S&F; Cell Communication Flashcards
why do cells have to communicate?
they need to respond as a cell, and as part of a whole tissue (environment)
signals are often chemical (can also be light,taste,smell)
what are the two different types of secreted signals?
local signaling + long distance signaling
what is local signaling + examples
signals that act on nearby target cells
1. paracine; growth factors such as fibroblast growth factor (FGF1)
2. synaptic; neurotransmitters such as acetylcholine
what is long distance signaling + examples
signals acting from a distance
- hormones produced by specialised cells -circulatory system-> to act on specific cells
e.g. insulin from pancreatic beta cells -> insulin receptors -> cascade -> glucose uptake.
what are the three main steps of cell signalling?
reception; primary messenger/ligand binds to receptor -> changes its shape/chemical state
transduction, altered receptor activates another protein (g-protein/adenylyl cyclase), cause a relay of changes. each activated protein causes a series of changes.
response; cause one or more functions to occur in the cell.
what are the two main types of receptors?
intracellular receptors + membrane bound receptors
what are intracellular receptors
primary messenger = hydrophobic/small, lipid soluble can enter the cell.
least common method of signalling
e.g. testosterone, estrogen, progesterone, thyroid hormones
what are membrane bound cell surface receptors
primary messenger = hydrophillic/large
most common method of signalling
e.g. GPCR, ligand gated, tyrosine kinase
what are the features of GPCRS?
transmembrane proteins, pass the pm 7 times
nobel prize, 1/3 of modern drugs
many diff ligans, diverse functions (development, sensory reception)
g proteins; molecular switches which are either on/off depending on whether gdp or gtp is bound
how do gpcrs work?
- at rest, [receptor is unbound], and [G protein is bound to gdp]
- [[ligand binds receptor] binds to the G protein], GTP displaces GDP, [enzyme = inactive] –> conformational change
- [activated G protein dissociates from receptor.], [g protein activates enzyme]
- g protein has GTPase activity (GTP is hydrolysed to GDP and P) –> is released from enzyme, and everything goes back to normal ;D
featuer of ligand gates ion channels
contains a gate
binding on site causes a change in shape
this changing of shape causes channels to open/close
ions (Na, K, Ca, Cl) can pass through
how to ligand gates ions work
- at rest, ligand is unbound + gate is closed
- ligand binds, gate opens, specific ions can flow into the cell
- ligand dissociates, gate closes.
which body system relies heavily on ligand gates ion channels?
the nervous system; released neurotransmitters binds as ligands to ion channels
what are signal transduction pathways made up of?
protein kinases and phosphatases
what are protein kinases
enzymes that transfer a phosphate group from atp to another specific protein (activating the protein).
what are phosphatases
enzymes that dephosphorylate, making the protein inactive + recyclable
what are the different types of second messengers?
cAMP and Ca2+/IP3
how does cAMP work?
GPCR -> activated enzyme is adenylyl cyclse (converts ATP to cAMP)
cAMP = second messenger, activates downstream protein (–> phosphorylation cascade)
features of calcium
low ca inside the cell
high ca outside the cell
maintenance of ca is important, so pumps pump Ca out of cell, into er, and into mitochondria
Ca and IP3 in gpcr signalling
- activated protein = phosphilipase C
- cleaves PIP2 (phospholopid) into DAG + IP3
- IP3 diffuses through cytosol + binds to a gated channel into ER
- calcium ions flow out of ER to activate other proteins
why are there so many steps?
amplifies the response
provides multiple control points
allows for specificity of response (temporal/spatial)
allows for coordination with other signalling pathways
what are the types of cellular responses
gene expression!!
alteration of protein function
opening/closing of ion channel
alteration of cellular metabolism
regulation of cellular organelles/organisation
rearrangement/movement of cytoskeleton
why do we have to turn off the response?
all signals are for a limited time.
means that cell is ready to respond again if required.
how does adrenaline work in GPCR?
- adrenalin activates cAMP and two protein kinass in phosphorylation cascade
- results in active glycogen phosphorylase which can convert glycogen to glucose 1 phosphate
- amplification = 1 adrenalin molecule can result in 10^8 glucose 1-phosphate molecules
