Lecture 23 Flashcards
Why would a cell send a signal to another cell?
To communicate with other cells, signalling them to change function.
How far are signals sent?
Signals can be between adjacent cells or cells that are in other parts of the organism. Different travel to different lengths.
What are the major components of a signalling pathway?
Signalling pathways usually involve signalling molecules, receptor proteins, intracellular signalling proteins and effector proteins.
What provides signalling pathways with their specificity?
Their specificity is observed in the binding site of the signalling molecule. Its binding site is very specific to its complementary signalling molecule. Other signalling molecules will not fit.
What can amplify a signal?
When certain molecules are activated by a signal, those molecules can affect a number of different molecules, amplifying the signal received.
Are signals usually transient or long-lived? How is this achieved?
Signals are usually transient (short lived), signals that have a stronger effect tends to be transient while signals with a weaker effect tends to be longer lived.
What does it mean that something is a molecular switch?
A molecular switch is a molecule that can reversibly switched between two or more different conformations in response to a stimulus.
What is on and what is off in each of the generalised molecular switches?
Signalling by phosphorylation: phosphorylation of the molecule results in being switched on, remove of phosphate turns it off.
Signalling by GTP-binding: the binding of GTP and removed of GDP turns molecule on, hydrolysis of GTP turns it off.
What is the basic structure of the components of the G protein-coupled receptor pathway?
G-protein has 3 subunits; α, beta and γ. The alpha subunit has a GDP - binding site and has GTPase activity. The gamma and alpha subunits have lipid molecules that insert insert into the membrane. It has a receptor.
How does a G protein-coupled receptor transmit the activation signal? How does it act as a molecular switch?
When the receptor is activated, the G protein-coupled receptor causes the GDP to leave and is replaced with GTP, activating it. The G-protein then moves to active other molecules, transmitting the activation signal.
What does the β-adrenergic receptor respond to, and what does it pass its signal to?
It responds to epinephrine. The receptor passes its signal to a G-protein.
What common intracellular pathways are involved in β-adrenergic? How is the signal amplified?
Epinephrine attaches to the receptor which activates the G protein coupled to the receptor. The G-protein then activates adenylyl cyclase which then catalyses the formation of cAMP which leads to a cellular response. The signal is amplified as more than one molecule is activated in each step.
What is a receptor tyrosine kinase? Give one example.
Receptor tyrosine kinase is a receptor with a tyrosine kinase domain that undergoes trans-autophosphorylation when signalling molecules binds. (ex: insulin receptor)
What is receptor tyrosine kinase’s immediate phosphorylation target?
Their immediate phosphorylation target is themselves.
What common intracellular signalling pathways are downstream of the insulin receptor?
Once insulin binds to the receptor, it undergoes trans-autophosphorylation on its carboxyl-terminal Tyr residue. It then phosphorylates IRS1 on its Tyr residue which leads to a cascade of events (activation of Ras - G protein) that results in the expression of certain genes.
