2. PROTEIN SORTING /PROTEIN TARGETING
• Protein sorting or transport is the mechanism by which a cell transports protein to the appropriate positions in the
cell or outside of it
• Both in prokaryotes and eukaryotes newly synthesized proteins must be delivered to a specific subcellular location
or exported from the cell for correct activity
• This delivery process is carried out on based on information carried in the protein itself
3.
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6. TARGETING PATHWAYS
Post translational translocation:
Proteins are transported in the cytosol and later to their
destination .this occurs for proteins that go to
mitochondria, chloroplast, or a peroxisome
Co translational translocation:
Synthesized proteins are transferred to an SRP receptor on
the endoplasmic reticulum ,there the nascent protein is
inserted into the translocation complex
7. TARGETING SIGNALS
• Targeting signals are the pieces of information that enable the cellular transport machinery to correctly position a
protein inside or outside the cell
• The information is contained in the polypeptide chain or in the folded protein
• In the absence of targeting signals a protein will remain in the cytoplasm the continuous stretch of amino acid residues
in the chain that enables targeting are called signal peptides or targeting peptides
• There are two types of targeting signals :
the presequences and
the internal targeting peptides
