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Monomers and Polymers

Ever wondered how your body is able to digest, store information, or manipulate everything? Macromolecules in your body carry out vital functions needed by cells and are essential to these processes. Macromolecules consist of joined monomers that form polymers. 

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Monomers and Polymers

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Ever wondered how your body is able to digest, store information, or manipulate everything? Macromolecules in your body carry out vital functions needed by cells and are essential to these processes. Macromolecules consist of joined monomers that form polymers.

Definition of a monomer

Monomers are small molecules that form larger molecules called polymers.

  • Mono- means 'one' or 'single', so monomers are single, individual units.

  • These can be one single molecule or a combination of units.

  • It is helpful to remember that monomers are simple molecules and the smallest repeating units in polymers.

Examples of monomers include glucose, amino acids and nucleotides.

Definition of a polymer

Polymers are molecules made from monomers that join together.

  • Polymers are very large molecules made of single, similar repeating units (monomers).

  • Poly- means 'many' or 'multi-', meaning that a polymer consists of many monomers.

Examples of polymers include glycogen, DNA and insulin.

Differences between monomers and polymers

A monomer is a molecule that can chemically bond with other molecules to form a longer chain. While a polymer is the longer chain, made up usually of an unspecified number of monomers. These are the differences that set apart the smaller molecules - monomers, and larger molecules - polymers:

Differences

Monomers

Polymers

SIZE

Small, simple molecules

Large, complex molecules

BUILDING BLOCKS

Can have a combination of units.

Monomers are small units that are the building blocks of polymers.

Contain monomers, single repeating units, as their building blocks.

What are the three categories of monomers?

There are three categories of monomers: monosaccharides, amino acids, and nucleotides.

1. Monosaccharides

When monosaccharides join together, they form polymers that are polysaccharides (complex carbohydrates). For this reason, monosaccharides are monomers of complex carbohydrates, such as starch and cellulose.

Monosaccharides are organic molecules. They contain carbon, hydrogen, and oxygen atoms. Examples include glucose, fructose, galactose, ribose (found in RNA), and deoxyribose (found in DNA).

Figure 1 shows the ring structures of each of synthesis important monosaccharide.

Monomers and Polymers, Ring structures of monosaccharides glucose, fructose, galactose, deoxyribose, and ribose, StudySmarterFig. 1 - Ring structures of monosaccharides glucose, fructose, galactose, deoxyribose, and ribose

2. Amino acids

Amino acids are the building blocks of polypeptides (proteins). For this reason, amino acids are monomers of proteins, such as haemoglobin and insulin.

Amino acids are also organic molecules. They contain carbon and hydrogen, but oxygen and nitrogen as well.

Amino acids consist of:

  • a central carbon atom

  • to amino group

  • a carboxyl group and

  • one organic R group that is unique to each amino acid.

Examples of amino acids include alanine and valine.

Monomers and Polymers, Structure of amino acid with its relevant groups, StudySmarterFig. 2 - Structure of amino acid with its relevant groups

3. Nucleotides

Nucleotides join together to form polynucleotides (nucleic acids). Therefore, nucleotides are monomers of nucleic acids (DNA and RNA).

Nucleotides are also organic molecules, as they contain carbon and hydrogen. They also contain oxygen, hydrogen, and one to three phosphates.

Nucleotides have a pentose (a five-carbon sugar) as a base, which is attached to a nitrogenous base and a phosphate group.

Nucleotides in DNA have deoxyribose as a base, while the ones in RNA have ribose.

Figure 3 illustrates a simplified structure of a nucleotide. Note the phosphodiester bond on the third carbon atom, linking it to the next nucleotide in the chain.

Monomers and Polymers, Simplified structure of a nucleotide, StudySmarterFig. 3 - Simplified structure of a nucleotide

Figure 3. Simplified structure of a nucleotide with a phosphodiester bond linking it to the next nucleotide.

Source: commons.wikimedia.org

What are the three categories of polymers?

Polymers are divided into three groups: polysaccharides, polypeptides, and polynucleotides.

They all have one clear property in common: Their long chains consist of repeating similar units - monomer.

1. Polysaccharides (Complex carbohydrates)

Polysaccharides are polymers composed of multiple monosaccharides. Complex carbohydrates are polysaccharides: starch, glycogen, and cellulose. All three are composed of repeating units of glucose. Figure 4 shows the complex branched structure of polysaccharide glycogen. Individual repeating circles are glucose molecules.

Monomers and Polymers, Complex branched structure of polysaccharide glycogen, StudySmarterFig. 4 - Complex branched structure of polysaccharide glycogen with individual glucose units joined together

2. Polypeptides (proteins)

Polypeptides are composed of monomers that are amino acids. Proteins are polypeptides. Examples of polypeptides include hemoglobin , insulin and keratin . Take a look at Figure 5, which illustrates the primary structure of a protein, a polypeptide. Similar to the image above, individual circles represent amino acids.

Monomers and Polymers, Structure of a protein, a polypeptide, StudySmarterFig. 5 - The primary structure of a protein, a polypeptide

3. Polynucleotides (Nucleic Acids)

Polynucleotides are composed of monomers that are nucleotides. Nucleic acids are polynucleotides. Biologically, the most essential polynucleotides are DNA and RNA .

Let's study the image below. It shows one part of the DNA structure. Can you spot individual nucleotides?

Monomers and Polymers, One part of DNA structure, StudySmarterFig. 6 - One part of DNA structure with nucleotides joined in a chain

MonomersPolymers
Monosaccharides Polysaccharides (complex carbohydrates)
Amino acidsPolypeptides (proteins)
NucleotidesPolynucleotides (nucleic acids)

There are four major biological macromolecules: carbohydrates, proteins, nucleic acids, and lipids.

So what about lipids? Why are lipids not mentioned here? Lipids are not polymers, and fatty acids and glycerols are not monomers. Yes, lipids are composed of smaller units (a combination of fatty acids and glycerol), but these units do not form repetitive chains. As a result, unlike polymers, lipids contain a chain of non-similar units.

How do monomers join together to form polymers?

Monomers bond together with chemical bonds to form polymers. This process is called polymerization.

Two different reactions form and break polymers: condensation reaction and hydrolysis reaction.

Let's have a look at what these two reactions look like on a diagram. Figure 7 illustrates a simplified diagram of how condensation and hydrolysis reactions make and break polymers. Note the addition and removal of water molecules.

Monomers and Polymers, Simplified diagram of condensation and hydrolysis, Study SmarterFig. 7 - Simplified diagram of condensation (dehydration synthesis) and hydrolysis of monomers and polymers

1. Condensation reaction

'Dehydration synthesis' is a synonym for condensation reaction. 'Dehydration' literally means the removal of water (or loss of water - think what happens when you say you are dehydrated). 'Synthesis' in biology refers to the creation of compounds (biological molecules).

As seen in the diagram above (a), monomers need to join together for a polymer to form. Monomers join with chemical bonds called covalent bonds. These bonds form with the help of water, which is removed during the reaction (it is "lost").

Three covalent bonds form between various monomers: glycosidic, peptide, and phosphodiester bonds.

As a result, we can conclude that:

  • Condensation of monosaccharides results in the formation of polysaccharides. The bond that forms between monosaccharides is a glycosidic bond.

  • Condensation of amino acids results in the formation of polypeptides. The bond that forms between amino acids is a peptide bond.

  • Condensation of nucleotides results in the formation of polynucleotides. The bond that forms between nucleotides is a phosphodiester bond.

2. Hydrolysis reaction

Above, in Figure 7 (b), you can see that polymers are broken down during the reaction of hydrolysis.

Hydrolysis is the opposite of condensation. Here, the covalent bonds between monomers are broken, not created, with the help of water. That is why we say that water is added to this reaction.

Similar to condensation, we can conclude that:

  • Hydrolysis of polysaccharides results in the breaking down of the molecule into its monomers: monosaccharides. The covalent glycosidic bonds between monosaccharides break down.

  • Hydrolysis of polypeptides results in the breaking down of the molecule into its monomers: amino acids. The covalent peptide bonds between amino acids break down.

  • Hydrolysis of polynucleotides results in the breaking down of the molecule into its monomers: nucleotides. The covalent phosphodiester bonds between nucleotides break down.

As already mentioned, lipids are not polymers. However, they are formed during condensation and broken down during hydrolysis. Therefore, condensation of fatty acids and glycerol results in the formation of lipids. Equally, hydrolysis of lipids results in the breaking down of lipids into fatty acids and glycerol.

Monomers and Polymers - Key takeaways

  • Monomers are simple molecules and the smallest repeating units in polymers.

  • Polymers are very large molecules (macromolecules) that are made from single repeating units (monomers).
  • There are three categories of monomers: monosaccharides, amino acids, and nucleotides.
  • There are three categories of polymers: polysaccharides, polypeptides, and polynucleotides.
  • Condensation is a reaction during which covalent bonds form between monomers that join to form polymers. Covalent bonds that form between various monomers during condensation are glycosidic, peptide, and phosphodiester bonds.
  • Hydrolysis is a reaction during which covalent bonds between monomers break down, which results in the breaking down of polymers into monomers.

Frequently Asked Questions about Monomers and Polymers

Differences between monomers and polymers: 

  • Size: Monomers are small, simple molecules, while polymers are large, complex molecules. 
  • Building blocks: Monomers can have a combination of units. Monomers are small units that are the building blocks of polymers. Polymers have monomers, single repeating units, as their building blocks.

Polymers are built of monomers. Monomers are the building blocks of all polymers.

The examples of the relationship between monomers and polymers: 

  • Polysaccharides are polymers and their monomers are called monosaccharides. Complex carbohydrates are polysaccharides.
  • Polypeptides are polymers and their monomers are amino acids. Proteins are polypeptides.
  • Polynucleotides are polymers and their monomers are nucleotides. Nucleic acids are polynucleotides. 

Monomers of carbohydrates are monosaccharides.

Monomers of proteins are amino acids.

Monomers of nucleic acids are nucleotides.

Test your knowledge with multiple choice flashcards

Which of the following is not a carbohydrate?

Which of these reactions is the opposite of a condensation reaction?

All condensation reactions remove water.

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