PH1123 - Protein structure Flashcards
what are proteins?
- large molecules composed of several hundred amino acids
what is the primary structure of a protein?
- the linear sequence of amino acids in a polypeptide chain
what is the polypeptide chain structure? (2)
- not linear
- folds into a biologically active shape
what properties do peptide bond have an impact on?
- the shape and function of proteins
what is the shape of a peptide bond?
- planar and rigid
Is rotation around the peptide bond permitted?
- not possible
what conformation do peptide bonds have and why? (2)
- trans
- steric hinderance between side chain groups favour the trans conformation
what is rotation of the phi and psi torsion angle limited by? (3)
- steric hinderance; bulky groups where side chains cannot approach each other
- ridigity of the peptide bond; ultimately restricts movement
- favourable interactions; with other regions of the peptide chain
what is the secondary structure of a protein?
the coiling and pleating of the polypeptide
what is the favourable interaction that stabilises the a helix?
- each backbone carbonyl oxygen is hydrogen bonded to the peptide nitrogen of the fourth residue along
what is the alpha helix?
- the secondary structure that results when consecutive amino acids residues have similar torsion angles
how many amino acid residues are required for one complete turn of the helix?
3.6
what is the beta sheet?
- a secondary protein structure in which several strands of the peptide backbone are hydrogen bonded to themselves
what stabilises the beta sheet? (2)
- interstrand hydrogen bonds between backbone carbonyl oxygen and amide nitrogens
- side chain interactions can provide additional stabilisation
what are the side chain interactions that can provide additional stabilisation?
- most hydrophobic interactions between small groups
