind of point out what I'm talking about. There's 23 pairs of chromosomes, right? So let's just say for the sake of argument, I'll use green. Let's say that the gene for dictating eye color is located right here. This is the loci. It's located on the first pair of chromosomes at the bottom half of the chromosome. That's probably not where it's actually located. I'm just, I'm making this up for an example, okay? If that was the location for the gene for eye color for this individual, then that would be the location for that gene for all humans. So the loci of a gene is constant within a species. All right, now I really want you to understand how these things all fit together. So I'm going to give you kind of an analogy to sort of help you understand what we're talking about here. Okay, the analogy that I like to use, I like to shop at Ikea. It's kind of one of my guilty pleasures. And I like to imagine, so just in case you don't shop at Ikea, it's a furniture store. They have all kinds of furniture from Sweden. You have to build it yourself, but it's pretty cheap. Anyway, they sell all kinds of stuff for every room of your house you could possibly imagine. And so I like to imagine that somewhere in their headquarters, they have this, they have all of the instructions for building all of the furniture, right? I mean, they have the instructions they give out with the furniture as you buy it. So somewhere they have to have the master copy of those instructions. that they put in with the products. And that's what I would consider the genome. So if we're thinking of the IKEA analogy, the genome would be the instructions for all the furniture they sell. Just like the genome is a compilation of all of the genetic information for all of the proteins that an organism can produce. Now, Ikea sells so much furniture that we're talking about lots and lots and lots and lots of instructions. And I'm going to say that there's like no way that they're going to fit that into one book, right? If they tried to fit that into one binder, that thing would be massive. So they probably have multiple volumes. They probably have multiple volumes to contain all of these instructions. For instance, Maybe they have a volume that is just for bath furniture. Maybe they have a volume that's for a living room. Maybe they have a volume for kitchen furniture, and so on and so forth. So all of their instructions are broken across and packaged into different binders for different sections of the house. And that's kind of analogous to the chromosome. So in the analogy, the analogous to the chromosome... would be the volumes that possess the instructions. And there'd probably be multiples because there are so many instructions. Now the gene, okay, within each one of these volumes, within each one of these volumes is going to be different sets of instructions for different pieces of furniture. So for instance, within the living room, um, Let's look at the living room section and use that as an example. Let's say that they sell multiple different coffee tables, okay? And let's say they have, they usually have Swedish names. I don't know, so I'm just making up. They have the broken coffee table. Very nice. Comes in hazel and dark brown. That you can buy and build, okay? There's going to be a set of instructions within this volume. specifically for that one type of table. That would be sort of analogous to a gene. A gene is a piece of a chromosome, so a piece of DNA on the chromosome that just codes for one protein. Just like within these volumes, there would be one or two pages or more, couple pages dedicated specifically to just building one of the products that they sell. And then if you were to take those instructions, and actually follow them, you would produce the coffee table that it gives you instructions for, which is analogous to the protein. The protein is the end result of the instructions embedded in the gene, just like the coffee table would be the end result of following the instructions for building the broken coffee table. Now, last thing to put in context, loci or locus, okay? Locus is kind of the plural term. Loci is singular, but they mean the same thing. Within the volume of living room furniture, okay, there would be a specific page number that would be dedicated to the broken coffee table. That's kind of like analogous to the loci or locus. That's the location of these instructions within that volume within the genome. And specifically, the loci of a gene is its location on a chromosome within the entire genome. So take some time, kind of work through this mentally, maybe watch this once or twice if you need to, and just work on getting these terms and understanding how they relate to one another. Don't just memorize what each term is by itself. Understand how that term connects to the other terms on this slide. Alright, now. that we've talked about what a gene is. What I want to kind of now tell you is that not all DNA result in genes. Essentially, there are portions of the DNA that don't code for proteins at all, okay? We call this non-coding DNA because it's not coding for a protein that is facilitating some function. Now, in terms of percentage, Organisms that have prokaryotic cells, so prokaryotic organisms versus eukaryotic organisms. Prokaryotic organisms have less non-coding DNA relative to many eukaryotic organisms have a much greater amount of non-coding DNA. In terms of just overall DNA coding and non-coding, prokaryotic organisms have less overall DNA and also have a smaller proportion of non-coding DNA. So they have less DNA, but the majority of the DNA that they do have is instructions for building some type of protein. Whereas eukaryotic cells have a greater amount of total DNA, but a decent percentage of that is non-coding and doesn't actually code for proteins at all. So the question becomes, if it doesn't code for proteins, if it's not a gene, then what is it? Like, what does it do? Or what does it have? Or why is it there? Well, there's a couple of things that non-coding DNA can be. It can be a fragment of a gene that is utilized. So think of like partial instructions embedded in the living room volume that don't actually get used, okay? It can be a duplicate version of a gene. So it can be another set of instructions for a protein that is somewhere else in the chromosome. Both copies are not utilized. the duplicate copy sort of just exists. Or it could be potentially a pseudogene. A pseudogene is a gene that was once utilized back in time but is no longer utilized by this organism. And then another one that's not on this list but that I want to add is it could be regulatory DNA. Regulatory DNA helps determine when specific proteins get built or when specific instructions are actually utilized. The instructions that are embedded in the DNA, the proteins, as we're going to find out towards the end of this chapter, not all cells need to make all proteins all the time. There needs to be some discernment of when proteins are produced. And so the regulatory DNA, the regulatory DNA that's not necessarily a gene, is going to help determine when the gene actually gets used. For instance, the analogy of regulatory DNA in context of IKEA might be some pages in the living room manual that say when the broken coffee table should be distributed and built at various stores across the nation. If that page was embedded in there, it's not giving instructions for building the coffee table, right? It's not part of the instruction manual for building the actual coffee table itself. It's instructions that say when and where the coffee table should be built. And that's kind of the idea of regulatory DNA. It's not information for building the protein. It's information that indicates when and where protein is built. And in terms of the where, we're talking about which cells. produce that rather than stores. All right, now there's two general types of non-coding DNA, one of which we really want to focus on. Sometimes non-coding DNA can be embedded within a gene. So within the instructions for building a protein, sometimes there can be segments of nitrogenous bases that don't contribute to the building of the protein itself. The word that we use for these, these are called introns. So for instance, in my picture here, I have a segment of DNA on a chromosome, okay? And we've highlighted the sections that are needed for building the protein in either purple or green for the various gene, okay? So this segment right here is one gene that would result. in the production of, we'll call it protein 1. And let's say that this gene is essential for the production of protein 2. The highlighted sections, these are what are needed. So these are the actual instructions. The unhighlighted sections, they represent non-coding DNA that's embedded within the gene. And so these are the introns. Non-coding DNA that is not embedded within a gene is called an exon. So this segment right here, which is in between genes, which is non-coding, is called an exon. Whereas if the non-coding segment is embedded within the gene, it is called an entron. And the one that we're going to need to really remember is the word entron, because we are going to refer back to that as we talk about how proteins get built. So the takeaway from this slide is that... Not all DNA codes for genes, not all code for instructions for building proteins.

Like we said kind of at the tail end of the last video, most organisms have so much DNA that it's not packaged onto just one chromosome structure. They have multiple chromosomes that's needed to package all of the DNA across. The number of chromosomes, the total number that encompasses all of the DNA, that is the organism's genome.

So you can think of kind of in shorthand that the genome is all the DNA that any given organism has, and specifically the total number of chromosomes that that DNA is packaged across. Now within the genome, there's generally two different categories of chromosomes. And I'll start with the second one first, the sex chromosomes. Many organisms just have one pair of sex chromosomes, although the number can vary. And these are essentially chromosomes that carry genetic information that dictate biological sex.

So these would be the chromosomes that would dictate whether the individual was biologically male or biologically female. The other classification of chromosomes are autosomes or somatic chromosomes. We can kind of use those terms interchangeably. And essentially, they are all the chromosomes excluding the sex chromosomes.

So they possess all kinds of information. They simply carry the information that isn't directly connected to determining biological sex. Now, like we said, many organisms have multiple chromosomes. And sort of the rule of thumb is this. Organisms within the same species will have the same number of chromosomes, barring some sort of genetic anomaly.

and we'll talk about what genetic anomalies might make the exception in chapter eight, but the number of chromosomes does not stay constant from one species to the next. So for instance, we have two different types of organisms down here. We have houseflies. The genome of a housefly has eight chromosomes in it, whereas the genome of some dogs, it can differ slightly from one breed to the next, have 78 chromosomes in total. Okay, now all house flies, barring a genetic anomaly, should have eight, and all dogs of the same breed should have 78. But clearly, between species, that's not constant.

Now, we're going to focus mostly on humans in genetics going forward, since we are humans, and humans have in their genome a total of 46 chromosomes for humans, or sometimes we say 23 pairs. And we'll talk about why we talk about them in pairs in a later video, okay? And actually what I have off here to the right is a picture of a human's genome. And this is a karyotype. So a karyotype is just a picture of an organism's genome.

And it shows all of the chromosomes that that organism possesses. So this is a karyotype of a human genome. And if we look at it, we can kind of classify the categories.

You can see that they are shown in pairs. So for instance, this is one chromosome, this is another chromosome, but these two are paired together. So that's one pair.

And if we look, we can see that they are numbered all the way up to 22 pairs. So let me draw like my little circle here. And then the last pair isn't numbered.

And the reason why is that the first 22 pairs within the human genome are the somatic or autosomal chromosomes. So this one right here. And then the last pair, so the 23rd pair, I'll pick a different color here.

This will show up, yeah. So 23rd pair. Those are the sex chromosomes that indicate biological sex.

This person has an X and a Y. That makes them biologically male. If it was two X chromosomes, that would make them biologically female.

And we'll talk a little bit more about gender determination in Chapter 8. All right, so moving on. The chromosome holds a whole bunch of DNA. So the chromosome is a highly compacted structure.

with some fraction of the total DNA wound up inside of it. Now, on one chromosome, there are multiple sets of instructions for different proteins. And the word that we use for these sets of instructions is we call them genes.

So a gene is a portion of the DNA that codes for a specific protein. And that specific protein that it codes for is then going to have some specific job or function within the living organism. So the gene is a fraction of a DNA that's compiled into a chromosome. Sorry.

And I like this image off here to the right because it kind of puts these things in context of one another, right? We have the genome. The genome is all of the DNA condensed into all of the chromosomes, right? So a genome will usually have multiple chromosomes.

Each chromosome contains a lot of DNA compacted into it, and segments of that DNA are going to contain different genes that code for different proteins. So a given chromosome is going to have multiple genes on it. Each gene, so here's one gene, each gene is going to have the genetic instructions for producing one protein. Now there's another set of terms that we're going to see, and that's the word locus or loci.

And really all this refers to is the location on a chromosome. If you want to talk about where a gene is located in a chromosome, the word we use is the loci. So the loci refers to the location of the gene on a specific chromosome.

And in terms of location, organisms of the same species have their genes in the same location. Okay, so let's go back for a moment to the last slide so we can look at the human genome, just to kind of point out what I'm talking about. There's 23 pairs of chromosomes, right? So let's just say for the sake of argument, I'll use green.

Let's say that the gene for dictating eye color is located right here. This is the loci. It's located on the first pair of chromosomes at the bottom half of the chromosome.

That's probably not where it's actually located. I'm just, I'm making this up for an example, okay? If that was the location for the gene for eye color for this individual, then that would be the location for that gene for all humans. So the loci of a gene is constant within a species. All right, now I really want you to understand how these things all fit together.

So I'm going to give you kind of an analogy to sort of help you understand what we're talking about here. Okay, the analogy that I like to use, I like to shop at Ikea. It's kind of one of my guilty pleasures.

And I like to imagine, so just in case you don't shop at Ikea, it's a furniture store. They have all kinds of furniture from Sweden. You have to build it yourself, but it's pretty cheap.

Anyway, they sell all kinds of stuff for every room of your house you could possibly imagine. And so I like to imagine that somewhere in their headquarters, they have this, they have all of the instructions for building all of the furniture, right? I mean, they have the instructions they give out with the furniture as you buy it.

So somewhere they have to have the master copy of those instructions. that they put in with the products. And that's what I would consider the genome. So if we're thinking of the IKEA analogy, the genome would be the instructions for all the furniture they sell. Just like the genome is a compilation of all of the genetic information for all of the proteins that an organism can produce.

Now, Ikea sells so much furniture that we're talking about lots and lots and lots and lots of instructions. And I'm going to say that there's like no way that they're going to fit that into one book, right? If they tried to fit that into one binder, that thing would be massive. So they probably have multiple volumes. They probably have multiple volumes to contain all of these instructions.

For instance, Maybe they have a volume that is just for bath furniture. Maybe they have a volume that's for a living room. Maybe they have a volume for kitchen furniture, and so on and so forth. So all of their instructions are broken across and packaged into different binders for different sections of the house.

And that's kind of analogous to the chromosome. So in the analogy, the analogous to the chromosome... would be the volumes that possess the instructions.

And there'd probably be multiples because there are so many instructions. Now the gene, okay, within each one of these volumes, within each one of these volumes is going to be different sets of instructions for different pieces of furniture. So for instance, within the living room, um, Let's look at the living room section and use that as an example.

Let's say that they sell multiple different coffee tables, okay? And let's say they have, they usually have Swedish names. I don't know, so I'm just making up.

They have the broken coffee table. Very nice. Comes in hazel and dark brown. That you can buy and build, okay?

There's going to be a set of instructions within this volume. specifically for that one type of table. That would be sort of analogous to a gene.

A gene is a piece of a chromosome, so a piece of DNA on the chromosome that just codes for one protein. Just like within these volumes, there would be one or two pages or more, couple pages dedicated specifically to just building one of the products that they sell. And then if you were to take those instructions, and actually follow them, you would produce the coffee table that it gives you instructions for, which is analogous to the protein.

The protein is the end result of the instructions embedded in the gene, just like the coffee table would be the end result of following the instructions for building the broken coffee table. Now, last thing to put in context, loci or locus, okay? Locus is kind of the plural term.

Loci is singular, but they mean the same thing. Within the volume of living room furniture, okay, there would be a specific page number that would be dedicated to the broken coffee table. That's kind of like analogous to the loci or locus. That's the location of these instructions within that volume within the genome. And specifically, the loci of a gene is its location on a chromosome within the entire genome.

So take some time, kind of work through this mentally, maybe watch this once or twice if you need to, and just work on getting these terms and understanding how they relate to one another. Don't just memorize what each term is by itself. Understand how that term connects to the other terms on this slide.

Alright, now. that we've talked about what a gene is. What I want to kind of now tell you is that not all DNA result in genes. Essentially, there are portions of the DNA that don't code for proteins at all, okay? We call this non-coding DNA because it's not coding for a protein that is facilitating some function.

Now, in terms of percentage, Organisms that have prokaryotic cells, so prokaryotic organisms versus eukaryotic organisms. Prokaryotic organisms have less non-coding DNA relative to many eukaryotic organisms have a much greater amount of non-coding DNA. In terms of just overall DNA coding and non-coding, prokaryotic organisms have less overall DNA and also have a smaller proportion of non-coding DNA.

So they have less DNA, but the majority of the DNA that they do have is instructions for building some type of protein. Whereas eukaryotic cells have a greater amount of total DNA, but a decent percentage of that is non-coding and doesn't actually code for proteins at all. So the question becomes, if it doesn't code for proteins, if it's not a gene, then what is it?

Like, what does it do? Or what does it have? Or why is it there? Well, there's a couple of things that non-coding DNA can be.

It can be a fragment of a gene that is utilized. So think of like partial instructions embedded in the living room volume that don't actually get used, okay? It can be a duplicate version of a gene.

So it can be another set of instructions for a protein that is somewhere else in the chromosome. Both copies are not utilized. the duplicate copy sort of just exists. Or it could be potentially a pseudogene.

A pseudogene is a gene that was once utilized back in time but is no longer utilized by this organism. And then another one that's not on this list but that I want to add is it could be regulatory DNA. Regulatory DNA helps determine when specific proteins get built or when specific instructions are actually utilized.

The instructions that are embedded in the DNA, the proteins, as we're going to find out towards the end of this chapter, not all cells need to make all proteins all the time. There needs to be some discernment of when proteins are produced. And so the regulatory DNA, the regulatory DNA that's not necessarily a gene, is going to help determine when the gene actually gets used. For instance, the analogy of regulatory DNA in context of IKEA might be some pages in the living room manual that say when the broken coffee table should be distributed and built at various stores across the nation.

If that page was embedded in there, it's not giving instructions for building the coffee table, right? It's not part of the instruction manual for building the actual coffee table itself. It's instructions that say when and where the coffee table should be built. And that's kind of the idea of regulatory DNA. It's not information for building the protein.

It's information that indicates when and where protein is built. And in terms of the where, we're talking about which cells. produce that rather than stores. All right, now there's two general types of non-coding DNA, one of which we really want to focus on. Sometimes non-coding DNA can be embedded within a gene.

So within the instructions for building a protein, sometimes there can be segments of nitrogenous bases that don't contribute to the building of the protein itself. The word that we use for these, these are called introns. So for instance, in my picture here, I have a segment of DNA on a chromosome, okay?

And we've highlighted the sections that are needed for building the protein in either purple or green for the various gene, okay? So this segment right here is one gene that would result. in the production of, we'll call it protein 1. And let's say that this gene is essential for the production of protein 2. The highlighted sections, these are what are needed. So these are the actual instructions.

The unhighlighted sections, they represent non-coding DNA that's embedded within the gene. And so these are the introns. Non-coding DNA that is not embedded within a gene is called an exon. So this segment right here, which is in between genes, which is non-coding, is called an exon. Whereas if the non-coding segment is embedded within the gene, it is called an entron.

And the one that we're going to need to really remember is the word entron, because we are going to refer back to that as we talk about how proteins get built. So the takeaway from this slide is that... Not all DNA codes for genes, not all code for instructions for building proteins.

Transcript for:VIDEO: Understanding DNA, Genes, and Chromosomes

Transcript for:
VIDEO: Understanding DNA, Genes, and Chromosomes