1.4 - Communication and Signalling Flashcards
Unit 1 (29 cards)
three examples of extracellular signalling molecules
*steroid hormones
*peptide hormes
*neurotransmitters
what are receptor molecules?
proteins on the target cell with a binding site specific to a signal molecule
how do hydrophobic signalling molecules enter the cell?
they diffuse directly through the phospholipid bilayer
where are the receptors for hydrophobic signalling molecules located?
inside the cell; either in the cytosol or in the nucleus
what term describes hydrophobic receptors?
transcription factors
define transcription factors:
proteins that, when bound to DNA, can either stimulate or inhibit the initiation of transcription
what is an example of hydrophobic signalling molecules?
steroid hormones: oestrogen and testosterone
what happens to cytosolic hormone receptor complexes?
move to the nucleus where they bind to specific sites on DNA and affect gene expression
what are the specific DNA sequences at these sites called?
Hormone response elements HRE’s
what is the action of hydrophilic signalling molecules?
They bind to transmembrane receptors as ligands and do not enter the cytosol
what are two examples of hydrophilic signalling molecules?
peptide hormones and neurotransmitters
what happens to transmembrane receptors following binding of a ligand?
conformational change
what happens following the conformational change of the transmembrane receptor?
the signal is transduced across the plasma membrane and the extracellular ligand-binding event is converted into intracellular signals which alter the behaviour of the cell
which proteins are involved in signal transduction?
G-proteins or kinase cascades enzymes
action of insulin:
insulin molecule released from pancreas binds to specific receptor on fat/muscle cells. Conformational change causes receptor to be phosphorylated. phosphorylation of receptor starts phosphorylation cascade and production of GLUT4. GLUT4 containing vesicles are translocated to cell membrane. glucose from blood enters the cell, reducing its concentration.
how can exercise improve the uptake of glucose into fat/muscle cells?
triggers the recruitment of GLUT4
what is the resting membrane potential of a neuron?
a state when there is no nervous impulse being generated.
describe two things about neurotransmitter receptors:
they are ligand-gated ion channels and located at the synaptic region at on end of a neuron
describe how a nerve impulse is generated:
neurotransmitter acts as ligand and binds to gate. channel opens and sodium ions enter cell. membrane is depolarised becoming less negative beyond threshold value and voltage-gated sodium channel open. sodium ions enter cell down their electrochemical gradient causing further depolarisation. this leads to a large change in the membrane potential, causing an action potential to be generated
how does the action potential travel?
depolarisation of the first region of the neuron causes the next region to depolarise and go through the same cycle of events, allowing the action potential to travel rapidly along the neuron, region after region
why is it important that the resting membrane potential is restored?
allows inactive voltage-gated sodium channels to return to a conformation that allows them to open again in response to further signals- allows the system to remain sensitive
what ultimately restores the membrane potential?
voltage-gated potassium channels open to allow potassium ions to flow out of the cell and restore the resting membrane potential
how are ion concentration gradients re-established?
sodium-potassium pump transports excess ions in and out of the cell
what happens when the action potential reaches the end of he neuron?
it causes vesicles containing neurotransmitters to fuse with the membrane, releasing neurotransmitter into the next synaptic cleft, which stimulates a response in the next connected cell
