Hi.

I'm Mrs. Hudson.

And today, I'm going to be teaching you a lesson called Errors in cell division and cancer, beyond the basics.

This is a biology lesson and it comes under the unit titled Cell division, mitosis and myosis.

The outcome of today's lesson is, I can describe cancer, including benign and malignant tumours, and explain how mutations can cause cancer.

There are some keywords in today's lesson.

They are mutation, genes, tumour, benign, and malignant.

Let's have a closer look at what those words mean.

So a mutation is a change in the nucleotide sequence of DNA that can cause mutated genes.

Genes are short sections of DNA that code for a specific characteristic or protein.

A tumour is a mass of cells that has been produced through uncontrolled cell division.

Benign is a tumour that is non-cancerous and contained to one area.

And malignant, a tumour that is cancerous and can spread.

If you want to pause the video to make a note of those keywords, please do, but we're going to look now at the structure of this lesson.

Today's lesson will be split into three different parts.

In the first part, we're going to look at cancer, cell division and tumours.

Then we're going to look at how mutations cause cancer.

And then in the final part of the lesson, we're going to look at risk factors for cancer.

Let's get going with the first part, though, cancer, cell division, and tumours.

Most cells in the body use a process called mitosis to divide and produce new cells.

Mitosis is needed in multicellular organisms for growth and repair of damaged tissues.

So humans are multicellular organisms and plants are multicellular organisms. And this image here is showing you the growth of a seedling.

The growth of a seedling into a plant will require new cells which are made through mitosis.

And then this image is showing you an X-ray of a broken arm.

New cells will be made through mitosis to heal the bone.

So in multicellular organisms, mitosis is needed for growth and repair of damaged tissue.

Mitosis forms part of the cell cycle.

The cell cycle is regulated by genes to ensure that cells only divide when they need to and stop dividing when necessary.

A really important part of staying healthy as a multicellular organism is that the cell cycle is regulated and genes normally are involved in that.

So here we can see an image which is showing you the cell cycle, and the cell cycle produces new cells through cell division.

And this image here is showing you a gene, which is a short section of DNA that codes for a characteristic or a protein.

Now what we can see here is we've got a gene and there's a tick next to it.

So some genes promote the cell cycle and encourage cell division, whereas here, the gene with a cross next to it, some genes stop the cell cycle and reduce cell division.

Let's quickly check our understanding so far.

So the first question.

What regulates the cell cycle? A, hormones.

B, mitosis.

Or C, genes.

This is C, genes.

Cancer is caused by changes to the DNA of a cell that leads to uncontrolled cell division and cell growth.

Uncontrolled cell division can lead to the formation of a tumour, a mass of cells.

So here we've got an image which is showing you healthy cell division, and you can see labelled there, we've got a healthy cell.

So in this healthy cell, the DNA is as it should be, it has not been changed, and that cell will divide and produce controlled cell division to create healthy tissue.

However, in uncontrolled cell division, you'll start with a healthy cell, but then there's a change to the DNA of that cell, and that means that there is uncontrolled cell division, which leads to the formation of a tumour, a mass of cells.

Not all tumours are cancerous.

There are two different types of tumour, benign and malignant.

This image here is showing you a benign tumour.

Benign tumours are not cancerous.

This image is a malignant tumour.

Malignant tumours are cancerous.

So the two different types of tumour are benign and malignant.

Benign tumours are not cancerous, but malignant tumours are cancerous.

Let's have a look at benign tumours in a little bit more detail.

Benign tumours are growths of abnormal cells which are contained within one area.

They usually grow slowly.

Benign tumours are usually contained within a membrane and do not invade neighbouring tissues.

So it's the fact that benign tumours have a membrane around them that contains those cells and it stops them from invading the healthy cells around it.

So we can see here we've got an image of a benign tumour and a label's going to come up now which circles where the tumour is.

So that is a benign tumour, which is a growth of abnormal cells that divide uncontrollably.

And then we can see labelled here, the membrane surrounding the benign tumour.

The membrane is a really important part of the benign tumour because it stops those cells from invading neighbouring tissue.

So we can see here that the neighbouring tissue is not invaded by the cells of the benign tumour.

If we look now more closely at a malignant tumour, malignant tumours are cancerous.

They are not contained within one area and usually grow quickly.

So here the label is pointing towards malignant tumour cells, and these are growths of abnormal cells that divide uncontrollably.

So both benign and malignant tumours are made up of cells where the DNA has changed and there's uncontrollable cell division.

But the main key difference is that a malignant tumour is not held within a membrane.

So malignant tumours invade neighbouring tissue and can spread to other parts of the body where they form secondary tumours.

And this is called metastasis.

And this label here is showing you that neighbouring tissue is invaded, as the tumour is not held within a membrane.

And then at the top, we can see as well that there's a cell that's kind of broken off.

So here we have a malignant cell has broken off and can spread to form secondary tumours, which we said was called metastasis.

Let's check our understanding again.

So which two factors cause tumours and cancer to develop? So we're picking two factors here.

A, uncontrolled cell division.

B, changes to the DNA of cells.

Or C, a sudden reduction in cell division.

This is A and B.

Well done if you got that right.

We're ready now to move on to the first task of the lesson, task A.

And in the first part of this, you need to complete the table to show if each statement is true or false.

So you need to read the statement and tick whether it's true or false.

And then in the second part of task A, you're going to label and annotate the diagrams to explain the difference between benign and malignant tumours.

There are some labels on there to help guide what you should be writing.

I'm sure you're going to do a really great job of this.

So pause the video now and then press play when you're ready for me to go through the answers.

Let's see how we did.

So the first statement is false.

The second statement is true.

The third statement is false.

And the fourth statement is true.

So well done if you managed to get those right.

Let's look in more detail at the first statement.

So cancer is caused by changes in the DNA of a cell.

This leads to cell division stopping.

The reason that is false is because it doesn't lead to cell division stopping.

It leads to uncontrolled cell division.

And then the third statement, the cell cycle is not normally regulated, that is also false because the cell cycle is normally regulated by genes and this may encourage cells to divide more or it might stop cells from dividing.

And part two of task A.

So the first picture's showing you a benign tumour, which is a growth of abnormal cells that divide uncontrollably.

And then we've got the membrane surrounding the benign tumour.

And the third label is showing that the neighbouring tissue is not invaded.

You may also have written there that they are healthy cells.

And then this image on the right is showing you a malignant tumour where there's a growth of abnormal cells that divide uncontrollably.

The key difference though here is, the neighbouring tissue is invaded, as the tumour is not held within a membrane.

And then that circle cell there is showing where a malignant cell has broken off and can spread to form secondary tumours, which is called metastasis.

There's quite a lot of information there, so if you need to pause the video and add anything into your answer to make it more detailed or just check what you've got, please do, and we'll move on with the rest of the lesson.

Brilliant job so far.

So we know about cancer, cell division, and tumours.

Let's have a look in more detail at how mutations can cause cancer.

The genetic code is determined by the order of bases on the nucleotides.

So we can see here that we've got an image of a section of DNA, which is made up of a double helix.

And then you've got the bases that run along the inside.

The four bases pair up in a particular way, called complementary base pairing.

So A always joins up with T and C always joins up with G.

And if we took a small section here of this DNA and looked at it in more detail, we would see that the structure looked something like this where we have repeating nucleotide chains.

So here we can see we have an individual nucleotide and then the order of bases form the genetic code.

So those lines there are pointing to the bases, and the order that they are in determines the genetic code.

An organism's genome is the entirety of its genetic material.

So here we've got an image again of the double-helix DNA and the dots at the end are trying to suggest that it would be much longer than this.

So the genome is the entirety of all the genetic material in an organism.

Genes are small sections of DNA that code for specific characteristics or proteins.

Some proteins regulate the cell cycle.

So we can see here, we've labelled just a small section of that DNA, and that is a gene.

And then the gene will code for a specific protein.

And certain proteins are involved in helping to regulate the cell cycle.

And it might do this by encouraging cell division, suppressing cell division, repairing damaged genes, or encouraging cell destruction.

The genetic code, carried by genes, is read in groups of three, and this is called the triplet code.

So here we've got an image of two triplet codes within a gene.

There's six nucleotides in this image, and we can see the three bases, C, A, and G, and then three more bases, T, C, and A.

Those three bases will code for one amino acid.

So each triplet codes for a specific single amino acid.

Therefore, the order of nucleotide bases is important.

So here, C, A, and G will code for a specific amino acid.

And T, C, and A will also code for another amino acid which is different.

And then those chains of amino acids are what leads to the structure of proteins.

Let's check our understanding of that.

So the first question.

What is a genome? A, a short section of DNA.

B, the entirety of an organism's genetic material.

Or C, a subunit of DNA consisting of a phosphate, sugar, and base.

This is B, the genome is the entirety of an organism's genetic material.

Great job if you remembered that.

Mutations are changes in the nucleotide base sequence.

This creates a genetic variant.

So mutations are going to be a really important part of the next phase of the lesson.

And you have to remember that a mutation is where there is a change in the nucleotide base sequence.

And we can see an image here of an original sequence of DNA.

So the DNA is made up of repeating nucleotides.

And remember that each nucleotide has a base and that three bases code for one amino acid.

So what would happen then if this one base was changed? A genetic variant is a region of DNA in which the sequence of nucleotide bases has been changed.

So here we've got just one change in the base and it will produce a genetic variant which looks potentially like this, where the A base has been changed and mutated to be a C base.

Now remember that because three bases code for an amino acid, it will change the amino acid that is coded for.

A mutation may be due to one of three things, substitution, deletion, or insertion of a base.

So if we look at this original DNA strand, we'll have a look at what these three mutations look like.

So DNA with a substituted nucleotide, we can see here that that one base has been substituted with another base.

If the DNA is inserted with a nucleotide, we can see here that we have inserted another nucleotide.

And if you compare it to the original DNA, you'll notice that the nucleotides are the same after that inserted nucleotide.

And then finally, we have a deleted nucleotide.

So this, rather than inserting a nucleotide, one has been deleted.

And so if you compare that DNA strand with the original DNA at the top, you'll notice that the blue base has been deleted.

Let's just check our understanding of that.

Select the types of mutation that can occur in DNA.

A, conversion.

B, deletion.

C, substitution.

Or D, insertion.

This is B, C, and D.

Deletion, substitution, and insertion are the three types of mutation you need to know about.

Well done if you remembered that.

Let's look at those mutations in more detail.

So here is an example of a genetic variant caused by a substitution mutation.

One nucleotide, A, has been substituted for another, C.

So in the first image, we've got the original DNA sequence, and that rectangle there is showing you where the substitution mutation is going to occur.

Remember, a substitution mutation is where one nucleotide is substituted with a different nucleotide.

So here the genetic variant produced, that one nucleotide will be different.

So rather than it having the base A, it has the base C.

What that means is only one triplet code has been changed.

So only one amino acid will be different.

If you compare the sequence of bases between the original and the genetic variant, then you'll notice that only the one triplet code has changed.

Let's now look at a deletion mutation.

A deletion mutation will alter every triplet code that comes after it.

So if this is our original sequence of DNA, and this is the nucleotide where the deletion mutation is occurring, the genetic variant would look like this.

So the nucleotides would be the same up until the point of the deletion mutation, but then we wouldn't have the nucleotide that has been deleted.

We would then follow on with a nucleotide that starts with the base C.

What this means is that the triplet code for this one and then every single triplet code afterward has been changed because of that deletion mutation.

So when there's a deletion mutation, every triplet code after it is altered.

And in an insertion mutation, the same thing happens.

So an insertion mutation will alter every triplet code that comes after it.

So here we've got the original sequence of DNA and then the dotted line there is showing you where the insertion mutation happens.

So that's where another nucleotide is added and inserted in.

So the genetic variant will have the same nucleotide sequence up until the point of the insertion mutation.

And then we have inserted a nucleotide that has the base G.

And then the nucleotide sequence continues to be what it was after it, so CAG, TCA.

But again, this alters every triplet code after the insertion.

So that triplet code has now changed, and that triplet code has, and every single triplet code afterwards will have changed, which obviously is going to alter the structure of the protein enormously.

So all the triplet codes change after the insertion.

Specific genes and the proteins they code for are involved in the regulation of the cell cycle.

They ensure that cell division is controlled to keep tissues healthy.

So here we have an image of a gene and that gene codes for a specific protein.

Our genes and coded proteins help regulate the cell cycle.

And normally what happens is when there's no mutations, the genes and the proteins work together to ensure that there's controlled cell division and therefore, healthy tissue is generated and maintained.

Substitution deletion and insertion mutations can lead to mutated genes.

So here, rather than having a healthy gene, we've got a mutated gene.

And as the genes carry the genetic code to make new proteins, mutated genes can give rise to altered proteins and this can lead to uncontrolled cell division.

So if that's our mutated gene, then that's going to code for altered proteins.

And if those two normally work together to help regulate the cell cycle, when they're mutated, it can actually give rise to uncontrolled cell division.

So here, altered proteins can no longer regulate the cell cycle and it leads to uncontrolled cell division, leading to tumours.

Let's quickly check our understanding.

What is a mutation? A, a change to the shape of the nucleus.

B, a change to the sequence of nucleotides in DNA.

Or C, a mass of cells that can cause cancer.

This is B.

A mutation is a change to the sequence of nucleotides in DNA.

Great job if you got that right.

We're ready now to move on to the second task of the lesson, task B.

And part one, you need to annotate this diagram to add definitions of genome and gene and explain how genes and proteins are linked to cell division.

And then in part two, you need to tick one box for each statement.

So it's, I am sure this is correct.

I think this is correct.

I think this is incorrect.

I'm sure this is incorrect.

Number three, rewrite each false statement in the table to make it true.

So whatever you have ticked on the table as being incorrect, write it out as being true.

And then question four, explain how mutations can lead to cancer.

I'm sure you're going to do a fabulous job.

Pause the video and then press play when you're ready for me to go through the answers.

Let's see how we did.

So at the top, we've got, it is only really a section of genome, but the dots are trying to suggest it continues on.

So the genome is an organism's entire genetic information.

And then a short section of DNA is a gene and that codes for a protein or a specific characteristic.

Certain proteins are involved in the regulation of the cell cycle.

Different proteins have different roles.

They can encourage cell division, suppress cell division, repair damaged genes, and instruct cell destruction.

If genes mutate, then the proteins become altered.

It may lead to uncontrolled cell division and the formation of tumours.

Brilliant job if you managed to remember all of that information.

If you need to add anything in, then please do.

For question two, A, the first statement is correct.

For B, the cell cycle is never affected by mutations.

That is incorrect.

C, deletion mutations only affect one triplet code in the DNA sequence.

That is also incorrect.

And D, mutations can lead to uncontrolled cell division is absolutely correct.

So well done if you identified those.

We're going to be looking at statement B and C in part three.

So you needed to rewrite each false statement in the table to make it true.

So mutations can change proteins that regulate the cell cycle.

This can lead to uncontrolled cell division.

And the second one was deletion mutations will affect every triplet code after the mutation and could therefore alter the protein significantly.

Deletion mutations do not just change one triplet code.

They change every triplet code after that deletion.

And then number four, explain how mutations can lead to cancer.

Mutations are changes in nucleotide sequences of DNA.

These can give rise to mutated genes that alter the structure of proteins.

Some proteins are involved in the regulation of the cell cycle.

Altered proteins may cause uncontrolled cell division, leading to tumour formation and cancer.

There is a lot of information in this task, so I would advise you to pause the video and go back and just check that you've got all the detail in that you need to.

But you've done a fantastic job.

So well done.

Let's move on now to the final part of our lesson, which is risk factors for cancer.

Anyone can develop cancer, but there are certain risk factors that increase the chances of a mutation occurring.

Being exposed to a risk factor does not mean you will definitely get cancer.

The risk factors are something that increase the likelihood of a certain disease or illness developing, but it doesn't mean if you're exposed to it, you're definitely going to get that disease.

Can you recognise any of the risk factors associated with cancer, using these pictures? So the first one is smoking, then obesity, UV radiation, and viral infections.

So all four of these are lifestyle risk factors that are associated with cancer.

They're lifestyle risk factors because you would have an element of choice of whether or not you would expose yourself to those things.

We will look at how viral infections are linked to lifestyle later on in the lesson.

But there are also genetic risk factors associated with cancer.

And the reason why genetic factors are not lifestyle related is because you inherit faulty genes and you have no choice in that matter.

The table below shows how lifestyle risk factors are linked to the development of different types of cancer.

The risk factor smoking is linked to lung, mouth, bowel, stomach, and cervical cancer.

Obesity is linked to bowel, liver, and kidney cancer.

UV exposure is linked to skin cancer.

And viral infections are linked to cervical cancer, if you have the HPV virus, and liver cancer, if you have hepatitis B and hepatitis C.

Let's look in a little bit more detail at smoking first.

So smoking contains chemicals that are carcinogenic.

That means they are cancer causing.

An example is tar, and every time you inhale tar from a cigarette, then you are increasing your chances of developing cancers such as lung cancer.

Lung cancer is probably the most prolifically-linked cancer with smoking.

And next, we're going to look at obesity.

Obesity is associated with an increased risk of developing bowel, liver, and kidney cancer.

Unhealthy diets, high in fat and salt, and drinking excess amounts of alcohol are associated with an increased risk of developing cancer.

UV exposure can be increased in the following ways.

Living in a sunny climate.

Spending lots of time outdoors.

Using sunbeds.

UV is ultraviolet, so the sun and its ultraviolet radiation.

So now let's think about now how could we reduce the risks? So if we're talking about UV radiation being emitted by the sun, what could you do to try and reduce the risk? You could spend less time in the sun, and if you are in the sun, you would wear suncream.

Let's now look at sunbeds.

Sunbeds expose users to UV radiation.

How could we reduce that risk? Well, just do not use sunbeds.

Viral infections such as hepatitis B and C can be spread through unprotected sex and sharing needles.

And remember that hepatitis B and C are linked to liver cancer.

HPV can be spread through unprotected sex.

And HPV is linked to cervical cancer.

The reason why these viral infections are linked to lifestyle choices is because not always, but sometimes, people choose, as part of their lifestyle, to have unprotected sex and to share needles, which therefore is increasing their chances of getting hepatitis B and C or HPV.

Let's check our understanding.

So match the type of cancer with its associated risk factor.

So have a go at that now.

So the first one is linked to viral infection.

Skin cancer is linked to UV exposure.

Bowel cancer is linked to obesity.

And lung cancer is linked to smoking.

So well done if you got those right.

We've looked in detail at lifestyle risk factors, but now let's look at risk factors associated with genetics.

The risk factors for cancer can also be associated with genetics.

You can inherit faulty genes that make you more at risk of developing cancer.

An example for this are the BRCA genes.

So BRCA is B-R-C-A, and there are two types of BRCA genes that we're going to look at today.

So BRCA1 and BRCA2.

Mutated BRCA genes have been linked to an increased likelihood of developing breast and ovarian cancer.

BRCA genes usually help prevent uncontrolled cell division and repair damaged DNA.

If they are faulty, cell division can become uncontrolled, leading to cancer.

Let's look at a question linked to this.

So risk factors for cancer are linked to, A, lifestyle, B, genetics, or C, lifestyle and genetics? This is C, lifestyle and genetics.

Which gene is linked to breast and ovarian cancer? A, RABC.

B, BRCA.

Or C, LCDA.

This is B, BRCA, which we call the BRCA genes.

Great job if you remembered that.

We're now ready to move on to the final task, task C.

So you need to use the images to identify the risk factor for cancer and which cancer it is linked to.

So we have one with an image, and then number two, which has another image.

Then we've got three and four which have images.

And then question five, Laura and Izzy are talking about risk factors for cancer.

Who is correct? Explain why and give examples.

So Laura said, risk factors are only caused by lifestyle.

And Izzy has said, risk factors can be caused by lifestyle or genes.

So have a go at those questions.

Pause the video and then press play when you're ready for me to go through the answers.

All right.

Let's see how we did.

So the first image is showing smoking as a risk factor for cancer, and it has been linked to lung, mouth, bowel, stomach, and cervical cancer.

Number two is showing obesity as a risk factor for cancer.

It has been linked to bowel, liver, and kidney cancer.

Unhealthy diets, high in fat and salt, and drinking excess amounts of alcohol are associated with an increased risk of developing cancer.

Great job if you got those right.

Question three, we're showing you exposure to UV radiation as a risk factor for skin cancer.

Living in sunny climates, spending too much time in the sun, or using sunbeds can increase this risk.

And then number four, certain viruses are linked to cancer.

HPV is linked to cervical cancer and is spread through unprotected sex.

And hepatitis B and C is linked to liver cancer and is spread through unprotected sex and needle sharing.

And then for question five, Izzy is correct.

Risk factors can be caused by lifestyle and genes.

But you needed to say why and give examples.

So smoking, obesity, UV exposure, and viral infections are all linked to lifestyle.

However, there are certain genes you can inherit that increase your chances of developing cancer.

The BRCA genes are associated with an increased risk of developing breast and ovarian cancer.

BRCA genes are tumour suppressors that usually control cell division.

If they are faulty, then cell division can become uncontrolled, leading to cancer.

There's a lot of information over those last few slides, so if you want to pause the video to add anything in, then please do.

We're going to summarise the lesson next.

You've done a great job today.

There's a lot of information in this lesson.

First of all, we said that mitosis forms part of the cell cycle and the cell cycle is regulated by genes.

Cancer is caused by changes in DNA that leads to uncontrollable cell division.

A mutation changes the sequence of nucleotides in DNA and can affect genes that regulate the cell cycle.

Tumours are masses of cells formed from uncontrolled cell division.

They can be benign or malignant.

Benign tumours are contained within a membrane and cannot invade neighbouring tissue.

They are non-cancerous.

Malignant tumours invade neighbouring tissue and can spread to other parts of the body.

They are cancerous.

And finally, we looked at risk factors for cancer.

So smoking, obesity, UV exposure, and viral infections are lifestyle risk factors linked to cancer.

And certain genes are also risk factors for developing cancer.

For example, the BRCA genes.

You've done an absolutely brilliant job in today's lesson.

I've really enjoyed it.

I hope you have too.

And I look forward to seeing you next time.