23. Peroxisomes Flashcards
1
Q
Peroxisomes
A
Peroxisomes are involved in the breakdown of long chain fatty acids-
- Branch chain fatty acids and polyamines all through oxidation
- These fatty acids are converted -> medium chain fatty acids, then shuttled to mitochondria where they are broken down to CO2 and H2O.
- Peroxisomes also remove Hydrogen Peroxide (H2O2) common product / toxic substance- from the cell by breaking it down into H2O
- Peroxisomes perform these reactions with the assistance of enzymes – that are held inside their membrane structure
- Peroxisomes utilize oxygen within these reactions.
- Peroxisomes are derived from the Endoplasmic Reticulum and replicated by fission.
- There are at least 32 peroxisomal proteins which participate in peroxisome assembly
- Peroxisomes are spherical organelles, enclosed by a single membrane
- Oxidases located here - oxidize substrates by removing hydrogen atoms that are transferred to molecular oxygen (O2) = producing H2O2
- Peroxidases catalase the break down H2O2 which is potentially damaging to the cell
- These enzymes also inactivate various potentially toxic molecules (prescription drugs - particularly in large/ abundant peroxisomes of liver and kidney cells)
- Other diverse enzymes in peroxisomes complement certain functions of the SER and mitochondria in the metabolism of lipids and other molecules.
- Thus, the β-oxidation of long-chain fatty acids (18 carbons and longer) is accomplished by peroxisomal enzymes that differ from their mitochondrial counterparts.
- Certain reactions leading to the formation of bile acids and cholesterol also occur in peroxisomes.
Peroxisomes form in two ways:
- Budding of precursor vesicles from the ER
- Growth and division of pre-existing peroxisomes
These organelles lack nucleic acids; their enzymes are synthesized on free cytosolic polyribosomes and bear a small signal sequence of amino acids at the carboxyl terminus. This signal is recognized by receptors located in the peroxisomal membrane and the proteins are imported.
