Communication and Signalling 1.4 Flashcards
what do multicellular organism signal between cells use?
extracellular signalling molecules
what are receptor molecules of target cells?
proteins with a binding site for a specific signal molecule
what happens when the receptor binds?
binding changes the conformation of the receptor
- initiates a response within the cell
different cell types produce specific signals that can only be detected and responded to by what?
cells with the specific receptor
in a multicellular organism, different cell types may show what?
tissue-specific response to the same signal
how can hydrophobic signalling molecules diffuse?
they can diffuse directly through the phospholipid bilayers of membranes, and so bind to the intracellular receptors
what are the receptors for the hydrophobic signalling molecules?
transcription factors
give examples of hydrophobic signalling molecules
steroid hormones
- oestrogen
-testosterone
where do steroid hormones bind?
they bind to specific receptors in the cytosol or the nucleus
what does the hormone-receptor complex do?
it moves to the nucleus where it binds to specific sites on DNA and affect gene expression
where do hydrophilic signalling molecules bind?
they bind to transmembrane receptors and do not enter the cytosol
what happens to transmembrane receptors when a ligand binds to the extracellular face?
the receptors change conformation
what happens to the signal molecule if it does not enter the cell?
signal is transduced across the plasma membrane
how do transmembrane receptors act?
they act as signal transducers by converting the extracellular ligand binding event into intracellular signals
- alters behaviour of the cell
describe the intracellular signalling cascade that is resulted from insulin
- binding of peptide hormone insulin to its receptors results in an intracellular signalling cascade (ISC)
- this ISC triggers the recruitment of GLUT4 transporter proteins to the cell membrane of fat and muscle cells
how is type 1 diabetes mellitus caused?
failure to produce insulin
how is type 2 diabetes mellitus caused?
loss of receptor function
what is type 2 diabetes generally associated with?
obesity
how can exercise be beneficial to someone with type 2 diabetes?
triggers the recruitment of GLUT4
- improves the uptake of glucose to fat and muscle cells
what is resting membrane potential?
state where there is no net flow of ions across the membrane
what is required for the transmission of a nerve impulse?
a change in the membrane potential of the neuron’s plasma membrane
what is action potential?
a wave of electrical excitation along a neuron’s plasma membrane
how do neurotransmitters initiate a response?
by binding to the receptors at a synapse
what is the result of a depolarisation of the plasma membrane ?
the entry of positive ions triggers the opening of voltage-gated sodium channels
- further depolarisation occurs
what restores the resting membrane potential?
inactivation of the sodium channels and the opening of the potassium channels
what does depolarisation of a patch of membrane cause?
causes neighbouring regions of membrane to depolarise and go through the same cycle
- as voltage-gated sodium channels are opened
how are ion concentration gradients re-established?
by the sodium-potassium pump - actively transports excess ions in and out of the cell
what is the retina?
an area within the eye that detects light
what are the two types of photoreceptor cells that the retina contains?
rods cand cones
how are photoreceptors of the eye in animals formed?
light-sensitive molecule retinal is combined with a membrane protein called opsin
what is the retinal-opsin complex called in rod cells?
rhodopsin
what does a very high degree of amplification of rod cells result in?
the ability to respond to low intensities of light
describe what happens in cone cells
different forms of opsin combine with retinal to give different photoreceptor proteins
- each with a maximal sensitivity to specific wavelengths: red, green, blue and UV
what is involved in transducer hydrophilic signals?
G-proteins or cascades of phosphorylation by kinase enzymes
what do phosphorylation cascades allow?
they allow more than one intracellular signalling pathway to be activated
what happens when the action potential reaches the end of the neuron?
cause vesicles containing neurotransmitter to fuse with the membrane - this releases neurotransmitter, which stimulates a response in a connecting cell
what does the restoration of the resting membrane potential allow?
allows inactive voltage-gated sodium channels to return to a conformation that allows them to open again in response to depolarisation of the membrane
describe what happens when retinal absorbs a photon of light
- rhodopsin changes conformation to photoexcited rhodopsin
- a cascade of proteins amplifies the signal
- photo excited rhodopsin activates a G-protein called transducin - activates the enzyme phosphodiesterase (PDE)
- PDE catalyses the hydrolysis of a molecule called cyclic GMP (cGMP)
- results in closure of ion channels in the membrane of rod cells - triggers the impulses in neuron’s in retina
