Communcation And Signalling Flashcards
Coordination
Multicellular organisms signal between cells using extra cellular signalling molecules
Examples of extra cellular signalling hormones
Steroid hormones, peptide hormones, and neurotransmitters
What is a receptor ?
They are proteins with a binding site for a specific signal molecule
What does binding do
It changes the confirmation of the receptor, which initiated a response in the cell
What do different cell types do ?
Different cell types produce specific signals that 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 intracellular signalling molecules and pathways that are involved.
What do multicellular organisms , different cell types show
A tissue specific response to the same signal
What are hydrophobic signals ?
Hydrophobic signalling molecules can diffuse directly through the phospholipid bilayer of membranes , and so bind to intracellular receptors
They can do this the tails of phospholipids in the plasma membrane are also hydrophobic and allow the molecules to pass across
What are the receptors of hydrophobic signalling
Transcription factors
They are proteins that when they bind to dna they inhibit initiation of transcription or stimulate it .
Examples of hydrophobic signalling molecules
Testosterone and oestrogen
What are steroid hormones and what do they do
They bind to specific receptors in the cytosol or the nucleus
The hormone-receptor complex moves to the nucleus where it binds to specific sites on DNA and affects gene expression
How do steroid hormones do this ?
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.
What do hydrophilic and transduction hydrophilic signalling molecules bind to ?
The transmembrane receptor and do not enter the cytosol
peptide hormone and neurotransmitters are examples of what ?
Hydrophilic extracellular signalling molecules
What do transmembrane receptors do ?
They change the confirmation when the ligand binds to the extracurricular face, signal molecules do not enter the cell but it’s transducer across the plasma membrane
What do transmembrane receptors act as ?
Signal transducers by converting the extracellular ligand binding event into intracellular signals which alters the behaviour of the cell
What are transduced hydrophilic signals often involved with ?
G-proteins or cascades of phosphorylation by kinase enzymes
What is the the function of 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. Details of G- proteins subunits are not required.
What is cascade phosphorylation ?
Phosphorylation cascades allow for more than one intracellular pathway to be activated
Describe the process of cascades phosphorylation?
Phosphorylation cascades involve a series of events with one kinase activating the next in the sequence and so on. Phosphorylation cascades can result in the phosphorylation of many proteins as a result of the original signalling event.
What is the action of insulin and how does it go about ?
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 does the binding of insulin to a receptor
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 because of failure of production production of insulin
What is type 2 diabetes?
Loss of receptor function, generally associated with obesity, Exercise also triggers recruitment of GLUT4, so can improve uptake of glucose to fat and muscle cells in subjects with type 2
Events of in cell signalling
- Extra cellular signal molecules released from cell
- Extracellular signal molecule travel to target cell
- Signal molecule binds to the receptor
- Binding causes a confirmational change
- This allows a response from the cell
What is membrane potential?
It is a state where there is no flow of ions across the membrane .
What does a transmission of a nerve impulse require ?
Change is the membrane potential of the neurons plasma membrane
What is an action potential ?
is a wave of electrical excitation along a neuron’s plasma membrane
How do neurotransmitters imitate a response
Binding to the synapses receptors
And neurotransmitters receptors are ligand gated channels
What is depolarisation of the plasma membrane?
It results in the entry of positive ions which then triggers the opening of voltage gated sodium channels and further depolarisation occurs
What is depolarisation?
It’s the change of membrane potential to the less negative value
What happens when you inactivate the sodium channels and open the potassium channels ?
It restore the resting membrane potential
How does this process happen ?
Binding of a neurotransmitter triggers the opening of ligand-gated ion channels at a synapse. Ion movement occurs and there is depolarisation of the plasma membrane. 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. This leads to a rapid and large change in the membrane potential. A short time after opening, the sodium channels become inactivated. 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 you depolarise a patch of membrane ?
It causes neighbouring regions to depolarise and go through the same process of other voltage gated channels
What happens 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
Restoring the membrane potential, how is this done ?
When you restore the resting membrane potential allows the inactive voltage gated sodium channel to return to the conformation that allows them to open again in response to depolarisation of the membrane.
What happens after repolarisation?
the sodium and potassium ion concentration gradients are reduced. The sodium-potassium pump restores the sodium and potassium ions back to resting potential levels.
Nerve impulses in the eyes
retina is the area within the eye that detects light and contains two types of photoreceptor cells: rods and cones
What do the rods do ?
The is 125 million rods
Rods are sensitive to light intensity, Rods function in dim light but do not allow colour perception.
Nocturnal animals have a greater degree of rods
What do cones do ?
The is 6 million cones
Not as sensitive to light as rods , they are sensitive to particular colours, Cones are responsible for colour vision and only function in bright light.
What are photoreceptors and how are they made ?
They are mode from retinal and ops in to form photoreceptors
What are rods cells in the retinal ops in complex called ?
Rhodopsin
What do come cells do in the process ?
Different forms of ops in combine with retinal give different photoreceptor proteins in each with a max sensitivity to specific wavelengths
What does a cascade of proteins do ?
Amplifies the signal
Retinal response to light ?
- Retinal absorbed light and rhodopsin changes confirmation to photoexcited rhodopsin
- Photoexcited rhodopsin activates a G- protein, called transducin, which activates the enzyme phosphodiesterase (PDE)
(A single photoexcited rhodopsin activates hundreds of molecules of G-protein.)(activated G-protein activates one molecule of PDE.) - PDE catalyses the hydrolysis of a molecule called cyclic GMP (cGMP)
Retinal response to light pt 2
- This results in the closure of ion channels in the membrane of the rod cells, which triggers nerve impulses in neurons in the retina
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Random facts
A very high degree of amplification results in rod cells being able to respond to low intensities of light
In cone cells, different forms of opsin combine with retinal to give different photoreceptor proteins, each with a maximal sensitivity to specific wavelengths: red, green, blue or UV
