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Lecture 10

BIO120H1 Lecture Notes - Lecture 10: Cell Membrane, Cytoskeleton, Hydrolysis

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Darrel Desveaux

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- How cells communicate with their extracellular environment
BIO241 Lecture 10 Cell Communication
- Developmental responses, e.g. stress, infections
- Unicellular organisms sense signals in environment, e.g. high [nutrients] or
stressful environments, to respond appropriately
- Multicellular organisms require complex signalling networks that are regulated
- E.g. plants are sessile and cannot move away from stress, cells must respond
appropriate so it may survive
- Receptor interact with extracellular
signalling molecules or enter cell
and become intracellular signal
molecule, inducing intracellular
communication from receptor to
effector proteins that will carry out
- Effector proteins may be metabolic
enzymes that alter metabolism, gene
regulatory proteins, e.g.
transcription factors to alter
transcriptional response like a
developmental change, or
cytoskeletal proteins that effect that
shape, polarity, movement of cells
and interactions between other cells
- regulation of growth and replication
of cells
o cancer is a misregulation
o signals can be positive influencing proliferation (EGF and EFGR)
o cancer cells are overexpressed or hyperactive Æ proliferative, many
signals overactive in cancer
o death factors or anti-growth factors knocked out leads to cell proliferation
o signals coming into cells to regulate
- e.g. dictyostelium (slime mold) once stressed, alters morphology and cell starts to
produce cAMP and aggregate towards highest [cAMP] by extending pseudopod
(chemotaxismoving towards high [chemical]) to form slug, going from
unicellular to multicellular then forms fruiting body and produces spores that
allows it to disperse away to new, better environment with no stress
o cells evolve to respond to cAMP
o movement initiated and activated by cAMP, intracellular signalling
cascade from receptors to cAMP
o PH domain required for chemotaxis, localizes to area of cell closest to
cAMP (polarization), reorganization of cells to highest [cAMP] to form
pseudopod (seen with GFP)
- cell surface receptors usually in plasma membrane bind to hydrophilic ligand
o ion channel linked receptors: ligand-gated, found in the membrane, e.g.
regulated by neurotransmitters
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o G-protein-lined receptors:
couple receptors (GPCRs),
largest family of receptors in
animals (>800 genes in
human), involved in
responding to many stimuli, 7
transmembrane domain and
activates with trimeric G-
proteins when activated
o Enzyme-linked receptors:
span membrane once with
cytosolic domain that has
enzyme activity/associated
with enzyme, ligand induces dimerization of receptors in the membrane
and activates catalytic domains in the cytosol which activates signalling
cytokine receptors
o Plant receptors
Enzyme-linked, especially receptor serine/threonine kinases which
phosphorylate Ser/Thr that play roles like development, growth
and disease resistance
Histidine kinases: hormone receptor, ethylene for ripening
Plants only have one G-protein but do have ion channels but not
ligand activated
o Other receptors: receptors that play roles in animal development and
specifying cell types, e.g. Hedgehog, Wnt, Notch receptors,
transmembrane and activate signalling pathways and regulate gene
expression, usually involved in protein degradation to activate signalling
downstream of receptor
- intracellular receptors bind to hydrophobic signalling molecules e.g. hormones
that move through plasma membrane and bind inside, carried by carrier proteins
in the extracellular fluid
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