Chemical Messengers Flashcards
cell signalling importance
important for regulation of physiological processes and homeostasis
is communication between cells
when does communication occur?
signalling cell sends a signal to target cell (usually a chemical messenger). this can involve direct or indirect signalling.
gap junction is what sort of signal?
direct signal
explain gap junctions
signalling cell and target cell are connected by gap junction (sort of proteins). this way the signal is directly passed from one cell to another. the openings are called pores, and the tubes are the hemichannels, in the connexin proteins
very fast!
draw it! (Slide 4)
explain indirect signalling
a way to send signals to distant cells.
signalling cell releases a chemical messenger that binds to receptor on target cell. this induces activation of signal transduction pathways and response in target cell.
draw it! (slide 5)
autocrine signalling
chemical message diffuses back to signalling cell
signalling cell and target cell are the same
paracrine signalling
chemical message diffuses to nearby cell (ex. neurotransmitters across synaptic cleft)
draw the autocrine and paracrine signalling pathway
yes!
slide 5 on chemical messengers
draw neural signaling pathway
yes! (slide 5 on chemical signalling)
endocrine system (cell signalling)
chemical messenger (hormone) is released by secretory gland, transported by circulatory system
longer lasting, slow acting
draw endocrine signalling pathway!
i will! (slide 6 chemical signalling)
exocrine signalling
released by one individual and travels through the environment for communication with other animals
6 types of chemical messengers
peptides/proteins
steroids
amines
eicosanoids/fatty acid derivatives
purines
gases
structure affects signalling mechanism
peptide/protein messengers
hundreds of amino acids, all made in rough ER
secreted by calcium-induced exocytosis
hydrophilic, bind to transmembrane receptors for signal transduction, causing rapid effects
draw the synthesis pathway! (slide 9)
steroid messengers
produced from cholesterol, by the gonads and placenta (sex hormones), and adrenal cortex (mineralocorticoids, glucocorticoids and sex hormones)
glucocorticoid and mineralcorticoid names come from functions. (gluco= glucose/metabolism, mineral=ion, then adrenal CORTex, location)
synthesized on demand
secreted by diffusion
hydrophobic, uses carrier proteins, or bind to intracellular receptors
draw pathway! (slide 11)
biogenic amine messengers and some examples
have an amine group, and many are made from amino acids
examples:
- catecholamines like dopamine, norepinephrine/epinephrine from tyrosine
-serotonin (sleep and mood) from tryptophan
-thyroid hormones (metabolism and growth) T4 thyroxine and T3 triodo-thyronine, derived from tyrosine
most are hydrophilic, except for thyroid hormones which are hydrophobic.
eicosanoids/fatty acid derivatives
lipid messengers made from phospholipids
can act as neurotransmitters (paracrine/autocrine signalling)
often involved in inflammation and pain
diffuse out of membrane of signalling cell, diffuse into target cells where they bind to transmembrane receptors.
purines
nucleotide + ribose sugar
includes adenosine and guanosine
ex. AMP, ATP, GMP, GTP
can move across membrane via nuceloside transporters and secretory vesicles
bind to purinergic receptors
gases examples as chemical messengers
nitric oxide and hydrogen sulfide and CO are all vasodilators
where do chemical messengers bind on target cells? where do hydrophilic/phobic ligands go?
they bind to receptor proteins.
hydrophilic binds to transmembrane receptors
hydrophobic binds to transmembrane or intercellular receptors
ligand-receptor interactions are very specific, the receptor changes shape when ligands are bound. a single cell may have many receptors for different ligands
explain ligand mimics and two types
ligand mimics are chemicals with structures similar to the natural ligand that can mimic the binding of that ligand to a receptor. Drugs or poisons can act as ligand mimics.
agonists: chemical mimic that binds to and activates receptor, mimicking response induced by natural ligand
antagonist: chemical mimic that binds to, but does not activate receptor, therefore blocking a natural ligand and inhibiting response
try to draw nad compare!
inactivation of ligand receptor interactions
ligand receptor interactions must be interrupted to allow for responses to changing conditions
may be removed by distant tissues
ligand taken up by adjacent cells
ligand degraded by extracellular enzymes
ligand receptor complex removed by endocytosis
receptor inactivation
inactivation of signal transduction pathway
draw some from slide 18!
signal transduction pathways
agonist binds receptor, it initiates signal transduction pathway. these usually amplify the signal.
receptor and ligand types and concentrations can affect the response of target cell.
STPs convert change in receptor shape to cellular response
types of receptors in STPs
ligand gated ion channel
receptor enzyme
g-protein coupled receptor
intracellular receptor
ligand gated ion channels
quick response time
results in change of electrical properties of the cell.
draw this! (slide 20)
receptor enzymes (STPs)
ligand binds to transmembrane receptor and alters the activity of the intracellular, catalytic enzyme domain of receptor.
starts phosphorylation cascade, and phosphorylation of intracellular proteins.
*kinases are enzymes that phosphorylate other proteins
draw these (slide 21)
G-protein coupled receptors (STPs)
activate intracellular G proteins which begin a signalling cascade
sometimes they regulate other ion channels. they respond slower due to the time required for the G protein subunit to be activated and bind. in this case, the channel itself isn’t the receptor
some Gprotein linked receptors regulate enzymes that produce second messengers (ex. cAMP)
draw this! (slide 22+23)
intracellular receptors (STPs)
intracellular receptors bind to hydrophobic messengers (ex. steroids). these receptors act as transcription factors to alter gene expression.
changes in gene expression takes time, so this is a slow acting response.
hydrophobic ligand passes thru membrane, binds to ligand binding domain inside cell, receptor changes shape, the complex moves to the nucleus, and the DNA binding domain of receptor binds and interacts with transcription factors, which alters transcription rate and mRNA.
draw this! (slide 24)
what do second messengers do?
they amplify signals.
the intercellular messengers is the “First messenger” ,and as second messengers they amplify this. ex. cAMP
first messenger binds to receptor, many g proteins are activated. each of them activates a second messenger, which triggers an STP.
draw this! (Slide 25)
