====== Cell membrane evolution ======

Most* living cells have cell membranes (a.k.a. cell walls) - a containing layer which separates the cell's contents from the outside world.

The membranes were discovered shortly after the invention of the microscope in the 17th century, and their structure was the subject of intense debate for more than two centuries. It's now known that the membranes are formed from a lipid layer and membrane proteins.

How the very first membranes evolved - making 'cells' possible - is currently unknown.

>Cell membranes are a key element of life because they keep the genetic material and metabolic machinery together. All present cell membranes are made of phospholipids, yet the nature of the first membranes and the origin of phospholipids are still under debate.\\ \\ Source : [[https://www.pnas.org/content/118/22/e2101314118|PNAS, 2021 118 (22)]]

The paper cited above notes the discovery of a  phospho-lipid precursor known as //thanolamine //(NH<sub>2</sub>CH<sub>2</sub>CH<sub>2</sub>OH) in a molecular cloud in interstellar space. Raising the question of whether the first lipids suitable for building cell walls may have arrived on Earth from space.

//* Note : //Some bacteria don't have cell walls - see [[content/life_sciences/human_body/cwd_bacteria|Cell wall deficient bacteria]]

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Also see :[[content:life_sciences:life_itself:life_on_earth|Life timespan]] and [[content:life_sciences:life_itself:primordial_soup]]