Lesson video

Hello, and welcome to this lesson from the unit DNA and the Genome.

The title of today's lesson is The Genome.

We're going to be looking at what the genome is, what it's made up of, and what its role is.

My name's Mrs. Barnard, and I'm going to be taking you through today's lesson.

So, by the end of today's lesson, you should be able to describe what a genome is, its role, and where it is stored in cells.

And our keywords for today's lesson are nucleus, DNA, chromosome, gene, and genome.

I'm gonna put a slide up with the definitions, so if you want time to copy them down, you can just pause the video.

But otherwise we'll be going through the definitions as we go through today's lesson.

Our lesson today is in three parts.

The first part is DNA, so the molecule of DNA and what it is.

Our second part is how that DNA is stored and chromosome in chromosomes and genes.

And finally, what the genome is overall.

So, we're gonna start with the first part of today's lesson, which is DNA.

So, a little bit of a recap from previous years and previous lessons.

All plant, animal, and fungi cells contain the same structures.

Now, can you recall them? You might want to talk to the person next to you, you might want to draw yourself a quick diagram, but how many can you recall? So, pause the video while you do this, and then we'll come back and we'll see how you've got on.

Okay, let's see how many you got right then.

So, here's an example of an animal cell in this case.

We're going to use that as our model cell for fungi and plants as well.

So, all of the common things that they share.

So, let's start with the first bit, cytoplasm, which is the jelly-like substance where all of the chemical reactions take place in a cell.

Then, we've got the cell membrane, so that's what goes around the outside of the cell and it controls what substances enter and leaves.

Now, with plant cells and fungi cells, they also have a cell wall around the outside of that.

Then, we've got the nucleus, so that's where we just store our genetic material.

Then, we've got the mitochondria.

The mitochondria is where respiration takes place and where a cell can release energy.

And we've got ribosomes.

So, all of those five things are common structures in animal cells, plant cells, and fungi cells.

So, if you got them all right, well done.

So, the genetic material is stored in the nucleus in animal, plant, and fungi cells.

So, you can see their cell structure is slightly different, but they all store their genetic material in the nucleus.

As I said before, you can see that the fungi cell and the plant cell have that cell wall around the outside.

I'm just pointing that out because that's sometimes people get confused between the cell membrane and the cell wall.

So, they all have a cell membrane, okay? But plant cells and fungi cells that have a cell wall around the outside of that as well.

So, bacteria though, they are unicellular microorganisms and they have a different structure.

So, they don't have all of those five things that we just listed.

They don't have a nucleus, so their genetic material is actually stored in the cytoplasm.

So, you can see it's that loop in there, that's their genetic material.

So, time for a quick check.

So, all cells store their genetic material in the nucleus.

Is this true or false? Now, once you've decided, I'd like you to say which of these statements justifies your answer.

So, read them carefully and decide which one would help you answer whether it was true or false.

So, pause the video while you do this and then we'll check back and we'll see how you've got on.

Okay, so our statement was, all cells store their genetic material in the nucleus.

Now that statement is false, and the reason that it is false is because animal, plant, and fungi cells store their genetic material in the nucleus.

But as we know, bacteria do not, they store it in a loop in the cytoplasm.

So, the genetic material of all organisms is made of a chemical substance.

Now, I'm hoping lots of you will have heard of this chemical substance before 'cause that chemical substance is called DNA.

DNA stands for deoxyribonucleic acid, so that's where the D, the N, and the A comes from.

So, here's our model of our animal cell and our nucleus.

And inside that nucleus, all wound up inside there is our chemical substance called DNA.

So, approximately two metres of DNA is packed into most animal cells.

Remember, we're talking about animal cells as our model here.

So, that's a lot of DNA that's stored in there.

We can't see the structure of DNA, it's really, really small.

Even with a light microscope, we can't see it because it is a chemical molecule.

It has the structure of a double helix, which, again, might be an image that you are already familiar with.

And you can see that we have to package it really tightly up into these chromosomes.

Again, you might have heard of the term chromosome.

So, we package our DNA very, very tightly into these chromosomes.

And then, these chromosomes are all stored within the nucleus of the cell.

So, let's have a little look at the structure of DNA a little bit more closely.

So, DNA is a long molecule and it's made of smaller chemical units.

So, it's a very, very long chemical molecule, but it's made of smaller chemical groups.

The smaller chemical groups form the genetic code.

And the genetic code is made of four different types of chemical group, which are called A, T, C, and G.

So, we can see those there now on our DNA molecule I've shown below.

Okay, they form the code that's in the middle of the double helix, and we call this the genetic code.

So, the code provides the instructions used to build inherited features and to control processes in living organisms, so that genetic code is really important.

And then, these features are passed from parents to offspring by reproduction because they transfer the DNA.

The parent transfers the DNA through its gametes into its offspring, and therefore the offspring receive DNA from its parents, which gives it the genetic code for building features and for controlling processes.

So, let's have a quick check then.

So, what I would like you to do is I'd like you to choose all of the statements that are correct ways to end this sentence.

So, the sentence starts with DNA is, (pauses) and then which of those options below would be the correct ending to this sentence? Okay, there can be more than one.

So, pause while you decide and then we'll come back and see how you've got on.

Okay then, correct ways to end this sentence.

So, DNA is a chemical molecule.

Yes, it is, so you can end the sentence with that.

DNA is made of smaller chemical groups.

Yes, it is.

DNA is stored in the nucleus of animal, plant, and fungi cells.

Yes, so you can finish that sentence that way too.

You can't finish the sentence with only inherited by animal offspring from their parents because it is also inherited by offspring of all living organisms on Earth.

So, if you've got those right, then well done.

Let's move on to a practise task.

So, here are our pupils: Izzy, Sam, and Alex, and they are discussing their understanding of DNA.

And Izzy says, "DNA is the genetic material passed from animals to their offspring." And Sam says, "DNA is a structure made up of chemicals." And Alex says, "DNA is stored inside the nucleus of animal and bacterial cells." So, in this case, all of the pupil's ideas are incorrect in part, so they might have some truth in their answers, some good understanding.

So, what I'd like you to do is take each of the pupil's statements and write it out again, but with corrections.

So, for each one, can you write it and correct it and possibly add a little bit of information? Okay, so I'm gonna pause while I give you the opportunity to have a go at this, and then we'll see how you got on after.

Okay, let's see how you got on with correcting those statements and improving them.

So, we've got the first one, Izzy.

So, "DNA is a genetic material passed from animals to offspring." So, she was right about that, but it is also passed from fungi, plants, and bacteria to their offspring.

So, that's how you would improve that statement from Izzy.

Sam, "DNA is made of smaller chemical groups." so he was right about that, but it is not a structure, it's actually a long chemical molecule.

And finally, Alex, "DNA is stored in the nucleus of animal cells," but it is not stored in the nucleus bacterial cells.

It is also stored in the nucleus of plant and fungi cells, so you could improve his statement in that way.

So, if you got those improvements correct, then well done, you've got a good understanding of what DNA is, and where it's stored.

So, let's move on to the second part of today's lesson, which is chromosomes and genes.

So, in animal, plant, and fungi cells, the DNA is stored in the cell nucleus, and the DNA is organised into packages called chromosomes.

So, here we go, we've got a cell here that's the animal cell and we've got a nucleus.

So, the nucleus is inside the cell, but we've just taken out for ease of looking at it.

And then, within that nucleus you can see these little packages called chromosomes.

And if you unwind one of those packages, it's a funny shaped package, but you get inside the DNA, which is sort of like the bundle of string, that's how I like to think about it, all wound up inside that package called a chromosome.

So, there are two copies of each chromosome in a nucleus, so you have one copy from each of your parents.

Okay, so humans have 23 pairs of chromosomes.

So, you have 46 chromosomes altogether, but you'd get 23 from your mom and 23 from your dad, and they match each other.

So, even though they might be slightly different in the versions of the DNA that they carry, each of the chromosomes match.

So, you can see here, just because of the space, I haven't drawn all 23 pairs.

I've just got four pairs to show you that you have matching chromosomes for each one.

So, bacteria don't have a cell nucleus, but they do still have DNA.

So, they have a single chromosome, which is a circle of DNA that is stored in the cell cytoplasm, so you can see that in the middle.

That's actually separate to the plasmid.

So, if you've heard of plasmids before, this is a separate structure.

So, this is the main DNA of the bacteria, and it's in a circular chromosome in the cytoplasm of the cell.

So, sections of chromosomes are called genes.

So, if we unwind that chromosome, remember the DNA that's packaged inside, we can then see the sections of the DNA, so the sections of the chromosomes.

And these short sections of the DNA code for features and processes.

So, we've got our chromosome here, our DNA, and then a short section of it is called a gene.

So, can we put these in order of the smallest to the largest in size order? So, if you pause up while you do this and then we will come back and we will see how you've got on.

Okay then, so starting with the smallest, we have got those chemical groups, A, T, C, and G, which make up our genetic code.

Okay, the next one is the gene.

Okay, so that's a short section of DNA that codes for a characteristic, a feature, or part of a process.

And the, next size up then is the DNA, that really long molecule, which is then packaged up tightly into a chromosome.

So, if you've got those in the correct order, then well done.

Time for a practise test now.

So, Aisha is trying to explain the storage of DNA to another pupil, and she's using diagrams with annotations to explain it.

Sometimes that's a good way of explaining things to other people, to draw diagrams and label it.

And she says, "The DNA is stored in the nucleus of the cell, it is made up of the genetic code and genes." And you can see in her diagram here the bits that she has labelled.

So, what I would like you to do for your task is I would like you to complete the labelling of this diagram as if you were explaining it to somebody else and write your own description of how all of the parts link together.

So, this is gonna take you a little bit of time.

So, if you pause and then when you come back, I'll give you some feedback just to check that you've got all of the detail that you need in your answer.

Right, shall we see how you got on with that task then? So, here is our labelled diagram, so you should have a cell labelled and then the nucleus labelled.

And then, within the nucleus you've got the chromosome, and then you've got a bigger version of the chromosome underneath.

And then, as the chromosome unwinds, you've got that long chemical molecule that's the DNA.

Then, a short section of that DNA is the gene.

And then right there made up of all those little chemical groups, A, T, C, and G, you have got the genetic code.

So, your description should be something like what follows.

DNA is a chemical molecule that is packaged tightly into chromosomes.

These are stored in the nucleus of animal, plant, and fungi cells.

The DNA is made of smaller chemical groups forming the genetic code.

A section of the DNA that contains the genetic code for a feature or a process is called a gene.

So, hopefully you've got all of those descriptions.

If not, then please feel free to add on now, and it's time to move on to the third part of our lesson, which is the genome.

So, all organisms have a genome.

The genome is all of the DNA of an organism.

So, if we look at this organism here, we've got a frog, which is an animal, so we've got a picture of an animal cell here.

And all of the DNA that's stored in its nucleus is called the genome.

Now, this would also be true of our other organisms, which we're showing here, which is the fungi, we've got a sunflower, which is plant, and we've got our bacteria.

All of the DNA that they store either in the nucleus or their cytoplasm is their genome.

So, the genome codes for all of the inherited features and processes of living organisms, and it's like the entire instruction manual for a living organism.

So, if you imagine in a book, you've got lots of letters in different orders, sometimes they're formed, well, they're always formed into words, so those words are sort of like genes.

And the letters make up the code, and we know what those letters mean.

And that's the same as when your cells are interpreting the information that's in the genetic code.

They can use that code as instructions for building features and for controlling life processes.

And they're made from those letters: A, T, C, and G.

So, unlike our alphabet where we've got 26 letters, the genetic code has only got four.

So, genes are sections of DNA that have a specific sequence of those letters: A, T, C, and G.

And each gene codes for a feature or a process.

Now, sometimes those processes will be things that you're not aware of or you might not be able to see.

So, in plants, for example, growth and in animals growth as well, but other things like digestion or respiration or other chemical reactions that take place in your body.

But also they will code for features that you can see, such as eye colour.

Some sections of DNA in the genome do not code for features and processes.

These sections are not genes.

So, these non-coding sections are found between genes and they help to control when the instructions in genes are used.

So, there you go.

We've got our genes and our non-coding DNA between them.

Now, people used to call this non-coding DNA junk DNA 'cause it was thought that it didn't have a role, but it does have a really important role in controlling when those genes give the instructions for creating those features and helping with those chemical processes.

Most cells will have a copy of the genome.

Now, the reason that I say most cells is because we know that some cells don't have a nucleus, so therefore they wouldn't have a copy of the genome, for example, a red blood cell.

But most cells will have a copy of the genome.

So, here is our genome, and our genome includes all of the genes and the non-coding sections of DNA.

So, all of those things are included in the term that we use genome.

So, all organisms on Earth have similarities in their genome sequence, and that's because at some point in time we were all related 'cause we've all evolved from one common species billions of years ago.

Differences in our genome sequence make us unique.

So, members of the same family have the most similarities in their genome and they would have very few differences.

Members of the same species who are unrelated to each other would still have many similarities, but a few more differences than if they were part of the same family.

And between species, you're gonna have many more differences in the genomes, however, probably less than you might think.

So, most differences between species and within species actually occur in the non-coding DNA part of our genome.

And that's because the genes actually code for processes and features that many living organisms would require.

So, for example, genes that might code for the structures involved in bones, lots of different organisms and species would need that, or for making muscles, or for things like chemical reactions like respiration, which all living organisms would need.

So, therefore lots of the differences actually occur in the non-coding DNA.

So, again, we've got our genome, we've got our genes, and we've got our non-coding DNA.

Therefore, the genomes of all living organisms are similar in part.

And the more similar the species, the more features and processes they will have in common.

So, the similarities between the genome of humans and other living organisms are shown in this table.

So, to start with humans and all other humans, whether you are related to them or not, 99.

9% of all of your genome will be the same.

So, let's go to our other closest relative, which is chimpanzee.

So, we shared a common ancestor with them most recently in time.

So, maybe talk to the person next to you, what do you guess what percentage of our DNA, our genome would be the same? So, the answer is 98%.

Maybe have a go now with chickens, what do you think? What percentage of your genome would be the same as a chicken? It would be 75%.

And then, we continue down to a fruit fly where we share 60% of our DNA down to a banana, which is also 60%, and then down to a daffodil, which is 30%.

So, we share far more similarities with the genome of a banana than we do with a daffodil.

So, let's have a quick check.

So, choose the correct definition of the genome from the options listed below.

So, pause while you do it and then we'll check how you've got on.

Okay, so the correct answer is c, the genome is all of the genes and the non-coding DNA of an organism.

So, if you've got that right, well done.

So, here's a practise test for you.

So, pupils are discussing the similarity in the genome between humans and daffodils and humans and chickens.

And Jacob says, "Humans and daffodils have no features in common, how can 30% of their DNA be similar?" And Sofia says, "Humans and birds are both animals, so more similar than daffodils." So, what I would like you to do for this task please is to explain the percentage similarities in the genomes of the organisms to Jacob and Sofia.

So, explain why there is a 30% similarity between humans and daffodils, and why the percentage is as it is for humans and chickens.

So, pause while you have a go at this, and then we'll come back and we'll see how you've got on with your explanation.

Okay, let's see how you got on explaining those percentages then.

So, explain the percentage similarities in the genomes of the organisms to Jacob and Sofia.

So, to start with, plants, chickens and humans are all living organisms, so they all carry out the same common processes.

Therefore, some of their genome needs to be the same.

For example, all three undergo respiration to provide energy for life processes.

So, that would be an example of what all living organisms do and why their genome would be the same for those particular genes involved in respiration.

And then, you could say the more similar the species, the higher the percentage similarity of the genome.

And chickens and humans are both animals, and therefore the percentage of their DNA that will be similar is greater than humans and daffodils because they have less features and processes that are the same, so therefore their genomes are going to be more different.

So, if you've got some answers that are sort of along those lines or to that effect, then well done.

So, we come to the end of today's lesson on the genome, and here is our summary.

Genetic material is stored in the nucleus of plant and animal cells, and in the cytoplasm of bacterial cells.

The genetic material of all organisms is made up of a chemical substance called DNA.

DNA is made up of smaller chemical units which form the genetic code.

The DNA in every cell is wound up into tightly-packed structures called chromosomes.

Sections of chromosomes are called genes.

They are short sections of DNA that carry the genetic code to provide instructions for an inherited feature or process.

Other sections are non-coding and control when the information in genes is used.

All of the DNA in a cell is called the genome.

This includes the genes and the non-coding sections of DNA.

The more similar a species or individuals, the more similar the genome.

So, well done for your work in today's lesson, and we'll hopefully see you soon.