Protein Structure & Bonding

Primary structure

Keywords

Primary structure: Sequence of amino acids found in a molecule

Secondary structure: Coiling/folding of an amino acid chain as a result of hydrogen bond formation

Tertiary structure: Overall 3D shape of a protein due to hydrogen bonding, disulphide bridges (cysteine), ionic bonding and hydrophobic/hydrophilic interactions

Quarternary structure: Protein consists of more than one polypeptide chain

Straight chain of amino acids

Determines structure/function of protein

Secondary structure

A-helix

36 amino acids per 10 turns of the helix

Held together by hydrogen bonds between the -NH group of one amino acid and the -CO group of an amino acid 4 places ahead

B-pleated sheet

Zig-zag structure folds over on itself

Held together by hydrogen bonds between the -NH group of one amino acid and the -CO group of another amino acid further down the stand

Many hydrogen bonds form, forming stable structures at the optimum pH/temperature

Tertiary structure

Precise shape held together by bonds between amino acids which lie close to each other

Either supercoiled (fibrous) or sperical (globular)

Quarternary structure

Made of more than one polypeptide chain

Makes complete protein molecule

Bonds

Hydrogen bonds: H atoms have a slight positive charge and other atoms have a slight negative charge

Ionic bonds: Between carboxyl and amine groups

Disulphide bridges: Between R groups in cysteine

Hydrophobic/hydrophilic interactions: Causes twisting of the amino acids/changes the shape of the protein