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Hannah Whitby
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Cards (17)
Cell signalling
The process by which cells
communicate
with each other and
respond
to their environment
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Types of cell signalling
Intercellular
signalling
Intracellular
signalling
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Types of ligands
Low
molecular weight organic compounds
Peptides
and
proteins
Lipids
Sugars
Gases
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Receptor
The
binding
site (usually a protein) for a
ligand
and often the site of signal transduction
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Signal transduction
Converting
one signal
type
to another
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Second
messenger
An
intracellular
molecule generated in response to receptor activation by a ligand (the "
first messenger
") that activates an effector
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Effector
An
enzyme
that responds to a
signal
e.g. to a second messenger
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Cell signalling
is used to
co-ordinate
body processes, respond to specific events, and regulate body functions
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Types of intercellular signalling
Endocrine
Paracrine
Autocrine
Contact-dependant
Synaptic
Gap junctions
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protein coupled receptors (
GPCRs
)
Very common receptor type that binds many
hormones
and
neurotransmitters
One of the most
common
drug targets (1/3 drugs target
GPCRs
)
Passes across the
plasma membrane
seven times (7 α helices)
Activates
G-proteins
on the
intracellular
side of the membrane
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protein
Regulated by binding of
GTP
Comprises
three
different subunits: α, β, γ
There are different
isoforms
(genes) for each of these subunits, and they activate different
intracellular
signalling pathways (effectors)
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protein signalling
1.
Receptor
acts as
guanine nucleotide exchange
factor (GEF)
2.
GTPase activating protein
(
GAP
) hydrolyses GTP to GDP
3.
Receptor
can be desensitized and
downregulated
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Intracellular signalling: cAMP pathway
1.
Adenylyl cyclase
(ACy) converts ATP to
cAMP
2. cAMP activates
Protein Kinase A
(
PKA
)
3. PKA
phosphorylates
substrates
4.
Phosphodiesterase
(PDE)
degrades
cAMP to AMP
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NO (
nitric oxide
) acts
locally
and has a short half-life
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Nuclear receptor signalling
Lipid soluble
signalling molecules penetrate the cell membrane and bind to intracellular receptors (typically transcription factors) to initiate changes in
gene expression
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Nuclear receptor ligands
Steroids
Thyroid hormones
Retinoids
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Nuclear receptors
Act as
homo
or
hetero
dimers
Steroid receptors act as
homodimers
and are found in the cytoplasm, activated upon binding ligand and transfer to the
nucleus
Vitamin D, retinoid &
thyroid
hormone receptors act as heterodimers, are located in the nucleus and repress gene expression in
absence
of ligand
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