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MCB Lecture 7 – Peroxisomes 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. 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.