BIOB10 Lecture 6.docx

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15 Apr 2012
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BIOB10 Lecture 6
-FRAP: track diffusion of membrane proteins
-transport across plasma membrane: non polar substances, small substances can
move through the bilayer
-facilitated diffusion is for large polar molecules, go through transporters (proteins
that carry facilitated diffusion, high to low concentration)
-active transport requires ATP to push things across their concentration gradient,
low to high.
-endocytosis: bringing things in to destroy them (hydrolyze, breaks up macro
molecules
-endocytosis is for substances that are too large. Includes: extracellular ligands,
signal receptors that are no longer in use
-endocytosis and phagocytosis: diff is size. Phagocytosis uptakes larger particles
-endocytosis: main time is Receptor Mediated Endocytosis: uptake of specific
extracellular macromolecules
-steps: ligand binds to the receptor, induces a conformational change that tells
clatherin thers something needs to be brought in. forms an early endosome, brought
in the ligand. clatherin falls off. Slow acidification causes the insulin to no longer
have affinity to the receptor. So the receptor pinch’s off, and the insulin keeps going
-the clathrin vesicles aren’t big enough for bigger particles
-phagocytosis is used in unicellular eukaryotes (amoeba), internalizing another
prokaryote (endosymbiosis)
-have capacity to target particles larger than themselves and internalize them
>very energy consuming, requires remodeling of the cell
-pseudopods come out and internalize the particle
-uptake of large matter (bigger then 0.5 micrometers in diameter)
-unicellular eukaryotes use this process for food, multicellular eukaryotes have
specialized cells (macrophage, dendritic cells and neutrophil immune cells) that can
carry out the process.
-they have receptors (Fc) that can bind to antibodies. Very specific. Macrophage
have this Fc receptor that recognizes antibodies
-antibodies (IgG) will coat something foreign (opsonization) and this is recognized
by the Fc receptors
-Fc receptor will bind to IgG that’s covering the bacteria. When a couple of them
bind, it signals the clustering of the Fc Receptors, will cluster into lipid wraps.
signals src. Binding of src causes PI3 kinase to come, adds phosphates to the lipid to
get PIP3. Changed the lipid configuration. Other proteins have a huge affinity for
PIP3. PH is one of these proteins, so it comes too (PH protein domain has a high
affinity to PIP3, all proteins with a PH domain will be recruited). PH proteins cause
cytoskeleton rearrangement.
-all this signaling causes actin to come and bring in the bacteria. Fuse it with
lysosome and it hydrolyzes the bacteria
-some pathogens get in the cell, and then escape the lysosomes and cant be
destroyed. (e.x mycobacterium, salmonella).
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