(02) Cell Communication Flashcards
how do cells communicate
often by chemical signals
(but can also be light, taste, smell etc)
two types of secreted signals
local signalling
long distance signalling
two types of local signals
Paracrine - eg. fibroblast growth factors
Synaptic - eg. neurotransmitters (acetylcholine - ACh)
example of long distance signalling
hormones (=endocrine signalling) produced by specialised cells travel via circulatory system to act on specific cells
eg. insulin
name the three steps of cell signalling
Reception
Transduction
Response
describe general processes involved in Reception
signalling protein (primary messenger) binds to receptor protein
–> shape / chemical change in receptor protein
describe general processes involved in the transduction stage of cell signalling
altered receptor protein activates another protein, causing a relay of changes
(via relay molecules (=second messengers))
what is a phosphorylation cascade
think about phosphorylation as a way that cells send signals (its a very general term)
so a phosphorylation cascade is a series of changes via phosphorylation in activated proteins in the transduction phase
describe the process involved in the response phase of cell signalling
all the activated proteins cause one or more functions to occur in the cell
(basically, something actually happens)
name the two main types of receptors
Intracellular receptors - located in cytoplasm of cell
Membrane-bound / cell surface receptor - attached to membrane
features of primary messengers of intracellular receptors
signalling protein / primary receptor is generally hydrophobic and/or small
lipid soluble, can enter cell
examples of intracellular signalling proteins
Testosterone
estrogen
progesterone
thyroid hormones
describe the features of primary messengers for membrane-bound / cell surface receptors
primary messenger is generally hydrophilic and/or large
what type of cell signalling is most common?
membrane-bound / cell surface receptors are most common
intracellular receptors are less common
examples of membrane-bound / cell surface receptor proteins
G Protein Coupled Receptor
receptor tyrosine kinase (this is probably cell surface bc we don’t cover in detail)
ligand-gated ion channel
what are GPCRs
G-protein coupled receptors
Transmembrane proteins that pass the plasma membrane 7 times
function of GPCRs
hundreds of different types exist, so they have VERY DIVERSE FUNCTIONS
what do GPCRs couple with and what is its function?
GPCRs couple with G proteins, which are MOLECULAR SWITCHES
(bound to GDP = off, bound to GTP = on)
stages of activating enzyme through GPCR
at rest, GPCR unbound, G protein bound to GDP, enzyme inactive
ligand binds receptor, and binds G protein. GTP displaces GDP. (enzyme remains inactive)
activated G protein dissociates from receptor and elevates enzyme (=cellular response)
G protein has GTPase activity, release from enzyme, back to resting state
describe the structure of a ligand gated ion channel
receptor in plasma membrane has a channel (“gate”)
binding ligand at receptor site –> change in shape –> open closes channel
what is the function of a ligand gated ion channel
ions (eg. Na+, K+ etc) can pass through
define ligand
signalling molecule that binds SPECIFICALLY to another protein
process of ligand gated ion channels
at rest, ligand unbound, gate closed
ligand binds, gate opens, SPECIFIC ions flow into cell (causing cell response)
ligand dissociates, gate closes
what body system relies heavily on ligand gated ion channels?
the nervous system!
released neurotransmitters bind as ligands to ion channels on target cells to propagate action potentials
what are protein kinases?
enzymes that transfer a phosphate group from ATP to another (specific) protein (activates it)
what are phosphatases?
enzymes that dephosphorylate (remove phosphate) so the protein is inactive but recyclable
-ase = destroy
what is a second messenger?
another small molecule included in the phosphorylation cascade
between the main enzyme in the PM and the first protein kinase
examples of second messengers
cAMP
Ca2+ ions
what is the enzyme activated by GPCR?
adenylyl cyclase
what does adenylyl cyclase convert ATP to
converts ATP to cAMP (which then acts as a second messenger in the phosphorylation cascade)
describe the differences in Ca ion concentration inside and outside the cell
LOW Ca2+ inside the cell
HIGH Ca2+ outside the cell (over 1000x higher)
how is Ca ion concentration maintained?
via calcium pumps, located
- out of cell
- into ER
- into mitochondria
How is GPCR signalling linked to Ca2+ signalling?
G protein activates the protein phospholipase C, which cleaves PIP2 (phospholipid) into DAG and IP3
IP3 (2nd messenger) diffuses through cytosol, bonds to a gated channel in ER
Ca ions flow out of ER, activated other proteins
G protein –> phospholipase C + PIP2 –> (DAG +) IP3 –> gated channel –> Ca2+
two reasons why there are many steps in cell signalling
AMPLIFICATION (of response)
multiple control points
specificity of response (spatial / temporal)
coordination w/ other signalling pathways
what is cell response + example
transduction of signal leads to activation / regulation of one or more cell activities
GENE EXPRESSION
how are cell signals turned off?
cAMP (2nd messenger) is broken down by phosphodiesterase (PDE)
(eg. caffeine blocks PDE)
cell signal processes involved in generating a lot of ATP quickly
glycogen –> glucose 1-phosphate –> glucose 6-phosphate, used in glycolysis to generate ATP
Adrenalin acts through GPCR, activates cAMP + 2 protein kinases in phos cascade
MASSIVE amplification
Is phospholipase C a membrane bound or peripheral enzyme?
peripheral
IP3 gated Ca channels are located on the:
endoplasmic reticulum lumen
IP3 diffuses where?
in cytosol
before binding to an ion gated channel in ER
phospholipase C cleaves…
PIP2 (phospholipid) –> DAG + IP3
