1.4 : communication and signalling Flashcards
how do multicellular organisms signal between molecules
through extracellular signalling molecules
examples of signalling molecules
steroid hormones, peptide hormones, neurotransmitters
what are receptor molecules
receptor molecules are proteins with a binding site for a specific molecule
what does the binding of the receptor change
changes the conformation of the receptor which initiates a response in the cell
signal specificity
different cell types produce different signals that can only be detected and responded by cells with the specific receptor
why do signalling molecules have different effects on different cell types
will have different effects due to differences in intracellular signalling molecules and the pathways involved
what will different cell types show in response to the same signal
a tissue specific response
hydrophobic
molecules that are seemingly repelled by large masses of water. these molecules are also known as non-polar
hydrophobic signalling molecules movement
diffuse directly through phospholipid bi layer of membrane and bind do intracellular receptors
what are the receptors for hydrophobic molecules
transcription factors
what are transcription factors
transcription factors proteins that when bound to DNA can either stimulate or inhibit initiation of transcription.
examples of hydrophobic signalling molecules
steroid hormones such as estrogen and testosterone
where do steroid hormones bind
they bind to specific receptors in the cytosol or the nucleus
what does the binding of steroid hormones form
hormone receptor complex
how does the hormone receptor complex work
The hormone-receptor complex moves to the nucleus where it binds to specific sites on DNA and affects gene expression .
The hormone-receptor complex binds to specific DNA sequences called hormone response elements (HRE’s)
what does the binding of the complex to HRE’s influence
influences the rate of transcription, with each steroid hormone affecting the gene expression of many different genes .
hydrophilic
A molecule that is attracted to water molecules and tends to be dissolved by water. Also known as polar molecules.
hydrophilic signalling molecules movement
they do not enter the cytosol and instead bind to transmembrane receptors
examples of hydrophilic extracellular signalling molecules
peptide hormones and neurotransmitters .
transmembrane receptors
Transmembrane receptors change conformation when the ligand binds to the extracellular face. The signal molecule does not enter the cell, but the signal is transduced across the plasma membrane.
transduction
Process by which a chemical or physical signal is transmitted through a cell by a series of molecular events resulting in a cellular response.
how to transmembrane receptors act as signal transducers
by converting the extracellular ligand-binding event into intracellular signals, which alters the behaviour of the cell.
what do transduced hydrophilic signals involve
G-protiens, cascades of phosphorylation by kinase enzymes
what do G-protiens do
relay signals from activated receptors to target proteins such as enzymes and ion channels .
what are activated receptors
receptors that have bound a signalling molecule
what do phosphorylation casacdes do
Phosphorylation cascades allow more than one intracellular signalling pathway to be activated. They involve a series of events with one kinase activating the next in the sequence and so on.
what do phosphorylation casacdes result in
Phosphorylation cascades can result in the phosphorylation of many proteins as a result of the original signalling event.
what does the binding of insulin do
Binding of the peptide hormone insulin to its receptor results in an intracellular signalling cascade that triggers recruitment of GLUT4 glucose transporter proteins to the cell membrane of fat and muscle cells.
step 1 of insulin binding
Binding of insulin to its receptor causes a conformational change that triggers phosphorylation of the receptor.
step 2 of insulin binding
This starts a phosphorylation cascade inside the cell
step 3 of insulin binding
This phosphorylation eventually leads to GLUT4-containing vesicles being transported to the cell membrane.
what is diabetes mellitus
caused by failure to produce insulin (type 1 ) or loss of receptor function (type 2 ).
Type 2 is generally associated with obesity.
what does exercise trigger
triggers recruitment of GLUT4, so can improve uptake of glucose to fat and muscle cells in subjects with type 2 diabetes.
what is a nerve impulse
a signal transmitted along a nerve fibre
what is the resting membrane
state where there is no net flow of ions across the membranes
what does the transmission of a nerve impulse require
requires change in the membrane potential of the neurons plasma membrane
what is the action potential
wave of electrical excitation along a neurons plasma membrane
what are neurotransmitters
chemicals that transmit a signal across a synapse
what do neurotransmitters do
initiate a response by binding to their receptors at the synapse
what type of receptors are neurotransmitter receptors
ligand gated ion channels
what is depolarisation
a sudden change in membrane potential, usually from a relatively negative to positive internal charge
what is depolarisation the result of
the entry of positive ions which triggers the opening of voltage gated sodium channels and causes further depolarisation
how does the restoration of the membrane potential occur
the inactivation of the sodium channels and the opening of potassium channels
what does the binding of a neurotransmitter do
triggers the opening of ligand-gated ion channels at the synapse
how do sodium ions enter the cell
down a concentration gradient
what do sodium ions lead to
rapid and large change in membrane potential
action potential graph step 1
an external stimulus starts a rapid change in the voltage or action potential, this must reach above the threshold to start depolarisation
action potential graph step 2
depolarisation is caused by a rapid rise in membrane potential by opening sodium channels in the membrane resulting in a large influx of sodium ions
action potential graph step 3
repolarisation results from rapid sodium channel inactivation leading to a large influx of potassium ions from activated protien channels
action potential graph step 4
hyperpolarisation is a lowered membrane potential caused by the effect of the loss of pottasium ions and the closing of pottasium channels
action potential graph step 5
resting state is when membrane potential returns to resting voltage that it was before stimulus occurred
what does depolarisation of a patch of membranes do
causes neighbouring regions of membranes to depolarise and go through same cycle as adjacent voltage gated sodium channels are opened
what happens when action potential reaches the end of the neuron
causes vesicles containing neurotransmitters to fuse with membrane which releases neurotransmitters to stimulate a response to a connecting cell
what does restoration of the resting membrane potential allow
inactive voltage gated sodium channels to return to original conformation that allows them to open again in response to depolarisation of the membrane
what is reestablished by the sodium pottasium pump
ion concentration gradient
how is ion concentration gradient re-established
by the sodium pottasium pump which actively transports excess ions in and out of the cell
what follows repolarisation
the sodium and pottasium ion concentration gradients are reduced. the sodium pottasium pump restores the sodium and pottasium ions back to resting potential levels
what is the retina
the area in the eye that detects light and contains 2 photoreceptor cells
what are the two photoreceptors cells in the retina
rods and cones
what are rods
function in dim light but do not allow colour perception
what are cones
responsible for colour vision, need bright light to function
what is combined to make the photoreceptors of the eye
retinal and opsin
what is the retinal-opsin complex called
rhodopsin
initiation of a nerve impulse in response to a stimulus (1)
rhodopsin absorbs a photon of light and changes conformation and becomes photoexcited rhodopsin
what amplifies the signal from photoexcited rhodopsin (2)
a cascade of protiens
initiation of a nerve impulse in response to a stimulus (3)
the photoexcited rhosopin activates G-protiens called transducin which activates enzyme PDE.
a single photoexcited molecule activates hundreds of transducin, each molecule then activates 1 PDE. PDE then catalyses the hydrolysis of cyclic GMP
initiation of a nerve impulse in response to stimulus (4)
each PDE molecule breaks down thousands of cGMP per second.
this affects the function of ion channels in membrane of rod cells
results in the closure of ion channels which trigger nerve umpulses across the retina
what allows opsin to function at low lights
a higher amplification allows opsin to function at lower light intensities
what do different forms of opsin do in cone cells
give different photoreceptor protiens, each with maximal sensitivy to different wavelegnths of light such as red, blue , green and UV
