Cell Signaling

Generic Signalling Pathway
communication network between cell
Extracelluar Signal
Intrcellular Communication
Membrane Signaling events
Second Messenger
Intracellular Signaling
Signal : ligand, molecule that binds to specific site on another molecule
Cellular Response
Concept of lock and Key, allow molecule of particular shape to trigger change in chemical activity
Eg : Hormones, Neurotransmitter, Growth Factor, Cytokines, Antigens
Receptor : G-protein coupled receptor, receptor tyrosine kinase, receptor guanylate cyclase, adenylate cyclase, phospholipase
Eg : Cyclic AMP, Calcium, inositol triphosphate, nitric oxide, cyclic GMP, diacyglycerol
Eg ; Nitric oxide synthase, Guanylate cyclase, Calmodulin, Phosphodiesterase, CRE, CREB, Protein kinase, Protein Phosphatase
Altered metabolism, altered gene expression or Altered cell shape or motility
Type of Receptor
Intracellular receptor
Cell surface receptor
alter proteins function
Nitric Oxide - directly activates enzymes
alters gene expression
superfamily : Steroid Hormones, Thyroid Hormones, retinoids, Vitamin D
Ion Channel Linked
G-protein linked
Enzyme Linked
channel protein in plasma membrane that can open and close in response to signal from ligand
important in functioning nervous system
Sub Topic
response to extracellular signal proteins that promote growth, proliferation, differentiation, or survival of cells in animal tissues
six classes
growth factor
Receptor tyrosine kinases
Sub Topic
Tyrosine-kinase-associated receptors
Receptorlike tyrosine phosphatases
Receptor serine kinases phosphorylate
Receptor guanylyl cyclases
Histidine-kinase-associated receptors
associate with intracellular proteins that have tyrosine kinase activity
remove phosphate groups from tyrosines of specific intracellular signaling proteins
catalyze production of cyclic GMP in cytosol
activate 'two-component' signaling pathway, transfer phosphate to 2nd intracellualr signaling protein
2nd Messenger & Intracellular Signaling Pathway
Type of Cell Signalling
Cells secreting substances by exocytosis.
Entire cells disintegrate to secrete substances.
A portion of plasma membrane containing secretion, bud off the cells.
Eg: Sweat glands, Saliva glands
Eg: Mammary gland
Eg: Sebaceous glands, meibomian glands of eyelids
Contact dependent
Signaling involves contact between ligand-receptor binding of two cells.
Signals secrete by one cell and diffuse over short ranges to bind with receptor of neighboring cells.
Signals secretes by a cell and bind to receptor of the same cell.
Adherent junction
Tight junction
Gap junction
Holds epithelial cells together by connecting integral membrane protein to other membrane cell.
Firmly bond adjacent cells together to prevent leaks within epithelial sheets.
Anchoring two closely adjacent non-touching cells. Mostly in considerable stretching tissue.
Eg: Cardiac muscle.
Connect cells to extracellular material.
Eg: Cells of gastrointestinal and bladder.
Eg: Epithelial tissue
Connecting cells by providing tiny space between plasma membranes of two cells.
Eg: Heart and smooth muscle of gut.
second messenger function is to amplify the strength of the signal
Cyclic AMP
modified ATP >stimulate G protein receptor > activate G protein > activate enzyme in membrane plasma
enzyme convert ATP into cyclic AMP > activate protein kinase
protein kinase phosphorylate other protein
another enzyme can inactivate cAMP
toxin release by bacteria keep G protein active and stimulate cell lining intestine secrete large amount of water and salt
physiological effect:
enzyme activation
nerve stimulation
hormone secretion
muscle relaxation
nitric oxide (NO)
soluble and highly reactive gas produced by natural chemical and physical reaction
small and diffusible through membrane plasma
biological signal
improve immune system
major factor control penile erection
play role in development, neuron to neuron signaling and contribute to formation of memories.
can inhibit oxygen consumption by mitochondria (firefly flash)
how Nitric acid and cyclic GMP related?
Nitric acid synthetase (NOS) synthesize NO from L-arginine to form L-citrulline and nitric oxide
NO diffuse out of blood vessel and enter muscle cell
NO bind with nitric acid receptor and convert GTP to cyclic GMP
cyclic GMP bind to protein kinase G
sperm nucleic acid synthesis
muscle relaxation
cell division