Lesson video

Hello, and welcome to this lesson from the Unit: Heredity and DNA.

The title of today's lesson is "The Discovery of the Structure of DNA." So we're gonna go back in time and we're gonna have a look at when DNA was first discovered, and then how scientists have worked together in order to discover the structure of that DNA.

And finally, how that knowledge is being used in modern science for new technologies.

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

So by the end of today's lesson, you should be able to describe how scientists have collected evidence and shared their findings in order to develop a model that describes the structure of DNA.

We've got some keywords to look out for in today's lesson, and those are DNA, X-ray, double helix, and genome.

I'm gonna put the definitions up for you now.

So if you want to pause the video to write these down, then you can, but we will be going through them as we go through the lesson today.

Our lesson is in three parts.

Part one is the early knowledge of DNA.

Part two is the discovery of the structure of DNA.

And part three is the importance of understanding that structure of DNA.

So, basically, what have we done about it since we gained this knowledge.

So, let's start with early knowledge of DNA.

You all may have had the chance to extract DNA.

You can extract it from fruits such as kiwi, or strawberry, or from peas.

You can even extract it from your own saliva.

But it was actually discovered in 1869, and it was by a Swiss scientist called Friedrich Miescher, and he extracted it from white blood cells from the nucleus of white blood cells.

And what he discovered was that it was a unique combination of elements and therefore it was a new chemical that we hadn't come across before.

He didn't know what it was for, but he knew that this specific chemical was packaged into the nucleus of cells.

Now we're gonna move forward, 70 years.

And 70 years later, in 1944, scientists discovered that that DNA, that unique combination of elements that was discovered before, was actually our genetic material.

It contained the genetic code, which coded for all of our inherited physical features and processes.

Then we come along to these two scientists who are quite famous.

So Francis Crick and James Watson.

And in early 1950s, they were working at the University of Cambridge.

Now, the University of Cambridge is quite a prestigious university in the UK.

And the job of universities isn't just to educate people, it's also to research to be able to make new discoveries.

And they were working there.

And what they were trying to do is create a model of DNA, a 3D model of DNA.

So they knew that it existed.

We knew that it contained genetic information.

But we didn't know what the structure of it was.

At the same time, there was another team of scientists looking at imaging the structure of DNA.

And those two people were Rosalind Franklin and Maurice Wilkins.

And they were using a new technique at a university in London called King's College.

And the new technique that they were using was called X-ray crystallography.

Now, that's something you don't need to know the process of, but it was a new technique and they were working on this together.

Both of them were using these imaging techniques.

And the technique itself uses X-ray radiation in order to be able to see the structure of very small substances like molecules.

So we know that we can use microscopes to look at very small objects like cells and the nuclei inside cells, but DNA molecule is much, much smaller than that.

There's two metres of DNA packed into every nucleus.

So it is really, really small so you can't use microscopes in order to visualise it.

And so it was a big team of people who were working on this, but these were the two notable scientists from that team, Rosalind Franklin and Maurice Wilkins.

So let's have a check.

So, do we think this statement is true or false? And when you've decided, have a think about which of those statements below would justify your answer.

So, the statement I'm asking you to decide on is, "DNA was first discovered by Watson and Crick." Do you think that's true or false? And then read just the statements and decide which one supports your answer.

So pause the video and then we'll come back and see how you've got on.

Okay, how did you do? So, DNA was first discovered by Watson and Crick.

The answer to that is false.

And the reason that it's false is because DNA was actually recognised to be a specific combination of chemicals in 1869.

Okay? So they already knew that DNA existed.

So Watson and Crick didn't discover it, all right? So let's move on to our next task.

So some pupils are discussing the knowledge of DNA in 1950.

Okay, so, Aisha says, "In 1950, no one knew what DNA was." And Jacob says, "In 1950, no one knew what DNA was made of." And Sam says, "In 1950, no one knew the role of DNA." and Alex says, "In 1950, no one knew the structure of DNA." So all of those sound quite similar, so you're gonna have to take your time to read through those again.

And what I would like you to do is choose the one that you think is correct and then explain why that pupil is correct, but also explain why the other pupils are incorrect.

So, pause the video and then we will come back and have a look at your answers.

Okay, let's see how you did with this one then.

So I've got the four answers that those pupils gave up the side there.

So we'll take them one by one.

So they were discussing the knowledge of DNA in 1950, and we're gonna choose which pupil was correct, and we're gonna explain why they are correct and why the other pupils are incorrect.

So let's take them one by one.

So Aisha is incorrect, because DNA was discovered in the nucleus in 1869, so people did know what DNA was.

And Jacob is incorrect, because when DNA was discovered, it was found to contain a specific combination of chemicals.

So people did know what DNA was made of.

And in 1950, Sam is incorrect, because DNA was actually discovered to be part of the genetic material that was inherited in 1944.

So people did know what the role of DNA was.

But Alex is correct, because scientists did not know the structure of DNA in 1950.

So they knew what it was, they knew what it was made of, they knew what its job was, but they did not know what the structure was.

So, well done if you got that right.

So we're gonna move on to our second part of today's lesson, which is the discovery of DNA structure.

And we're gonna talk about Rosalind Franklin.

And that's a picture of her there working in her laboratory.

She was a chemist, and she was working with X-rays in order to find the structure of DNA.

The technique was new, but she did produce an image that showed that the DNA had a helix shape.

She sent the image to one side, and this image was shown by her boss at the time, Maurice Wilkins, to James Watson from Cambridge.

Unfortunately, he showed this image without her permission and without her knowledge.

James Watson and Francis Crick then went on to produce a 3D model of DNA using that image to support their work.

They modelled it in 3D to show that there are two strands, and they spiral around one another to form a double helix, and the fact that there are links across the middle of these two chains that hold it together.

So it's a bit like a ladder.

So if you imagine a ladder goes straight with rungs across the middle, and then if you took the top and the bottom and you could apply pressure and twist it, that is what the DNA model would look like.

They completed this model in 1953, and this is the first time that DNA had been modelled.

So Watson, Crick, and Wilkins, who, if you remember, was Rosalind Franklin's boss on this piece of work, received a Nobel Prize in 1962.

So you can see that was quite a while after the discovery of the structure of DNA had actually been made.

This is a very prestigious prize, and it does have some money associated with it, but it really does award the most brilliant scientists in their field.

Rosalind Franklin was not included, or was she referenced for her crucial research that she added to finding the discovery of DNA.

So time for a check.

What I'd like you to do is I'd like you to put these statements in order to outline the discovery of DNA.

So the statements are as follows.

The structure of DNA was worked out.

DNA was extracted from the nucleus of a cell.

The chemical parts of the DNA were identified.

And the DNA was imaged using X-rays.

So put those in order, and pause the video, and then we'll come back to check how you've got 'em.

Okay, let's see how we got on them.

So the first thing that happened was the DNA was extracted from the nucleus of a cell.

The next thing was that the chemical parts of DNA were identified.

Next, the DNA was imaged using X-rays.

And finally, the structure of the DNA was worked out.

So let's next look at how scientists have to work in order to find these new discoveries.

So what things do scientists do to work out the structure of DNA? Would they have to collect evidence, share findings, build models, or develop an explanation that fits the evidence? So just pause the video and then we'll see how you've got on.

Okay, so they would've had to collect evidence, they would've had to shared findings, they built models, and they developed an explanation that fit the evidence.

So it's a bit of a cheeky one that one.

All of them were things that scientists would've done to work out the structure of DNA.

So if you got all of those right then well done.

Right, so let's do a little practise task now.

So there are some pupils here and they're discussing what an online article would use as a headline to grab an audience's attention if the discovery of DNA structure was made today.

So Laura says, "Two eggheads crack the code to life." And Andeep says, "Three's company and four's a crowd in the race to be the top scientists in the discovery of DNA." So what I'd like you to do is to discuss Laura and Andeep's headline.

Do they grab your attention? Do you think they're good summaries? And then once you've done that, why don't you have a go at writing a new story headline that would grab an audience's attention.

And then once you've done that, you need to explain to somebody else why your headline is a good summary of the discovery of the structure of DNA.

So you'll need a little bit of time to do this.

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

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

So, discuss Laura and Andeep's headline.

Do they grab your attention? Are they good summaries? Well, I guess only you can decide whether they grab your attention or not.

But let's look at them summaries.

So, Andeep is summarising the scientists that won the Nobel Prize, Watson, Crick, and Wilkins.

Franklin was not included in the list for her contribution of imaging the DNA using X-rays.

And Laura is summarising Watson and Crick discovering the structure of DNA.

This does not acknowledge the contributions of Franklin and Wilkins.

So, hopefully you've had an opportunity as well to have a go at your own headline and you've been able to explain to somebody else why your headline is a good summary.

So let's move on to the third part of our lesson today, which is the importance of understanding DNA.

So the discovery of DNA confirmed ideas of how features are passed on from one generation to the next.

So, remember, they already knew that DNA was stored in the nucleus and that it had a role in heredity.

But now the structure was known, then they could move on to the idea of where the genetic code came from.

So DNA uses a genetic code to store instructions for all of the inherited features and processes of living organisms, and it is passed on through reproduction from parents to their offspring.

So here's an example here of adult monkey, and it's passing on its DNA through reproduction to its baby.

And that happens in all living organisms on earth, that the DNA is passed from the parent to the offspring through heredity.

All of the DNA of an organism is called the genome.

And the genome includes all of the instructions for physical features and processes of a living organism.

In 2003, the entire human genome was sequenced for the first time.

This means that the scientists could work out which sections of the genome provided instructions for which features and which processes.

And you can see this image is part of the process of being able to sequence DNA.

So they're all extractions of DNA in those little tubes there in that picture there.

And because they've sequenced DNA, it means that they've been able to go on and sequence other organisms as well.

And that's led to huge advances in technology, particularly in areas of medicine and disease control.

So, for example, testing to see if you're carrying the DNA of a virus, now, you might have had a go at a test like this, or been vaccinated by virus DNA.

So now we know about DNA, we can use it to our advantage.

And finally, another example, is editing the genomes of organisms, not just microorganisms, but also larger organisms in order to treat disease.

So let's do a quick check.

So, understanding DNA helps us to improve people's health.

Do you think that's true or false? And once you've decided whether it's true or false, can you justify your answer with one of the statements below? So pause the video while you have a go at that, and we'll come back soon.

Okay, so understanding DNA helps us to improve people's health.

That is true.

And the reason is because understanding DNA has led to advances in medicine and disease control.

Right, let's have a practise test now.

So Jun is making a timeline of the discovery of DNA.

So we started off there in 1869.

So that's where we started with today's lesson, where DNA was extracted from the nucleus and the chemical groups were discovered that made up that DNA.

So what I would like you to do is I'd like you to complete a timeline of the different events that happened from 1869.

Now, if you've got some extra time, you could add in any events before, you could add in extra events that we've not discussed in today's lesson, or things that have happened after 2003 and what scientists have done with the knowledge of DNA.

So it's gonna take you a little bit of time to construct this.

So pause the video, and we'll come back and see how you've got on to.

Okay, I hope you managed to make a really successful timeline.

Let's just check it's got all the key components on it.

So we are gonna start with that one that was already there, which is in 1869, DNA was extracted from a nucleus and the chemical groups were discovered.

Next, in 1944, DNA was discovered to be the genetic material of heredity.

And then next, we move on to 1952, and that's when Franklin produced an image of DNA using X-rays.

And then in 1953, Watson and Crick produced a 3D model of DNA.

And then in 1962, Watson, Crick, and Wilkins win the Nobel Prize for the discovery of the structure of DNA.

And then finally in 2003, the human genome is sequenced.

So hopefully you had all of the events on yours that are listed there, but maybe you had the opportunity to put a few others on.

So, well done for that.

And that brings us to the end of our lesson on the discovery of the structure of DNA.

So now let's summarise.

So DNA was discovered in 1869, but scientists did not work out its structure until 1953.

DNA was discovered to be the molecule of heredity in 1944.

Rosalind Franklin's team in London used X-rays to produce an image of DNA molecule in 1952.

Maurice Wilkins from Franklin's group, showed the picture to James Watson from Cambridge.

James Watson and Francis Crick used the picture evidence from Rosalind Franklin to develop a model to describe the double helix structure of DNA.

Our increasing understanding of DNA has led to the advancements in medicine and disease control.

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