Cell Signalling (Biomedical Science)

Cells To Systems - Cell Signalling
Cell Signalling - Signal Transduction & Receptor Tyrosine Kinases

Cellular Communication:

 No cells exist in isolation (each cell needs to know what the neighbouring cells are doing)
 Signals are constantly produced
 Signals need to be constantly received, processed, interpreted and response has to be generated
 Signals are generally transmitted across the environment in the form of soluble/insoluble molecules
 These molecules must be detected and appropriate responses must be produced
 The biggest barrier to this process is the cell membrane

 The membrane is impermeable to large soluble molecules
 Some are transported across the membrane
 Others are detected outside of the cell through the receptor and a signal has to be transmitted/conveyed into the
cell

Receptors - Receive signalling from the outside of the cell

Different Modes For A Cell To Receive Stimuli:

1. Contact dependent
2. Paracrine signalling
3. Synaptic signalling
4. Endocrine signalling
5. Autocrine/Self-signalling

Contact Dependent:
For a signal to be received, 2 components are needed to start this

1. Signalling molecule
2. Receptor on the cell surface

In The Form Of How This Is Passed Is Different:

 Sometimes, both the receptor and the signalling molecule will be transmembrane proteins
 Signalling cell will have a molecule which is sitting on the plasma membrane
 Receiving cell will have a receptor which will be embedded in the membrane
 Both cells have to be in very close contact for the signal to be passed on from 1 cell to another

Paracrine Signalling:

 Secreting soluble molecules
 They can diffuse
 The cells that are in close neighbourhood (if they have the receptors for these ligands/signal molecules) can receive
signals
 The closer the responding cells are to a signalling cell, the stronger response they will produce as they receive most
of the signal there. However, this a short distance signalling

Synaptic Signalling:

 Specific form of cell signalling
 When we think of neurons, they have cell bodies, 1 axon which is going to emit signals and they have other signals
coming in through dendrites
 With the target cell, there is a special formation of a synapse
 From the axon they have molecules that are secreted and the target cell is going to receive them
 Sometimes the signals have to cross a very long distance e.g synaptic nerve to the foot
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, Cells To Systems - Cell Signalling
Endocrine Signalling:

 The signalling molecules have to travel through the bloodstream to go to the target cell
 Can be a very long distance until they meet their target cell

Autocrine/Self-Signalling:

 A very specific type of signalling
 The same cell is secreting signals and receiving them




Receptors & Ligands:

 For signalling to be initiated, receptors and signalling molecules are needed
 If the cell does not express an appropriate receptor for certain types of signalling molecules, then the particular
signal cannot respond

Ligand - A molecule that binds to a receptor e.g. the ligand of the insulin receptor is insulin

 Some receptors will be very specific and can only bind to 1 type of signal, but for some receptors, they can bind to
different types of ligands
 There will be ligands which will be very specific and can only bind to 1 receptor, or there will be ligands that can
bind to multiple receptors
 Different ligands can produce different responses at the same receptor e.g. agonist/antagonist
 So-called receptors communicate signals to cells
 Thousands of receptors exist in humans

Ligands:
Detects a vast array of signals

 Dissolved gases (NO, CO, H2S)
 Peptides/Proteins
 Fatty acids
 Amino acids
 Retinoids
 Nucleotides

Receptors:

 Intracellular
 Cell surface (ion channel-, G protein- and enzyme- coupled

Single Transduction - Process where 1 type of signal is converted to another




The Plasma Membrane As Interaction Surface With The Surrounding Of A Cell:

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