chapter eleven Flashcards
eukaryotic example of single-celled organisms communicating
Baker’s yeast - uses chemical signaling when producing sexually, then shape/fuse toward each other
- 2 sexes: a and alpha
prokaryotic example of single-celled organisms communicating
Bacterial cells - secrete signaling molecules, cell density monitored by quorum sensing, biofilms
biofilms
aggregation of bacterial cells attached to surface by molecules secreted by cells
- only after cells have reached certain density
- protects and provides nutrition
need for cell communication in eukaryotic multicellular organisms
embryonic development, immune response, adult stem pop. maintenance
external signals (primary messenger)
- steroid molecules, proteins/glycoproteins, dipeptides, amino acids, gases
- lead to response within cell
signal transduction pathway
sequence of changes in series of different molecules
1. signal reception
2. signal transduction
3. cellular response
examples of local distance signaling
paracrine, synaptic, autocrine
examples of long distance signaling
endocrine
paracrine signaling
signals/molecules only travel short distance to neighboring cells
- local regulators
- fast (just into ECF)
- handful of target cells
- growth factors
synaptic signaling
nerve cell releases neurotransmitter into synapse of target cell
- very targeted
- like subset of paracrine
- super fast (1 cell to 1 target across synaptic cleft)
autocrine signaling
cell secretes signal, but cell has receptors for own signal
- subset of paracrine
endocrine signaling
hormones secreted into fluids, only bounded by and affect some cells
- travels through blood
- slow-ish
- large number of possible target cells, but can only respond if it has receptors
what signaling molecules use receptors in the cytoplasm?
steroids and gases
- can diffuse through membrane
- hydrophobic/smal molecules
what signaling molecules use receptors on the plasma membrane?
proteins, dipeptides, amino acids
- most water-soluble molecules
3 stages of cell signaling
- reception - target cell receives signaling molecule, which binds to receptor protein
- transduction - protein receptor changed
- response - transducer signal triggers cellular response
signal reception
signaling molecule acts as ligand (specifically binds to another molecule)
examples of plasma membrane receptors
- G-protein coupled receptors
- receptor tyrosine kinases
- ligand-gated ion channels
G-protein coupled receptors (GPCR)
- 7 transmembrane alpha helices, provide binding sites for signaling molecule and G protein
- G protein binds to GDP when inactive and GTP when active
- GTP + G-protein go to enzyme
receptor tyrosine kinases
- ligand binding pushes them together to form dimer
- dimer autophosphorylates, transferring P group from ATP to another protein
- an activate 10+ different transduction pathways
ion-channel receptors (ligand-gated ion channels)
after the ligand binds, channel opens/closes to allow/block specific ions
- ions will only go through w/ gradient
ex. of steroid hormones
aldosterone, testosterone, progesterone, estrogen
ex. of signaling gases
NO, CO
what happens to cytoplasm receptors upon binding
active form of receptor protein enters nucleus and turns on specific genes
- acts as transcription factor for mRNA
- both receptor and transducer
what is being transducer?
proteins
what does protein phosphorylation and dephosphorylation do?
transduction and shape change of proteins
kinases
phosphorylation - transfer P from ATP to protein
- can act on each other to produce phosphorylation cascade
phosphatases
dephosphorylation - remove phosphate groups from proteins, inactivating kinases
- turn off signal transduction pathway when initial signal no longer present
- make kinases available for reuse
second messengers
small, nonprotein, water-soluble molecules or ions used in pathways
2 main types of second messengers
- cyclic AMP
- calcium ions
cAMP
- made from ATP
- catalyzed by adenylyl cyclase
- binding of signal molecule to receptor (sometimes GPCR)
calcium ions
- cytosol concentrations of Ca2+ increase
- transported out of cell and into ER by protein pumps
- both GPCR/RTK
where are calcium ion concentrations kept low?
in the cytosol
inositol triphosphate
- hydrolysis of PIP2
- soluble
- generated by phospholipase C
- diffuses through cytosol and binds to IP3 gated calcium channel in ER membrane to open it
diacylglycerol
- hydrolysis of PIP2
- insoluble
- generated by phospholipase C
- stays within PM and goes to other pathways
what second messengers lead to Ca2+ release?
inositol triphosphate and diacylglyercol
- produced by cleavage of certain kind of phospholipid in membrane
why are there different cellular responses to signaling molecules?
different collections of proteins
gene regulation via activated transcription factor controlling
- synthesis of mRNA, which will be translated into specific proteins
gene regulation via regulating activity of proteins
- outside nucleus
- uses both second messengers and kinases
- epinephrine -> breakdown of glycogen
scaffolding protein
large relay protein to which several other relay proteins are attached
what does termination of the signal depend on?
reversible ligand binding
- external concentration of ligands falls, fewer receptors bound, unbound receptors revert to inactive form
apoptosis
type of controlled/programmed cell suicide
how does apoptosis occur
DNA and organelles chopped, cell shrinks and becomes lobed, parts packaged in vesicles and digested by scavenger cells
what is apoptosis essential for
embryonic development, metamorphosis, maintenance, nervous system, immune system
external signals for life/death of cells
come from other cells
internal sources for life/death signals
series of protein-protein interactions, nucleus (DNA) damage, ER (excessive protein misfolding)
blebs
membrane-bound cell fragments in apoptosis
- cytoskeleton breaks up and forms bulges
main proteases of apoptosis
caspases
secondary messenger
internal, small, non-enzymatic, usually soluble
