STEPTRACKERBIOCHEMISTRY + CELL BIOLOGY | CELL BIOLOGY | HIGH-YIELD REVIEW

Organelles: ER, Golgi, Peroxisome & Proteasome

Each compartment has a job — and a disease when that job fails. Learn which cells are packed with which organelle.

FOCUS ON
RER = secretory and membrane proteins (plasma cells, goblet cells, Nissl bodies in neurons). SER = steroids, detoxification, glycogen release (adrenal cortex, gonads, hepatocytes). Golgi = modify and sort (M6P). Peroxisome = very-long-chain and branched fatty acid oxidation, plasmalogens — Zellweger, Refsum, adrenoleukodystrophy. Proteasome = ubiquitin-tagged protein disposal.
ORGANELLE
FUNCTION
CELLS RICH IN IT
DISEASE · CLUE
Rough ER
Synthesis of secretory, membrane and lysosomal proteins; N-glycosylation
Plasma cells, pancreatic acinar cells, goblet cells, neurons (Nissl bodies)
Nissl bodies are RER — not in axons
Smooth ER
Steroid synthesis, drug detoxification (CYP450), glucose-6-phosphatase
Adrenal cortex, Leydig cells, ovary, hepatocytes
Barbiturates/alcohol → SER hypertrophy (enzyme induction)
Free ribosomes
Cytosolic, nuclear, peroxisomal and mitochondrial proteins
All cells
—
Golgi apparatus
Modifies N-oligosaccharides, adds O-sugars, sulfates proteoglycans, M6P tag, sorting
Secretory cells
I-cell disease (2.04)
Lysosome
Acid hydrolases degrade macromolecules and organelles (autophagy)
Macrophages, neutrophils
Storage diseases (10.05) · Chédiak-Higashi (trafficking)
Peroxisome
β-oxidation of very-long-chain FA, α-oxidation of branched (phytanic) acid, plasmalogen synthesis, catalase (H₂O₂)
Liver, kidney
Plasmalogens = key myelin phospholipid
Zellweger syndrome
AR · PEX genes
Peroxisomes fail to form (protein import defect)
Hypotonia, seizures, hepatomegaly, craniofacial dysmorphism, early death
↑ VLCFA and phytanic acid
Refsum disease
AR
Can't α-oxidize phytanic acid
Retinitis pigmentosa, neuropathy, ichthyosis, shortened 4th toe, deafness
Diet low in phytanic acid; plasmapheresis
X-linked adrenoleukodystrophy
ABCD1 transporter defect → VLCFA can't enter peroxisome
Boys: adrenal insufficiency + progressive white-matter loss
↑ VLCFA in plasma
Proteasome
Barrel complex degrading ubiquitin-tagged proteins
All cells
Defects linked to Parkinson (parkin = ubiquitin ligase) · bortezomib
Mitochondria
Oxidative phosphorylation, TCA, β-oxidation, intrinsic apoptosis, maternal DNA
Muscle, brain, kidney tubules, brown fat
Mitochondrial myopathies (5.09)

Mechanism — where fatty acids are burned

Long-chain FA
→
Carnitine shuttle
→
Mitochondrial β-oxidation
Very-long-chain (> C22) FA
→
ABCD1 import
→
Peroxisomal β-oxidationShortened → mitochondria
Phytanic (branched) acid
→
Peroxisomal α-oxidationRefsum if absent

Peroxisomal disorders compared

DISEASE
DEFECT
BUILDUP
CLUE
Zellweger
No peroxisomes
VLCFA, phytanic acid
Floppy newborn, liver, face
Refsum
α-Oxidation
Phytanic acid
RP, neuropathy, ichthyosis
X-ALD
ABCD1 transporter
VLCFA
Boy, Addison + white matter

How it's tested

COMMON CONFUSIONSteroid-making cells are rich in SER, protein-secreting cells in RER. The adrenal cortex makes steroids (SER); the medulla makes catecholamines in granules.
THE TRAPNissl substance disappears after axonal injury (chromatolysis) — it is RER in the cell body and dendrites, absent from the axon hillock and axon.
YOUR APPROACHAsk what the cell exports → organelle that must be abundant → its disease when absent.

If you see… think…

Plasma cell with abundant cytoplasmic organelle → RER
Leydig or adrenal cortical cell → SER (steroids)
Nissl bodies → RER in neuronal cell bodies
Floppy newborn with hepatomegaly, ↑ VLCFA → Zellweger
Retinitis pigmentosa + ichthyosis + neuropathy → Refsum (phytanic acid)
Boy with Addison disease and white-matter loss → X-linked adrenoleukodystrophy
Organelle with catalase and plasmalogen synthesis → peroxisome
Ubiquitin-tagged protein disposal → proteasome
Chronic alcohol use induces drug metabolism → SER hypertrophy (CYP450)
Glucose-6-phosphatase location → SER (ER lumen)