Cell Organelles and Protein Transport: Endomembrane System Overview

Nucleus

Stores DNA, makes rRNA in nucleolus, sends out instructions.

Ribosomes

Build proteins from mRNA instructions (protein factories).

Rough ER

Folds/edits proteins, sticks carbs on them → makes glycoproteins.

Smooth ER

Makes lipids, detoxes drugs/poisons, stores Ca²⁺.

Golgi apparatus

Post office: modifies, sorts, packages proteins into vesicles.

Lysosomes

Break down junk, recycle old parts (little stomachs).

Vacuoles

Storage (water, food, ions).

Transport vesicles

Ubers/shipping boxes moving proteins and lipids around.

Relationship between ribosomes and nucleus

The nucleus holds DNA and makes rRNA in the nucleolus. That rRNA + proteins = ribosomes. Ribosomes read mRNA, which was transcribed in the nucleus, to actually build proteins.

Role of transport vesicles in the endomembrane system

They're the delivery trucks of the cell. Carry proteins and lipids between organelles (ER → Golgi → plasma membrane or lysosome). Keep things separated so molecules don't just float randomly in cytoplasm.

Step-by-step protein pipeline

1. DNA → mRNA in nucleus. 2. Ribosome on rough ER makes the protein. 3. Protein enters Rough ER lumen → folded, sometimes tagged with carbs. 4. Packaged into a transport vesicle → sent to Golgi. 5. Golgi modifies/sorts proteins, puts them in new vesicles. 6. Vesicle either fuses with plasma membrane → secretion out of the cell (exocytosis), OR goes to a lysosome or another organelle for use.