4. Proteins Flashcards
Rotation of bonds between amino acids
-Limited rotation around N-C=O as the electrons are shared across (resonance)
-bonds around α-carbon can rotate
Types of diagrams showing protiens
-space-filling
-ball and stick
-backbone
-ribbon
Collagen
Repeating unit of Gly-X-Y, and ringed stucture of proline and hydroxyproline put additional restraint on polypeptide chains
3 possible non-polypeptide components in proteins
-heme group
-metal ions
-glycosylation (saccharides)
When are proteins “native”?
-under physiological condition
-most stable structure
- biologically active structure.
When are proteins denatured?
-Extreme temp breaks non-covalent bonds
-pH changes, ionization state of side-chains change; disrupts of electrostatic and H bonds
-Denaturation reagents e.g. ionic detergents (SDS), hydrogen bonding agents (urea), metal chelators (EDTA) [pull metal ions out to form bonds]
-Reducing agent (dithiothreitol) breaks disulphide bonds
-biologically inactive
Structures lost after folding
- Preproinsulin–> lose signal sequence= proinsulin
- Di-sulfide bonds formed in the proinsulin
- C-peptide bond is lost and leaves a mature insulin, holding the chains by the bonds
Driving force of folded proteins
Unfolded proteins have:
-solvation of hydrophobic domains = neither entropy or enthalpy are favoured
Folded proteins have:
-stronger intermolecular forces as amino acids are in closer prximity = enthalpy favoured
-hydrophobic effect = entrophy favoured
Levinthal paradox
-the large number of degree of freedom in the unfolded protein means the number of possible conformations is astronomical
Conformational entropy in protein folding
-Unfolded protein=high entropy
-formation of 1st interaction = large loss in conformational entropy
-subsequent interactions occur and entropy decreases until no further loss of
Chaperones
Bind to non-native proteins, assist in protein folding
Prion
-a protein infective agent
-caused by mis-folding of a protein
-causes mis-folding of its natural counterpart which goes on to do the same; chain reaction