Macromolecules: Protein

- There are only four important types of organic molecules in biology: proteins, carbohydrates, lipids and nucleic acids
- These four macromolecules are polymers (= string of repeated units, the individual units of polymers are called monomers) ➟ think about pearls

Protein
- Proteins are polymers of amino acids. There are 20 different amino acids, and they all have the same basic structure (the backbone of the amino acid):

- There are two carbon atoms in the back bone. The first one is bonded to a hydrogen (H), atom on one side and an NH2 group which is called the amino group. The second carbon is bonded to an oxygen (O) (notice the double bond!) and an OH group which is called the carboxyl group. 

- The R part of the molecule is called the side-chain. It differentiates each amino acid. R can be anything from a simple hydrogen atom to a long chain of carbon atoms and its bonds. 

- In the amino acid glycine, R is just a hydrogen atom. In cysteine, R is a carbon and a sulfur (S) atom along with hydrogen atoms.