Biochemistry · Topic
Cell organelles and their metabolism !
Each organelle has its own metabolic job: mitochondria make ATP, lysosomes recycle, peroxisomes oxidise, and the ER and Golgi build.
Updated 2026-11-01
Key facts
- Cytosol: glycolysis, pentose phosphate pathway, fatty acid synthesis, part of gluconeogenesis and of the urea cycle.
- Mitochondrion: Krebs cycle, β-oxidation, respiratory chain, ketogenesis and the first steps of urea and haem synthesis; it has its own DNA (maternal inheritance).
- Lysosome: acid hydrolases (pH ≈ 5) that break down macromolecules; marker enzyme, acid phosphatase.
- Peroxisome: β-oxidation of very-long-chain fatty acids, plasmalogen and bile acid synthesis; catalase as marker.
- Rough ER: secretory and membrane protein synthesis; smooth ER: lipids, steroids and detoxification (cytochrome P450). Golgi: modifies, sorts and tags (mannose 6-phosphate).
In detail
- 1. Nucleus: DNA replication and transcription; the nucleolus makes ribosomes.
- 2. Proteins with a signal peptide enter the rough ER while being made, are glycosylated on asparagines and move to the Golgi in vesicles.
- 3. In the cis-Golgi, lysosomal hydrolases receive mannose 6-phosphate; in the trans-Golgi they are sorted to lysosomes, membrane or secretion.
- 4. Mitochondrial and peroxisomal proteins are made in the cytosol and imported afterwards using their own signals (mitochondrial presequence, PTS1/PTS2).
- 5. The urea cycle, gluconeogenesis and haem synthesis use both the mitochondrion and the cytosol.
- 6. Classic marker enzymes: succinate dehydrogenase (inner mitochondrial membrane), glucose 6-phosphatase (ER), galactosyltransferase (Golgi), catalase (peroxisome), acid phosphatase (lysosome).
Memory aid
Split mitochondria–cytosol pathways: "HUG" (Haem, Urea, Gluconeogenesis).
- Also called
- Compartments of the cell
Clinical notes
- Mitochondrial diseases (MELAS, Leigh syndrome): the organs that use the most energy, brain and muscle, fail.
- Peroxisomal diseases (Zellweger syndrome, X-linked adrenoleukodystrophy): very-long-chain fatty acids accumulate.
- Lysosomal diseases (Gaucher, Tay–Sachs, Hurler, I-cell disease): lysosomes fill with undegraded material.
Pathways
Related conditions
- Zellweger syndrome (Zellweger spectrum)
- MELAS (mitochondrial encephalomyopathy, lactic acidosis and stroke-like episodes)
- Pompe disease (glycogen storage disease type II)
- I-cell disease (mucolipidosis II)
Related
- Membrane structure
- Lysosomal storage diseases
- Mannose 6-phosphate tagging (sending enzymes to the lysosome)
- Peroxisomal oxidation (β- and α-oxidation)
- Electron transport chain and oxidative phosphorylation
- Catalase
Test yourself
Think of the answer, then tap the question to see it.
In which organelle are very-long-chain fatty acids β-oxidised?
In the peroxisome; the mitochondrion then finishes oxidising the shorter products.
Which marker enzyme identifies peroxisomes?
Catalase, which breaks down the hydrogen peroxide they produce.
Why are mitochondrial DNA diseases inherited from the mother?
The embryo's mitochondria come from the egg; those of the sperm are eliminated.
Which pathways use both the mitochondrion and the cytosol?
The urea cycle, gluconeogenesis and haem synthesis.
Educational information, not medical advice. For any symptom, see a health professional.
Sources: Membrane Trafficking (Reactome, 2026); Mitochondrial protein import (Reactome, 2026); Peroxisomal protein import (Reactome, 2026); Transport to the Golgi and subsequent modification (Reactome, 2026); Textbook of Biochemistry for Medical Students, 6th ed. (Jaypee Brothers Medical Publishers (Vasudevan DM, Sreekumari S, Vaidyanathan K), 2011).
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Representative model, for educational purposes only.