[brasarehot]

When drawing glycerophospholipids, do the two fatty acid residues have to be different or can they be the same? In my book is says R' and R'', but sometimes I see pictures of both R groups being identical.

[Arkcon]

Sure, living things make their lipids with a variety of fatty acid chains, sometimes all the same, sometimes slightly different.  It all depends on the properties the lipid needs to have.  Look at some examples, and see if you can figure out what the differences may be, and how the fatty acid chain may help.  That info could come in handy, come exam time.