L13 Flashcards
what are the 3 stages of signal transduction
an extracellular signal molecule activates a membrane receptor (stage 1)
that in turn alters intracellular molecules to be transduced via a certain pathway (stage 2)
to activate a cellular response (stage 3)”
what is the first messenger
The extracellular signal molecule
what is second messenger system
a system formed by intracellular molecules
what are transducers
membrane proteins in between first and second messenger system that convert the message of extracellular signals into intracellular messenger molecules that trigger a response
what are the Types of response in signal transduction
altered ion transport
altered metabolism
altered gene expression
altered cell shape or movement
altered cell growth and division
what chemicals can serve as extracellular signalling molecules? give examples
Amines (e.g. epinephrine, adrenaline)
Peptides & Proteins (e.g. angiotensin II, insulin)
Steroids (e.g. hormones)
Other small molecules (e.g. amino acids, ions, gases)
what are the differences between cell surface and intracellular receptors interaction
molecules that bind trans membrane receptors can’t cross the plasma membrane
nuclear receptors are hydrophobic and mostly act as transcription factors and give a slow response
Membrane receptors are hydrophilic and signaling molecules activate a wide variety of intracellular “signal transduction” pathways (e.g. ion-channels, G proteins coupled receptors and catalytic receptor), including gene regulation. they give a fast response
what are the types of receptors
Ligand-gated ion channels
G-protein coupled receptors
Enzyme-linked receptors
Nuclear receptors
what receptors give rise to the fastest response
Ligand-gated ion channels
then G protein channels
what are Ionotropic receptors
receptors that are ion channels
give examples of Ionotropic receptors
Nicotinic acetylcholine receptor
The gamma-amino buytyric acid (gaba)A receptor
what are the features of Nicotinic acetylcholine receptor
Ligand gated ion channel that mediates effects of acetylcholine (ACh) on muscle etc
Binding of acetylcholine between alpha and delta subunits opens a channel and allows Na+ entry
Binds nicotin
Electrical event (inward Na+ current) triggers response
Calcium may also enter from this channel
what are the features of The gamma-amino buytyric acid (gaba)A receptor
selective for Cl- ions
Naturally activated by g-\amino butyric acid – CNS neurotransmitter
Inhibitory receptor
Very important role in CNS
Activated by benzodiazepines
Also by alcohol and anesthetics
what are Benzodiazepines
sedative drugs that activate The g-amino buytyric acid (gaba)A receptor
what are Metabotropic receptors
receptors that are not ion channels but cause the opening of ion channels. they are indirectly linked with ion channels on the plasma membrane through signal transduction pathways, generally G proteins mediated
give examples of Metabotropic receptors
Muscarininc
Gaba B
what are the features of Muscarinic receptors
activated by ACh
More sensitive to muscarine than nicotine
what are the features of Gaba B receptors
activates a Potassium channel
More sensitive to muscarine than nicotine
what are the features of G protein coupled receptors
Receptors that activate G proteins all have 7 transmembrane domains
At least 800 genes encode G protein coupled receptors
what are the polypeptide chains of g proteins
alpha, beta and gamma
how many subunits are there for each G protein polypeptide
16 alpha subunits,
5 beta
11 gamma
what 2 G protein subunits bind tightly, effectively forming a single subunit
beta and gamma
what subunit has a guanine nucleotide binding site that binds GTP or GDP
alpha
compare alpha GDP and alpha GTP
alpha-GDP has high affinity for beta gamma (resting conditions)
alpha-GTP has low affinity for beta gamma
