Download MCB Lecture 7 – Peroxisomes

MCB Lecture 7 – Peroxisomes
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Where do peroxisomes originate?
o ER and pre-existing peroxisomes
Where are the enzymes synthesized (that peroxisomes use)?
o Free Ribosomes
What type of reactions do they mainly carry out?
o Oxidative Reactions
What do they generate during Oxidative Reactions?
o H2O2
What is the significance of catalase in the peroxisome?
o To act as a peroxidase and break down H2O2 (by using it to oxidate
toxins)
What are Peroxins?
o Receptors in the peroxisome membrane that recognize and import
cytostolic proteins.
Proteins contain a signal that allows them to be imported into the
peroxisome. What is this signal?
o SKL (Ser-Lys-Leu)
Where does the SKL Signal Bind?
o The Peroxins
What is the name of the gene that the Peroxin originates from?
o PEX Genes
Does input require ATP?
o Yes
The Peroxisome can be biosynthetic. What is one of the important molecules
it synthesizes?
o It undergoes Plasmalogen synthesis, which is used in Myelin Sheaths
of Axons
The Peroxisome is also degradative. What is one of the important molecules
it breaks down?
o VLCFA (Very Long Chain Fatty Acids)
What type of oxidation does it use to break down VLCFA?
o B-Oxidation
One of the enzymes that Peroxisomes contain is Xanthine Oxidase. What is
this?
o An enzyme that degrades Nucleic Acid Purines (A,G) into Uric Acid
Hyperuricaemia, as a result of too much Uric Acid produced by the enzyme
Xanthine Oxidase, can cause pathology. What is it?
o Gout
o The buildup of Uric Acid in the joints. The direct cause is unknown,
because the enzyme is working fine.
What is Allopurinol?
o An inhibitor of Xanthine Oxidase, which they give patients will Gout so
that less Uric Acid is produced.
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When the Peroxisome synthesizes phospholipids to make Plasmologen for
Myelin Sheaths, what type of bond are the Fatty Acids linked to the Glycerol
Chain by?
o Ether Bonds (NOT ESTER)
Discuss Zellweger Syndrome
o Autosomal Recessive
o Congenital
o Peroxins do not recognize SKL signal on the enzymes so they are not
imported  everything that is usually broken down is not (VLCFA and
no Myelin Sheaths are produced)
o There is an accumulation of VLCFA and LACK OF BILE ACIDS  NO
FAT ABSORPTION
What is one important feature that children with Zellweger’s Syndrome
present with?
o Large Fontanelles (prominent forehead)
Discuss Adrenoleukodystrophy (XALD)
o X-Linked
o Defect of transport of VLCFA to the peroxisome
o VLCFA accumulate, causing myelin breakdown in the brain.