local spatial arrangement of the polypeptide chain without regard of the structure of the amino acid residues
Tertiary structure (3°)
three-dimensional structure of a polypeptide chain
Quaternary structure (4°)
refers to the spatial arrangement of the protein’s subunit
Homologous
proteins that perform the same function in different organisms
Homologous example
Hemoglobin transports oxygen in all vertebrates
Homologous proteins are divided in
Orthologous
Paralogous
Orthologous
proteins from different species that have homologous a.a. sequences and arose from common ancestral gene
Paralogous
proteins found within a single species that have homologous a.a. sequences. They arose form gene duplication
Paralogous example
α and β globulin chains
Allowed Conformations of Polypeptides Are Indicated by the
Ramachandran Diagram
P (pitch)
the distance the helix rises along its axis per turn
n
number of peptide units per helical turns
In β pleated sheets
hydrogen bonding occurs between neighboring polypeptide chains rather than within one as in α helices
β pleated sheets come in two varieties:
Antiparallel pleated sheet
Parallel pleated sheet
Antiparallel pleated sheet
Neighboring hydrogen bonded polypeptide chains run in opposite directions
Parallel pleated sheet
The hydrogen bonded chains extend in the same direction
A protein’s primary structure dictates
its three-dimensional structure
Levinthal’s paradox
Many conformations are possible for a typical protein that the protein does not have sufficient time to reach its most stable conformational state by sampling all the possible conformations.
Molecular Chaperonins
Proteins that direct the proper folding of proteins due to hydrophobic interactions of side chains that might cause a defect in folding