Mitochondria & Peroxisomes

In today's class, we discussed the role of TOM and TIM complexes in the mitochondria. The TOM (transmembrane of the outer membrane) are proteins found in the outer membrane of the mitochondria. There are many different types that provide movement of proteins through this barrier, and into the interspace membrane. 

http://oregonstate.edu/instruction/bi314/summer09/mito.html

In this pathway, the precursor protein is recognized by TOM 20/22 receptors. Then transferred to TOM 40, the general import pore of the outer membrane, entering the TIM 23. After the protein passes through TIM23 channel, there's hydrophobic halt anchor sequence that blocks the translocation across the inner membrane. Proteins from internal domains are recognized by Oxa1. After transfer, the matrix targeting sequenced is cleaved. The protein reacts with Oxa1 [in the inner membrane]. After this reaction, the pathway is followed by multipass proteins like the ATP/ADP antiporter that lack an N-terminal matrix targeting sequence. The importer proteins are then recognized by TOM70/22, and the proteins pass through the outer membrane via the general import pore. 

On the other hand, peroxisome is an organelle found in the cytoplasm of many cells. It has many functions like reducing enzyme catalase, degrades uric acid/methanol/purines/fatty acids, and many more. In the liver, dolichol and cholesterol are synthesized in the organelle. There are two targeting pathways in peroxisomes: PTS1 and PTS2.