1.4 communication and signalling Flashcards
receptor molecules
proteins with a binding site of a specific signalling molecule
binding causes a conformational change, initiating a response
hydrophobic signalling molecules
diffuse through the bilayer
bind to intracellular receptors
examples of hydrophobic signalling molecules
steroid hormones:
oestrogen and testosterone
transcription factors
receptors for hydrophobic signalling molecules
when bound to DNA, can initiate/prevent transcription
hydrophobic signalling molecules pathway
steroid hormones bind to specific receptors in the cytosol/nucleus
hormone-receptor complex moves to the nucleus and binds to hormone response elements (specific DNA sequences)
the rate of transcription and gene expression is altered
hydrophilic signalling molecules
bind to transmembrane receptors
don’t enter the cytosol
examples of hydrophilic signalling molecules
peptide hormones (insulin)
neurotransmitters
transmembrane receptors
act as signal transducers across the plasma membrane
convert extracellular ligand-binding to intracellular signals
G-proteins
relay signals from activated receptors to target proteins
phosphorylation cascades
a series of events with one kinase activating the next in the sequence etc.
results in the phosphorylation of many proteins
activates multiple intracellular signalling pathways
insulin binding pathway
insulin binds to its receptor
receptor changes conformation
receptor undergoes phosphorylation
phosphorylation cascade is triggered in the cell
vesicles containing GLUT4 are transported to the cell membrane
type 1 diabetes
caused by the failure to produce insulin
type 2 diabetes
caused by the loss of receptor function
exercise triggers recruitment of GLUT4, so can improve glucose uptake in fat and muscle cells
resting membrane potential
a state where there is no net flow of ions across the membrane
action potential
a wave of electrical excitation along a neuron’s plasma membrane
nerve impulse transmissions
requires a change in membrane potential
when action potential reaches the end of a neuron, vesicles containing neurotransmitters fuse with the membrane
neurotransmitters are released and stimulate a response in a connecting cell
neurotransmitter receptors
ligand-gated ion channels at a synapse
define depolarisation
change in membrane potential to a less negative value inside the cell
effects of depolarisation of plasma membrane
(due to entry of positive ions) opens voltage-gated sodium channels
neighbouring regions of membrane are also depolarised
depolarisation cycle
neurotransmitter binding opens ligand-gated ion channels at synapse
ion movement and depolarisation
depolarisation beyond a certain threshold opens voltage-gated sodium channels
sodium enters down electrochemical gradient
change in membrane potential inactivates sodium channels
voltage-gated potassium channels open
potassium enters, restoring resting membrane potential
define retina
area within the eye that detects light
function of rods
function in dim light
don’t allow colour perception
function of cones
function in bright light
allow colour colour perception
formation of photoreceptors
retinal (light-sensitive molecule) combined with opsin (membrane protein)
define rhodopsin
retinal-opsin complex in rod cells
nerve impulse in retina pathway
retinal absorbs a photon of light
rhodopsin changes conformation to form photoexcited rhodopsin
activates transducin (G-protein)
activates phosphodiesterase (PDE)
catalyses hydrolysis of cyclin GMP (cGMP)
ion channels in rod cell membrane close
nerve impulse in retina neurons
why rod cells function in dim light
protein cascade amplifies the signal
why cone cells detect colour
different forms of opsin combine with retinal producing different photoreceptor proteins
each have maximal sensitivity to specific wavelengths
