bio - cell communication/signal transduction

types of local signaling

cell junctions; cell-cell recognition; paracrine signaling; autocrine signaling; synaptic signaling

paracrine signaling (local)

signals sent to cells in the near vicinity

autocrine signaling (local)

cells release signals to themselves

synaptic signaling (local)

specialized form of paracrine signaling in neurons

types of long distance signaling

endocrine/hormone signaling and pheromone signaling

endocrine/hormone signaling

cells secrete hormones that regulate cells

pheromone signaling

an organism triggers behavior in a pheromone

signal transduction pathway

series of steps by which a signal on a cell's surface is converted into a specific cellular response

reception

step 1 of cell communication; a chemical messenger binds to a receptor

transduction

step 2 of cell communication; relay molecules change the message

response

step 3 of cell communication; activates the cell to respond to the message

ligand

signaling molecule that binds to a receptor

how does reception work

ligand binding changes the shape in a receptor, which is the initial transduction of the signal

what type of molecule can a ligand be

just about anything (protein, carb, lipid, ion, proton, etc); usually a protein though

membrane receptors

extracellular receptors

g-protein coupled receptors (GPCRs)

membrane receptors that work with the help of a G-protein, which bonds to GDP as an on or off switch

receptor tyrosine kinases (RTKs)

membrane receptors that attach phosphates to tyrosines (an amino acid)

ion channel receptors

membrane receptors that act as a gate that opens or closes when a ligand bonds

importance of ion channel receptors

they allow specific ions or compounds to get through and give ligands a place to bond to

intracellular receptors

small or hydrophobic chemical messengers that can cross the plasma membrane (ex. steroids)

what do intracellular receptors do

the ligands activate intracellular receptors found in the cytosol or nucleus of target cells; often act as transcription factors

transcription factors

essentially turns DNA on, which makes mRNA

importance of signal transduction

it prevents cells from doing things like dying based off of one signal

how does signal transduction work

multistep pathways provide opportunities for amplification, coordination, and regulation

protein kinases

transfer phosphates from ATP to protein (phosphorylation)

protein phosphatases

remove phosphates from proteins (dephosphorylation)

phosphorylation cascade

signaling pathway involving multiple kinases

how does phosphorylation/dephosphorylation play into cell communication

shape changes caused by phosphorylation and dephosphorylation turn proteins on and off (essentially turn it from an active to deactivate state)

second messengers

small, nonprotein, water soluble molecules or ions that spread throughout the cell by diffusion

what triggers second messengers

GPCRs and RTKs

examples of second messengers

cyclic AMP, calcium ions, inositol phosphate (IP3), diaglycerol (DAG)

why are second messengers so efficient

they don't need a ribosome or DNA, so they are easy to make, store, and release when needed

where do cellular responses occur

the cytoplasm or the nucleus

what is included in cellular responses

the regulation and/or synthesis of enzymes or other proteins

fine tuning of cell communication

amplification, specificity, efficiency, termination (always seek emergency treatment)

signal amplification

enzymes bind and amplify

specificity

the secondary messengers in different cells can cause responses from the same molecule

what are some things other than secondary messengers that can cause different responses in a cell

cross talk and different receptors

scaffolding proteins (signaling efficiency)

large relay proteins to which other relay proteins are attached

signal termination

involves removal of ligands and/or dephosphorylation that returns receptors to an inactive state

apoptosis

programmed or controlled cell death