Secondary structure, fibrous proteins, tertiary structure

trans conformation

where successive alpha carbon atoms are on opposite sides of the peptide bond joining them

primary structure

the amino acid sequence in a polypeptide chain

secondary structure

shows the influence of side chains in conformation

tertiary structure

one complete protein chain 

quaternary structure

four separate chains of haemoglobin assembled into an oligomeric protein

the alpha-helix

right handed helical conformation has 3.6 residues per turn

pitch of 5.4 angstroms 

dashed lines indicate

hydrogen bonds between C=O and N-H groups that are 4 residues further along the peptide chain

antiparallel beta sheet

neighbouring hydrogen bonded polypeptide chains run in opposite directions

connections between adjacent strands in beta-sheets

• antiparallel strands may be connected by a small loop

• parallel strands require a more extensive crossover connection

higher order alpha-keratin structure

• 2 keratin polypeptides form a dimeric coiled coil

• protofilaments are formed from 2 staggered rows of head to tail coiled coils 

• 4 protofibrils form a microfibril

protofilaments dimerise to form…

protofibril

alpha keratin is rich in

cysteine - form disulphide bonds that cross link adjacent polypeptide chains 

coiled coils - alpha keratin

exhibits a 5.1 angstroms spacing

2 alpha keratin polypeptides each of which form an alpha helix which twist around each other to form a left handed coil - known as a coiled coil structure

GFP

Green Fluorescent protein

GFP structure

Carbonyl carbon atom of Ser forms a covalent bond to the amino N atom of Gly. Elimination of water and oxidation of alpha carbon - beta carbon bond of Tyr to a double bond. Resulting structure contains a system of conjugated double bonds giving the protein its fluorescent properties

post translational modifications

hydroxylation, methylation, lipidation, acetylation, disulphide bond, SUMOylation, ubiquitination, glycosylation, phosphorylation