CELL SIGNALLING AND COMMUNICATION
General Process
1 Signal reception ● Signal molecule (ligand) binds specifically to a complementary
site on a receptor protein (located at the cell’s surface or inside
the target cell) to form a ligand-receptor complex
● Receptor protein undergoes a conformational change, often
becoming activated and able to interact with other molecules in
the cell
● Intracellular or extracellular/membrane/cell surface receptors
2 Signal transduction ● Process by which the target cell converts an extracellular signal
into an intracellular signal that results in a specific cellular
response
● Occurs either in a single step (e.g. intracellular receptors) or via a
multistep pathway consisting of a series of relay molecules
(usually proteins such as enzymes)
○ Each protein in the pathway typically acts by altering the
conformation of and hence activating or inhibiting the
protein immediately downstream (usually through
phosphorylation; phosphorylation cascade)
○ Second messengers
Phosphorylation and dephosphorylation
Protein kinase (PK) - phosphorylation (activates other PKs)
Protein phosphatase (PP) - dephosphorylation (inactivates PKs for reuse)
3 Cellular response ● Signal transduction pathway eventually leads to regulation of
one or more cellular activities
○ Cytoplasmic response: changes in cell metabolism
○ Nuclear response: change in gene expression
Cell surface/membrane receptors
● Transmembrane proteins embedded in cell membrane of target cell
● Bind to hydrophilic/water soluble signal molecules
● Types:
○ G-protein linked receptors
○ Receptor tyrosine kinases
○ Ion channel receptors (ligand-gated ion channels)
○ Integrin receptors
G-protein linked receptors (GPLR)
Structure:
● Primary: 1 polypeptide chain
● Secondary: 7 α-helices spanning the cell membrane, connected by non-helical segments
Copyright © 2019 tonyndr
General Process
1 Signal reception ● Signal molecule (ligand) binds specifically to a complementary
site on a receptor protein (located at the cell’s surface or inside
the target cell) to form a ligand-receptor complex
● Receptor protein undergoes a conformational change, often
becoming activated and able to interact with other molecules in
the cell
● Intracellular or extracellular/membrane/cell surface receptors
2 Signal transduction ● Process by which the target cell converts an extracellular signal
into an intracellular signal that results in a specific cellular
response
● Occurs either in a single step (e.g. intracellular receptors) or via a
multistep pathway consisting of a series of relay molecules
(usually proteins such as enzymes)
○ Each protein in the pathway typically acts by altering the
conformation of and hence activating or inhibiting the
protein immediately downstream (usually through
phosphorylation; phosphorylation cascade)
○ Second messengers
Phosphorylation and dephosphorylation
Protein kinase (PK) - phosphorylation (activates other PKs)
Protein phosphatase (PP) - dephosphorylation (inactivates PKs for reuse)
3 Cellular response ● Signal transduction pathway eventually leads to regulation of
one or more cellular activities
○ Cytoplasmic response: changes in cell metabolism
○ Nuclear response: change in gene expression
Cell surface/membrane receptors
● Transmembrane proteins embedded in cell membrane of target cell
● Bind to hydrophilic/water soluble signal molecules
● Types:
○ G-protein linked receptors
○ Receptor tyrosine kinases
○ Ion channel receptors (ligand-gated ion channels)
○ Integrin receptors
G-protein linked receptors (GPLR)
Structure:
● Primary: 1 polypeptide chain
● Secondary: 7 α-helices spanning the cell membrane, connected by non-helical segments
Copyright © 2019 tonyndr
