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Lecture

BIOB10H3 Lecture Notes - Peroxisomal Targeting Signal, Listeria Monocytogenes, Phagocytosis


Department
Biological Sciences
Course Code
BIOB10H3
Professor
Tanya Da Sylva

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Cellular uptake of particles and macromolecules
Two separate categories:
Endocytosis
Phagocytosis
Phagocytosis: Cell eating
Uptake of relatively large particulate matter
(>0.5 mm in diameter)
For food, eg. Unicellular heterotrophic protists
For protection
Eg., macrophage, neutrophilimmune cells
Entrapment (pseudopods) -> engulfment -> Digestion ->
Absorption
Macrophage Receptors on cell binds particle
(bacteria, dead cells, etc.)
macrophages have Fc-receptors that binds to
antibodies (IgG) coating (opsonize) pathogens
Phagocytosis by macrophages is induced in both innate(fast and first) and adaptive
(antibody) immunity
Phagocytosis
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IgG(antibody) binds FcR (Fc receptor that lies on the plasma membrane)
receptors cluster into lipid rafts or microdomains
clustering signals makes tails of Fc come together and helps recruitment of
signalling proteins like src and PI3K
PI3K phosphorylates PI (phosphatidylinositol) on plasma membrane to make PIP3
PI is composed of a Inositol Ring (head) Diglyceride (tail)
PIP3 recruits PH-domain containing proteins: this protein domain has a
high affinity to PIP3 (will bind to it)
PH-proteins bind to actin proteins and cause the underlying actin cytoskeleton to
rearrange
actin rearrangement causes large membrane extensions which engulf particle
IgG-opsonized particle: bacteria/ virus or infected cell that is covered with
antibodies: IgG molecules
recognized by IgG receptors that rearranges the underlying cytoskeleton which
causes engulfment of the particle and internalization of the opsonized particle
particle internalized into membrane-bound compartment called phagosome
Difference between endosome and phagosome: endocytosis is the budding on the
membrane and is pinched off and phagocytosis there are pseudopods, the membrane moves
forwards and takes it in.
Phagosome fuses with lysosome: -> Phagolysosome
Acid hydrolases kill/digest bacteria
Some pathogens escape lysosomes
Not killed and can proliferate in macrophages
Modes of bacteria escaping the lysosomes/phagosome:
1)Escape: Listeria monocytogenes
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