Cell signaling
Receptors specific 3D conformation bind to specific ligand specific response
Deprive of appropriate survival signals undergoes apoptosis (programmed cell
death)
tight regulation
signal reception
signal molecule: ligand
o bind to specific complementary site (receptors)
o Receptor protein changes in shape (activation): ligand-receptor complex
reacts with the molecules in the cell
intracellular receptors
extracellular/cell surface /membrane receptors
signal transduction
one step intracellular
multi step (cell surface membrane receptors)
o multi step signals (enzymes)
Specific sequence
first messenger
acts by changing its shape
phosphorylation
phosphorylation cascade
o cell surface membrane into the cell
cellular response
signal transduction pathway regulation of one or more cellular activities
cytoplasmic response/nuclear response
o cytoplasmic response
cell metabolism
regulation of enzyme activities
cytoskeletal arrangement
o nuclear response
gene expression
turning specific genes on or off in the nucleus
cell surface membrane receptors signaling
majority of the cells signal receptors (cell surface/ membrane receptors)
o transmembrane protein
* Hydrophilic or water-soluble molecules are unable to diffuse across the hydrophobic core
of the cell membrane
thus, bind to specific sites on cell surface receptor proteins
, Activate via confirmation changes: phosphorylation
initiates more than one in the cellular signal transduction pathway
o involves a series of relay multi step molecules (enzymes)
operate in sequence
a cascade of intercellular interactions that relay the signal (cell surface
membrane) to target molecules (in the cell): cellular response
Original signal molecule is NOT physically passed
Protein phosphorylation and dephosphorylation (molecular switch)
protein kinase (PK)
o enzymes that transfer phosphate groups from ATP to a protein
protein phosphatases (PP)
o enzymes that can remove phosphate groups from proteins
PK phosphorylates activates protein kinases (phosphorylation) turns on the signal
transduction pathway
PP dephosphorylates deactivate protein kinases (dephosphorylation)
turns off the signal transduction pathway protein kinase (available for reuse)
Activity of a protein is regulated by phosphorylation:
o balance of protein kinase (active) and protein phosphatases (active)
small molecules and ions (second messenger)
To transmit the message carried by the extracellular signal molecule (ligand) into the cell’s
interior
Small, non-protein, water soluble molecules/ ions
Diffusion (in the cytosol)
large scale, coordinated response
2 most common second messengers
o cyclic AMP (cAMP)
o calcium ions (Ca2+)
Mechanism of second messengers
First messenger binds to receptors stimulate increase in concentration of second
messengers alter the behaviors of relay proteins
Types of cell surface receptors
Receptors specific 3D conformation bind to specific ligand specific response
Deprive of appropriate survival signals undergoes apoptosis (programmed cell
death)
tight regulation
signal reception
signal molecule: ligand
o bind to specific complementary site (receptors)
o Receptor protein changes in shape (activation): ligand-receptor complex
reacts with the molecules in the cell
intracellular receptors
extracellular/cell surface /membrane receptors
signal transduction
one step intracellular
multi step (cell surface membrane receptors)
o multi step signals (enzymes)
Specific sequence
first messenger
acts by changing its shape
phosphorylation
phosphorylation cascade
o cell surface membrane into the cell
cellular response
signal transduction pathway regulation of one or more cellular activities
cytoplasmic response/nuclear response
o cytoplasmic response
cell metabolism
regulation of enzyme activities
cytoskeletal arrangement
o nuclear response
gene expression
turning specific genes on or off in the nucleus
cell surface membrane receptors signaling
majority of the cells signal receptors (cell surface/ membrane receptors)
o transmembrane protein
* Hydrophilic or water-soluble molecules are unable to diffuse across the hydrophobic core
of the cell membrane
thus, bind to specific sites on cell surface receptor proteins
, Activate via confirmation changes: phosphorylation
initiates more than one in the cellular signal transduction pathway
o involves a series of relay multi step molecules (enzymes)
operate in sequence
a cascade of intercellular interactions that relay the signal (cell surface
membrane) to target molecules (in the cell): cellular response
Original signal molecule is NOT physically passed
Protein phosphorylation and dephosphorylation (molecular switch)
protein kinase (PK)
o enzymes that transfer phosphate groups from ATP to a protein
protein phosphatases (PP)
o enzymes that can remove phosphate groups from proteins
PK phosphorylates activates protein kinases (phosphorylation) turns on the signal
transduction pathway
PP dephosphorylates deactivate protein kinases (dephosphorylation)
turns off the signal transduction pathway protein kinase (available for reuse)
Activity of a protein is regulated by phosphorylation:
o balance of protein kinase (active) and protein phosphatases (active)
small molecules and ions (second messenger)
To transmit the message carried by the extracellular signal molecule (ligand) into the cell’s
interior
Small, non-protein, water soluble molecules/ ions
Diffusion (in the cytosol)
large scale, coordinated response
2 most common second messengers
o cyclic AMP (cAMP)
o calcium ions (Ca2+)
Mechanism of second messengers
First messenger binds to receptors stimulate increase in concentration of second
messengers alter the behaviors of relay proteins
Types of cell surface receptors
