Are all/most/any membranes comprised of lipids from the smooth ER?

Question

I'm attending an introductory high school course to cell biology. Based on my understanding, lipids – the building blocks of membranes – are formed in the smooth ER. Are all/most/any membranes comprised of lipids that are formed in the smooth ER? If not, where do the lipids of membranes come from?

Answer 1

Your statement is true for all eukaryotes where smooth ER is the main source of lipid biosysnthesis. However, in some cases, mitochondria also contribute in synthesizing lipids. Also, lipid biosynthesis being a complex process, a majority of steps get doenin smooth ER, but some certain specific chemical groups are added in other cytosolic locations.

Your statement is not true for prokaryotes as they lack ER and the lipid synthesis in their case takes place in the cytosol.