The picture above shows a few examples of amino acids- they all have different properties that depend on their structure, for example histidine is often found in the active site of enzymes- ie. The bit that carries out the proteins job. Below is the structure of an amino acid. When these are joined together to make a protein, the amino and carboxyl groups become chemically fused to make the backbone of the protein.
The sequence of amino acids in a protein is known as the primary structure. The secondary structure is how the amino acid chains are structured in the protein. An alpha helical secondary structure involves the coiling of the chain while a beta-sheet structure involves folding of the chain into parallel layers running in opposite directions. The tertiary structure of the protein describes its overall three dimensional structure, ie. How the individual secondary structure components all fold up together to form a compact protein often consisting of more than one domain. The quaternary structure refers to how in some cases more than one polypeptide chain can interact non-covalently to form a whole protein.
So now you know what a protein is made up of, but what is the point of them? Well proteins carry out pretty much every job in our body. The dry weight of every cell is around half protein -they are important for the structure of the cell, for allowing recognition between different cells, and they are involved in a huge number of chemical reactions in the body. Some proteins carry molecules around the body, some protect other important proteins from damage, some modify other proteins, some are involved in signaling within the cells, others are involved in making new proteins, and the list goes on. The group of proteins involved in chemical reaction within a cell are particularly interesting- these proteins are known as enzymes and are discussed in more detail in the What are enzymes? page.
