Quorum Sensing in Bacteria
Method of communication that allows bacteria to detect population density, controls bioluminescence
Local Signalling
Can occur at local or long distance scales through direct contact, or a specific target called synaptic signalling
Long distance signalling
Based on secretion and detection of hormones known as endocrine signalling in animals
Stages of Cell Signalling
Reception, transduction, response
Reception
Requires a receptor protein with the correct binding site to recognize a signalling molecule, signalling molecule acts as ligands whose binding impacts the shape and function of the receptor
Cell surface receptors
Integral membrane proteins, three main types
G protein coupled receptors
Work with G protein that binds GDP/GTP specificity for both signal molecule and type of G protein
Receptor tyrosine kinases
Self-phosphorylates, dimerizes and structurally modifies relay proteins, can activate up to 10 signal transduction pathways
Ligand gated ion Channel receptors
A channel that opens in response to signal molecule binding
Histidine Kinases
Self-phosphorylates, then phosphorylates a response regulator protein
Intracellular receptors
Signalling molecules are hydrophobic or small enough to pass through the plasma membrane such as steroids, often function as transcription factors
Signal transduction
The conversion of a signal into a form that can cause a specific cellular response
Protein kinase
Enzyme that adds a phosphate group to a protein from ATP , cytoplasmic protein kinases often phosphorylation serine or threonine
Protein phosphatase
Enzyme that removes a phosphate group from a protein
Phosphorylation cascade
A signallling pathway involving a series of phosphorylation events
Second messengers
Small, nonprotein water-soluble molecules involved in signal transduction, can diffuse through the cytoplasm
