BIOSYNTHESIS AND REGULATION OF PEPTIDES
Peptide structure is directly coded in the genome it is in some ways simpler for a cell to produce a petide than a conventional neurotransmitter like acetylcholine to do the later it had to produce a series of carrier molecules (to collect the necessary precursors and store the product) and enzymes to perform the synthesis to make a peptide it has to produces a precursor protein in which the peptide sequence is embedded along with specific proteolytic enzymes that excise the active peptide the precursor protein is packaged into vesicles at the point of synthesis and the active peptide is formed in situ ready for release there is no need for special uptake mechanisms for procuring the starting materials and there are in general no mechanisms for recapturing released mediators such as are important for non peptides
proteins synthesised by ribosomes are threaded through the membrane of the rough endoplasmic reticulum where they are conveyed via transport vesicles to the golgi apparatus they are sorted and packaged into secretory vesicles processing (cleavage glycosylation amidation sulphation etc) occurs within the transport and secretory vesicles and the products are released from the cell by exocytosis constitutive secretion (e.g.secretion of plasma proteins clotting factors etc by liver cells ) occurs continuously and little material is stored in secretory vesicles Regulated secretion (e.g. neurosecretion or cytokine secretion ) occurs in response to increased [Ca2+] or other intracellular signals and material is typically stored in significant amounts in an accumulation of secretory vesicles
0 Comments