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 Protein Synthesis, and we're gonna look at how we can use that genetic code that stores within DNA in order to make proteins.

So what the details of that protein synthesis process 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 how cells use the instructions coded in DNA to assemble proteins.

So we've got some keywords in today's lesson and our keywords are base, amino acid, gene, mRNA, and ribosome.

Now, I'll put a slide up with the definitions.

If you want to write them down, I'll pause the video, but otherwise, we'll be going through them in the lesson so you can write them down as we go.

So our lesson today is in two parts.

The first part of our lesson is how we make a copy of the gene from the DNA in the nucleus.

And the second is how we use that copy to actually make, synthesise our protein.

So let's get started with the first part of today's lesson, making a gene copy.

The DNA is a chemical molecule and it is stored in the nucleus of an animal plant and a fungi cell.

It's packaged very tightly into chromosome.

So it's wrapped around proteins to make these packages and that stops it from being affected by the chemical reactions that take place in the cytoplasm.

So it keeps it nice and safe inside the nucleus.

This is only the case for animal plant and fungi cells because in bacteria cells, the DNA is still in the cytoplasm.

The cells of an organism contain ribosomes in the cytoplasm.

Now, you might remember this from when you were doing the structure of the cell when you were a bit younger, but can you recall what the job of a ribosome is? Okay, I wonder how many of you remembered.

So the job of a ribosome is to build proteins from amino acids, and the amino acids are joined together in an order that is determined by the genetic code carried in the DNA.

So this is a ribosome.

There's lots of ribosomes within the cells.

Some of them are free in the cytoplasm, some of them are joined onto a membrane that's close to the nucleus.

They're very small little structures and they're made of these two parts.

So that's why they have this particular shape.

So can you complete the following sentences for me, please? So DNA is found where in animal plant and fungi cells, and ribosomes are found where in all cells? Okay.

Hopefully you were able to complete those sentences.

So DNA is found in the nucleus of animal plant and fungi cells and ribosomes are found in the cytoplasm of all cells.

So that includes bacteria.

So if you got those right, well done.

So just a little bit of a reminder, I think, DNA is a long chemical molecule.

It is a polymer, which it means it's made of many repeating units.

And this particular polymer is made up of nucleotides.

And nucleotides are that group there, and they're always made of these same three parts, and they are bonded together to form this long polymer.

So we've got two chains that are wrapped around each other.

Nucleotides all have the same basic structure, but the part that differs is called the base, and these bases form the genetic code, and we've got A, T, C and G.

So time for another check.

A nucleotide and a base are different words for the same molecule.

Now, do you think that's true or false? And then once you've decided which of these statements do you think best justifies your answer? 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 false.

And the reason is because a base is part of a nucleotide, they're not the same thing.

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

So the genetic code is determined by the order of those bases on the nucleotides and they're stored down the middle of the double helix structure.

So we can see that they're right there down the middle and the nucleotides make up the whole polynucleotide strand, but it's the basis there across the middle.

The double helix shape of the DNA is really important because it protects the genetic code.

So the backbone that's made up that sort of peach colour in this particular model is actually made up of those other two chemical groups, which are actually called sugar and phosphate.

And then the base code is the bit that's coming across the middle.

The genetic code provides the instructions to build proteins, but the DNA must remain within the nucleus and that keeps it safe.

So genes are short sections of DNA, that code for proteins.

Not all of the genome is genes.

Some sections are non-coding and they help to control when proteins are actually made.

So the genes there will code for the protein, but the non-coding DNA would code for or help to code for when that was actually made.

So for example, some cells will make proteins.

If we think about the digestive system, the cells in your digestive system that will make enzymes that are needed in digestion, but you don't need those enzymes that are present all of the time.

So at points that you do, those non-coding sections of DNA will help to control those genes to make those enzymes that are needed at that particular time.

So that's just an example.

So in order to build a protein, the first thing we need to do is we need to get a copy of that gene and we need to get it from the nucleus.

So a copy of the gene is made and it is moved from the nucleus to the ribosomes.

So we've got the gene there, you can see it's gonna be packaged up inside those chromosomes.

So we get a copy of that gene, we take a single stranded copy because we need to be able to read the code and then it's moved over to the ribosome, which is in the cytoplasm.

But you can see the original code that's in the DNA remains in the nucleus and that keeps it safe because we're gonna need to use it, again, many, many times during the life of that cell.

So a copy of the gene is made inside the nucleus and then the non-coding sections are not copied.

Not all of the genes are copied at the same time.

Only those for which you need to make the protein, like that example that I discussed to do with enzymes.

So we wouldn't necessarily make all the genes at the same time, as copies of the genes at the same time, but we might make a number of copies of genes at the same time.

Enzymes are proteins that speed up chemical reactions and they themselves are made of proteins that are coded for by DNA.

It's confusing, goes round and round.

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

So RNA polymerase works in the nucleus and it works to make a copy of the DNA and it makes this copy, which is called mRNA.

The process of copying the gene and making mRNA is called transcription.

So let's put these statements in the correct order to describe the first stage of protein synthesis or sometimes we call this transcription.

Okay? So if you number these statements, pause the video, we'll come back and we'll see how you've got on.

Okay, hopefully you got on with that okay.

Let's get the correct order then.

So number one is a gene is copied in the nucleus to form mRNA.

The second stage is the mRNA moves out of the nucleus into the cytoplasm.

The third stage is that the mRNA attaches to the ribosome.

And the fourth stage is, this whole process is called transcription.

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

So time for another practise task.

Now, in this practise task, this is a confidence grid.

So I want you to decide for each statement whether you think the statement is correct or incorrect, but then I want you to decide how sure you are about that.

So are you sure it's correct or do you just think it's correct? So it's about how confident you are.

And are you sure it's incorrect or do you think it's incorrect? So tick one box for each statement and then we'll come back and we'll check that you've got the correct understanding.

Okay, so let's just check if we've got these right then.

So the first one, protein structure is coded by genes.

That is correct.

Protein structure is coded by genes.

Proteins are synthesised in the nucleus, that is incorrect, okay? They are synthesised on the ribosomes in the cytoplasm.

mRNA is a copy of a gene, that is correct.

And genes are made up of nucleotides, that's correct, because genes are short sections of DNA and DNA is made of nucleotides.

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

So it's time to move on to the second part of our lesson.

And the second part of our lesson is making a protein.

So the next stage in protein synthesis is being able to put the repeating units, amino acids, of a protein together in the correct order that is determined by the genetic code.

So we've got that copy of the genetic code, the mRNA, that has been made in the nucleus by RNA polymerase.

And the mRNA carries that genetic code that's a copy of the gene and it carries it to the ribosome.

So we've got a sort of big image of this now.

So we're looking at the ribosome quite closely and we can see this gene copy.

We've just got one strand because we only copy one strand of the DNA.

Remember, the DNA's a double helix because it protects the code within the nucleus.

But when we want to be able to read that code in the cytoplasm to build proteins, we just need a single strand, so we're able to read the genetic code.

So the genetic code there is attached to the ribosome and we can see all of those bases.

So the ribosome uses the mRNA now to build a protein.

So let's have a little look through that process.

The genetic code carried by the mRNA, if we look closely at the mRNA, is read in groups of three, and that is called the Triplet Code.

And each triplet codes for a single amino acid.

So for in this example, we've got two triplet codes shown.

So that first one will code for a specific amino acid and then that second triplet code will code for a second amino acid.

And then the ribosome will join those two amino acids together and that's the start of us making our protein.

Now, that code is a very specific, so each of the triplet codes codes for an amino acid and here is an extract of the genetic code table.

Now, this is a big table, so this only covers six of the acids.

So the amino acid that each triplet codes for does not change between living organisms because the code is universal.

All living organisms use the same triplet code to code for the same amino acid.

Each amino acid can have more than one code.

Now, the reason for this is because if you do a combination of three and you've got four options because your bases are A, T, C and G, then you can actually make 64 different combinations, but there's only 20 amino acids, which means that more than one of the triplets will code for the same amino acid.

And you can see that example in this table here.

So true or false, quick check, each nucleotide in the mRNA codes for one amino acid.

So do you think that's true or false? And when you've decided, which of these statements do you think best justifies that answer? Okay, so each nucleotide in the mRNA codes for one amino acid, that is false.

And the reason is because the mRNA is read in threes, so the triplet codes for one amino acid.

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

So let's have a look at this process now of getting these amino acids.

So we've got these transfer molecules.

Now, they are a funny shaped chemical molecule, but they're just shown as this shape in this particular image, but they do have on the bottom these complementary bases.

Now, that means that the correct transfer molecule, tRNA, will bind to the correct triplet code, so it brings its specific amino acid with it.

So we say that transfer molecules called tRNA will bring the correct amino acids to the ribosome.

So we can see there was one tRNA molecule there, and you can see another tRNA molecule is coming in there to bind to that next triplet code.

Once we've got two of them together, that means we've got two amino acids next to each other, which means that those two amino acids can now join together, and that's the start of our protein.

And we can see we've got a third transfer molecule, a third tRNA molecule, now coming in with another amino acid.

So I'm sure you can see what's gonna happen next.

That's gonna bind to the next triplet, and then that means that we then have three amino acids in the first stage of our protein.

Once you have two that have joined together, actually, the first transfer molecule, tRNA, can then leave and it leaves its amino acid behind, okay? And that's how you manage to build this sequence of amino acids.

So eventually what you get when the last tRNA molecule is left, you can see it leaving there, we're left with a whole chain of amino acids that have been joined together.

Now obviously, this is a model of a chain of amino acids because they don't look like little circles, but we keep going until we've got a full chain.

And that's the first stage of the structure of a protein.

It's having a sequence, a specific sequence of amino acids, which has been determined by the order of basis in the mRNA, which is a copy of the DNA.

So a chain of amino acids, that first stage of making a protein is called a polypeptide, poly meaning many.

And these then will fold to give us the 3D structure of a protein, because the 3D structure of a protein is really important.

That's what allows it to do its job.

So the process of using the genetic code that's been carried by the mRNA to make a polypeptide is called translation.

So if you remember, we talked about the process transcription.

So transcription is making the copy of the gene, so making the mRNA in the nucleus, and the translation is the second part, which is making the amino acid sequence based on that genetic code.

So transcription and translation.

So we've got here a simple model of a polypeptide, which is amino acids joined together, and then a little bit more of a detailed model of polypeptide because we've discussed previously that an amino acid is made up of these four groups, three that are always the same, and then that fourth group that is variable and that's what makes the amino acids different.

So we can see this structure at the bottom is our amino acids that have been bonded together in our polypeptide.

So different orders of amino acids form different protein structures.

These are used in living organisms for their structure or their function.

So it might be that they're used for something structural, they have to have a particular shape like in your skin or your hair, or they may be involved in chemical reactions like enzymes, so therefore their shape is very important for their function.

So the order of those amino acids in that first polypeptide will determine how it folds and the shape that it makes in order for it to carry out its function in the living organism.

So time for another quick check.

So I'd like you to put these statements in the correct order to describe the whole process of protein and protein synthesis, or we might call that transcription and translation.

Okay.

So pause the video while you read those.

You might actually want to write them down in order, but otherwise just number them and then come back and we'll see how you've got on.

Okay.

So hopefully you managed that okay.

So the correct order.

So we need to start in the nucleus.

So mRNA, a copy of the gene is made in the nucleus.

That's number one.

So then number two is that mRNA moves to the cytoplasm and joins a ribosome.

And then number three, tRNA molecules transport specific amino acids to the ribosome.

And then finally, amino acids joined together in order determined by the triplet code on the mRNA to form a protein.

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

And it's time for us now to move onto another check.

So we're gonna have a go at analogy.

Now, you might have done an analogy before.

Your teachers will certainly have used them in class just because lots of ideas in science are difficult to explain without comparing them to something that you might be more familiar with.

So an analogy is a model that uses a familiar idea to explain an unfamiliar idea.

So for example, protein synthesis is our unfamiliar idea.

So I'm gonna take you through one for this chair.

So DNA is a bit like a flat-pack chair instruction manual.

So you get your flat-pack chair from your shop and you get the instruction manual out.

That's like your DNA.

And one person is reading it out and looking through it and talking to somebody else to get all the pieces together.

And that person reading it out is like the mRNA because they are making a copy of the instructions, a verbal copy of the instructions.

Then all of the pieces inside the pack then would be your, like your amino acids, so all your pieces of wood and your screws are like your amino acids that then you're gonna join together to make your final product, which has got this 3D shape.

So that's your chair.

Your chair is like your protein, your final shape.

So let's have a go at this one.

So what I would like you to do is possibly discuss it with the person next to you, maybe write it down.

Can you create an analogy for protein synthesis using a takeaway pizza as a model? So look carefully at this first one and see if you can match up some statements, but using a pizza takeaway instead.

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

Okay, hopefully you managed that okay.

So let's start with our instructions.

So DNA is like the takeaway menu.

So the copy of the takeaway menu would be you reading those instructions over the phone.

So one person reading the pizza choice to another over the phone is like the mRNA.

Then the pizza ingredients and the toppings are like the amino acids being put together, and then you get your final product made up of all of those things, which is your pizza.

So your pizza is like the protein.

Okay.

So hopefully you got those correct.

So we're going to move on to Jun and Alex.

Now, they have been creating analogies for protein synthesis.

So Jun says, protein synthesis is like building a wall.

You cement all the bricks together, like joining amino acids together to make a protein.

Alex says, protein synthesis is like writing an essay.

The research is taken from reference books in the library.

This is a copy like mRNA.

So both Jun and Alex have some good ideas, but their analogies could be improved and a bit more detailed to make sure you include all of the stages.

So what I would like you to do for your task is to improve their explanations by breaking them down to show how each part models each stage of making a protein, just like we did in that previous activity.

And then I would like you to have a go at creating your own analogy for protein synthesis.

So see how creative you can be and if you can make it different from the examples that we've already looked at.

Okay.

So if you pause the video while you do that, and then we'll come back and we'll have a look at how you've got on.

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

We'll do these one at a time because quite a lot of writing involved.

So, Jun.

He said protein synthesis is like building a wall and you cement all the bricks together, like joining amino acids together to make a protein.

So the way that we could improve this, we could say the instructions for building the wall are like DNA.

The person reading out the instructions is the mRNA.

So you sort of missed out that copying stage.

And the bricks are like the amino acids because they're a similar shape and structure.

So that's quite good in his analogy that they're quite similar to each other, all of the bricks, and they're able to join together to build a wall like a protein.

So that's an improved version of his idea.

So let's move on to Alex's idea.

So Alex said that protein synthesis is like writing an essay.

The research is taken from reference books in the library.

This is like a copy like mRNA.

So it's quite good that you had this idea that you can't leave the library, the reference books.

So the reference book does not leave the library, like the DNA does not leave the nucleus.

And the copied research is like the mRNA and that does move out of the library, like the mRNA moves out of the nucleus.

And then putting together the references and quotes are like the amino acids which are put together.

And then eventually you form an essay, which is like the protein.

So if you've got all of those stages compared, then well done, and then hopefully you had a go at writing your own analogy.

Now, unfortunately, I don't know what your analogies are, but in order for it to be a good analogy, it needs to have included all of the following things.

It should have included some kind of written element, some kind of code that starts the process.

It should have somewhere in there a copy of that being made, whether it's a verbal copy or a written copy.

And then you should have had parts that are being put together.

So smaller parts that are being put together in order to make a final product.

So if you had all of those things in your analogy, they're quite tricky to create.

So well done if you did.

So it's time for the end of our lesson and our summary on protein synthesis.

So DNA is a polymer made up of nucleotides.

Each nucleotide contains a base and there are four different bases coded A, T, C and G.

The sequence of nucleotides in a gene is a template for assembling proteins from amino acids in a particular order.

The triplet code is universal and each one always codes for the same amino acid.

To make a protein, a copy of a gene is made in the nucleus to form messenger RNA or mRNA.

The mRNA leaves the nucleus and moves to a ribosome in the cytoplasm.

The ribosome joins amino acids in order determined by the sequence of triplet codes in the mRNA.

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