L8 Cell Communication Flashcards
(29 cards)
dictyostelium (slime mould) life cycle
usually free living, unicellular organism when food (bacterium) is plentiful
when food is scarce > secrete high levels of cAMP > attract unicellular slime mould > form compact structure called slug > move to another location with more food > some differentiate into spores (germinate > free unicellular slime mould again)and some into stalk cells
how do unicellular and multicellular organisms differ in using cell communication
unicellular: needed for mating, aggregation or differentiation into other cell types
multicellular: needed for development, differentiation and other metabolic functions
types of extracellular signalling molecules
- signalling cell secretes signalling molecule > bind to receptor on target cell
- signalling molecule (transmembrane protein) on signalling cell binds to receptor on target cell (requires both cells to be in close proximity
what is angina and how does nitroglycerine act as treatment
angina: chest pain due to insufficient blood supply to heart
nitroglycerin is converted into NO in the body (signalling molecule) > relaxes blood vessels > reduce workload on heart > reduce oxygen requirement of heart muscles
difference between water soluble and insoluble signalling molecules
water soluble: removed/ broken down within minutes of entering blood; local mediators and neurotransmitters removed from extracellular space within seconds > usually mediate short duration responses
insoluble: persist in blood for hours and thyroid hormones for days > mediate responses that are longer lasting
definition of paracrine intracellular signalling
when cells release signaling molecules (like hormones or growth factors) that act on nearby cells
difference between endocrine and synaptic signalling
endocrine: long range signalling > slow because hormones secreted and carried by blood to target cells (may be far away) > low concentration needed
synaptic: much faster and more precise > information transmitted by electrical impulses > work at higher concentrations
difference between endocrine and autocrine signalling
endocrine: cell releases hormones into bloodstream
autocrine: cell releases molecule and responds to it itself (self regulation)
(cancer cells often use autocrine to overcome the normal controls on cell proliferation and survival)
what are gap junctions
specialised cell-cell junctions
water-filled channels to allow exchange of intracellular signalling molecules like Ca2+ and cAMP
gap junctions of both cells must be aligned for channel to be formed
what are connexons
channel made of 6 protein subunits called connexins
one connexon from one cell lines up with connexon from neighbouring cell > form full gap junction channel
properties of cell signalling
each cell is capable of having different responses from different signals
different cells can respond differently to the same extracellular signalling molecule
- different receptors
- different internal signalling molecules
- different target proteins or genes activated
extracellular molecules bind to specific receptors
what are intracellular receptors
hydrophobic signal molecules that diffuse across plasma membrane and bind to intracellular receptor proteins
mostly intracellular receptors belong to nuclear receptor superfamily
signal molecules: steroid hormones, thyroid, retinoids and vitamin D
type I receptors
sex hormone receptors
glucocorticoid receptor
mineralocorticoid receptor
type II receptor
vitamin A receptor
vitamin D receptor
retinoid receptor
thyroid hormone receptor
difference between type I and type II receptor
type I: inactive form associated with heat shock protein (hsp) > released when receptor interacts with ligand > dimerise > translocated to nucleus > bind got specific dna sequences > influence transcription
type II: no hsp > already located in nucleus > may have inhibitory proteins bind to it to keep in inactive form > ligand binding > dissociation of inhibitory proteins > recruitment of transcription co-activators
do plants have endocrine signalling
no but have signalling molecules that can travel to other parts of the plant to elicit signalling
types of cell surface receptors
ion channel coupled receptors
G-protein coupled receptors
enzyme coupled receptors
how does ion channel couple receptors work
ligand (eg neurotransmitter) binds to receptor > channel opens > allow specific ions to pass through
what are enzyme coupled receptors
either function directly as enzymes or directly associated with enzymes that they activate
single pass transmembrane domain proteins that have their ligand binding site outside cell and catalytic or enzyme binding site inside
eg: tyrosine receptor kinase, PDGFR, EGFR
functions of GPCR
embryonic development
vision and hearing
yeast mating
mating hormone systems
many neurotransmitters signalling pathways
structure of G protein
made of alpha, beta and gamma subunits
alpha: binds to GTP or GDP; is a GTPase (GTP hydrolysed to GDP > G protein becomes inactive)
beta and gamma: joined together to form dimer > help anchor G protein to cell membrane
mechanism of GPCR
G protein with GDP binds loosely to receptor > signal molecule binds to receptor > conformational change in receptor > activate G protein > alpha subunit of G protein release GDP and binds GTP > expose sites on alpha and beta-gamma subunits to allow interaction with target proteins
what are 2nd messengers
diverse family of low MW compounds like cAMP and Ca2+ > transmit biological signals initiated by receptor ligand binding at cell surface to intracellular targets or effector proteins
types of 2nd messengers
hydrophobic: membrane associated > regulate membrane associated effector proteins
hydrophilic: water soluble > located within cytosol
gases: eg NO and CO > can diffuse both through cytosol and across cytosol membranes
