Eukaryotic Organelles

Secretory Pathway Route

Rough ER -> Vesicle -> Golgi Apparatus -> Secretory Vesicle -> Plasma Membrane.

Signal Sequence

An amino acid tag that directs a translating ribosome to dock onto the Rough ER for the secretory pathway.

Free Ribosomes

Ribosomes floating in the cytosol; synthesize proteins destined to remain in the cytoplasm.

Rough Endoplasmic Reticulum (RER)

Studded with ribosomes. Synthesizes proteins destined for the membrane, secretion, or lysosomes.

Smooth Endoplasmic Reticulum (SER)

Lacks ribosomes. Site of lipid synthesis (phospholipids/steroids) and detoxification of drugs/poisons.

Golgi Apparatus

The cell's "post office." Modifies proteins, sorts them, and packages them into vesicles.

Glycosylation

The addition of carbohydrates to a protein, a major post-translational modification occurring in the Golgi.

Exocytosis

The process by which secretory vesicles fuse with the plasma membrane to release their proteins outside the cell.

Lysosome

The cell's garbage disposal. Contains hydrolytic enzymes functioning at an acidic pH (~4.5) to break down waste.

Autolysis

The rupture of the lysosome, releasing acidic enzymes that trigger apoptosis by digesting the cell from the inside.

Lysosomal Storage Diseases (e.g., Tay-Sachs)

Fatal conditions caused by a missing hydrolytic enzyme in the lysosome, leading to toxic waste buildup.

Peroxisome

Contains hydrogen peroxide (H2O2). Responsible for breaking down very long-chain fatty acids via beta-oxidation.

Mitochondria

Site of ATP production. Exhibits extranuclear inheritance and initiates apoptosis.

Extranuclear Inheritance

Genetic transmission of traits from DNA located outside the nucleus (e.g., Mitochondrial DNA is strictly maternal).

Apoptosis (Mitochondrial Pathway)

Programmed cell death initiated by the release of cytochrome c from the mitochondria into the cytosol.

Cytochrome c

A mitochondrial protein released into the cytosol to initiate apoptosis when a cell is irreparably damaged.

Nucleolus

The dense region within the nucleus where ribosomal RNA (rRNA) is synthesized.