Unit 1 - Communication and Signalling Flashcards
How do multicellular organisms signal between cells?
using extracellular signalling molecules
What are examples of extracellular signalling molecules?
Steroid hormones, peptide hormones, and
neurotransmitters are examples of
extracellular signalling molecules.
What are receptor molecules of target cells?
Receptor molecules of target cells are
proteins with a binding site for a specific
signal molecule
What does the binding of a signal molecule result in?
Binding changes the conformation of the
receptor, which initiates a response within the
cell
Why do signalling molecules have different effects on different cell type?
due to differences in the intracellular signalling molecules and pathways that are involved
How do different cell types attract to a specific receptor?
produce specific signals that can only be detected and responded to by cells with the specific receptor
How do hydrophobic signalling molecules work?
Hydrophobic signalling molecules can diffuse
directly through the phospholipid bilayers of
membranes, and so bind to intracellular
receptors
What are the receptors for hydrophobic signalling molecules?
The receptors for hydrophobic signalling
molecules are transcription factors
What are transcription factors?
Transcription factors are proteins that when
bound to DNA can either stimulate or inhibit
initiation of transcription
Where do steroid hormones bind to?
Steroid hormones bind to specific receptors
in the cytosol or the nucleus
What do hormone- receptor complex bind to?
Specific DNA sequenced called Hormone Response Elements (HREs)
What does binding at HRE sites influence?
influences the rate of transcription, with each steroid hormone affecting the gene expression of many different genes
What doe hydrophilic signalling molecules bind to?
bind to transmembrane receptors and do not enter the cytosol
What are examples of extracellular signalling molecules?
Peptide hormones and neurotransmitters are
examples of hydrophilic extracellular
signalling molecules.
What happens when an extracellular signalling molecule bind to the membrane?
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
What do transmembrane proteins act as in Hydrophilic signalling?
Transmembrane receptors act as signal
transducers by converting the extracellular
ligand-binding event into intracellular signals,
which alters the behaviour of the cell
What does transduced hydrophilic signalling often involve?
Transduced hydrophilic signals often involve
G-proteins or cascades of phosphorylation by
kinase enzymes
What do G-proteins do?
G-proteins relay signals from activated
receptors (receptors that have bound a
signalling molecule) to target proteins such
as enzymes and ion channels
What do protein cascades allow?
allow more than one intracellular signalling pathway to be activated
What do phosphorylation cascades involve?
Phosphorylation cascades involve a series of events with one kinase activating the next in the sequence and so on.
What does the binding of peptide hormone insulin do to its receptor in intracellular signalling?
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
What happens to the receptor when insulin binds to it?
Binding of insulin to its receptor causes a
conformational change that triggers
phosphorylation of the receptor. This starts a
phosphorylation cascade inside the cell,
which eventually leads to GLUT4-containing
vesicles being transported to the cell
membrane.
What is Type 1 diabetes caused by?
by failure to
produce insulin
What is Type 2 diabetes caused by?
loss of receptor
function
What is Type 2 diabetes associated with?
Obesity
What does exercise do for diabetes?
Exercise also triggers recruitment of GLUT4,
so can improve uptake of glucose to fat and
muscle cells in subjects with type 2
What is the resting membrane potential?
Resting membrane potential is a state where there is no net flow of ions across the membrane
What does the transmission of a nerve impulse require?
changes in the membrane potential of the neuron’s plasma membrane
What is an action potential?
a wave of electrical
excitation along a neuron’s plasma membrane
What do neurotransmitters do?
Neurotransmitters initiate a response by
binding to their receptors at a synapse
What are neurotransmitter receptors?
Neurotransmitter receptors are ligand-gated ion channels
What is depolarisation?
Depolarisation is a change in the membrane
potential to a less negative value inside
What causes depolarisation?
Depolarisation of the plasma membrane as a
result of the entry of positive ions triggers the
opening of voltage-gated sodium channels,
and further depolarisation occurs
What restores the resting membrane potential?
The Inactivation of the sodium channels and the opening of potassium channels
What does the binding of neurotransmitters trigger?
- the opening of ligand-gated ion channels at a synapse
- Ion movement occurs and there is
depolarisation of the plasma membrane
What happens if there is sufficient ion movement and the threshold is met?
If sufficient ion movement occurs, and the membrane is depolarised beyond a threshold value, the opening of voltage-gated sodium channels is triggered and sodium ions enter the cell down their electrochemical gradient
What does sodium ions entering the cell cause?
This leads to a rapid and large change in the
membrane potential. A short time after
opening, the sodium channels become
inactivated.
What happens when the sodium channels are inactivate?
Voltage-gated potassium
channels then open to allow potassium ions
to move out of the cell to restore the resting
membrane potential
What happens when the action potential reaches the end of the neuron?
When the action potential reaches the end of
the neuron it causes vesicles containing
neurotransmitter to fuse with the membrane
— this releases neurotransmitter, which
stimulates a response in a connecting cell
What happens to the sodium channels during restoration of the resting membrane potential do?
allows the inactive voltage-gated sodium channels to return to a conformation that allows them to open again in response to depolarisation of the membrane.
What does the sodium-potassium pump do?
The sodium-potassium pump restores the sodium and potassium ions back to resting potential levels.
What cells of the eye detects light?
Two types of
photoreceptor cells: rods and cones
What is the function of rods?
Rods function in dim light but do not allow
colour perception.
What are cones responsible for?
Cones are responsible for colour vision and only function in bright light.
What does retinal combine with to form?
retinal is combined with a membrane protein, opsin, to form the photoreceptors of the eye
What is the retinal-opsin complex called?
Rhodopsin
What happens when retinal absorbs a photon of light?
Retinal absorbs a photon of light and
rhodopsin changes conformation to
photoexcited rhodopsin
What does photoexcited rhodopsin activate?
G-protein called transducin.
What does transducin activate?
which activates the
enzyme phosphodiesterase (PDE)
What does each G-protein molecule activate?
PDE
What does PDE catalyse?
the hydrolysis of a molecule
called cyclic GMP (cGMP)
What does cGMP cause?
This results in the closure of ion channels in
the membrane of the rod cells, which triggers
nerve impulses in neurons in the retina
Why do rod cells respond to low intensities of light?
A very high degree of amplification
What does opsin combine with retinal to form different form of?
Photoreceptor proteins with specific wavelengths, red, green, blue or UV
What happens to the ion concentration gradients during the restoration of the resting membrane potential.
Ion concentration gradients are re-established by the sodium-potassium pump, which actively transports excess ions in and out of the cell
what do phosphorylation cascades result in?
Phosphorylation cascades can result in the phosphorylation of many proteins as a result of the original
signalling event
