chapter 11. what even is cell communication

:|

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