Protein structure Flashcards
Primary structure
sequence of amino acids in the polypeptide chain
Protein is linear polymer of amino acids it is only functional when the polypeptide chain folds in a defined way to give an individual 3D structure
Secondary structure
𝛼-Helix- partial -ve charge on carbonyl oxygen and partial +ve charge on the amino nitrogen in the peptide bond leads to the formation of a dipole moment, the dipole moment across each peptide bond accumulates in the 𝛼-helix.
β-Pleated sheets- comprise of two or more stretches of polypeptide chain running either parallel to each other
or antiparallel, bonded together by hydrogen bonds between the carbonyl oxygens and amide protons of the peptide bonds in each strand. This forms a sheet-like pleated structure with the amino acid side chains above and below the plane of the sheet.
Tertiary
Units of secondary structure combine to form motifs that then combine to form the tertiary structure
B-turns
Tight turns that link adjacent sections of antiparallel b-sheet where the polypeptide chain undergoes a 180° turn in the space of 4 amino acids. Adjacent segments of parallel b-sheets are connected by much less sterically constrained loops. Pro and Gly are commonly found at b-turns, Gly because it has a small side chain (H) so reduces any steric hindrance and Pro which, because of the ring structure of its side chain and a cis configuration of the peptide bond on the N-terminal side of proline, produces a natural turn in the polypeptide chain.
ψ and ɸ angles
- The rigid nature of the peptide bond (owing to its partial double bond character) means that they behave like planes which can rotate about the aC-C or aC-N bonds, with angles of rotation called ψ (Psi) and ɸ (Phi) respectively. steric clashes between the amide proton and the carbonyl oxygen of one peptide bond with those of the adjacent restrict the number of possible values that the angles can have.
