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Peroxisomes are single-membrane-bound organelles with oxidative enzymes that help break down organic molecules.

The shape, number, and size of peroxisomes vary according to the cell type and environmental signals. For example, liver and kidney cells often have lots of peroxisomes because they handle many chemical reactions and detoxification processes.

Peroxisomes can form through the growth and division of existing peroxisomes. They can also form from vesicles that bud off from the endoplasmic reticulum.

Peroxisomal enzymes are imported from the cytoplasm into the peroxisomal matrix through a membrane-associated protein translocation complex involving peroxins or PEX proteins.

These enzymes use molecular oxygen during the beta-oxidation of fatty acids, producing shorter-chain fatty acids and hydrogen peroxide as by-products.

Because hydrogen peroxide is cytotoxic, catalase, a peroxisomal enzyme, rapidly converts it into water and oxygen.

Peroxisomes help with cellular detoxification and lipid metabolism. They also help make lipids such as dolichol and contain enzymes required to make bile acids from cholesterol.