Chapter 11 Cell Communication

Concept 11.1: External signals are converted into responses within the cell Signal-transduction pathway

LE 11-2 Exchange of mating factors a factor Receptor a a a factor Yeast cell, mating type a Yeast cell, mating type a Mating a a New a/a cell a/a

LE 11-3 Plasma membranes Gap junctions between animal cells Plasmodesmata between plant cells Cell junctions Cell-cell recognition

Local regulators - short distances Hormones - long-distance signaling Paracrine signaling Local regulator diffuses through extracellular fluid Secretory vesicle Secreting cell Target cell Local signaling Electrical signal along nerve cell triggers release of neurotransmitter Neurotransmitter diffuses across synapse Endocrine cell Blood vessel Long-distance signaling Hormone travels in bloodstream to target cells Synaptic signaling is stimulated Hormonal signaling Target

The Three Stages of Cell Signaling: A Preview Cells receiving signals go through three processes: Reception Transduction Response Animation: Overview of Cell Signaling

LE 11-5_1 EXTRACELLULAR FLUID CYTOPLASM Plasma membrane Reception Transduction Receptor Signal molecule

Relay molecules in a signal transduction EXTRACELLULAR FLUID CYTOPLASM Plasma membrane Reception Transduction Receptor Relay molecules in a signal transduction pathway Signal molecule

Relay molecules in a signal transduction EXTRACELLULAR FLUID CYTOPLASM Plasma membrane Reception Transduction Response Receptor Activation of cellular response Relay molecules in a signal transduction pathway Signal molecule

Concept 11.2: Reception: A signal molecule binds to a receptor protein, causing it to change shape Ligand Binding is highly specific Conformational change

LE 11-6 Hormone EXTRACELLULAR (testosterone) FLUID The steroid hormone testosterone passes through the plasma membrane. Plasma membrane Testosterone binds to a receptor protein in the cytoplasm, activating it. Receptor protein Hormone- receptor complex The hormone- receptor complex enters the nucleus and binds to specific genes. DNA mRNA The bound protein stimulates the transcription of the gene into mRNA. NUCLEUS New protein The mRNA is translated into a specific protein. CYTOPLASM

Receptors in the Plasma Membrane There are three main types of membrane receptors: G-protein-linked receptors Receptor tyrosine kinases Ion channel receptors

G-protein-linked receptor LE 11-7aa Signal-binding site Segment that interacts with G proteins G-protein-linked receptor

LE 11-7b Signal molecule Signal-binding site a Helix in the membrane Tyrosines Tyr Tyr Tyr Tyr Tyr Tyr Tyr Tyr Tyr Tyr Tyr Tyr Tyr Tyr Tyr Tyr Tyr Tyr Receptor tyrosine kinase proteins (inactive monomers) Dimer CYTOPLASM Activated relay proteins Cellular response 1 Tyr Tyr P Tyr P Tyr P Tyr Tyr P Tyr Tyr P Tyr Tyr P P P Tyr Tyr Tyr Tyr P Tyr Tyr P P Tyr Tyr P Cellular response 2 6 ATP 6 ADP Activated tyrosine- kinase regions (unphosphorylated dimer) Fully activated receptor tyrosine-kinase (phosphorylated dimer) Inactive relay proteins

LE 11-7c Signal molecule (ligand) Gate closed Ions Plasma membrane Ligand-gated ion channel receptor Gate open Cellular response Gate closed

Transduction usually involves multiple steps Can amplify a signal Concept 11.3: Transduction: Cascades of molecular interactions relay signals from receptors to target molecules in the cell Transduction usually involves multiple steps Can amplify a signal More opportunities for coordination and regulation

LE 11-8 Signal molecule Receptor Activated relay molecule Inactive protein kinase 1 Active protein kinase 1 Inactive protein kinase 2 ATP ADP Active protein kinase 2 P Phosphorylation cascade PP P i Inactive protein kinase 3 ATP ADP Active protein kinase 3 P PP P i Inactive protein ATP ADP P Active protein Cellular response PP P i

Small Molecules and Ions as Second Messengers Second messengers are small, nonprotein, water-soluble molecules or ions Cyclic AMP (cAMP) cAMP ATP Second messenger First messenger (signal molecule such as epinephrine) G-protein-linked receptor G protein Adenylyl cyclase Protein kinase A Cellular responses GTP

LE 11-10 First messenger (signal molecule such as epinephrine) cAMP ATP Second messenger First messenger (signal molecule such as epinephrine) G-protein-linked receptor G protein Adenylyl cyclase Protein kinase A Cellular responses GTP

Calcium ions and Inositol Triphosphate (IP3) Calcium ions (Ca2+) act as a second messenger in many pathways ATP EXTRACELLULAR FLUID Mitochondrion Ca2+ pump Plasma membrane CYTOSOL Endoplasmic reticulum (ER) High [Ca2+] Key Nucleus Low [Ca2+]

Concept 11.4: Response: Cell signaling leads to regulation of cytoplasmic activities or transcription “output response” cytoplasm nucleus Many pathways regulate the activity of enzymes

LE 11-13 Reception Binding of epinephrine to G-protein-linked receptor (1 molecule) Transduction Inactive G protein Active G protein (102 molecules) Inactive adenylyl cyclase Active adenylyl cyclase (102) ATP Cyclic AMP (104) Inactive protein kinase A Active protein kinase A (104) Inactive phosphorylase kinase Active phosphorylase kinase (105) Inactive glycogen phosphorylase Active glycogen phosphorylase (106) Response Glycogen Glucose-1-phosphate (108 molecules)

Transcription factor Growth factor Reception Receptor Phosphorylation cascade Transduction CYTOPLASM Inactive transcription factor Active P Response Gene mRNA DNA NUCLEUS

Signaling Efficiency: Scaffolding Proteins and Signaling Complexes Scaffolding proteins can increase the signal transduction efficiency Signal molecule Plasma membrane Receptor Scaffolding protein Three different kinases