Lesson video

<v Mrs. Barnard>Hello and welcome to this lesson from the unit "DNA and the genome".

The title of today's lesson is "Genetic Variance in non-coding DNA can influence phenotype".

So what we're going to be looking at today is that DNA that's between the genes in the genome and what impact it has, what its effect is on the phenotype.

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 explain how a genetic variant in the non-coding part of the genome can influence an organism's phenotype.

So we're gonna have some key terms in today's lesson, here they are, "gene", "protein", "genetic variant", "gene expression" and "phenotype".

So I'm gonna put the definitions up.

If you want to write them down, then I'll give you a chance to pause the video.

If not, we'll be going through them in today's lesson so you might want to jot them down as we go along.

Okay, so our lesson today is going to be in two parts.

The two parts are gene expression, it's the first part of the lesson.

So we're looking at how those genes are activated to produce proteins.

And then we're looking at how the non-coding DNA between the genes affects the phenotypes.

So that's the characteristics of the organism.

So let's get started with the first part of today's lesson, which is gene expression.

So the genome is made up of genes and non-coding DNA.

There are over 20,000 genes in human DNA.

And remember lots of those were discovered and sequenced in the genome project that was completed in 2003.

So we basically know what all of those genes do and therefore we can target treatments and medicines at those and we can look for mutations and changes in people's DNA.

We can also look at it in order to track the evolutionary history of organisms through time.

So that genome project was a really, really big deal and lots has been done to work on that in the intervening years.

So we've got these 20,000 genes or over 20,000 genes, but that is only actually 1 to 2% of all of the DNA that we've got.

Most of our DNA is actually non-coding DNA.

So most of our genome is actually made up of non-coding DNA.

So the non-coding DNA doesn't code for proteins, but the genes do code for proteins.

So genes carry our genetic code and they determine the order of amino acids in a polypeptide chain.

So a polypeptide chain is the first part of building a protein.

So it's the first structure, we call it the primary structure.

And we need to put those amino acids together in a particular sequence in order to build different proteins.

And the order that those amino acids are put into is determined by the order of bases in the genes.

And you will have covered that in previous lessons.

So quick check now.

So what are proteins made up of? Are they made up of nucleotides, bases, genes or amino acids? So pause the video while you decide and then we'll check if you're correct.

Okay, hopefully you got that one correct and it's amino acids.

So proteins are made up of amino acids.

So gene expression is the process in which genes are activated to produce a protein because not all genes are activated in all cells all of the time.

So it's in some cells they will produce a protein, but they won't want to produce it all the time.

So let's think about an example that you might have heard of.

So for example, insulin.

So insulin is a protein hormone and it is made in the pancreas, but we only need that when our blood glucose levels are high after a meal, after we've eaten and we've digested our food.

So therefore those cells are not going to want to produce insulin all the time.

They just go on and want to produce it some of the time.

Some proteins are never needed by certain cells and therefore those proteins would not be expressed in those cells.

So some of the non-coding DNA that's between the genes, it does have a role.

So even though it doesn't have a role to code for proteins, its job is controlling when the genes do produce the protein.

So they control gene expression.

So therefore non-coding DNA is involved in gene expression.

And here's a little graphic to show what I mean.

So we've got these two genes here as examples of all those over 20,000 genes and some non-coding DNA that's between them.

So how that DNA interacts, that non-coding DNA interacts with the genes will determine whether those genes make that protein or not.

And when they make that protein, and that is gene expression.

So when a gene is activated to make a protein, a copy of the gene is made inside the nucleus, then the non-coding sections are not copied.

So it's only the genes that are copied, but they can control whether that copy is made or not.

So we're determining whether a copy is being made in the nucleus and whether it's going to leave the nucleus to code for a protein.

Not all genes are copied at the same time.

Only those for which their body needs the protein are going to be copied at that particular time in that particular cell.

So non-coding DNA can control gene expression, so when those proteins are actually made and if they're ever made.

So we can see here we've got our non-coding DNA, and we have gene expression activated and gene expression suppressed And when it's activated, we have a copy of the gene that is made.

And when it's suppressed, we have no copy of a gene that is made.

So time for a quick check.

Gene expression is the process of genes being activated to produce what? So pause the video while you decide and then we'll check if you're right.

Okay, hopefully you got this right.

So they are being activated to produce protein.

So gene expression is the process of genes being activated to produce proteins.

So if you got that right, then well done.

So if a mutation takes place in non-coding DNA, then that region of the DNA, it will become what we call a genetic variant.

So remember, "variant" means something that's different.

So "a different version of".

So we have a slightly different base sequence that's gonna occur in that non-coding DNA.

So therefore the sequence of the nucleotide bases in the non-coding DNA will change.

And that is important in protein synthesis because it controls gene expression.

So as we know these non-coding sections of DNA help to determine when a gene is gonna be expressed or not, if the sequence of nucleotides and bases in that non-coding DNA is changed, that's going to affect the way that it interacts with the gene.

So it's gonna affect whether it does activate or whether it does suppress that copy of the DNA being made, so that gene being expressed.

So we can see that in this picture here.

So we're focusing now on the non-coding DNA, and we can see there's two different genetic variants of this.

And that means that a nucleotide has changed, which therefore means that the base sequence has changed due to a mutation.

So for example of substitution, you will have learned about these in previous lessons but this is when you would substitute one nucleotide for a different nucleotide and therefore the sequence of your bases would be different in the two variants.

So time for a quick check.

So non-coding DNA does not affect the production of proteins.

So first of all, I want you to decide whether that is true or false.

And then once you've decided, which of the statements below do you think best justifies your response.

Is it that non-coding DNA does not code for proteins and is the section between genes? Or is it better justification, "Non-coding DNA is the section between genes that can control whether a gene produces a protein"? So pause the video while you decide and then we'll check if you've got it right.

Okay, how did we get on with that one then? So, "Non-coding DNA does not affect the production of proteins." This is false.

And the statement that best justifies this is the second one because non-coding DNA is the section between genes, but it can control whether a gene produces a protein or not, so whether that gene expression actually takes place.

So if you got that right, then well done.

Let's move on.

Another check.

So we've got lots of key terms this lesson.

So our four key terms that I'd like you to match up are, "gene expression", "genetic variant", "mutation" and "gene".

So match 'em up with the correct definition and then we will check if you've got those right before we move on to another task.

Okay, let's have a look then.

So "gene expression", that should link up with this one, it's the process of activating genes to synthesise proteins.

We've got "genetic variant", which is a region of DNA with a different base sequence due to a mutation.

"Mutation" is a change in the nucleotide base sequence of DNA.

And finally, a "gene" is a section of DNA that carries the genetic code for a protein.

So if you've got those right, well done, we'll need those in our next task.

And our next task is based on some pupils having a discussion and they are discussing the term "gene expression".

So Jacob says it's a different term for protein synthesis.

And Jun says," It is when all the proteins coded for by genes are made at the same time." And Sophia says," It is a process of activating genes to produce proteins." So your task is as follows.

Number one, which of the pupils has got the correct understanding? So decide which ones of those pupils is correct.

And secondly, give positive feedback to the other pupils on the scientific idea they have explained correctly 'cause there is something correct in their understanding, the ones that have got it wrong.

And we want to give some positive feedback about the thing that they have got wrong.

Okay, so pause the video while you do this 'cause you'll need to do a little bit of extended writing and then we'll come back and look at some feedback after.

Okay, so let's see how we got on then.

So the person with the correct understanding was Sophia because she said gene expression is the process of activating genes to produce proteins.

So that is correct but hopefully you managed to be positive to Jacob and Jun when you gave them some feedback about their scientific understanding.

So Jacob has correctly understood that gene expression leads to proteins being made, it's just not exactly the same as protein synthesis, which comes after gene expression.

And Jun has understood that genes code for protein.

So he's got that bit of his scientific understanding correct but the thing that he got wrong was that not all of them are being made at the same time, expressed at the same time.

Okay, right then.

Let's move on to the second part of our lesson.

And the second part of our lesson today is non-coding DNA and phenotype.

So protein structure is determined by the genetic code carried by genes.

And the features that these proteins create are called an organism's phenotype.

Now you should have come across the word phenotype before, that's the physical characteristics of an organism.

So the pheno- oh, it's already there.

The phenotype is the physical characteristics of an organism.

And an example here is the colour in a caterpillar.

So this particular protein may lead to some kind of pathway that produces this colour.

There might also be proteins involved in hair development, like whether your hair is curly or whether your hair is straight.

The colour of your eyes, the structure of your muscles, the structural proteins that make your skin stretchy, all of those things are our physical characteristics and those are our phenotype.

So sections of non-coding DNA control whether proteins are made.

So therefore, they are going to have an impact on our phenotype.

So our physical characteristics, or all organisms' physical characteristics 'cause this isn't just true of humans, this is true of all living organisms that have non-coding DNA.

So we can see here that if we have a gene that is activated, a copy of that gene is going to be made in the form of mRNA and it's going to go to the ribosomes and that protein is going to be put together, the amino acids put in the correct order and then that protein is going to give us some physical characteristics, our phenotype.

But if the non-coding DNA suppresses a gene, then a copy will not be made and therefore a protein won't be made and therefore that will affect our phenotype.

So mutations in non-coding DNA can have a big impact on our phenotypes.

I've got a couple of examples to work through with you.

So the first one is a chimpanzee.

So the chimpanzee is actually our closest relative.

We've had other more closely related organisms through time, but most of those have become extinct.

You might have heard of Neanderthals, for example.

So alive today on earth, our closest relative is a chimpanzee.

And our hands are much smaller and we can fully bend our thumbs over our palms. So that means we're better at gripping and using tools and building.

So you might wanna have a little go at that, see if you can get it work, so your thumb fully bends over your palm, okay? Like that, okay? It allows us to do lots of different things.

And because of that, those differences are due to mutations that have taken place in our non-coding DNA.

So we have a mutation in our non-coding DNA, and that affects how genes are expressed when our hands are formed as in the embryo.

So in development, inside the uterus of our moms, when we are developing, these different genes are expressed or not expressed and that will affect how our hands develop and that's what's made us different from chimpanzees in terms of how we use our hands.

And that's been really important because our different phenotype has affected our evolutionary history, its made us different from chimpanzees due to that mutation in non-coding DNA.

Another example is that it can have a big impact on our health.

So when a person has cancer, some of their cells will form a tumour or a lesion.

So these cells are sort of growing differently or abnormally or growing more than they should be.

And this is due to mutations in non-coding DNA.

And they would normally control genes that are expressed, that are important in cell growth and cell division.

So therefore the mutations that are in the non-coding DNA, remember that's the DNA that is controlling whether a gene is expressed or not, can be lost.

And therefore the cells then divide over and over again, making many copies of these abnormal cells and that's when we get a tumour or a lesion.

So really important in our phenotype here, and that can happen during our lifetime, as opposed to the hand development which happens during our development.

So time for a quick check then.

So choose the statements about non-coding DNA that are correct.

So pause the video while you decide and then we will come back and we'll see if you've got them correct.

Okay, so let's have a look at our correct statements.

So "non-coding DNA are sections of DNA between genes", this is correct.

"Genetic variants of non-coding DNA can occur", this is correct.

"Non-coding DNA has no effect on protein production", that is incorrect.

And "Non-coding DNA are not genes but can affect protein production", that is also correct.

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

So let's move on.

So making proteins or protein synthesis starts when a copy of the gene is made and we call that copy of the gene "mRNA".

And the process of copying the gene and making the mRNA is called "transcription" and it takes place in the nucleus of the cell because that's where all of our DNA is stored.

So mRNA is moved from the nucleus to the ribosome in the cytoplasm because the ribosomes is where proteins are synthesised, so where amino acids are joined together to form that first stage of a protein, which is a polypeptide.

The non-coding DNA controls if and when the mRNA is made.

So we can see our copy of our mRNA there and then it moves to our ribosome.

The enzyme, RNA polymerase, is used to make the copy of the gene from the DNA.

So we need RNA polymerase to be present and we also need it to be able to bind to the section of DNA, the non-coding DNA, that's immediately before the gene and then that allows the gene to be copied or for transcription to take place.

Therefore the non-coding DNA will control whether transcription can take place.

Can RNA polymerase bind or can RNA polymerase not bind? And that will determine whether a copy of the gene is made or not.

So let's have a quick check.

So for these three images here, I want you to select the one where you think gene expression would take place.

Okay, so hopefully you got here A.

So only A because we've got RNA polymerase binding, we haven't got it in B and we haven't got it in C.

So if you got that right, well done.

So the next task is I would like you to copy this diagram and add labels to explain how gene expression can be controlled by non-coding DNA.

So copy this diagram as it is and then draw a label and make sure you describe the role of RNA polymerase in your answer.

So draw it as a diagram and annotate around the outside and we'll just get checked that you've got the correct ideas when you are ready.

So pause the video until then and I'll see you soon.

Okay, let's see how you got on with that then.

Hopefully you didn't find it too difficult to draw.

So we've got our picture here and we've labelled the "gene" on there and the term "transcription".

So that's when we're making a copy of our gene in order to form mRNA.

Label here, something similar, doesn't have to be exactly the same, but something along these lines that RNA polymerase binds to the non-coding section of the DNA and it allows the gene to initiate or to begin transcription.

And if RNA polymerase binds, then a copy of this gene is made.

And finally, mRNA is the copy of the gene that moves to the ribosome in order for the protein to be made.

So if all of those things happen, then this is an example of a gene that is being expressed and its ability to be expressed is controlled by the non-coding DNA that allows the RNA polymerase to bind.

So if you've got those labels correct, if not, add to your diagram so you've got a good, finished model answer.

So well done for your work in today's lesson.

It was quite tricky.

So let's go through the key points.

So gene expression is when a cell copies a gene, which is mRNA, and it uses it as instructions to make a protein.

Only around 1 to 2% of the genome actually codes for genes.

The non-coding DNA contains code that controls gene expression.

A genetic variant in the non-coding section of the genome can affect gene expression because it can affect when RNA polymerase that copies the gene as the first step in protein synthesis, whether it combined.

This change may impact the proteins that are produced by an organism and so therefore change its physical characteristics or its phenotype.

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