Table of Contents
Endomembrane System Components Excluding Ribosomes Mitochondria Biology Guide
Eukaryotic endomembrane system includes endoplasmic reticulum, Golgi apparatus, and lysosomes for protein/lipid processing—not ribosomes or mitochondria—essential vesicular trafficking network for General Biology certification.
Question
Which of the following structures are part of the endomembrane system of eukaryotic cells?
A. Endoplasmic reticulum
B. Golgi apparatus
C. Ribosomes
D. Lysosomes
E. Mitochondria
Answer
A. Endoplasmic reticulum
Explanation
The endomembrane system in eukaryotic cells comprises interconnected membrane-bound organelles that process, modify, sort, and transport proteins and lipids through vesicular trafficking, including the rough and smooth endoplasmic reticulum (ER), Golgi apparatus, lysosomes, endosomes, vesicles, and the nuclear envelope, but excluding ribosomes (free or ER-bound protein synthesizers) and mitochondria (independent double-membrane organelles for ATP production via oxidative phosphorylation).
The rough ER synthesizes secretory and membrane proteins into its lumen for folding and initial glycosylation, while smooth ER handles lipid synthesis, detoxification, and calcium storage; these proteins/lipids traffic via COPII-coated vesicles to the Golgi apparatus for further modification (e.g., complex glycosylation, proteolytic cleavage) and sorting into lysosomes (for hydrolytic degradation via acid hydrolases), secretory vesicles, or plasma membrane insertion.
This dynamic network maintains cellular homeostasis, with mitochondria relying on separate import machinery and ribosomes catalyzing translation outside the system proper.