AP Biology Cell Communication

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

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

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 VIDEO

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.

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

AP Biology How Does it Work?  Signal Transduction Pathways  Convert signals on a cell’s surface into cellular responses  Are similar in microbes and mammals, suggesting an early origin

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

AP Biology Step One - Reception  Reception occurs when a signal molecule (ligand) binds to a receptor protein. Ligand and receptor have a unique bonding

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

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

AP Biology Signal molecule Active protein kinase 1 Active protein kinase 2 Active protein kinase 3 Inactive protein kinase 1 Inactive protein kinase 2 Inactive protein kinase 3 Inactive protein Active protein Cellular response Receptor P P P ATP ADP ATP PP Activated relay molecule i Phosphorylation cascade P P i i P  A phosphorylation cascade Figure 11.8 A relay molecule activates protein kinase Active protein kinase 1 transfers a phosphate from ATP to an inactive molecule of protein kinase 2, thus activating this second kinase. Active protein kinase 2 then catalyzes the phos- phorylation (and activation) of protein kinase 3. 3 Finally, active protein kinase 3 phosphorylates a protein (pink) that brings about the cell’s response to the signal. 4 Enzymes called protein phosphatases (PP) catalyze the removal of the phosphate groups from the proteins, making them inactive and available for reuse. 5

AP Biology Benefits of a 2° messenger system Amplification! signal receptor protein Activated adenylyl cyclase amplification GTPG protein product enzyme protein kinase cAMP Not yet activated FAST response! amplification Cascade multiplier! VIDEO

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…

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

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

AP Biology G-protein-linked receptors  Very common  Results in a 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

AP Biology 3 21 IP 3 quickly diffuses through the cytosol and binds to an IP 3 – gated calcium channel in the ER membrane, causing it to open. 4 The calcium ions activate the next protein in one or more signaling pathways. 6 Calcium ions flow out of the ER (down their con- centration gradient), raising the Ca 2+ level in the cytosol. 5 DAG functions as a second messenger in other pathways. Phospholipase C cleaves a plasma membrane phospholipid called PIP 2 into DAG and IP 3. A signal molecule binds to a receptor, leading to activation of phospholipase C. EXTRA- CELLULAR FLUID Signal molecule (first messenger) G protein G-protein-linked receptor Various proteins activated Endoplasmic reticulum (ER) Phospholipase C PIP 2 IP 3 (second messenger) DAG Cellular response GTP Ca 2+ (second messenger) Ca 2+ IP 3 -gated calcium channel Ex: Inositol P3 and calcium

AP Biology Receptor tyrosine kinases  Multiple pathway response 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

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 Na+ ion channels

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 Why can the signal molecule meet its target INSIDE the cell?

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) TEDED on Quorum Sensing