Lesson video

Hello, I am Mrs. Adcock and welcome to today's lesson.

Today's lesson is on natural polymers.

We are going to be looking at proteins, starch, cellulose, and DNA, and thinking about what are the monomers that make up these natural polymers.

Today's lesson outcome is, I can name the monomers of some natural polymers and understand their importance for life.

Some of the keywords that we will be using in today's lesson include amino acids, polypeptides, proteins, DNA, and nucleotides.

Here you can see each of those keywords written in a sentence.

It would be a good idea to pause the video now and read through those sentences.

You might like to make some notes also so that you can refer back to them later in the lesson if you need to.

Today's lesson on natural polymers is split into three parts.

First of all, we are going to be looking at proteins.

Then we are going to move on to look at those two carbohydrates, starch and cellulose.

And finally, we will finish the lesson by looking at DNA.

Let's get started by looking at proteins.

Amino acids are monomers, and remember that monomers are small molecules that can join together to form a polymer.

Amino acids are monomers and they contain the carboxylic acid and the amine functional group.

We can see an example of an amino acid shown.

You will notice the amino acid has an R group, and the R is any atom or group of atoms specific to an amino acid.

Amino acids always look similar to that molecule shown there, but that R group can vary.

We can see that the amino acid has the carboxylic acid functional group.

Just a reminder that the carboxylic acid functional group is that carbon double-bond to an O, and then an OH group as well, so COOH.

And then our amino acid also contains that amine functional group, so the NH2.

Which two functional groups do all amino acids contain? A, alkene, B, amine, C, alcohol, D, carboxylic acid.

You are looking for two functional groups that all amino acids contain.

The correct answer is B, the amine functional group, and D, the carboxylic acid functional group.

Well done, if you identified those two functional groups, there are 20 different amino acids that are essential for life, and here are examples of just two of those amino acids.

We've got glycine, and here the R group has been replaced with a hydrogen atom.

And alanine, and in alanine, you will notice that that R group is a CH3 group.

Both of these amino acids have got that carboxylic acid and the amine functional group.

Amino acids join together to form polypeptides.

Polypeptides are polymers made from amino acids and they contain a peptide bond.

Here we've got amino acid 1, we've got an amino acid, and we are going to join that together with another amino acid that we've called amino acid 2.

And these join together to form a polymer, and this polymer is known as a polypeptide.

The nitrogen atom from the amine group of one amino acid has bonded with the carbon atom of the carboxylic acid group of another amino acid, and these join together to form our peptide bond, and we can see that shown there in our polypeptide or our polymer at the bottom.

When these bond together, the amine group also loses a hydrogen atom and the carboxylic acid functional group loses an oxygen and hydrogen atom, and these bond together to form a second product, and that's water.

So our amino acids can join together to form polymers, these polymers are known as polypeptides, and in this process we also form water.

When amino acids polymerize to form polypeptides, water is also produced.

Here we have a section of a polypeptide chain, and here we've highlighted the amino acids that joined together, and as they joined together, water molecules were also produced.

Here we can see another amino acid that joined on, and as that joined onto the chain, a water molecule would've been produced.

The polymerization of amino acids is a condensation reaction because when we form our polymer, we also form water molecules.

Time for a question.

The formation of polypeptides is a.

A, condensation reaction, B, hydration reaction, or C, hydrogenation reaction.

The correct answer is A, the formation of polypeptides is a condensation reaction, because in the process of forming our polymer, we also form a small molecule, and in this case, that small molecule is water.

Hydration reactions involve the addition of water, and hydrogenation reactions involve the addition of hydrogen.

When making polypeptides from amino acids, an example of the overall equation is: we have glycine, our amino acid, and that is our monomer.

So we have n number of our monomer and they join together to form our polymer.

And when we represent our polymer, we show the repeating unit, we surround that with brackets, and we put an n on the outside to show that we have that repeating unit n number of times.

In this case, we used glycine as our monomer, so we will form a polypeptide made from glycine, and also we will form n number of water molecules, because this is a condensation reaction.

It's an example of condensation polymerization.

Proteins are polymers that are made from amino acids.

Proteins contain one or more polypeptide chains.

Here we can see a section of a polypeptide chain, and that polypeptide chain is made of amino acids.

We've got glycine, alanine, and serine that have all joined together to make that section of a polypeptide chain.

Time for a question.

Proteins are formed from which monomers? Is it A, glucose, B nucleotides or C amino acids? The correct answer is C, amino acids.

So, well done if this is the option you chose.

Amino acids are the monomers that join together to make protein molecules that are polymers.

Time for our first practise task of today's lesson.

You can see there a molecule of serine.

Question 1, serine is an amino acid.

Hopefully you can spot those two functional groups, the carboxylic acid and that amine functional group on that molecule of serine.

Name the polymer that can be formed using amino acid monomers.

And then Question 2, you need to draw the repeating unit of a polypeptide formed from serine monomers.

And Question 3, write an overall equation for the formation of a polypeptide from serine.

When you're answering Question 2 and 3, remember that when those amino acid molecules join together, that this is a condensation reaction, so we are going to also produce a small molecule of water.

Just think about where those hydrogen and oxygen atoms have come from.

Pause the video now, have a go at answering these three questions, then come back when you're ready to go over the answers.

Question 1, serine is an amino acid.

Name the polymer that can be formed using amino acid monomers.

Amino acids form polypeptides or proteins.

Well done, if you've got that one correct.

Question 2, draw the repeat unit of the polypeptide formed from serine.

And your repeat unit should look similar to this, so we have drawn out that serine molecule, and then we've removed a hydrogen atom from the amine group, and we've removed OH atoms from that carboxylic acid functional group.

When we then draw out the overall equation, we will have n number of that serine monomer, and they will join together to produce a polymer.

And when we've drawn our polymer, we have the repeat unit, and we've drawn around brackets and put an n on the outside, so we then have our polypeptide polymer, and then don't forget, we will also have n number of H2O molecules.

That was a tricky question, so well done if you got Question 3 correct.

We have looked at proteins, now we're going to move on to look at starch and cellulose.

Starch, cellulose and glucose are all carbohydrates, and these biological molecules contain carbon, hydrogen and oxygen atoms. We can see a molecule here of glucose.

Glucose has the molecular formula C6H12O6, and those grey balls represent carbon atoms. The white balls represent hydrogen atoms, and the red balls represent oxygen atoms. So if you count those carefully, you will see that glucose is C6H12O6.

What is the molecular formula of glucose? Is it A, C5H11OH, B, 6CO2, C, C6H12O6, or D, C5H10O5? The correct answer is C.

So, well done, if you identified the molecular formula of glucose as C6H12O6.

Starch and cellulose are natural polymers, and they're made from the monomer glucose.

Here we've got a model showing a section from a polymer chain of starch or cellulose, where those green hexagons represent a molecule of glucose.

So we can see those glucose molecules have joined together to form a polymer of starch or cellulose.

Starch and cellulose are both made from the monomer glucose, but they differ in the way that the glucose molecules join together, and that gives these polymers different properties.

Here we can see a section from a starch polymer chain, and we can see those glucose molecules joined together.

And here we've got a section from a cellulose polymer chain, and hopefully you can notice that although we've got those glucose monomers joined together to form that polymer, that they're joined together in a different way, and that gives these two polymers different properties.

Which monomer are the carbohydrates, starch, and cellulose made from? Are they made from A, amino acids, B, proteins, or C, glucose? The correct answer is C, glucose.

Well done if you got that one correct.

Those glucose monomers can join together to form either the polymer starch or they can form that polymer cellulose.

Proteins are another natural polymer, and they are made from the monomer amino acids.

Time for another practise task.

You can see you have a diagram there of a polymer.

Question one, the image shows a section of a polymer, and you need to draw around the repeating unit.

Look carefully at that polymer and see if you can work out which section of it is repeating.

Question 2, work out the molecular formula of the monomer.

So once you've identified that repeating unit, can you work out the formula of the monomer? Can you, in Question Three, then name the monomer, and Question Four, suggest the name of this polymer that's shown.

Pause the video now, have a go at answering those four questions, then when you come back, we'll go over the answers.

Question one, you needed to draw around the repeat unit, and here we can see the repeat unit of that polymer.

Now we've identified that repeating unit, we can work out the molecular formula of the monomer, and the monomer had the molecular formula C6H12O6.

Hopefully now you can name that monomer and notice because it has the molecular formula C6H12O6, that the monomer will be glucose, and glucose molecules can join together to form starch or cellulose.

Actually, that polymer is a section of starch, but writing cellulose would also have been an acceptable answer.

We've looked at proteins and we've looked at starch and cellulose, and we've identified the monomers of these natural polymers.

Now we're going to move on to have a look at DNA.

DNA, which is deoxyribonucleic acid, is essential for life.

It carries the genetic code required by living organisms and viruses to develop and carry out life processes.

Here we've got a bacterium cell, and we can see it contains DNA.

A plant cell.

And a plant cell has a nucleus that contains the DNA.

And here we've got a fungi cell, and the fungi cell contains a nucleus that contains that DNA.

We have some examples there, but we also know we have DNA in animal cells and viruses, and that this DNA is essential for life.

What does DNA contain? Does it contain A, a genetic code, B, amino acids, or C, the nucleus? The correct answer is A, DNA contains a genetic code.

Amino acids are a monomer that join together to form polypeptides or proteins.

The nucleus is where we will find the DNA in some cells such as plants and animal cells.

The nucleus of these cells contains chromosomes that are made of DNA.

Here we have a eukaryotic cell, and in that cell is a nucleus.

In the nucleus are chromosomes, and these chromosomes are made of DNA.

At the bottom, we can see a strand of DNA.

Usually, DNA is made up of two, long polymer chains.

We can see in the image there, polymer chain 1, and also polymer chain 2, and these polymer chains wrap around each other to form a double helix structure.

You can see this double helix structure of DNA shown in that image.

How many polymer chains does DNA contain? Is it A, 2, B, 20, C, 200, or D, 2,000? The correct answer, A, 2.

There are two polymer chains that wrap around each other to form that double helix structure of DNA.

Each polymer chain is made up of monomers called nucleotides.

So nucleotides are the monomers that join together to make those polymer chains that we find in DNA.

Here we have a model of DNA, and we can see in this model that there are four different nucleotides that join together to make each of those polymer strands in DNA.

Here we've got an example of a nucleotide, and here is a slightly different nucleotide.

And here's another one, and here's our fourth different nucleotide.

And this polymer chain, polymer chain 1, is made from repeating nucleotides, and on the other side, where we've got our other polymer chain, so polymer chain 2, we can see this is also made from repeating inverted, so they're upside down, nucleotides.

What is this monomer of DNA called? Is it A, a ribosome, B, a nucleotide, or C, a mitochondria? The correct answer is B, a nucleotide.

So, DNA is made up of nucleotides.

The nucleotides that make up DNA are made up of a phosphate, a sugar, and a nitrogenous base.

Here we can see a diagram of a nucleotide, and we can see the phosphate, the sugar, and the nitrogenous base.

There are four different nucleotides that we can get, and that's because there are four different bases.

They are: adenine, which we represent with an A, thymine, T, guanine, G, and cytosine, C.

Each polymer chain in DNA has a sugar phosphate backbone, so this contains the sugar and the phosphate parts of the nucleotides.

In the diagram, we can see a section of DNA, and you can see you have the sugar part of a nucleotide and the phosphate part, and these form the backbone of our polymer chain.

So we can see there we have the sugar and phosphate part, and this repeats throughout that polymer chain.

We have just looked at how the nucleotides bond together, and we have that sugar phosphate backbone of a polymer chain.

But what holds those two polymer chains together within our DNA molecule? The two polymer chains in DNA are held together in a double helix structure by bonding between the bases in the nucleotides.

We can see the bonding between those bases shown in that image of the structure of DNA.

Time for a quick check for understanding.

The nucleotides in a single polymer chain of DNA are held together by.

A, bonding between the sugar and base, B, bonding between the bases, C, bonding between the sugar and phosphate, or D, bonding between the phosphate and base.

What is it that is holding those monomers, those nucleotides together, within a single polymer chain of DNA? The correct answer is C, bonding between the sugar and phosphate.

It's bonds between the sugar and phosphates of those nucleotides that keeps them together in a single polymer chain of DNA.

Those two polymer chains are then held together by bonding between the bases.

Well done, if you got this question correct.

Time for our final practise task of today's lesson, and you need to describe the structure of DNA.

Include the following keywords in your answer: polymer, monomer, helix, and nucleotide, and there's an image there of DNA to help you.

Pause the video now, have a go answering this question, then come back when you're ready to go over the answer.

Let's see how you got on with describing the structure of DNA.

DNA consists of two polymer chains held together in a double helix structure.

The polymer chains are made from four different monomers known as nucleotides, and the polymer chains have a sugar phosphate backbone and bond to each other via the bases which are A, T, G and C.

Well done if you got that question correct.

You might like to pause the video now, and just add any details to your answer that you missed.

We have reached the end of today's lesson on natural polymers.

We're just gonna summarise some of the key points that we've covered in today's lesson.

Natural polymers are important for life.

DNA contains two polymer strands, and these are made from monomers called nucleotides.

The carbohydrates, starch and cellulose are made from the monomer glucose.

Amino acids contain two functional groups, the carboxylic acid functional group, and the amine functional group, and these can join together to form polypeptides and proteins.

Well done for all your excellent work in today's lesson.

I've really enjoyed the lesson, I hope you have too, and I hope that you're able to join me for another lesson soon.