1. AP Biology Cell Communication

2. AP Biology Communication Methods  Cell-to-cell contact  Local signaling  Long distance signaling

3. AP Biology Cell-to-Cell Communications  Cell junctions directly connect the cytoplasm of adjacent cells  Ex: cardiac cells for rhythmicity  Surface receptors can give/send information  Ex: specific immune response Plasma membranes Plasmodesmata between plant cells Gap junctions between animal cells

4. AP Biology Local Signaling  Adjacent cells are signaled.  Chemical messengers released  Ex: Neurotransmitters via neurons (a) Paracrine signaling. A secreting cell acts on nearby target cells by discharging molecules of a local regulator (a growth factor, for example) into the extracellular fluid. (b) Synaptic signaling. A nerve cell releases neurotransmitter molecules into a synapse, stimulating the target cell. Local regulator diffuses through extracellular fluid Target cell Secretory vesicle Electrical signal along nerve cell triggers release of neurotransmitter Neurotransmitter diffuses across synapse Target cell is stimulated Local signaling

5. AP Biology Long Distance Signaling  Use of hormones  Both plants and animals use hormones (e.g. Insulin)  Can affect many cells in Other parts of the body  Protein or Steroid types Hormone travels in bloodstream to target cells (c) Hormonal signaling. Specialized endocrine cells secrete hormones into body fluids, often the blood. Hormones may reach virtually all body cells. Long-distance signaling Blood vessel Target cell Endocrine cell Figure 11.4 C

6. AP Biology How Do Cells Communicate?  Signal Transduction Pathways  Convert signals on a cell’s surface into cellular responses  Are similar in microbes and mammals, suggesting an early origin

7. AP Biology EXTRACELLULAR FLUID Receptor Signal molecule Relay molecules in a signal transduction pathway Plasma membrane CYTOPLASM Activation of cellular response Figure 11.5 3 Phases of Signal Transduction 3 Phases of Signal Transduction Reception 1 Transduction 2 Response 3

8. AP Biology Step One - Reception  Reception occurs when a signal molecule (ligand) binds to a receptor protein. Receptor protein is on the cell surface Ligand and receptor have a unique bonding

9. AP Biology Step Two - Transduction  Signal initiated by conformational change of receptor protein  Signal is turned into a cellular response.  Signaling cascades relay signals to target  Multistep pathways can amplify a signal  Second messengers involved

10. AP Biology Step Three - Response  Cell signaling leads to regulation of cytoplasmic activities or transcription Signaling pathways regulate a variety of cellular activities

11. AP Biology ATP GTP cAMP Protein kinase A Cellular responses G-protein-linked receptor Adenylyl cyclase G protein First messenger (signal molecule such as epinephrine) Cyclic AMP example…

12. AP Biology Pathways can also regulate genes by activating transcription factors that turn genes on or off Reception Transduction Response mRNA NUCLEUS Gene P Active transcription factor Inactive transcription factor DNA Phosphorylation cascade CYTOPLASM Receptor Growth factor Figure 11.14

13. AP Biology  There are three main types of plasma membrane receptors:  G-protein-linked  Tyrosine kinases  Ion channel Types of Receptors

14. AP Biology G-protein-linked receptors  Very common, diverse functions  Only results in single pathway response G-protein-linked Receptor Plasma Membrane Enzyme G-protein (inactive) CYTOPLASM Cellular response Activated enzyme Activated Receptor Signal molecule Inactivate enzyme GDP GTP P iP i GDP

15. AP Biology Receptor tyrosine kinases  Multiple pathway response  Regulates/coordinates many cell functions Signal molecule Signal-binding site CYTOPLASM Tyrosines Signal molecule  Helix in the Membrane Tyr Dimer Receptor tyrosine kinase proteins (inactive monomers) P P P P P P Tyr P P P P P P Cellular response 1 Inactive relay proteins Activated relay proteins Cellular response 2 Activated tyrosine- kinase regions (unphosphorylated dimer) Fully activated receptor tyrosine-kinase (phosphorylated dimer) 6 ATP 6 ADP Figure 11.7

16. AP Biology Ion channel receptors Cellular response Gate open Gate close Ligand-gated ion channel receptor Plasma Membrane Signal molecule (ligand) Figure 11.7 Gate closed Ions When ligand binds, channel can open or close. Ex: neurotransmitters bind as ligands for ion channels

17. AP Biology Hormone (testosterone) EXTRACELLULAR FLUID Receptor protein DNA mRNA NUCLEUS CYTOPLASM Plasma membrane Hormone- receptor complex New protein Figure 11.6 *Intracellular Receptors  Target protein is INSIDE the cell  Must be hydrophobic molecule 1 The steroid hormone testosterone passes through the plasma membrane. The bound protein stimulates the transcription of the gene into mRNA. 4 The mRNA is translated into a specific protein. 5 Testosterone binds to a receptor protein in the cytoplasm, activating it. 2 The hormone- receptor complex enters the nucleus and binds to specific genes. 3

18. AP Biology Evolutionary Significance  Unicellular and multicellular cell communication have similarities  Yeast cells signal for sexual reproduction through signal transduction process.  Bacteria secrete molecules to sense density of own population.  Quorum Sensing (survival purpose)

19. AP Biology Yeast Sexual Reproduction  factor Receptor Exchange of mating factors. Each cell type secretes a mating factor that binds to receptors on the other cell type. 1 Mating. Binding of the factors to receptors induces changes in the cells that lead to their fusion. New a/  cell. The nucleus of the fused cell includes all the genes from the a and a cells. 2 3  factor Yeast cell, mating type a Yeast cell, mating type    a/  a a Yeast cells identify their mates by cell signaling. Suggests early evidence of cell signaling.