Signal transduction pathway
Sequence of molecular events and chemical reactions that lead to a cell's response to a signal
In large organisms, signals travel by diffusion or by blood.
Diffuse to and affect the cells that make them
Diffuse to and affect nearby cells
receives signal...and perpetuates it or starts a reaction
travel to distant cells
inactive signal transduction molecules
can phosphorylate other molecules - donate phosphate
removes phosphate - opposite of kinase protein
binding sites for chemical signal molecules
can also bind to ligands - but tie up or reverse productivity
Small or nonpolar ligands that can diffuse across plasma membrane - i.e., small enough, so what are they able to use?
Large or polar ligands bind to plasma membrane receptors (i.e., too large to go thru membrane so what do they have to use?)
Ion channel receptors
Channel proteins that alllow ions to enter/leave cell.
g-protein linked receptors
Ligand binding changes the shape of the cytoplasmic region which binds to a g protein
distinct functional part of a protein
mobile membrane proteins with 3 subunits. They bind gdp and gtp.
Produced from adrenaline
direct signal transduction
happens at plasma membrane, function of its own receptor. Ligand itself becomes an enzyme.
Indirect signal transduction
Another molecule - second messenger - mediates reaction
Cascade of events
What happens in a signal transduction relay. Protein kinase cascade, pathway in which one protein kinase activates the next
small molecules that diffuse into the cytoplasm to activate the enzyme (binding of hormone to membrane receptor)
hydrophobic portion embedded in plasma membrane...also has a hydrophilic portion IP3, projecting into cytoplasm.
chaperone protein? something receptor can be bound to; released once ligand binds.
signal - growth factor
stimulates cell division
how info goes from membrane to nucleus
protein kinase cascade. Also provides specificity. Different target proteins provide variation.
enzyme that catalyzes formation of cAMP from ATP. located on cytoplasmic side of the plasma membrane.
cAMP target types (2)
either ion channels in sensory cells (opens channel) or protein kinases in cytoplasm (exposes active side, starts cascade)
synthesizes phospholipids from membrane into second messengers
(phosphatidyl inositol-bisphosphate) hydrophobic DAG in membrane, hydrophylic IP3 in cytoplasm
too much IP3/DAG
inhibits synthesis of IP3
Lithium ions (Li) ...stop G protiens from activating phospholipase C...
acts as a second messenger. Activates protein kinase C, controls other channels, and stimulates secretion by exocytosis.
(nitric oxide - related to nitroglycerin) another second messenger
Cells alter balance between enzymes that activate/inactivate BY
either synthesis, breakdown of enzymes, or activation/inhibition of enzymes by other molecules.
general effects of a signal
opening ion channels, changing enzyme activity, or differential gene transcription.
1 molecule of ephiephrine that arrives at plasma membrane =
10,000 molecules of blood glucose
equivalent of plasmodesmata in plants
gap junctions in animals. Cell junction, allows communication.
channel between adjacent cells
proteins that traverse gap junctions
continuous cytoplasm of fused plasma membranes ... in plasmodesmata?
fills space in plasmodesmata channel
steps of signal transduction pathway
signal causes receptor protein to change conformation; conformation change gives it protein kinase activity; phosphorylation alters function of responder protein; signal amplified; protein binds to DNA activated; expression of genes altered; cell altered
example of a gated ion channel (on muscle cells)
Ca is a second messenger; sends signal to ...
protein kinase C, controls other channels, stimulates secretion by exocytosis.
gap junctions permit...
metabolic cooperation...and sharing of atp, enzymes, amino acids...