Peroxisomes and Centrosomes

Peroxisomes and centrosomes are two functionally unrelated organelles often grouped together as smaller specialised structures of the cell. The peroxisome is a single-membrane organelle housing oxidative reactions that generate and detoxify hydrogen peroxide and that carry out specific lipid metabolism. The centrosome is a membraneless organelle that organises the microtubule cytoskeleton and nucleates the mitotic spindle.

Definition

Peroxisomes are single-membrane organelles that carry out oxidative metabolism, notably hydrogen-peroxide handling and specific lipid reactions; centrosomes are membraneless microtubule-organising centres, built around a pair of centrioles, that nucleate the cytoskeleton and the mitotic spindle.

Scope

The entry covers two distinct organelles. For the peroxisome it addresses its oxidative metabolism, lipid roles such as fatty-acid oxidation and ether-lipid synthesis, and its biogenesis. For the centrosome it addresses centriole structure, microtubule nucleation, and the duplication cycle that links it to the spindle. It is a cell-biology and histology reference topic, not clinical guidance.

Core questions

• What oxidative and lipid-metabolic reactions are confined to the peroxisome and why?
• How are peroxisomes formed and how do their proteins enter without a vesicular pathway?
• How does the centrosome nucleate and organise microtubules?
• How is centriole and centrosome number controlled across the cell cycle?

Key concepts

• Peroxisomal oxidation and hydrogen peroxide handling
• Peroxisomal fatty-acid oxidation and ether-lipid synthesis
• Peroxisome biogenesis and peroxins
• Peroxisomal membrane permeability
• Centrioles and pericentriolar material
• Microtubule nucleation and the microtubule-organising centre
• Centrosome and the mitotic spindle

Key theories

Centriole duplication control

Centrioles duplicate exactly once per cell cycle in a tightly licensed process; loss of this 'once and only once' control leads to abnormal centrosome number and contributes to genome instability.

Mechanisms

Peroxisomes enclose oxidases that transfer hydrogen to oxygen to form hydrogen peroxide and catalase that disposes of it, and they perform the oxidation of very-long-chain fatty acids and the synthesis of ether phospholipids; their matrix proteins are imported post-translationally by dedicated peroxin machinery rather than through a vesicular route, and the organelle can both grow and divide and form anew. The centrosome, lacking any membrane, consists of a pair of centrioles surrounded by pericentriolar material that recruits the factors which nucleate microtubules; it serves as the cell's principal microtubule-organising centre and, after duplicating exactly once per cycle, templates the two poles of the mitotic spindle.

Clinical relevance

Defects in peroxisome biogenesis or in single peroxisomal enzymes cause inherited metabolic disorders, while abnormal centrosome number and function are associated with genome instability and developmental disorders. This entry describes the normal organelle biology involved and is not a basis for individual diagnostic or treatment decisions.

History

The peroxisome was characterised biochemically by Christian de Duve and colleagues in the 1960s, who recognised the oxidase-and-catalase 'microbody' as a distinct organelle. The centrosome was described by Theodor Boveri in the late nineteenth century as the cell's division centre and a determinant of orderly chromosome segregation, an insight that anticipated later understanding of its role in genome stability.

Key figures

• Christian de Duve
• Theodor Boveri
• Ronald Wanders
• Erich Nigg
• Jordan Raff

Seminal works

• smith2013
• conduit2015

Frequently asked questions

Why are peroxisomes and centrosomes discussed together?

They are grouped as smaller specialised organelles for convenience, but they are functionally unrelated: the peroxisome is a single-membrane metabolic compartment, whereas the centrosome is a membraneless microtubule-organising centre.

What does the centrosome do during cell division?

After duplicating once per cell cycle, the two centrosomes move to opposite ends of the cell and nucleate the microtubules of the mitotic spindle that segregates the chromosomes.