fungi, protists, and bacteria use...
internal and external signals to regulate a variety of physiological responses (fruiting bodies of slime molds)
dicytostelium
slime mold, lives life as single cells which come together as multicellular structures called fruiting bodies for sexual reproduction
cAMP
cyclic AMP, produced by a cell to guide them based on concentration. cells aggregate and seek an appropriate place to attatch
ligands
small molecules that bind specifically to a larger molecule
signal molecule
binds to receptor protein causing it to change shape, initiating the transduction of the signal
3 stages of cell signaling
reception, transduction, and response
reception
chemical signal binds to a cellular protein, usually at the cells surface. signal could be proteins, small chemicals, or peptides
transduction
binding leads to a change in the shape of the intracellular domain of the receptor, triggering changes along a signal-transduction pathway (chain of phosphorylation)
response
the transduced signal triggers a specific cellular activity, cell may regulate activities in the cytoplasm or transcription in the nucleus leading to cell growth, secretion of molecules, or gene expression
transduction pathways
protein phosphorylation cascades (adding phosphate groups to protein), protein modification (adding a functional group such as a methyl group)
signal receptors
usually plasma membrane proteins, G-protein-linked receptors, tyrosine-kinase receptors, ion-channel receptors
g-protein-linked receptor
7 alpha helixes that span the membrane, interacts with g-proteins on the cytoplasmic side and signal molecules on the extracellular fluid side.
g protein
acts as on-off switch, when ligand attaches to g-protein-linked receptor, inactive GDP diffuses across the cell to gain a phosphate to become active GTP which will travel to an enzyme and cause cell response
tyrosine kinase
triggers more than one pathway at once, kinase transfers a phosphate group from ATP to a protein. extracellular growth factors often bind to tyrosine kinase receptors, nerve growth factor involved in the growth and maintenance of nerve cells
tyrosine kinase receptor is composed of...
an extracellular signal binding site, a single alpha helix spanning the membrane, and an intracellular tail with several tyrosines
dimerization
two ligands bond to receptor polypeptides, which aggregate forming a dimer (activating tyrosine regions, but still not phosphorylated)
phosphorylation
kinase transfers a phosphate from ATP to each tyrosine, creating a fully activated and phosphorylated tyrosine kinase
activation
specific relay proteins are activated, triggering many other different transduction pathways
ligand gated ion channels
protein pores that open or close in response to a chemical signal. this allows or blocks ion flow (NA+ Ca2+). binding a ligand to the extracellular side opens the channel, changing ion concentration in the cell (important in nerve and muscle cells)
why are signaling systems so complicated >:(
more opportunities for coordination and regulation than simple systems, larger signal amplification causing major cell response
amplification
signal molecule bonds to receptor, activating effector proteins, which activate multiple second messenger molecules, which change enzyme activity, open ion channels, or increase intracellular Ca2+, in turn activating even more enzymes
secondary messengers
small non-protein water-soluble molecules or ions also make pathways (cAMP, Ca2+, DAG, IP3). rapidly spread throughout the cell via diffusion
first messenger
hormone or neurotransmitter; signaling molecule
hormonal birth control
hormones estrogen and progesterone bind to g-protein receptors blocking production of FSH and LH
Cholera
bacteria in the intestine release a protein toxin that binds to the g-protein receptor resulting in cAMP production
how are signals terminated
degradation of the ligand, removal or the ligand, remove the ligand receptor complex
messengers that pass through cell membrane
small hydrophobic molecules (nonpolar), NO and lipids