The special cases: glycine and proline.
Amino Acids: Special Cases
Glycine
- Has the simplest R group: a hydrogen atom.
- Glycine’s fake R-group gives it many possible angles of rotation, which makes it unfavorable in some protein structures.
Proline
- The Proline “R group” is a ring structure that includes the amino group and the alpha carbon, which is different from the other amino acids.
- Proline uses a pentagon (an imino ring) to connect the central carbon to the nitrogen atom of the amino group.
- Proline is unfavorable (like glycine) but for the opposite reason: its bulky imino ring constrains its flexibility.