What is chirality? Why is it seen in amino acids?

All amino acids except glycine are chiral molecules. This is also known as optical isomerism.

This means that they form isomers that are non-superimposable mirror images of each other. When drawing these draw a dotted line (the plane) but imagine it is a mirror. Draw the alpha-carbon in the middle and the 4 bonded groups. Then on the other side draw what you would expect the reflection to look like. You can always use an actual mirror the first time or to check your image. The number of isomers depends on the number of chiral carbons (aka chiral centres).

In amino acids, the chiral carbon is the alpha-carbon that is bonded to a hydrogen, amino group, carboxyl group and R-group. As it is bonded to 4 different atoms or groups of atoms it shows chirality and has two optical isomers.

Glycine is the exception because its R-group is a hydrogen so it is not bonded to 4 different groups of atoms and will not produce isomers that are non-superimposable mirror images so does not demonstrate chirality.