Peroxisomes Flashcards
Why are peroxisomes not part of the endomembrane system?
peroxisomes are not derived from the endoplasmic reticulum
What is the defining characteristic of peroxisomes?
the presence of catalase, which degrades hydrogen peroxide
How do peroxisomes protect the cell from H2O2?
the generation and degradation of H2O2 occur within the same organelle
What are the five general categries of peroxisomal functions?
hydrogen peroxide metabolism, detoxification of harmful compounds, oxidation of fatty acids, metabolism of nitrogen-containing compounds and catabolism of unusual substances
Hydrogen Peroxide Metabolism:
How do peroxisomes do this?
oxidases that generate H2O2 in peroxisomes transfer electrons plus hydrogen ions from their substances to molecular oxygen, reducing it to H2O2
RH2 + O2 — R + H2O2
Detoxification of Harmful Compounds:
How do peroxisomes do this?
catalase can use a variety of toxic substances as electron donors (ethanol, methanol, formic acid etc.)
Detoxification of Harmful Compounds:
How are peroxisomes important in the detoxification of reactive oxygen species?
the reactive oxygen species like H2O2, O2- and OH are harmful to the cell and the peroxisomes can use enzymes such as superoxide dismutase and catalas to detoxify these reactive oxygen species preventing their accumulation
Oxidation of Fatty Acids:
How do peroxisomes do this?
Peroxisomes contain enzymes that can oxidate fatty acids via beta oxidation to provide energy for the cell
Note: Beta oxidation has a primary product of Acetyl CoA in animal cells which goes to the TCA cycle
Metabolism of Nitrogen- Containing Compounds:
How do peroxisomes do this?
urate oxidase is required to oxidize urate which is a purine
urate + O2 —- allantoin + H2O2
the peroxisomes can then eat up the H2O2 into H20 and O2
the allantoin is further metabolized and excreted by the organism either as allantoinic acid or urea
Catabolism of Unusual Substances:
How do peroxisomes do this?
What are xenobiotics?
Peroxisomes contain enzymes that break down unusual substances that are not ususally originated in the cell
xenobiotics are chemical compounds foreign to biological organisms such as alkanes
What are glyoxysomes?
plant peroxisomes that contain some of the enxymes responsible for the conversion of stored fat to carbohydrate in germinating seeds
Where do the lipids that make up the newly synthesized peroxisomal membrane come from?
some lipids are synthesized by peroxisomal ennzymes
others syntehsized in the ER and carried to the peroxisome by phospholipid exchange proteins
Where are the new enxymes and other proteins that are present in the peroxisomal membrane and matrix syntehsized?
in free cytosolic ribosomes and are incorporated into preexisitng peroxisomes posttranslationally
ATP-dependent process
