Lecture 1 - Overview of cellular regulation Flashcards
Cell signalling
Cell to cell communication its also called cell signalling. Cell signalling provides an external (signal can come to the cell from another cell) means of regulating cellular activity)
Cellular activity can also be regulated by internally (signals within itself which can affect the way it behaves) generated signals although there are also often influenced by external signals.
Multiple steps of cell signalling
Synthesis of signal molecule, release of signal molecule, transport of signal molecule to target, detection of signal (reception) by target cell, response by target cell, some sort of feedback (to let the initial cell know that the signal has been received and acted upon)
Ligand is…
the signal and it can be lipid soluble or water soluble
Chemical nature of the signal can be varied - steroid, amino acid, amine, gas, peptide, protein
Water soluble
Can be stored in lipid vesicles within the signalling cell
Vesicles are little phospholipid membrane spheres that within can trap water soluble molecules.
The molecules are trapped in the vesicles because these molecules are soluble in water but not in lipids therefore they cannot cross the phospholipid bilayer that makes up the vesicles membrane
Allows for rapid release via exocytosis (since the molecules are ready to go and can be released when required)
Can travel in the blood without a carrier as it is soluble
Cannot enter the target cell (just like why they cannot exit the vesicles)
Message transduced via cell surface receptor
Lipid soluble
Cannot be stored in lipid vesicles within the signaling cell (as they can cross the phospholipid membrane of the vesicle)
Slow response because it is made on demand
Travels in blood with a carrier protein - may be longer lasting
Carrier protein since the blood is an aqueous environment and the carrier protein can also protect the molecule from being broken down by enzymes meaning that it can help the signal have a longer lasting effect
Can enter target cell
Acts on intracellular receptors often to directly regulate gene expression
Juxtacrine
Requires direct cell to cell contact
May be mediated by gap junctions
Composed of proteins called connexions
Allows ions and small molecules to move between cells
Gap junctions are bi-directional
Provide electrical and chemical coupling between cells
Allow very rapid communication between for example cardiac muscle cells or groups of neurons
Specificity achieved by direct contact
Specificity of juxtacrine
Specificity achieved by direct contact
Autocrine
Signalling between nearby cells of the same type (one cell signalling to cells of the same type so that they can operate as a group)
Requires the release and detection off a chemical message
Often employed to coordinate activity between a group of similar cells - makes them act together
Specificity is achieved by receptor expression and rapid ligand degradation (therefore cannot travel far)
Specificity of autocrine
Specificity is achieved by receptor expression and rapid ligand degradation (therefore cannot travel far)
Paracrine
Still local but it is from one cell type to another cell type
Employed for local signalling between different cell types
Requires the release and detection of a chemical message
For example endothelial cells communicate with nearby vascular smooth muscle via the release of nitric oxide - of major importance in blood pressure regulation
Specificity is achieved by receptor expression and rapid ligand metabolism (so when it travels further away it will not be available as it will be metabolised)
Specificity of paracrine
Specificity is achieved by receptor expression and rapid ligand metabolism (so when it travels further away it will not be available as it will be metabolised)
Juxtacrine - receptors
Signalling between adjacent cells can also involve receptors
But unlike other receptor forms of receptor mediated cell to cell communication, the signalling message is not released
The notch pathway is an example of this type of signalling
Can deliver more complex information to the target cell than gap junctions
Involved a membrane bound signal molecule on the signalling cell and then the target cell has the corresponding receptor
Involved in development (and cancer)
Specificity achieved by receptor expression and direct contact
Endocrine
Cell produces a signal called a hormone which travels through the blood to a distant target cell where it is detected via a specific receptor and then the target cell performs its task
Often involves signalling between distant cells in the body
Chemical signals called hormones carried in the blood
Hormones produced from discrete endocrine glands, endocrine tissues and isolated cells
Multiple chemical types of hormones (steroids, modified amino acids, peptides)
Endocrine system controlled by complex whole body physiology
Specificity is achieved by receptor expression being limited to target cells
Specificity of endocrine
Specificity is achieved by receptor expression being limited to target cells
Neuronal
One neuron sending a signal to another target such as muscle or endocrine cell
Signalling molecules (neurotransmitter) released from neurons at specialised highly localised synaptic sites
Acts on local or distant targets (neurons, muscle or glial cells)
Multiple chemical types of neurotransmitter (amino acids, amines, peptides)
Provides rapid, short lasting effects
Specificity is achieved by precise contacts and rapid removal of neurotransmitter to prevent diffusion
