Lecture 13 and 14 Flashcards
what are examples of substances that activate and inhibit proteins
- antibiotics
- alcohol
- animal or insect venoms
- chemical compounds from fungi
- hormones
- neurotransmitters
- drugs or medicines
what are the steps that cause protein activation or inhibition
- chemical substance = travels from its source
- chemical substance interacts with target protein = binding or reception
- binding event affects the protein = either activates or inhibits it
- leads to functional consequences that change the cellular response
how many active sites do enzymes have compared to receptors
enzymes = one active site
receptors = can have several binding sites
what do enzymes bind to compared to receptors
enzymes = bind to substrates
receptors = bind to ligands
what do enzymes do compared to receptors
enzymes = change substrate into product
receptors = release ligands unchanged
where can enzymes and receptors be found
both can be membrane bound or free in the cytosol
what is signal transduction
messages passed on through the cell
- often multi step pathways, that provide opportunities for coordination and regulation of the cellular response
what do second messengers do
they can transmit signals from a receptor to other relay molecules
where are second messengers found
they are not attached to the membrane so free to move in the cell
what can phosphorylation and de-phosphorylation do
can turn protein on and off or up and down as required
what is phosphorylation
kinases transfer phosphates from ATP to protein (for regulating protein activity)
what is dephosphorylation
protein phosphatases rapidly remove phosphates from proteins (to carefully control signal transduction)
common mechanisms to control signal transduction
- ligand dissociation
- internalisation (receptor is removed from cell surface through endocytosis so it can no longer respond to ligand)
- phosphatases (removal of phosphate group?)
why can the same receptor/ligand pairing have different effects in different cells
because they use different combinations of relay molecules for signal transduction
what does different cells having different collections of receptors and relay molecules allow for
allows cells to detect and respond differently to different ligands
what are the different classes of receptors
- ligand gated ion channels
- G protein coupled receptor
- receptor tyrosine kinase
how do G protein-coupled receptors work
- use G protein to start signal transduction
- GPCR activates the G protein, which communicates with other proteins in the cell
- receptor activation causes G protein activation and further signal transduction events
what are Gas G proteins
Gas = stimulatory G protein, which activates an enzyme called adenylate cyclase
what are Gai G proteins
Gai - inhibitory G protein, decreases the activity of adenylate
how do receptor tyrosine kinase work
- use phosphorylation of so called adaptor proteins to start signal transduction
process of receptor tyrosine kinase
- agonist binds to ligand
- receptor changes conformation and becomes activated
-receptor autophosphorylation occurs - adaptor protein is phosphorylated
- adaptor proteins communicate with other proteins in the cell
do all adaptor proteins have the same effect (receptor tyrosine kinase)
no, different types of adaptor proteins will have different effects
how do ligand gated ion channels work and whats the BUT that makes them different
agonist that binds ligand causes conformational change to adaptive receptor
BUT
instead of ‘relay’ proteins like G coupled proteins or adaptors being used, ions flow directly through the channel to produce effects
are ligand gated ion channels fast or slow signalling
compared to GPCR’s and RTK’s they are FAST signalling
what is a receptor
a cellular protein(or assembly or proteins) that control chemical signalling between and within cells
what is a ligand
chemical substance that specifically binds to a receptor
what is an agonist
chemical substance (ligand) that binds to a receptor to activate it
what is an antagonist
chemical substance (ligand) that binds to a receptor and prevents activation by an agonist
what are endogenous ligands
ligands produced in the body
what are exogenous ligands
like drugs and toxins
what is important about the binding pocket of a receptor and a ligand
the size and shape of the ligand must match the binding pocket of the receptor for chemical interactions to occur
what occurs when an agonist binds to receptor
activation occurs when the receptor undergoes conformational change
what occurs when an antagonist binds to a receptor
the antagonist will bind and block the agonist from binding, the receptor will remain inactive
what occurs after activation of a receptor
a chain of events will be passed on through the cell = signal transduction
