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Protein Structure & Bonding (Keywords (Primary structure: Sequence of…
Protein Structure & Bonding
Primary structure
Straight chain of amino acids
Determines structure/function of protein
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
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