Cell Communication

Cell signaling

one cell makes a signal and affects a cell

Chemical messengers

direct contact and local and long distance signaling

direct contact

direct translation, tunnels, attach to communicate

Local and long distance signaling

close or far away from production

autocrine

cell makes messenger and is affected

paracrine

affects neighboring cell

endocrine

affects cells at some distance

Phases of cell signaling

reception, transduction, and response

reception

signaling molecule binds to receptors

transduction

receptor changes shape and relay molecules are activated across pathway

receptor

transmembrane protein, commonly found in plasma membrane and bind to certain signaling molecules

response

depends on molecule and type of cell, some change occure

ligand

signaling molecules, bound to receptor, changes shape, “lock and key fit”

agonists

binds to receptor and activates it, triggers response

antagonists

binds to receptor and inhibits receptor activation

G protein-coupled receptors (GPCRs)

when binded and activated to ligand, g protein binds to GDP, agonist binds and triggers interaction with g protein, GDP leaves, GTP binds to g protein, moves, and interacts with enzyme

receptor tyrosine kinases (RTKs)

receptors with kinase activity, bind to agonist and proteins form dimers and when activated phosphorylate each other, recruits other signaling molecules

GTP

active g protein, eventually exchanged with GDP to rest

Ligand gated ion channels

transports ions across a membrane, signaling molecule opens gate, CNS role

intracellular hormone receptors

found in cytosol/plasm, steroids bind to receptors, normally inactive, agonist must be able to get inside, cell can make genes

steroids in receptors

hydrophobic so can get inside

transduction

-Cascades of molecular interactions relay signals from receptors to target molecules in the cell
-Cell signaling is usually a multistep process
- Multistep pathways can greatly amplify a signal

second messengers

small molecules and ions

kinases

protein phosphorylation

phosphatases

dephosphorylation

second messengers participate in…

pathways initiated by GCPRs and RTKs

Cyclic AMP (cAMP)

converts ATP to cAMP in response to extracellular signal, activates PKA, phosphorylates other proteins

Adenylyl cyclase

enzyme in plasma membrane responsible for cAMP

Calcium Ions and Inositol Triphosphate (IP3)

calcium ions used, ca2+ concentration in cytosol lower than outside of the cell

IP3 formula

phspholipase C —> PIP2 —> DAG and IP3

response

signal transduction pathway leads to regulation of one or more cell activities

Response Types

regulation of gene expression, enzyme activity, and cellular activity

Termination of signal

dephosphorylation and signaling molecule degradation

signaling molecule degradation

ubiquitination and ubiquitin ligases mark for destruction in proteosome

PIP2

regulates function of ion channels