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Human Body Study

Endoplasmic Reticulum

An extensive network of membranes folded throughout the cytoplasm — the cell’s manufacturing and processing system. Often shortened to ER.

Schematic of a generalized animal cell A labelled cross-section of a generalized animal cell. Each label links to the article for that part: the cell membrane, cytoplasm, nucleus, mitochondria, ribosomes, endoplasmic reticulum, Golgi apparatus, lysosomes and cytoskeleton. rough ER smooth ER Cell membrane Mitochondria Nucleus Endoplasmicreticulum Lysosomes Cytoskeleton Cytoplasm Ribosomes Golgi apparatus A generalized animal cell — schematic, not to scale. Not every cell contains every structure.

Two kinds

Section titled “Two kinds”
  • Rough ER — studded with ribosomes; builds and folds proteins, especially those bound for membranes or export.
  • Smooth ER — no ribosomes; makes lipids, processes fats, stores calcium, and detoxifies chemicals (very active in liver cells).

What it does

Section titled “What it does”
  • Synthesis — produces proteins and lipids.
  • Folding and quality control — shapes new proteins correctly and rejects faulty ones.
  • Transport — packages finished molecules into bubbles (vesicles) for delivery to the Golgi apparatus.

Key idea

Section titled “Key idea”

The ER is the first stop on the cell’s assembly line — where most proteins and lipids are made and prepared for shipping.