What is a microsome? This site says: > In cell biology, microsomes are vesicle-like artifacts re-formed from pieces of the endoplasmic reticulum (ER) when eukaryotic cells are broken-up in the laboratory; microsomes are not present in healthy, living cells. Whereas this other site says: > Microsome is another name for the smooth endoplasmic reticulum (ER). Are they both correct? Which one is correct?

The first quote is correct. 'Microsome' is more of a _lab term_. This is because, as said they are found (re-formed) after centrifugation and as such aren't seen in an intact cell. Differential centrifugation is a technique used to separate cellular constituents into fractions. To quote,

> The microsomal fraction is the pellet produced when the postmitochondrial supernatant is centrifuged at 50,000g for 60 minutes. Microsomes are small vesicles enclosed by a biological membrane. During centrifugation, the endoplasmic reticulum is fragmented into microsomes

The microsomal fraction may also contain pieces from the plasma membranes apart from those from the ER.

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