Lecture 11 part 2 Flashcards
How does the extracellular signalling molecules function?
Function within an organism to control:
➢metabolic processes within cells;
➢ the growth and differentiation of tissues;
➢ the synthesis and secretion of proteins;
➢the composition of intracellular and extracellular fluids.
Communication by extracellular signals involves which six steps?
➢Synthesis of the signalling molecule; ➢Release of the signalling molecule; ➢Transport to the target cell; ➢Detection of the signal by a specific receptor protein; ➢Cellular response to the signal; ➢Removal of the signal.
Extracellular signalling molecules are synthesized and
released by signalling cells. Signalling molecules operate over which five distances?
➢paracrine, ➢endocrine, ➢autocrine, ➢signalling across gap junctions, ➢neuronal.
What are paracrine signals?
Signals from one cell can act on nearby cells, e.g. growth factors.
What are endocrine signals?
Signals from one cell can act on distant cells,
e.g. sending a signal throughout the whole body by
secreting hormones into the bloodstream.
What are autocrine signals?
Signals act on the signaling cell itself , e.g. strengthening response.
What are signalling across gap junctions signals?
Direct diffusion of ions and small molecules between adjacent cells , e.g. epithelial tissue.
What are neuronal signals?
The signalling cells (neurons) release the chemical
ligands (neurotransmitters), a long distance from the cell body.
Physical extension of the cell itself (axon) spans the long distance to a specific target so the ligand is released in a space very close to the target cell (synapse), e.g. neurons and muscle cells.
What are juxtacrine signals?
Contact-dependent signalling. Direct physical contact through signal molecules found in the plasma membrane of the signaling cells and receptor proteins present in the plasma membrane of the target cell.
What are receptors?
Specifics that take the signalling molecules.
Receptors can be activated by:
binding of secreted or membrane-bound molecules,
changes in the concentration of a metabolite and physical interaction.
What is primary messenger?
The signaling molecule acts as a ligand (primary
messenger), which binds to a structurally complementary site on the extracellular or membrane-spanning domains of the receptor.
Where does hydrophilic- and hydrophobic messengers bind to?
Hydrophilic messengers bind to cell membrane (extracellular) receptors.
Hydrophobic messengers bind to intracellular receptors which regulate expression of specific genes.
How does a ligand bind its receptor?
A ligand binds its receptor through a number of specific weak non-covalent bonds by fitting into a specific binding site.
What does high- and low receptor affinity means?
High receptor affinity - low concentrations of a ligand will result in binding of most of the corresponding receptors.
Low receptor affinity - high concentration of the ligand is required for most receptors to be occupied
Prolonged exposure to a ligand may lead to?
Desensitization of the cell
