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Lecture 6

Lecture 6 - Receptor Mediated Endocytosis.docx

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Biology 2382B
Robert Cumming

Lecture 6 – Receptor-mediated Endocytosis Looking to get stuff from outside the cell into the cell How can cells internalize the extracellular materials  Phagocytosis o This is generally in a non specific manner – looking at larger things  Pinocytosis o Looking at very small things ( a little fluid) this is also non specific  Receptor-mediated endocytosis - a method of selective internalization of specific extracellular molecules (ligands) : o LDL (Low density lipoprotein) o Transferrin o Hormone s(e.g. insulin) certain glycoproteins, etc. Low Density Lipoprotein (LDL)  LLipids are transported in large, well-defined water soluble complexes (particles called lipoproteins)  LDL contains approximately 88% cholesteryl esters and mediate cholesteoral transport o Lipids don’t like to hang around in an aqueous enviroment – they are hydrophobic!  LDL receptors on plasma membrane (localized clathrin coated pits)  Amphipathic shell – composed of phospholipid monolayer and apolipoprotein  Apolar Core – Hydrophopbicm most ly cholesteryl esters  Apolipoprotein B - important in o Interaction with cell membrane receptors o Transport of the LDL o Associates with the outermembrane Electron Microscopy Data  Take LDL particles o Covalently link with iron binding substance – ferritin  (This is an artificial situation) o Ferriten is electron dense – when doing electron microscopy we need something that’s electron dense so you can visualize it (to interfere with the electrons going through) o Exposed the LDL ferriten to human fibroblasts and would then process them o Starting at the beginning – begin associating with the cell membrane and pits begin to form – the association of the Labelled LDL with the plasma membranes  Associated with proteins called clathrin o The clathrin associated parts of the membrane begin to fold over and form an early endosome (The LDL ferritin particles can be foundinside Lecture 6 – Receptor-mediated Endocytosis o As we move forward the endosome becomes formed and is completely off o The LDL proteins eventually are found inside the smooth-surfaced early endosome  Binding of the LDL to the plasmama membrane and the association of clathrin proteins  Process of invagination to incorporate theLDL proteins inside the newly forming vesicle (Clathrin still associated  Completely pinches off  Over time shedding of the protein Clathrin/AP Coated Vesicles  This is a two layer coat – clathrin and dapter protein (AP) complexes o AP1 – TGN (trans golgi network) o AP2 – PM (plasma membrane)
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