proteins

• proteins are comprised of long chains of amino acids joined together by peptide bonds. Polypeptides are synthesised on ribosomes via translation (peptide bonds formed through condensation reactions)
• polypeptides fold into shapes essential to their functions with four levels of protein structure; primary, secondary, tertiary, quaternary
• proteins primary structure describes the order of amino acids in the polypeptide sequence, formed by covalent peptide bonds of adjacent amino acids, and it controls all subsequent levels of protein structures
• proteins secondary structure describes the folding of the chain into repeating arrangements, formed by stabilising hydrogen bonds between non-adjacent amino acids, to form alpha helices (tight coil) or beta-pleated sheet (random coils)
• proteins tertiary structure describes the way a chain folds into a 3D shape, formed by different groups interacting (like ionic and hydrogen bonds), and the overall folding is determined by different side chains (repulsion and affinity)
• proteins quaternary structure describes the presence of more than one polypeptide chain (or prosthetic group) in an active protein. not all proteins will necessarily possess this structure.
• proteins have lots of different roles; structure (collagen), hormones (insulin), immunity (immunoglobulins), transport (haemoglobin), sensation (rhodopsin), movement (actin) and enzymes (catalase)
• denaturation is when the protein structure changes and loses its biological properties, like losing its tertiary structure = loss of biological activity (tightly folded protein to an unfolded protein after denaturation)
• denaturation occurs as a result of either thermal energy (temperature disrupts the bonds) or pH (affecting the charge, thus changing its solubility and shape)
• pathway for the production of proteins goes from the nucleus → ribosome → ER → vesicle → Golgi apparatus (→ plasma membrane if it wants to leave the cell)