Endoplasmic Reticulum
You walk into a kitchen while dinner is being cooked. The counter is covered in cutting boards, bowls, and knives. It looks crowded and messy. But an hour later, the meal is on the table, the dishes are in the sink, and the counter is bare again. Things land on a work surface only when there is work to do. They stay while they are useful, and they move on when the job is finished.
The endoplasmic reticulum is a folded network of membrane running through the cell. The rough part is studded with ribosomes making proteins that will end up in a membrane or be sent out of the cell. The smooth part has no ribosomes and makes fats, stores calcium, and in liver cells helps break down drugs. The memory line says "Rough ER is rough because it's covered in ribosomes." This is where the memory line stops being true, because "rough" only describes how it looked in the first electron microscope pictures. The ribosomes are not fixed in place. They attach while making a particular protein and let go when they are done.
Therefore
When you look at a cell diagram, do not picture a frozen sculpture. Look instead for which parts attach and leave as the work gets done.
Keith Porter and Albert Claude, 1945
In 1944, Keith Porter and Albert Claude worked at the Rockefeller Institute in New York. Early electron microscopes could not see through thick tissue, so the two scientists grew chick cells in thin layers on plastic film. On July 6, 1944, Porter teamed up with Ernest Fullam to photograph the cells under an RCA electron microscope. They published the picture in March 1945. Inside the cell they saw a delicate, lace-like network that nobody had seen before. Porter later called it the endoplasmic reticulum. It was the first time anyone saw the folds inside a whole cell.
A small reminder, on a laptop lid or a notebook cover, that cell surfaces are busy workbenches, holding tools only while the work is being done.
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Related patterns
pairs with
Nucleus — Where the Instructions Are Kept
The nucleus sends messenger RNA out to the ribosomes waiting on the endoplasmic reticulum.
extends to
Cell Membrane — What Comes In and What Goes Out
Proteins made on the rough endoplasmic reticulum are delivered directly to the outer membrane.
contrasts with
Mitochondrion — Powerhouse of the Cell
Mitochondria produce fuel, while the endoplasmic reticulum consumes it to build fats and proteins.