Chapter 11: Cell Signaling Flashcards
Mating factors
a and α factors of yeast cells. when exposed a pair of cells of the opposite type fuse into new a/α cell
Signal transduction pathway
Signal binds to receptor and is transduced (changed) into response
Quorum sensing
Bacteria sense concentration of signaling molecules to monitor local density of cells
Local signaling
Signaling for nearby cells
- cell junctions
- cell cell recognition (surface molecules)
Local regulators
Signaling molecules for short distances
- growth factors (growth/division)
Paracrine signaling
Numerous cells simultaneously recieve/respond to signaling molecules produced by a single nearby cell
Synaptic signaling
Electrical signal along nerve cell triggers secretion of neurotransmitters, which diffuse across the synapse to the target cell
Hormones
Chemicals for long distance signaling
Endocrine signaling
Specialized endocrine cells release hormones which travel through the circulatory system to target cells
Plant hormones
Sometimes travel in vessels but mostly move through cells or diffuse through the air as gas
Epinephrine
Hormone that stimulates breakdown of glycogen
Glycogen breakdown
Releases glucose 1-phosphate, which is converted to glucose 6-phosphate. Then used by liver/muscle cell for energy production, or stripped of phosphate and released into blood as glucose
Glycogen phosphorylase
Cytosolic enzyme activated by epinephrine through a series of steps (plasma membrane is necessary)
Reception
Detection; Signal binds to receptor protein on target cell
Transduction
Converts signal to a form that causes a specific cellular response
Signal transduction pathway
Sequence of changes in a series of different molecules
Response
Cellular activity caused by signal
Ligand
Molecule that specifically binds to another molecule. Binding generally causes a shape change in receptor
GPCR
G protein
GTPase enzyme
GPCR pathway
Receptor tyrosine kinase
Plasma membrane receptor that attaches phosphate to tyrosine because of ligand. Can activate 10+ transduction pathways/results -> abnormal ones cause many cancers
RTK pathway
Ligand gated ion channel
Membrane receptor with a ion channel that opens/closes if bound to ligand.
Cell surface receptors
GPCR, RTK, ligand gated ion channels. 30% of all proteins. Flexible and unstable (difficult for X-ray crystallography)
Intracellular receptors
In nucleus or cytoplasm. Signaling molecules must be small and/or hydrophobic.
- transcription factors
Relay molecules
Relay a signal from receptor to response
Protein kinase
Enzyme that transfers phosphate from ATP to protein
- most act on other proteins not themselves
- serine/threonine are often phosphorylated
Phosphorylation cascade
Pathway of protein phosphorylation
Protein Phosphatase
Enzyme catalyze removal of phosphate from protein (dephosphorylation)
Second messengers
Small, non protein, water soluble molecules in signaling pathways
Adenyl Cyclase
Converts ATP to cyclic AMP in response to extracellular signal. Can greatly increase cytosolic concentration of cAMP
cAMP
Important second messenger. Activated by epinephrine and many other hormones/signals. Included in G protein, GPCR, and protein kinase pathways. High levels of cAMP activates protein kinase A.
Protein kinase A
Serine/threonine kinase which phosphorylates a variety of other proteins
Phosphodiesterase
Converts cAMP to AMP
Cholera
Cholera toxin permanently activates G protein involved in salt/water regulation by stopping it from hydrolyzing GTP to GDP. G protein continually activates adenyl cyclase, and resulting high concentration of cAMP causes lots of salt and water (osmosis) to be released from intestinal cells.
Ca 2+
Important second messenger
Functions: muscle cell contraction, secretion of certain substances, cell division, etc.
-low cytosolic concentration (actively transported into ER, outside the cell, sometimes to mitochondria/chloroplasts)
- signal increases cytosolic concentration of ca 2+ (usually through ER)
IP3 (inositol triphosphate)
Second messenger involved in calcium release. Diffuses through cytosol and binds to IP3 gated channel on ER membrane, causing it to open (calcium is released to cytosol)
DAG (diacylglycerol)
Second messenger involved in calcium release
Phospholipase C
Cleaves plasma membrane phospholipid PIP2 into IP3 and DAG
Calcium release pathway
- Signal activates receptor
- Receptor activates phospholipase C
- Phospholipase C forms IP3
- IP3 binds to ER membrane protein
- Calcium released from ER
Scaffolding proteins
Large relay proteins that attach to several other relay proteins
- can permanently hold together signaling pathway proteins at synapses
Apoptosis
Controlled cell suicide. DNA and organelles are cut up. Cell shrinks and becomes lobed, packaged into vesicles. Scavenger cells digest vesicles.
C. Elegans apoptosis
- Ced-9 protein in outer mitochondrial membrane inhibits Ced-3 and ced-4.
- Death signal inactivated ced-9
- Activated ced-3 (protease) and ced-4 activates nucleuses and proteases
Caspases
Main proteases of apoptosis
