Lecture 22 - Cell Signalling Flashcards
What is the basic concept of cell signalling
A chemical signal released by one cell is recognised by another cell
Usually involves a receptor molecule that recognises the signal in a highly specific manner
Allows the recipient cell to make a characteristic response
Why is cell signalling important
Essential for co-ordination of cell behaviour
Single cell organisms, such as yeast, use signalling to identify and interact with cells of the correct mating type in sexual reproduction
Multicellular organisms depend on cell signaling for correct development, tissue maintenance and homeostasis
What are the different types of cell signalling
Endocrine
Paracrine
Neuronal
Contact dependent
Examples of actions of molevules
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What is lateral inhibition mediation by the delta-notch signalling system
During development in parts of the nervous system two specialized cell types (neurons and support cells) are formed in an organised manner through contact mediated cell signaling involving Delta (signal) and Notch (receptor).
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What is Delta-Notch signalling
Unspecified epithelial cells are essentially equivalent, with each cell signaling to it’s neighbours to promote degradation of neurogenin (in turn promoting low levels of Delta expression)
Some cells will by chance express slightly higher levels of Delta. This signals to surrounding cells to prevent neurogenin expression and; i) stops them from differentiating as neurons; ii) reduces their expression of Delta.
Neurogenin levels increase in cells not receiving Delta signal, this allows expression of the factor Neuro D, that initiates neuronal differentiation
What other mechanisms could be used to ensure local signals do not act too far from their origin?
Rapid breakdown (e.g. proteases)
2) Sequestration (e.g. by the ECM
Response to a signal is cell-type specific
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xChanges in cell behaviour may result from the integration of many signals
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What does the molecular relay (intracellular signalling pathway) allow
i) modulation of the signaling pathway, for instance cross-talk with other signalling pathways;
ii) amplification of the pathway, to increase sensitivity
iii) Distribution of the signal to all parts of the cell
What are the functions of intracellular signalling molecules (eg. how could they function)
Localisation
Amplification and Distribution
Integration of information
Positive & negative feedback
Distribution to different cellular compartments
What are the 2 types of receptors
Cell-surface
Intracellular
what is an example of a cell-surface receptor
e.g. G-protein coupled receptors (Cell Signaling Lecture 2);
e.g. enzyme-linked receptors (Cell Signaling Lecture 3)
What is an example of intracellular signalling molecule
Intracellular receptors that act directly as transcription factors (e.g. steroid and thyroid hormone receptors)
or
Enzymes directly activated by the signal molecule (e.g. guanylyl cyclase activated by NO
What are features of steroid hormones
Steroid and thyroid hormones are small, hydrophobic signal molecules that interact with intracellular receptors
Steroid hormones (e.g. cortisol, testosterone) and thyroid hormones (e.g. thyroxine) interact with intracellular receptors.
The hormone-receptor complex acts directly as a transcription factor to regulate expression of specific genes
Where is testosterone produced
Leydig cells in the testis
Actions during fetal
development and at puberty
Androgen insensitivity syndrome
XY individuals lack receptors for
testosterone and develop female
Physical characteristics
Demonstrate coordinated actions
Of hormone on multiple tissues
What does Nitric oxide do physiologicaly
NO – dissolved gas with many physiological roles
Nitroglycerin has been used for >100 years to treat angina
Early 80’s shown to be the endothelial derived signals that relaxes blood vessels
What type of signalling does NO do
Rapid, short lived,
half life of 5-10 seconds
Ensures local actions
How does viagra work
sustains vasodilation by blocking signal reversal
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