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More signal transduction Cell-cell contact via gap junctions or plasmodesmata; signal molecule passes between cells Cell-cell recognition molecule binds to specific receptor; “receptor-ligand interaction”. These ligands are primary messengers What happens next?.
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via gap junctions or plasmodesmata;
signal molecule passes between cells
molecule binds to specific receptor;
What happens next?
produced within the cell
“second messengers” relay the signal from
interior of cell
May trigger cell activity and/or gene expression
Hydrophilic molecules bind to membrane
receptors. Receptor may be found on many
Hydrophobic molecules bind to intracellular
tyrosine kinase receptors
Have similar structures but different amino
Seven transmembrane -helices
N-terminus on extracellular side, C-terminus
on cytosolic side
Large heterotrimeric G proteins mediate
Small monomeric G proteins help regulate
When a ligand binds it (G) releases GDP and
G separates from other subunits. These can
move freely along membrane and bind
to enzymes or other proteins, activating
them. Both the G and G can bind to and
activate different cellular proteins
G protein can hydrolyze the GTP and quickly
revert to inactive state
with different cellular proteins
Acetylcholine receptors: one “family” are ion
channels (contraction), another are
G protein receptors (relaxation)
What does G protein activation accomplish?
Activation of second messenger system
Levels are elevated
(what is a kinase? Adds phosphate groups
to a particular amino acid)
Growth, proliferation, specialization
“cytoplasmic tail” portion of receptor has several
tyrosines. Proteins are found as separate
peptides in inactive form?
What activates it? You know by now!
are phosphorylated via ATP hydrolysis
“relay” proteins bind to tyrosines, become
These can now move through the cell and
activate other pathways
Think about it: growth, differentiation, etc.
require many different activities
G protein pathways are not as diffuse
activated when a specific molecule binds
example: acetylcholine receptor
in postsynaptic cell
stimulus is electrical, not chemical
Both important in neervous system activity
In nucleus or cytosol
Ligand is small and hydrophobic
Promotes transcription or cell activation
activates the cell, how is the signal