《食品化学 Food Chemistry》课程教学课件（讲稿，英文版）Primary sequence

Primary sequence •The order of amino acids in a protein is genetically determined •Contains all the information to assume its correct 3-D structure

Primary sequence •The order of amino acids in a protein is genetically determined •Contains all the information to assume its correct 3-D structure

Peptides

Peptides

Primary structure z The oxygen and hydrogen of the CO-NH group are in the trans position as consequence of the stabilization resonance z α-carbon atoms are the only ones that may rotate freely z -NH- group does not protonate z Polypetidic chain may be presented by a series of rigid planes separated by HCR- groups

Primary structure z The oxygen and hydrogen of the CO-NH group are in the trans position as consequence of the stabilization resonance z α-carbon atoms are the only ones that may rotate freely z -NH- group does not protonate z Polypetidic chain may be presented by a series of rigid planes separated by HCR- groups

Protein Folding z Balance between Chain entropy and Solvent Entropy z Non-covalent interactions – Steric restraints: bulky side chains – Hydrogen bonding – Interchain electrostatic interactions – Hydrophobic interactions – Disulfide bonds

Protein Folding z Balance between Chain entropy and Solvent Entropy z Non-covalent interactions – Steric restraints: bulky side chains – Hydrogen bonding – Interchain electrostatic interactions – Hydrophobic interactions – Disulfide bonds

Secondary Structure z Spatial structure the polypeptide chain assumes exclusively along the axis z Native conformation – Minimal free energy z Main structures: – helix – β-structures

Secondary Structure z Spatial structure the polypeptide chain assumes exclusively along the axis z Native conformation – Minimal free energy z Main structures: – helix – β-structures

z Adds new properties to a protein such as flexibility, strength Secondary Structure

z Adds new properties to a protein such as flexibility, strength Secondary Structure

z Each peptide bond is engaged in formation of H￾bonds z Very compact structure – High density that restricts interaction with other molecules z Proteins – Rigid, long, narrow rod – 5-80% content z High stability z Proline – not compatible; interrupts, bending of the chain α-helix

z Each peptide bond is engaged in formation of H￾bonds z Very compact structure – High density that restricts interaction with other molecules z Proteins – Rigid, long, narrow rod – 5-80% content z High stability z Proline – not compatible; interrupts, bending of the chain α-helix

C-terminal end 3.6 amino acid residues per tum .Hbonds ●-Carbon ●Carbonyl carbon Hydrogen ●Nitrogen ●Oxygen Side chain erminal end

β-structure z Pleated sheets z Interchain H-bonds – All peptide bonds participate z Parallel or antiparallel z R-groups – Anti-parallel: sides with either all hydrophillic or hydrophobic chains – Parallel: more uniformly hydrophobic, rarely exposed to solvent z More stable than α-helix z Anti-parallel: associate in barrels – Core is very hydrophobic

β-structure z Pleated sheets z Interchain H-bonds – All peptide bonds participate z Parallel or antiparallel z R-groups – Anti-parallel: sides with either all hydrophillic or hydrophobic chains – Parallel: more uniformly hydrophobic, rarely exposed to solvent z More stable than α-helix z Anti-parallel: associate in barrels – Core is very hydrophobic

β-bends z A chain folds back on itself to form an antiparallel β-sheet z Important to protein structure – Direct chains of proteins to allow proper interactions z Protein folding z 20-45% of total structure of all proteins z proline and glycine are prevalent

β-bends z A chain folds back on itself to form an antiparallel β-sheet z Important to protein structure – Direct chains of proteins to allow proper interactions z Protein folding z 20-45% of total structure of all proteins z proline and glycine are prevalent