Monomers are small molecules present in compounds. They are mostly organic but can also be synthetic. The easy availability of cheap chemicals and diversifications during industrialization led to an increased interest in monomers and the rise of the plastic age.

Every living organism on this planet has cells that consist of several molecules like nucleic acids, polysaccharides, and proteins. These large molecules are made up of smaller structures called monomers. These monomers combine to form polymers through a process called polymerisation. 

Amino acids polymerise to form proteins. Amino acids contain hydrogen, amine, R-group, and the carboxyl group. These elements form various bonds covalently to produce proteins. These bonds are called peptide bonds.  

Scientists are now able to produce similar protein-like polymers through the polymerisation of amino acids under controlled conditions. Similar abiotic polymerisation of nucleotides and sugars is also possible and has helped us develop various biomolecules. Owing to the highly polar and reactive protein structure, we can also make different biopolymers using polymeric materials. 

Carbon, hydrogen, oxygen, nitrogen, and sulfur form covalent bonds to produce proteins. Globular proteins occur when about one-third of residues turn in loops and reverse the polypeptide chain. These loops are known as the third type of ordered secondary structure.

Apart from this, there are four main structures of proteins:

1. Primary structure: Protein consists of both amino acid sequence and hydrogen bonds. The amino acid sequence makes up the primary structure of a protein molecule. The hydrogen bonds play a role in determining the secondary structure of the protein. 
2. Secondary structure: The alpha-helix structure of a protein is its secondary structure. In this structure, a single protein chain forms a coiled spring-like shape. The hydrogen bonds maintain this coil-like structure.
3. Tertiary structure: A secondary folding can occur due to the peptide bond interaction with sulfur atoms present in some proteins. This interaction can change the structure and affect the function of the proteins.
4. Quaternary structure: The spatial distance and relationship between the protein's amino acids will determine the quaternary structure.

There are about 20 kinds of amino acids that serve as building blocks for the protein. 

Non-essential amino acids are acids that can be synthesised in the body. The amino acids which cannot be synthesised in the body are called essential amino acids. A balanced diet can help in the procurement of essential amino acids for the body. 

These amino acids are further classified into hydrophobic, hydrophilic, and neutral categories.

The names of these 20 amino acids are as follows:

1. Valine (Val)
2. Leucine (Leu)
3. Isoleucine (Ile)
4. Methionine (Met)
5. Phenylalanine (Phe)
6. Cysteine (Cys)
7. Asparagine (Asn)
8. Glutamic acid (Glu)
9. Glutamine (Gln)
10. Histidine (His)
11. Lysine (Lys)
12. Arginine (Arg)
13. Aspartic acid (Asp)
14. Glycine (Gly)
15. Alanine (Ala)
16. Serine (Ser)
17. Threonine (Thr)
18. Tyrosine (Tyr)
19. Tryptophan (Trp)
20. Proline (Pro)

The chapter Biomolecules in class 11 defines and states the uses of monomers and polymers. The process of polymerisation is also thoroughly explained in it.

The chapter Biomolecules in class 12 defines and explains the structure and functions of proteins and amino acids.

[Image courtesy: NCERT]