Communication and Signalling Flashcards
Multicellular organisms signal between cells using?
Extracellular signalling molecules.
Examples of extra cellular signalling molecules?
Steroid hormones, peptide hormones and neurotransmitters
Receptor molecules of target cell are?
Proteins with a binding site for a specific signal molecule.
How do receptors work?
Binding changes the conformation of the receptor which initiates a response within the cell.
Different cell types produce —— ——
Specific signals
The specific signals produced by different cell types can only be detected and responded to by cells with the —— ——
Specific receptor
Signalling molecules may have different effects on different target cell types due to?
Differences in the intercellular signalling molecules and pathways that are involved.
In a multicellular organism, differnt cell types may show a ———— response to the same signal
Tissue-specific
How do hydrophobic signalling molecules interact with the cell?
Diffuse directly through the phospholipid bilayer of membranes and so bind to intercellular receptors.
What are the receptors of hydrophobic signalling molecules called?
Transcription factors.
What are transcription factors?
Proteins that when bound to DNA can either stimulate or inhibit initiation of transcription.
Examples of hydrophobic signalling molecules?
Steroid hormones oestrogen and testosterone.
How does hydrophobic signalling work?
Steroid hormones bind to specific receptors in the cytoskeleton or the nucleus. The hormone-receptor complex moves to the nucleus where it binds to specific sites on DNA called HRE’s. Binding at these sites influences the rate of transcription, with each steroid hormone affecting the gene expression of many different genes.
How do hydrophilic signalling molecules interact with the cell?
Bind to transmembrane receptors and do not enter the cytosol.
Examples of hydrophilic signalling molecules?
Peptide hormones and neurotransmitters.
Stage 1 of hydrophilic signalling. (Reception)
Transmembrane receptors change conformation when the ligand binds to the extra cellular face; the signal molecule does not enter the cell but the signal is transduced across the plasma membrane.
Stage 2 of hydrophilic signalling. (Transduction)
Transmembrane receptors act as signal transducers by converting the extra cellular ligand-binding event into intracellular signals, which alters the behaviour of the cell. Transduced hydrophilic signals involve G proteins or cascades of phosphorylation by kinase enzymes.
Transduction by G proteins?
G-proteins relay signals from activated receptors (receptors that have bound a signalling molecule) to target proteins such as enzymes and ion channels.
Transduction by phosphorylation?
Phosphorylation cascades allow more than 1 intracellular signalling pathway to be activated. They involve a series of events with 1 kinase activating the next in the sequence and so on.
Phosphorylation cascades can result in the phosphorylation of ——proteins as a result of the —— —— ——
many proteins as a result of the original signalling event
Stage 3 of hydrophilic signalling. (Response)
Response of the cell will vary depending on the signal.
INSULIN - binding of the peptide hormone to its receptor results in an?
Intracellular signalling cascade.
INSULIN - What does this intracellular signalling cascade trigger?
The recruitment of GLUT4 glucose transporter proteins to the cell membrane of fat and muscle cells.
INSULIN - what does insulin binding to its receptor cause?
A conformational change
INSULIN - what does the conformational change caused by insulin binding to its receptor trigger?
Phosphorylation of the receptor.
INSULIN - What does phosphorylation of the receptor start?
A phosphorylation cascade inside the cell.
INSULIN - What does the phosphorylation cascade inside the cell lead to?
GLUT4 containing vesicles being transported to the cell membrane.
What is diabetes caused by?
Failure to produce insulin (type 1)
OR
Loss or receptor function (type 2)
What is type 2 diabetes generally associated with?
Obesity.
What improves the uptake of glucose to fat and muscle cells in subjects with type 2 diabetes?
Exercise as it triggers the recruitment of GLUT4, so it can improve the uptake of glucose to fat and muscle cells in subjects with type 2
What is resting membrane potential?
A state where there is no net flow of ions across the membrane.
What does 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 neurons plasma membrane.
What do neurotransmitters do?
Initiate a response by binding to their receptors at a synapse.
What are neurotransmitter receptors?
Ligand gated ion channels which open in response to binding.
What do neurotransmitter receptors allow entry of?
And what do they therefore cause.
+vely charged ions and therefore cause depolarisation of the plasma membrane.
Depolarisation of the plasma membrane as a result of the entry of +ve ions triggers? And what occurs?
The opening of voltage gates sodium channels and further depolarisation occurs.
What is depolarisation?
Change in the membrane potential to a less negative value inside.
What restores the resting membrane potential?
Inactivation of Na channels and the opening of K channels.
Restoration of the resting membrane potential allows?
The inactive voltage-gated Na channels to return to a conformation that allows them to open again in response to depolarisation of the membrane.
Restoration of the resting membrane potential causes?
Ion concentration gradients to be reestablished by the sodium-potassium pump, which actively transports excess ions in and out of the cell.
Restoration of the resting membrane potential - following repolarisation what happens?
Sodium and potassium ion concentration gradients are reduced. The sodium potassium pump restores the sodium and potassium ions back to resting potential levels.
The process of restoring the resting membrane potential? (7 steps)
1) Binding of neurotransmitter triggers the opening of ligand-gated ion channels at a synapse.
2) Ion movement occurs and there is depolarisation of the plasma membrane.
3) If sufficient ion movement occurs, and the membrane is depolarised beyond a threshold value, the opening of voltage gates Na channels is triggered and Na+ ions enter the cell down their electrochemical gradient.
4) This leads to a rapid and large change in the membrane potential.
5) A short time after opening, the Na channels become inactivated.
6) Voltage-gated K channels then open to allow K+ ions to move out of the cell to restore the resting membrane potential.
7) ion concentration gradients are reestablished by the sodium-potassium pump.
What does depolarisation of a patch of membrane cause?
Neighbouring regions of the membrane to depolarise and go through the same cycle, as adjacent voltage-gated Na channels are opened.
When the action potential reaches the end of the neuron it causes…
vesicles containing neurotransmitter to fuse with the membrane.
When vesicles containing neurotransmitter fuse with the membrane what happens?
This releases neurotransmitter which stimulates a response in a connecting cell.
What is the retina?
The area within the eye that detects light and contains 2 types of photoreceptor cells (Rods and cones)
Rods?
Function in dim light but don’t allow colour perception.
Cones?
Responsible for colour vision and only function in bright light.
How rhodopsin formed?
In animals the light sensitive molecule retinal is combined with a membrane protein, opsin, to form the photoreceptors of the eye. In rod cells the retinal opsin complex is called rhodopsin.
Generation of a nerve impulse is brought about when? (6 step process)
1) Retinal absorbs a photon of light and rhodopsin changes confirmation to photoexcited rhodopsin.
2) A cascade of phosphorylation amplifies the signal. Photoexcited rhodopsin activates a G protein (transducin), which activates the enzyme PDE. A single photoexcited rhodopsin activates 100s of molecules of G protein.
3) each activated G-protein activates 1 molecule of PDE
4) PDE catalyses the hydrolysis of a molecule called cGMP. Each active PDE molecule breaks down 1000s of cMGP molecules per second.
5) The reduction in cGMP concentration as a result of its hydrolysis affects the function of ion channels in the membrane of rod cells. This results in the closure of ion channels in the membrane of rod cells.
6) This triggers nerve impulses in neurons in the retina.
What allows rod cells to be able to respond to low intensities of light?
A very high degree of amplification.
What causes cone cells to allow colour vision?
Different forms of opsin combine with retinal to give different photoreceptor proteins, each with maximal sensitivity to specific wavelengths: red, green, blue or UV.
