Chapter 11 Cell Communication

Cell-Cell Communication Animal cells use gap junctions to send signals Cells must be in direct contact Protein channels connecting two adjoining cells Gap junctions between animal cells

Cell-Cell Communication Plant cells use plasmodesmata to send signals Cells must be in direct contact Gaps in the cell wall connecting the two adjoining cells together Plasmodesmata between plant cells

Local Signaling Other types of signaling over a short distance Cell-cell recognition Membrane bound cell surface molecules Glycoproteins Glyolipids Local regulators Growth factors Only work over a short distance

Long-Distance Signaling Nervous System in Animals Electrical signals through neurons Endocrine System in Animals Uses hormones to transmit messages over long distances Plants also use hormones Some transported through vascular system Others are released into the air

Three Stages of Cell Signaling EXTRACELLULAR FLUID CYTOPLASM Plasma membrane 1 1 Reception The receptor and signaling molecules fit together (lock and key model, induced fit model, just like enzymes!) Receptor Signaling molecule Signaling molecule binds to the receptor protein

Three Stages of Cell Signaling EXTRACELLULAR FLUID CYTOPLASM Plasma membrane 1 1 Reception 2 Transduction Receptor 2nd Messenger! Relay molecules in a signal transduction pathway Signaling molecule The signal is converted into a form that can produce a cellular response

Three Stages of Cell Signaling EXTRACELLULAR FLUID CYTOPLASM Plasma membrane 1 Reception 2 Transduction 3 Response Receptor Activation of cellular response Relay molecules in a signal transduction pathway Can be catalysis, activation of a gene, triggering apoptosis, almost anything! Signaling molecule The transduced signal triggers a cellular response

G-Protein Receptors Inactive enzyme Plasma membrane G protein-coupled Activated receptor Signaling molecule Enzyme GDP 1 2 GDP GTP CYTOPLASM G protein (inactive) Activated enzyme i GTP GDP P 3 4 Cellular response

Ion Channel Receptors Very important in the nervous system Gate closed 1 Ions Signaling molecule (ligand) Very important in the nervous system Signal triggers the opening of an ion channel depolarization Triggered by neurotransmitters Ligand-gated ion channel receptor Plasma membrane 2 Gate open Cellular response 3 Gate closed

Phosphorylation cascade Fig. 11-9 Signaling molecule Transduction: A Phosphorylation Cascade Receptor Activated relay molecule Inactive protein kinase 1 Active protein kinase 1 Inactive protein kinase 2 ATP Phosphorylation cascade ADP Active protein kinase 2 P 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

Transduction in a G-protein pathway Fig. 11-11 First messenger Adenylyl cyclase G protein G protein-coupled receptor GTP ATP Second messenger cAMP Transduction in a G-protein pathway Protein kinase A Cellular responses

Response Many possible outcomes Growth factor Response Receptor Reception Many possible outcomes This example shows a transcription response Phosphorylation cascade Transduction CYTOPLASM Inactive transcription factor Active transcription factor Response P DNA Gene NUCLEUS mRNA

Specificity of the signal Signaling molecule Specificity of the signal The same signal molecule can trigger different responses Many responses can come from one signal! Receptor Relay molecules Response 1 Response 2 Response 3 Cell A. Pathway leads to a single response. Cell B. Pathway branches, leading to two responses.

The signal can also trigger an activator or inhibitor The signal can also trigger multiple receptors and different responses Activation or inhibition Response 4 Response 5 Cell C. Cross-talk occurs between two pathways. Cell D. Different receptor leads to a different response.

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