Communication and signalling Flashcards
What do multicellular organisms signal between?
Multicellular organisms signal between cells using 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 happens when receptor molecules of a target cell bind to a specific signal molecule?
Binding changes the conformation of the receptor, which initiates a response within the cell.
What can only be detected and responded to by cells with the specific receptor?
Different cell types produce specific signals that can only be detected and responded to by cells with the specific receptor.
What happens in multicellular organisms (in relation to signalling)?
In a multicellular organism, different cell types may show a tissue-specific response to the same signal.
Can hydrophobic signalling molecules diffuse through the phospholipid bilayer?
Hydrophobic signalling molecules can diffuse directly through the phospholipid bilayers of membrane, 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 examples of hydrophobic signalling molecules?
The steroid hormones oestrogen and testosterone are examples of transcription factors/hydrophobic signalling molecules.
Where do steroid hormones bind to?
Steroid hormones bind to specific receptors in the cytosol or the nucleus.
Where does the horomone-receptor complex move to?
The hormone-receptor complex binds to
specific DNA sequences called hormone
response elements (HREs). Binding at these
sites influences the rate of transcription, with
each steroid hormone affecting the gene
expression of many different genes.
Where do hydrophobic signalling molecules bind to?
Hydrophobic signalling molecules bind to transmembrane receptors and do not enter the cytosol.
What happens when transmembrane receptors bind to a ligand?
Transmembrane receptors change conformation when the ligand binds to the extracellular face.
Does the signal molecule enter the cell when transmembrane receptors bind to a ligand?
The signal molecule does not enter the cell, but the signal is transduced across the plasma membrane.
What do transmembrane receptors act as?
Transmembrane receptors act as signal transducers by converting the extracellular ligand-binding event into intracellular signals, which alters the behaviour of the cell.
What involves G-proteins or cascades of phosphorylation by kinase enzymes?
Transduced hydrophilic signals often involve G-proteins or cascades of phosphorylation by kinase enzymes.
What do phosphorylation cascades allow?
Phosphorylation cascades allow more than one intracellular signalling pathway to be activated.
What does binding of a peptide hormone insulin to its receptor result in?
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 is diabetes mellitus caused by?
Diabetes mellitus can be caused by failure to produce insulin (type 1) or loss of receptor function (type 2).
What is type 2 generally associated with?
Type 2 is generally associated with obesity.
What also triggers more recruitment of GLUT4?
Exercise also triggers recruitment of GLUT4, so can improve uptake of glucose to fat and muscle cells in subjects with type 2 diabetes.
What is the resting membrane potential?
The 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?
The transmission of a nerve impulse requires changes in the membrane potential of the neurons plasma membrane.
What is an action potential?
An action potential is a wave of electrical excitation along a neuron’s plasma membrane.
What do neurotransmitters initiate?
Neurotransmitters initiate a response by binding to their receptors at a synapse.
What is depolarisation of the plasma membrane a result of?
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?
Inactivation of the sodium channels and the opening of potassium channels restores the resting membrane potential.
What causes neighbouring regions of membrane to depolarise?
Depolarisation of a patch membrane causes neighbouring regions of membrane to depolarise and go through the same cycle as adjacent voltage-gated sodium channels are opened.
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 a neurotransmitters to fuse with the membrane- this releases the neurotransmitter, which stimulates a response in a connecting cell
What does restoration of the resting potential membrane allow?
Restoration of the resting membrane potential 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 actively transports excess ions in and out of the cell?
Ion concentration gradients are re-established by the sodium-potassium pump, which actively transports excess ions in and out the cell.
What is the retina?
The retina is the area within the eye that detects light and contains two types of photoreceptor cells: rods and cones.
How do rods function?
Rods function in dim light but do not allow colour perception.
What are cones responsible for?
Responsible for colour vision and only function in bright light.
What does light-sensitive retinal combine within animals?
In animals the light-sensitive molecule retinal is combined with a membrane protein, opsin, to form the photoexcited rhodopsin.
What is rhodopsin in rod cells?
In rod cells, the retinal-opsin complex is called rhodopsin.
What does retinal absorb?
Retinal absorbs a photon of light and rhodopsin changes conformation to photoexcited rhodopsin.
What does a cascade of proteins do?
A cascade of proteins amplifies the signal.
What does photoexcited rhodopsin activate?
Photoexcited rhodopsin activates a G-protein, called transducin, which activates the enzyme phosphodiesterase (PDE).
What does PDE do?
PDE catalyses the hydrolysis of a molecule called cyclic GMP (cGMP).
What does the hydrolysis of cGMP do?
This results in a closure of ion channels in the membrane of the rod cells, which triggers nerve impulses in neurons in the retina.
What does a very high degree of amplification result in?
A very high degree of amplification results in rod cells being able to respond to low intensities of light.
What happens when opsin combines with retinal in cone cells?
In cone cells, different forms of opsin combine with retinal to give different photoreceptor proteins, each with a meximal sensitivity to specific wavelengths: red, green, blue or UV
