Lesson video

Hello and welcome to this lesson from the unit DNA and the genome.

The title of today's lesson is the genetic code, and we're going to be looking at that genetic code today, how it's carried in DNA, and how it's possible that it codes for all of the proteins that require by living organisms, but also how that code is universal to all living organisms on earth.

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 how instructions for making proteins are coded into DNA.

So we've got some key words in today's lesson and our keywords are DNA, polymer, nucleotide, protein and amino acid.

Now I'll put a slide up of the definition, so if you want to pause the video to write them down, you can, but otherwise we'll be going through the definitions as we work through the slides today.

So our lesson today is in two parts.

First of all, we're gonna look at the genetic code and what that's made up of and what its role is, and then we're gonna look at how that's universal.

So it's the same for all living organisms on earth.

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

So all of the DNA in a cell is called the genome.

So that includes all of the genes and all of the non-coding DNA and DNA itself is a polymer.

It's called deoxyribonucleic acid.

I've highlighted where the D, the N and the A come from then in our abbreviation that we use.

So all organisms have a genome, so that's all living organisms and most cells in an organism store a copy.

So not all of our cells.

There are some accept exceptions like red blood cells don't have a copy of the genome, but that's 'cause they don't have a nucleus.

And so our DNA is wrapped up into these packages called chromosomes that you may already be aware of.

And then those chromosomes are packed within the nucleus of an animal cell in the case of humans or all animals, but also in the nucleus of other cells of other living organisms except bacteria.

So DNA is a long chemical molecule called a nucleic acid.

It's part of a group of chemicals called nucleic acids and that's because they are made up of nucleotides.

It's a polymer and a polymer is any chemical that is made up of repeating chemical groups.

So smaller repeating chemical groups.

And in this case, in DNA, the smaller repeating chemical groups are called nucleotides.

So if we look at that DNA closely, the sort of beige peach colour there, that's actually made up of these two chemical groups at the same at the back.

So one is actually a sugar, the one that's a pentagon shape and then a phosphate at the back.

And then we've got these bases that stretch across the middle.

So that whole group there is called nucleotide.

So it makes up the DNA strand and those nucleotides are bonded together.

So that's why it becomes a polymer.

So it's made up of two of these polymer chains.

So two of these nucleic acid chains side by side, they spiral around each other but then they connect across the middle.

So the part of the nucleotide that makes up the genetic code, the base connects across the middle of the DNA.

And again, if we look very closely here, we can see we've got the two strands that are made up of those repeating chemical groups, those nucleotides with a very, very similar structure.

The only difference being the base that's across the middle.

And then you can see that that base is what makes up the genetic code.

So let's have a quick check then.

So which of these statements would correctly finish this sentence? DNA is a polymer because, so pause while you decide and then we'll come back and we'll see if you've got it right.

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

So DNA is a polymer because it is made up of many nucleotides, but you could also finish that sentence with, because it is made up of repeating units.

So if you chose both of those then that's correct.

Well done.

So the double helix shape of DNA actually protects the genetic code.

So those common chemical groups in the nucleotides, the sugars and the phosphates so that pentagon and that little round circle, they're the same in every nucleotide and they make up the backbone with the base going across the middle.

And that makes up the genetic code and that's in the middle of that double helix which protects it.

And that genetic code gives the instructions to build proteins.

And that genetic code is made up of the letters A, T, C, and G.

So the genetic code is determined by the order that these nucleotides make up the the polynucleotide chain.

So what sequence that they make gives you the code.

So it's like putting the letters of the alphabet in order to make words.

So depending on what order you put the letters in, you get different words.

And that's exactly the same with the genetic code.

Depending on the order that you put those nucleotides together gives you a different code.

So genes are short sections of DNA, that code for proteins and but not all of the genome is genes.

Some of it is made up of these non-coding sections.

So they don't code for proteins, but they are important because they help to control when proteins are made.

So they have a controlling function.

So the order that different nucleotides are within the gene determines the structure of the protein that it for.

So let's have a look at this in detail.

So we've got a gene here and not all of the DNA, we've just specifically got the gene and then we'll look across and if we look at the structure of that gene, we can see it's made of these nucleotides and they are in a particular order.

So we can see the code there and then that code will determine the structure of a protein.

So time for another quick check, true or false.

Genes are the sections of DNA that hold the genetic code for a protein.

Now once you've decided whether that's statement is true or false, you then need to justify it.

So which of these statements below would justify whether that's true or false? So pause the video while you decide and then we'll come back and we'll see how you've got 'em.

Okay, then let's see.

So genes are sections of DNA that hold the genetic code for a protein.

So that is true.

And the statement which best justifies that is, this is because the order of nucleotides in a gene will determine the structure of a protein.

So if you got that right, then well done.

So proteins are polymers as they are made of repeating chemical units.

So the repeating units in proteins.

So we've talked about the polymer, that's DNA, that's made of nucleotides.

So now we're talking about the polymer of a protein and the repeating units in proteins that are called amino acids.

So you might have heard of this term amino acids 'cause when you break down proteins in your digestive system, you break them down into amino acids.

But when we're building proteins, we have to put those building blocks, those amino acids together.

Your body needs 20 different types of amino acid and you get those from your food and then you break them down during digestion.

The main structure of all amino acids is the same, but each of the 20 have a different variable group.

So if we look at this model of an amino acid here, there's three of the groups that would always be the same.

So that's those three at the top.

And then they would have a variable group.

So that's the thing that changes.

So in the images that follows the little diamond at the bottom is going to be our variable group.

And we'll see that it's different because it changes colour in the model.

So a protein is made of amino acids bonded together in a particular order.

So that was is what makes one protein different from another.

The order that those amino acids are bonded together and the order that you bond those amino acids together is determined by the genetic code within the gene.

So here is our genetic code in the gene.

So this is a single strand of DNA so that we can read the genetic code and then that will determine what order you put these different amino acids together in.

And you can see we've got four different amino acids at the bottom because that little diamond group is a different colour.

So that variable group is different in each of those amino acids.

So let's choose the correct order for protein production.

So read these carefully 'cause they're quite similar.

You need to get the correct order for making a protein from a gene.

Okay, so pause the video, will you decide, and then we'll come back and we'll see how you've got 'em.

Okay, this one's quite tricky.

So the correct answer is C genome, which is all of the genes.

Then we've got genes which are within the genome, short sections of DNA, that code for proteins.

And then we've got the genetic code within that gene, which would code for the amino acids, which then gives you the protein.

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

So time for another task.

And this time we need to match up some key terms. There's lots of key terms that can easily be mixed up in this topic.

So take your time to make sure that you get the correct definitions.

So pause while you do this and then we'll just check that you've got them right after.

Okay, so let's see if we can get these matched up correctly.

So we've got DNA.

So the definition of DNA is a long chemical polymer made up of nucleotides.

And then we've got nucleotide, which is a small chemical group.

There are four types, A, T, C, and G.

Then we've got gene, which is a short section of DNA that holds the genetic code for a protein.

And then we've got amino acid, which is a small chemical group that make up proteins and there are 20 types.

And then we've got protein, which is a large chemical polymer that is made up of amino acids.

So if you've got them, write them well done.

If you've got any wrong, then just make sure that you correct them so you've got the right definition.

Okay, another task for you now.

So use your understanding of the role of the genetic code to explain how DNA codes for protein structure.

So in your answer, please try to use the following key terms. So DNA, nucleotide, gene, genetic code, amino acid and protein.

And you can refer back to your matching activity to make sure you've got the correct definitions for those.

And then use those in your extended writing.

So pause where you do this 'cause this'll take you a little bit of time and then we'll come back and we'll have a look at and model answer after.

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

So we are going to use your understanding of the role of the genetic code to explain how a gene codes for protein structure.

So your answers don't have to be exactly the same as this, but you want words to this effect.

And also you want the order of those key words to be fairly similar.

So we're gonna start with saying that DNA is a molecule, it's a polymer and it's made up of nucleotides and there are four different types of nucleotide and their order determines the genetic code.

And then a gene is a short section of DNA that carries the genetic code for one protein and the order of nucleotides in the gene will determine the order of amino acids that make the protein.

So if you've got that right and you've got the key terms in the correct order, then well done.

And it's time to move on to the second part of our lesson, which is the universal code.

So the genetic code is actually read in groups of three.

This is called the triplet code.

So each triplet codes for a single amino acids.

So you can see what I mean by this image here.

So we've got a section of DNA and we can see it's made of those nucleotides, those repeating units.

And we're looking at the code there across that would be across the middle of the double helix.

So we start here with CAG, that's CAG codes for one amino acid.

And then the next three along, okay, in this case TCA code for a different amino acid.

And then those two amino acids are then joined together to start making a protein.

So all of your amino acids join together.

So it's always read in threes, you don't overlap, you read three, and then you read the next three.

And each of those codes will code for different amino acids.

Some of them code for the same amino acid, but that's because there's more codes than we need.

So the different sequences of amino acids gives you different proteins.

So again, we've just extended that model a little bit further.

So we can see the genetic code of a gene and we take each triplets, each three of those will code for a amino acid.

And you can see then we bond those amino acids together and that gives us the order of amino acids in a protein.

Now, because the order of these amino acids changes with each gene, then you get a different protein coded for, it's quite clever, isn't it? So it's time for a quick check.

If there are 330 nucleotides that make up a genetic code of a gene, how many amino acids will be in the protein? So if you read that and then you fill in the gap.

Okay, so the correct answer is 110 'cause for every three nucleotides you get one a amino acid.

So 330 divided by three is 110.

So you got that right, well done.

So all organisms on earth have evolved from the same bacteria.

It was about 3.

8 billion years ago.

Don't have an exact time.

And I think this is just amazing to think about that every living on earth originally came from bacteria.

And over millions and millions of years of evolution, we've all evolved to have our own genes, genetic codes, proteins that make us all different from one another.

But because we all came from the same bacteria, we all share common ancestors, we're all related to each other in some way.

And as we all share a common ancestor, that means that the genetic material that has been copied and pasted and passed on through all those organisms through all of those millions of years is DNA.

So we all have DNA and in an animal cell we store that DNA in our nucleus, but in a plant cell.

And sorry, that is also the case in a plant cell and in a fungi cell.

So therefore that's an indication that we're all related to each other because we all have DNA, which is our genetic material, and we all store it in a nucleus.

We're even related to bacteria.

Our unicellular microorganisms, they also have DNA as their genetic material.

But instead of having it in the nucleus, they have their DNA stored in the cytoplasm.

We're still related to them, but you can see we're more distantly related to them because they don't store their DNA in a nucleus.

Whereas fungi and plants do the same as animal cells.

What that tells us is that DNA is the universal storage molecule for the genetic code, okay? We all have DNA and the genetic code stored in DNA as our genetic material.

So as the DNA has been passed on from one generation to the next, the genetic code, it carries slowly changes.

So even though the DNA, the molecule itself is the same, that genetic code, that order of nucleotides inside the DNA has slowly changed over time through evolution.

So that has led to the phenotypes of individuals becoming more and more different and eventually they can become different enough to form a new species 'cause remember as the order of nucleotides changes the proteins that it codes for changes, which means the features change and that gives us a different phenotype.

And we can see that evolution often when we look at fossils and we can look backwards in time and see how things have changed.

So this is an example of the evolution of horse leg bones, and we can see how that's changed through time as the organism has evolved.

So time for a quick check.

All organisms on earth use DNA as their genetic material.

Is that true or false? And once you've decided, which of the statements below do you think best justifies your choice? Okay, all organisms on earth use DNA as their genetic material.

This is true.

And the statement which best justifies this is that all organisms evolve from the same ancestor and DNA has been passed by reproduction.

So if you got that right, then well done.

So even though the genetic code has altered in species through time, the amino acids that each triplet codes for has not changed.

So even though you might have different orders, the same triplet will always code for the same amino acid, whatever species you are, you just might have different triplet codes in a different order when you're in a different species.

So what we say is that makes the genetic code universal.

All organisms make proteins using the same triplet code for specific amino acids.

Now, there's a whole big table that you can refer to that uses that you can see all of the amino acids in the codes.

So here is just a little extract, and you can see the triplets are there on the DNA, and then those are the amino acids that they code for.

You can see that there's more than one triplet for each amino acid.

That's because there are 64 different combinations of the three letters, the three bases, but there's only 20 amino acids.

So some of the triplets will code for the same amino acid, even though they're slightly different.

So the variation in individuals and species is due to the different order of amino acids and therefore the proteins that are formed.

The triplet code for each amino acid is the same.

So even though the code for the amino acid is the same, the codes that you actually receive in your DNA are different.

So therefore you'll get different amino acids and different proteins.

And that's how we get variation between our species.

So the genetic code is universal because, which of those statements do you think finishes this sentence correctly? So pause the video while you decide and then we'll come back and we'll see if you've got it right.

Okay, so the correct answer is the genetic code is universal because the triplet code always codes for the same amino acid.

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

Time for a quick practise task.

So Andeep and Laura are discussing their confusion about the genetic code.

It is quite confusing.

So Laura says, "I don't understand how the genetic code can be universal if all species on earth are different." And Andeep says, "I don't understand how differences in genetic code in genes can lead to differences in individuals of the same species and between species." So what I would like you to do is to use your knowledge of the genetic code to help them to understand the ideas that they are confused about.

So pause the video while you decide, will you write your answers and then we will come back and we will see how you've got on.

So let's see how you on with explaining this to Laura and Andeep.

So Laura said, "I don't understand how the genetic code can be universal if all species on earth are different." And your response should be along the lines of, all species on earth are different because they have a different order of nucleotides that make up the genetic code in their genes.

The triplet code is universal as it always codes for the same amino acid.

And Andeep is confused 'cause he says, "I don't understand how differences in the genetic code in genes can lead to differences in individuals of the same species and between species." So our response to him would be, that the differences in the triplet codes within the genes will code for different amino acids and therefore different proteins.

This gives variation within and between species.

So if you manage to describe those, that understanding to those two pupils correctly then well done.

So that brings us to the end of today's lesson and time for our summary.

So DNA is a polymer of four different nucleotides, A, C, G, and T and proteins are polymers of amino acids.

Polymers are chemical molecules made up of smaller chemical groups.

DNA is a double helix structure with the genetic code stored within a gene is a short section of DNA that holds the genetic code for a protein.

The sequence of nucleotides will determine the order of amino acids in a protein.

The genetic code is read in groups of three, three nucleotides form the triplet code that corresponds to a specific amino acid.

Different organisms have different sequences of nucleotides in their DNA producing variation within and between species.

However, the triplet code is universal, i.

e, the amino acid that each triplet codes for stays the same.

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