What is extracellular signalling?
The process by which cells communicate with each other using signalling molecules.
Why is signalling fundamental in multicellular organisms?
It coordinates activities essential for survival and proper organism function.
What cellular functions depend on extracellular signalling?
Response to environment, growth and development, homeostasis, immune responses, and metabolism.
What enables a cell to respond to a signal?
Specific receptor proteins.
Why must receptors have high affinity for signalling molecules?
Because signalling molecules may be present at very low concentrations.
What determines receptor specificity for a signal?
The three-dimensional structure of the receptor protein.
How can extracellular signals act over long distances?
They are secreted and diffuse through the extracellular environment.
How can extracellular signals be localised?
They remain associated with the signalling cell or extracellular matrix.
what are the 2 versions of localised signalling?
Signals can be membrane-bound or tightly associated with the extracellular matrix.
What is juxtacrine (contact) signalling?
Signalling that requires direct contact between signalling and receiving cells.
What is paracrine signalling?
Secreted signals acting over a few cell diameters.
What is autocrine signalling?
Signals that act on the same cell that produced them.
What is synaptic signalling?
A specialised form of paracrine signalling involving neurotransmitters at synapses.
What is endocrine signalling?
Hormones produced locally but transported systemically through the organism.
What types of molecules act as signalling molecules?
Peptides, small molecules, metabolic products, and lipids.
Give examples of peptide signalling molecules.
Insulin and VEGF.
What are small molecule signalling examples?
Nitric oxide (NO).
Why is nitric oxide used for short-range signalling?
It is short-lived and breaks down rapidly.
What are metabolic product signalling molecules?
Non-gene-encoded molecules produced by enzyme pathways, such as steroids.
What are lipid signalling molecules like?
Membrane-bound molecules such as phospholipids.
what is the process of the use of nitric oxide during vasodilation?
-endothilial cells release nitric oxide synthase due to NOS3, increase nitric oxide.
-platelets and smooth muscle cells release guanuylyl cyclase due to GUCY1A3
-this increases cGMP which then causes vasodilation, reduced blood pressure and effects of the nitric oxide continue downstream
What determines the range and persistence of a signal?
The type of signalling molecule.
Why must signalling be terminated?
To prevent continuous activation of the pathway.
How can signalling be terminated by receptor internalisation?
The receptor is brought into the cell and can no longer respond to the signal.
