BSI EXAM 2 Flashcards
What are GPRs? (sometimes called GPCRs).
G-protein receptors (or G-protein Coupled receptors) which activate heterotrimeric G-proteins intracellularly after binding the messenger extracellularly
What are RTKs?
Receptor tyrosine kinases which dimerize and phosphorylate each other (intracellularly) after binding the specific messenger (extracellularly); they either directly activate kinase cascades or act via low molecular weight G-proteins.
What are RTKs? Functions?
These signal transduction pathways can affect all aspects of cell function from synaptic transmission to gene transcription. They allow cells to integrate their functions effectively and are obviously very important pharmacological targets.
What are G-proteins?
They are sites of signal transduction pathway integration and regulation; these pathways are not linear and cross-talk extensively. There are 2 main types; heterotrimeric G-proteins have 3 subunits and are self-limiting (on a timer) whereas low molecular weight G-proteins (LMW G-proteins; also called monomeric) have one subunit and need accessory proteins to turn them off. Heterotrimerics are activated by GPR’s whereas LMW G-proteins need RTK’s plus additional accessory proteins to be activated.
Why are they called G-proteins?
Because they bind guanosine nucleotides; both LMW G-proteins and the -subunit of heterotrimerics bind GDP when inactive and GTP when activated.
What is a secondary messenger?
A small molecule such as cAMP which is produced intracellularly in response to a messenger and diffuses across the cell affecting target proteins such as enzymes and ion channels.
What is the most well-known secondary messenger?
OOPS! Try cAMP (but also cGMP and Ca2+).
What is a GEF?
A Guanosine Exchange Factor; this is the activated GPR for heterotrimerics and the dimerized (so active) RTK’s c/w other proteins AND the specific GEF. As the name suggests, these allow the exchange of bound GDP (inactive) for GTP (active).
What is a GAP?
A GTP’ase Activating Protein; this is intrinsic in the -subunit (heterotrimerics; self-limiting) but must be supplied via a separate accessory protein for LMW G-proteins.
What is a GIP?
A GTP’ase Inhibiting Protein; they antagonize GAP’s so keeping LMW G-proteins turned on.
What is a GDI?
A Guanosine nucleotide Dissociation Inhibitor; currently only associated with LMW G-proteins where they antagonize GEF’s so keeping LMW G-proteins turned off.
The cell secreted by ___ ____ ____ to affect other neurons or “_____” such as muscles and glands (neurotransmitters)
neurons across synapses; effectors
These messengers can affect every aspect of cell function from what? (4)
growth
differentiation to metabolism
processing of data
programmed cell death (apoptosis)
2nd messengers
= AC (adenylyl cyclase)
intercellularly response to the chemical messenger
AC (adenylyl cyclase)
produces many molecules of cAMP which can affect target proteins so acting as amplification stage
Some chemical messengers are able to cross the memebrane (_____ ____) but are still recognized by ______ ________ receptors or enzymes such as (4)
hydrophobic molecules specific intraceullar steroid hormones thyroid hormones t3,t4 nitric oxide (NO) and carbon monoxide (CO)
Receptor
specific protein in either the plasma membrane or interior of a target cell that a messenger combines with.
Specificity
the ability of a receptor to bind only one type or a limited number of structurally related types of chemical messengers
Saturation; If all are occupied, 100 saturation. If 50% are occupied, 50% saturation. ETC
the degree to which receptors are occupied by messengers.
Affinity
the strength with which a chemical messenger binds to its receptor.
Competition
the ability of different molecules that are very similar in structure to compete with each other to combine with the same receptor.
Agonist
a chemical messenger that binds to a receptor and triggers the cell’s response; often refers to a drug that mimics a normal messenger’s action.
Down-regulation
a decrease in the total number of target-cell receptors for a given messenger; may occur in response to chronic high extracellular concentration of the messenger.
Up-regulation
an increase in the total number of target-cell receptors for a given messenger; may occur in response to chronic low extracellular concentration of the messenger