A signal ___________________ pathway is a series of steps by which a signal on a cell’s surface is _______________into a specific cellular ______________ Signal transduction pathways convert signals on a cell’s surface into cellular responses

Plasma membranes Gap junctions between animal cells (a) Cell junctions Plasmodesmata between plant cells (b) Cell-cell recognition Local and Long- Distance Signaling Cells in a multicellular organism communicate by ____________ _________________ In local signaling, animal cells may communicate by __________contact, or cell-cell recognition

Local signaling Target cell Secretory vesicle Secreting cell Local regulator diffuses through extracellular fluid (a) Paracrine signaling (b) Synaptic signaling Target cell is stimulated Neurotransmitter diffuses across synapse Electrical signal along nerve cell triggers release of neurotransmitter In many other cases, animal cells communicate using ___________________, messenger molecules that travel only ______ distances

Long-distance signaling Endocrine cell Blood vessel Hormone travels in bloodstream to target cells Target cell (c) Hormonal signaling In long-distance signaling, plants and animals use chemicals called ________________ _

Regulation by chemical messengers axon endocrine gland receptor proteins target cell ___________________________ released by neurons ______________release by endocrine glands receptor proteins hormone ____________________ neurotransmitter Lock & Key system

How do hormones act on target cells _______________-based hormones – Hydro________ic & lipid-soluble _______diffuse across cell membrane & enter cells bind to receptor proteins in cytoplasm & nucleus bind to DNA as transcription factors -__________________ __________-based hormones – Hydro_________ic & not lipid soluble ________ diffuse across cell membrane bind to receptor proteins in cell membrane trigger secondary messenger pathway activate internal cellular response – enzyme action, uptake or secretion of molecules…

The binding between a ___________________ _____________________ (ligand) and ________________is highly ______________ A shape ________________ in a receptor is often the initial transduction of the signal Sutherland suggested that cells receiving signals went through three processes: – __________________________ – _____________________________________ – _________________________ ]The Three Stages of Cell Signaling: A Preview

Fig EXTRACELLULAR FLUID Plasma membrane CYTOPLASM Receptor Signaling molecule Relay molecules in a signal transduction pathway Activation of cellular response 2 3 1

A _____________-coupled receptor is a plasma membrane receptor that works with the help of a G protein that acts as an on/off switch: If GDP is bound to the G protein, the G protein is inactive Receptor ______________________ are membrane receptors that attach phosphates to tyrosines. A receptor tyrosine kinase can trigger multiple signal transduction pathways at once A ligand-gated ________channel receptor acts as a gate when the receptor changes shape, the gate allows specific ions, such as Na + or Ca 2+, through a channel in the receptor Receptors in the Plasma Membrane

Fig. 11-7b G protein-coupled receptor Plasma membrane Enzyme G protein (inactive) GDP CYTOPLASM Activated enzyme GTP Cellular response GDP P i Activated receptor GDP GTP Signaling molecule Inactive enzyme

Fig. 11-7c Signaling molecule (ligand) Ligand-binding site  Helix Tyrosines Tyr Receptor tyrosine kinase proteins CYTOPLASM Signaling molecule Tyr Dimer Activated relay proteins Tyr P P P P P P Cellular response 1 Cellular response 2 Inactive relay proteins Activated tyrosine kinase regions Fully activated receptor tyrosine kinase 6 6 ADP ATP Tyr P P P P P P

Fig. 11-7d Signaling molecule (ligand) Gate closed Ions Ligand-gated ion channel receptor Plasma membrane Gate open Cellular response Gate closed 3 2 1

Intracellular Receptors Some receptor proteins are intracellular, found _______________ or ___________of target cells Small or hydrophobic chemical messengers can readily cross the membrane and activate receptors Examples of hydrophobic messengers are the ____________________hormones of animals An activated hormone-receptor complex can act as a __________________________________, turning on specific genes Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig (testosterone) EXTRACELLULAR FLUID protein Plasma membrane Hormone- receptor complex DNA mRNA NUCLEUS New protein CYTOPLASM

Concept 11.3: Transduction: Cascades of molecular interactions relay signals from receptors to target molecules in the cell Signal transduction usually involves multiple steps Multistep pathways can ____________a signal: A few molecules can produce a large cellular response Multistep pathways provide more opportunities for ____________________and regulation of the cellular response Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Signal Transduction Pathways The molecules that relay a signal from receptor to response are mostly __________________ Like falling dominoes, the receptor activates another protein, which activates another, and so on, until the protein producing the response is activated In many pathways, the signal is transmitted by a cascade of protein phosphorylations ___________________________from ATP to protein, a process called ___________________ Protein Phosphorylation and Dephosphorylation

Small Molecules and Ions as Second Messengers The extracellular signal molecule that binds to the receptor is a pathway’s “first messenger” __________________________ are small, nonprotein, water-soluble molecules or ions that spread throughout a cell by diffusion Cyclic AMP and calcium ions are common second messengers Cyclic AMP (____________) is one of the most widely used second messengers Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

The Specificity of Cell Signaling and Coordination of the Response Different kinds of cells have different collections of proteins These different proteins allow cells to detect and respond to different signals Even the _______________ can have _________________ in cells with different proteins and pathways Pathway branching and “cross-talk” further help the cell coordinate incoming signals Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings