Cell Signaling
Figure 11.6-3 EXTRACELLULAR FLUID Plasma membrane CYTOPLASM 1 Reception 2 Transduction 3 Response Receptor Relay molecules in a signal transduction pathway Activation of cellular response Signaling molecule
Signal Transduction Pathway 1. Reception = target cell detects signal from outside; signal molecule binds to receptor protein 2. Transduction = binding of signal molecule changes receptor protein; may be single step or pathway 3. Response = transduced signal causes cellular activity
Figure 11.6-3 EXTRACELLULAR FLUID Plasma membrane CYTOPLASM 1 Reception 2 Transduction 3 Response Receptor Relay molecules in a signal transduction pathway Activation of cellular response Signaling molecule
Figure 11.2 Example: Mating in Yeast 1 Exchange of mating factors Receptor a α factor α a factor Yeast cell, mating type a Yeast cell, mating type α 2 Mating a α 3 New a/α cell Advantages of the a/α new a/α cell?
Types of Cell Signaling
Local v. Long-Distance Signaling Local Signaling direct contact = cell to cell recognition, cell junctions messenger molecules = paracrine signaling, synaptic signaling, quorum sensing
Figure 11.4 Plasma membranes Gap junctions between animal cells Plasmodesmata between plant cells (a) Cell junctions (b) Cell-cell recognition
Figure 11.5 Local signaling Target cell Electrical signal along nerve cell triggers release of neurotransmitter. Secreting cell Secretory vesicle Neurotransmitter diffuses across synapse. Local regulator diffuses through extracellular fluid. Target cell is stimulated. (a) Paracrine signaling *Growth factors* (b) Synaptic signaling *Nervous system*
Local Signaling- Quorum Sensing Accumulating signal molecule allows bacteria to determine density; coordinates behavior
Local v. Long-Distance Signaling (cont.) Long-Distance Signaling hormones = endocrine signaling molecules travel through circulatory system to target cells; molecular structures vary ex: insulin & glucagon (more on this later!)
Signals and Receptors
Cell-Surface Transmembrane Receptors 1. G-protein coupled receptors 2. Receptor tyrosine kinases 3. Ion channel receptors
Figure 11.7a G Protein-Coupled Receptor Signaling molecule binding site Segment that interacts with G proteins G protein-coupled receptor
Figure 11.7b G protein-coupled receptor G protein-coupled receptor Plasma membrane Activated receptor Signaling molecule Inactive enzyme CYTOPLASM 1 GDP G protein (inactive) Enzyme 2 GDP GTP GDP GTP Activated enzyme GTP GDP P i 3 Cellular response 4
Figure 11.7c Signaling molecule (ligand) α helix in the membrane Receptor osine Kinase Ligand-binding site Signaling molecule osines CYTOPLASM 1 Receptor tyrosine kinase proteins (inactive monomers) 2 Dimer Activated relay proteins 6 ATP 6 ADP P P P P P P P P P P P P Cellular response 1 Cellular response 2 Activated tyrosine Fully activated kinase regions receptor tyrosine (unphosphorylated kinase dimer) (phosphorylated 3 dimer) 4 Inactive relay proteins
Insulin released by pancreas; hormone causes cells to pull glucose out of blood when blood glucose level rises too high 1. reception = liver cells receive insulin (signal) released by pancreas - enzymes/dimers are activated; phosphorylated 2. transduction = activated enzymes begin relay to proteins 3. response = liver takes in glucose and stores as glycogen
Glucagon released by pancreas; hormone causes glucose to be released from liver when blood glucose level gets too low functions with a g protein receptor
Glucagon/Insulin Feedback Loop
Figure 11.7d Ion Gated Channel Receptors 1 2 3 Signaling molecule (ligand) Gate closed Ions Gate open Gate closed Ligand-gated ion channel receptor Plasma membrane Cellular response Ex. Neurotransmission
Why all the steps?! Many steps amplify the signal (cascade) Well coordinated; do not affect outside cells Different types of cells > Different genes expressed > Different types of responses!
Figure 11.10 Signaling molecule Receptor Activated relay molecule Inactive protein kinase 1 Active protein kinase 1 Phosphorylation cascade Inactive protein kinase 2 P i ATP PP ADP Active protein kinase 2 P Inactive protein kinase 3 P i ATP PP ADP Active protein kinase 3 P Inactive protein ATP PP ADP Active protein P Cellular response P i
Figure 11.16 Reception Binding of epinephrine to G protein-coupled receptor (1 molecule) Ex. Epinephrine Transduction Inactive G protein Active G protein (10 2 molecules) Inactive adenylyl cyclase Active adenylyl cyclase (10 2 ) ATP Cyclic AMP (10 4 ) Inactive protein kinase A Active protein kinase A (10 4 ) Inactive phosphorylase kinase Active phosphorylase kinase (10 5 ) Inactive glycogen phosphorylase Active glycogen phosphorylase (10 6 ) Response Glycogen Glucose 1-phosphate (10 8 molecules)
Secondary Messenger (camp)
Figure 11.12 First messenger (signaling molecule such as epinephrine) G protein Adenylyl cyclase G protein-coupled receptor GTP ATP camp Second messenger Protein kinase A Cellular responses
Cholera caused by Vibrio cholerae from human feces in drinking water produce toxins that modify G protein to remain stuck in active form high concentration of camp = large secretions of salt into intestines = profuse diarrhea = dehydration
Cholera Pathway
Apoptosis=programmed cell death DNA is chopped, organelles are split cell shrinks & forms lobes (blebbing) vesicles package up blebs, then are engulfed process often begins with signal from outside cell
Figure 11.20 2 µm
Figure 11.21 Ced-9 protein (active) inhibits Ced-4 activity Ced-9 (inactive) Cell forms blebs Mitochondrion Death- signaling molecule Active Ced-4 Active Ced-3 Other proteases Receptor for death- signaling molecule Ced-4 Ced-3 Inactive proteins Activation cascade Nucleases (a) No death signal (b) Death signal
Anatomy of Taste Synaptic Signaling!
Taste Transduction
PTC Paper Taste Transduction
Tongue Anatomy The pink bumps are fungiform papillae. - Each is made of dozens of taste receptors - More papillae = Better at tasting diff. flavors
Procedures Determine if you express the TAS2R38 gene Determine if you are a super, normal, or nontaster Eat jolly rancher, focusing on dying the end of the tongue. Place a binder circle to create a counting field Count # of papillae Suggestion: Photograph tongue
Super Taster= >30 fungiform papillae Normal Tasters= 15-30 fungiform papillae Non-Tasters= <15 fungiform papillae
Task: Does a certain level of taster relate to expressing the PTC tasting gene? Collect data and decide! Super Taster= >30 fungiform papillae Normal Tasters= 15-30 fungiform papillae Non-Tasters= <15 fungiform papillae