Proteins CAQ

🥛 Proteins Describing and explaining how the different bonds and intermolecular interactions maintain the different levels of protein structures Explaining Hydrogen bonds can be formed between a hydrogen is attached to a highly electronegative atom such as nitrogen and atom making the hydrogen carry a partial positive charge, and a electronegative atom such as oxygen and nitrogen Ionic bonds are formed between oppositely charged R groups of amino acids Hydrophobic interactions is formed between hydrophobic non-polar R groups of amino acids Disulfide bond or bridges are formed only between two cytesine amino acids by oxidation of sulfydryl, SH groups which contains sulphur In collagen, covalent cross links form between lysine residues at C and N ends of adjacent parallel tropocollagen molecules Describing Primary structure: The single polypeptide chain contains a precise number, type and sequence of amino acids held together by peptide bonds within each chain, which determines the chemical interactions and bonds of R groups Secondary structure: The polypeptide chain coils and folds into the regular repeating secondary structures (a-helices/ beta pleated sheets) held together by hydrogen bonds between C0 and NH groups (of peptide linkages) of the amino acids in the main chain  R group not involved) Pr ot eins 1

Tertiary structure: The polypeptide chain further bends, coils and folds, to form a 3D shape / specific tertiary structure, maintained by intramolecular ionic bonds, hydrogen bonds, disulfide bonds and hydrophobic interactions between R groups of amino acids Questions regarding the amino acid residue cysteine Tips Note that only cysteine has a SH R group, making it the only one being able to form disulfide bridges with another cysteine molecule Disulfide bridges unaffected by temperature and PH For temperature, only hydrogen bonds and hydrophobic interactions are disrupted (aka weak intermolecular forces between covalent molecules) For pH, only hydrogen and ionic bonds affected Ionic as there is charge, can affect the charge Hydrogen bonds as there it can release H Pr ot eins 2

Compare hydrogen bonds in tropocollagen and alpha helix secondary structure Notes Do not write hydrogen bonds in tropocollagen formed between R groups (very vague) Tropocollagen also forms hydrogen bonds with CO and NH groups in its secondary structure Pr ot eins 3

Structure and properties of haemoglobin Common mistake: Consist of 2 alpha helices and 2 beta sheets Consist of 2 alpha globin and 2 beta globin Structure Properties It is a globular protein and has a quaternary structure compromising of 4 polypeptide subunits consisting of 2 alpha globin subunits and 2 beta globin subunits tightly packed into a tetrahedral conformation, making the structure compact, allowing many haemoglobin molecules to be packed Made up of 4 polypeptides packed in a tetrahedral conformation and held by weak hydrogen bonds which each carry a hae