Natural Polymers

If you investigate your surroundings, you will be able to see polymers everywhere. This can be the bags that you use to carry your shopping, the clothes that you use to dress yourself and even the food that you eat. Polymers are types of molecules which are made up of single molecules that are joined together through various bonds, and we will see that there are actually two types; natural and synthetic.

• Firstly, we will explore the differences between synthetic and natural polymers.
• We will then explore polysaccharides, this will include what polysaccharides are, how polysaccharides are formed, as well as exploring the structure of some polysaccharides.
• After this, we will explore polypeptides, this will also include what polypeptides are and how polypeptides are formed – this is only for those taking GCSE Chemistry at the higher tier.
• Finally, we will explore DNA as a polymer, as well as the structure of DNA.

What are Natural Polymers?

A key matter that we first need to discuss is what are natural polymers and how are they different to synthetic polymers. So, first let’s look at what synthetic polymers are, then explore how natural polymers differ.

Synthetic polymers are types of polymers that are not naturally found. Instead, humans have discovered a process in which we can join molecules together to form polymers. We can clearly explore this with a lot of our clothes. If you look at the tag attached to your clothes, you will be able to see what they have been made from, a common material you will see is polyester and this is a type of synthetic polymer. To explore these types of polymers further, you can look at Polymers, Addition Polymerisation and Condensation Polymerisation.

Now that we have explored synthetic polymers, we can deduce their difference from natural polymers. As you can probably tell by its name, they are natural, meaning they naturally occur. Natural polymers are mainly focussed within our bodies and also allows us to explore how our body functions and how it makes it easier for our body to work more efficiently.

Now, let us get right into the two different types of natural polymers!

Polysaccharides

Polysaccharides are a type of polymer that is made from carbohydrates. Now, you may be thinking, why are we using a term that we use for bread or pasta for chemistry? Actually, in Chemistry, or in Science in general, when we talk about carbohydrates we are talking about a molecule that has carbon, hydrogen and oxygen atoms.

We will mostly talk about one sugar which is glucose, this has the formula of C₆H₁₂O₆. A molecule of glucose is called a monosaccharide, and it has a six carbon ring shape, as you can see on the image on your left. Multiple single glucose molecules can join together and make a much larger molecule, and this is what a polysaccharide is. This takes place through a reaction called a condensation reaction whereby H₂O is lost, and a bond called a glycosidic bond is formed.

Structure of polysaccharides

We have explored what the monosaccharide glucose looks like, and how multiple monosaccharides can bond together to form a polysaccharide, so now we can explore what this will look like. In terms of polysaccharides, we can explore this through a few different types. We can first look at starch.

Starch is a sugar that is found in plants and is made of glucose. The main function of starch is to act as an energy storage for plants, as glucose can be used for respiration – but you do not need to know this in so much depth. If you look at the image on the left, you can see multiple 6-sided molecules joined together, some in a straight line and some branched out. As you can see, that multiple monosaccharides have joined together to form a big molecule. This is an example of one structure of polysaccharide.

Cellulose is another example of a polysaccharide. Cellulose is also made from glucose, but it is a different type of glucose than what is used to made starch. As a result, we have different types of bonds in addition to glycosidic bonds, which gives it a different looking structure of parallel lines. Although you do not need to know this in depth, this will help you understand the concept of polysaccharides and their structure.

You must also remember whenever monosaccharides are joined together they not only form a polymer, but also water.

Polypeptides

Polypeptides are also another example of natural polymers. Polypeptides are made from monomers that are called amino acid. If you look at the image on the right, you can explore the structure of an amino acid. You will first notice a carbon in the central, this carbon is attached to 4 different groups. It is attached to a carboxylic acid (COOH), on another side of the carbon it is attached to hydrogen, on the third side it is attached to a basic amine group (NH₂) and finally, it is attached to what we call an ‘R’ group. The reason why we call it, this is because there are many different amino acids, and it is what is linked in the R group section that differentiates them all.

So amino acids, which are monomers, join together to form a polypeptide chain. It is similar to the formation of polysaccharides as a condensation reaction takes whereby H₂O is produces, but instead of a glycosidic bond being formed, a peptide bond is formed.

For polypeptides, we are going to go into a bit more in how polypeptides form. As an amino acid has a basic side and an acidic side, through a base and acid reaction, the base from one amino acid can react with the acid from another amino acid and also why we get H₂O as a product.

DNA

Another example of natural polymers is DNA, which is also known as deoxyribonucleic acid is how we as humans have all our features and is known as being our genetic code, as it codes for our genes. It determines what eye colour we have, influences our height and can even be used to see how we are related to family members. From the sequence of our DNA, the exact sequence of proteins we need is determined.

Our DNA is formed out of monomers called nucleotides. Nucleotides are quite different from monosaccharides and amino acids, as they are not just a single structure. You can see from the image on the right nucleotides have 3 components; a 5-sugar carbon, a phosphate group and one of 4 bases – you do not need to remember this, but it will help you understand have DNA is a natural polymer.

Structure of DNA

DNA is made up of two polynucleotide strands, which form a double helix shape. The two strands run in opposite direction, with the bases being able to form hydrogen bonds together, to keep the strands in place. There are 4 different bases: adenine which can bond with thymine, and guanine which bonds with cytosine.