Proteins Flashcards
Describe the various classes of naturally occuring amino acids.
Aliphatic (linear side chain, simplest in glycine.
Aromatic (cyclical aromatic ring side chain eg phenylalanine)
Sulphur containing (eg methionine)
Basic (unusally positively charged, polar and hydrophilic. Side chain contains nitrogen eg lysine)
Acidic (carboxylix acid group in side chain, it can lose a proton to become negative eg aspartate)
Uncharged polar (side group contains a hydroxyl group and is water soluble eg serine)
Other (round like structure but not cyclical eg proline)
Describe the function of proteins
They are important in cell signalling, immune responses, cell adhesion and the cell cycle. Eg myosin and actin in muscle.
Primary structure
The sequence of amino acids in a polypeptide chain, joined by covalent peptide bonds with the loss of H2O.
Secondary structure
The spatial arrangement of amino acid residues that are near each other in the sequence joined by H bonds.
Tertiary structure
The spatial arrangement of amino acid residues that are far apart in a linear sequence held by ionic interactions, van der waals, H bonds, hydrophilic interactions and di-sulphide bridges.
Quaternary structure
The spatial arrangement of individual polypeptide chains in a multi-subunit protein held together by non-covalent interactions.
Properties of quaternary structure
The sub-units may either function independently or may work together e.g. haemoglobin, the binding of O2 to one subunit alters it’s shape and that of the other subunits so increases the affinity other subunits have for O2.
Fibrous proteins
The overall shape and structure of these proteins is determined by the secondary structure. They serve structural functions in the body. Eg Collagen and elastin.
Globular proteins
Haemoproteins that contain haem as a tightly bound prosthetic group. Functions include enzymes, hormones, transporters, stock of a/as and structure. Eg actin amd tubulin.
