Cell Communication AP Biology Cell to Cell Communication

Cell Communication AP Biology

Cell to Cell Communication § Paracrine – local communication § Examples- cell junctions, neurotransmitters, immune response Endocrine- long distance communication ( hormones and nerve responses [some]) AP Biology

Cell-to-Cell ( Local) § Cell junctions directly connect the § cytoplasm of adjacent cells u Ex: cardiac cells for common rhythm Surface receptors can give/send information u Ex: specific immune response Plasma membranes Gap junctions between animal cells AP Biology Plasmodesmata between plant cells

Local Signaling § Adjacent cells are signaled. u Chemical messengers released § Ex: Neurotransmitters via neurons Local signaling Target cell Electrical signal along nerve cell triggers release of neurotransmitter Neurotransmitter diffuses across synapse Secretory vesicle Local regulator diffuses through extracellular fluid (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. AP Biology Target cell is stimulated (b) Synaptic signaling. A nerve cell releases neurotransmitter molecules into a synapse, stimulating the target cell.

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 u § Long-distance signaling Endocrine cell § Protein or Steroid types Blood vessel Hormone travels in bloodstream to target cells Target cell AP Biology Figure 11. 4 (c) Hormonal signaling. Specialized endocrine cells secrete hormones into body fluids, often the blood. Hormones may reach virtually all C body cells.

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 AP Biology

3 Phases of Signal Transduction EXTRACELLULAR FLUID 1 Reception CYTOPLASM Plasma membrane 2 Transduction 3 Response Receptor Activation of cellular response Relay molecules in a signal transduction pathway Signal molecule Figure 11. 5 AP Biology

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

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

G -protein-linked receptors § Very common, diverse functions § Act as molecular “switches” G-protein-linked Receptor Plasma Membrane GDP CYTOPLASM G-protein (inactive) Enzyme Activated Receptor GDP Signal molecule GTP Activated enzyme GTP GDP Pi Cellular response AP Biology Inactivate enzyme

Receptor tyrosine kinases (enzyme that transfers ATP) § Multiple pathway response § Regulates/coordinates many cell functions - growth factors, cytokines (chemicals that affect other cells)and hormones Signal-binding site molecule Helix in the Membrane Tyr Tyrosines Tyr Tyr AP Biology Tyr Tyr Receptor tyrosine kinase proteins (inactive monomers) CYTOPLASM Tyr Tyr 6 ATP Signal molecule P Tyr 6 ADP Activated tyrosinekinase regions (unphosphorylated dimer) Tyr P Tyr Tyr Tyr Dimer Figure 11. 7 Fully activated receptor tyrosine-kinase (phosphorylated dimer) P Tyr Activated relay proteins Cellular Tyr P response 1 Tyr P Cellular Tyr P response 2 Inactive relay proteins

Ion channel receptors When the ligand binds, channels can open or close. Converts chemical to electrical signals Ex: neurotransmitters bind as ligands for ion channels AP Biology Figure 11. 7 Signal molecule (ligand) Gate closed Ligand-gated ion channel receptor Ions Plasma Membrane Gate open Cellular response Gate close

Step Two - Transduction § Cell responds by activating kinases. § Phosphorylating kinase 1 changes its § structure and relay signals as a cascade of changed kinases Multistep pathways can amplify a signal u AP Biology Second messengers involved (c. AMP)

Step Three - Response § Cell signaling leads to regulation of transcription ( makes a product) Signaling pathways regulate a variety of cellular activities AP Biology

Pathways regulate genes by activating transcription factors that turn genes on or off Growth factor Receptor Phosphorylation cascade Reception Transduction CYTOPLASM Inactive transcription Active transcription factor P Response Figure 11. 14 DNA Gene AP Biology NUCLEUS m. RNA

Evolutionary Significance § Unicellular and multicellular cell § communication have similarities Bacteria secrete molecules to sense density of own population. u Quorum Sensing (survival of the group) AP Biology

Yeast Sexual Reproduction 1 Yeast cells identify their mates by cell signaling. Suggests early evidence of cell signaling. 2 3 AP Biology Exchange of mating factors. Each cell type secretes a mating factor that binds to receptors on the other cell type. 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. factor Receptor a Yeast cell, mating type a factor a Yeast cell, mating type a/

Local Regulators § Histamine- triggers § § dilation and increased permeability in the immune response Interleukins-a cytokine protein that activates lymphocytes Retinoic acid- necessary for vision and bone growth (anti aging hormones in cosmetics) AP Biology

Paracrine signaling § Cell to cell § § § communication Induces a change in nearby cells Travel in short distances Example-Hedgehog proteins ( important for organ development) AP Biology https: //www. youtube. com/watch? v= U 4 A_1 Igh_2 w

Hedgehog Signaling § In embryos, signal pathways are § established for proper tissue and organ development In adults a malfunction in these pathways may cause cancer AP Biology

Local regulators § Nitric oxide (NO)` § § vessel dilation, increase blood flow for more O 2 Growth factors ~ proteins for cell proliferation Prostaglandins~ immune, reproduction, blood clotting AP Biology

Endocrine and Nervous System Regulation – short and long distance § Nervous system § Can be short distance- neurotransmitters - Electrical signals - Fast acting for immediate response § Endocrine system - Hormones - Slower and longer acting AP Biology

Water and Fat Soluble Hormones § Water soluble- faster § acting, reversible, protein based, removed from blood quickly– insulin, ADH: attaches to cell membrane Fat soluble hormonesslower acting and longer lasting, irreversible, stimulated by a trophic hormone – steroids: enters the cell AP Biology

Example of Pathway § Steroid hormones bind to intracellular receptors Hormone EXTRACELLULAR (testosterone) FLUID Receptor protein Plasma membrane Hormonereceptor complex 1 The steroid hormone testosterone passes through the plasma membrane. 2 Testosterone binds to a receptor protein in the cytoplasm, activating it. 3 The hormone- DNA m. RNA NUCLEUS Figure 11. 6 AP Biology CYTOPLASM receptor complex enters the nucleus and binds to specific genes. 4 New protein The bound protein stimulates the transcription of the gene into m. RNA. 5 The m. RNA is translated into a specific protein.

Epinephrine/ Adrenaline Release § Fight or flight Stress hormone § Increases blood pressure § Increases diameter of blood vessels AP Biology

Gonadotropic Hormones § Stimulates gonads § FSH- follicle § stimulating hormone (in women regulates menstruation and ovulation) LH- luteinizing hormone (ovulation in women and production of testosterone in men) AP Biology

Other Common Human Hormones § Calcitonin- bone growth § Dopamine- heart rate, reality § Gastrin- digestion § Ghrelin- appetite hormone § HCG- pregnancy test, weight loss § § § “drug” Leptin- slows down appetite Melatonin- biological clock Seratonin- mood, appetite and sleep AP Biology

· Arthropods have extensive endocrine systems regulating molting in insects and crustaceans. · The regulation of molting in insects. · Neurosecretory cells in the brain produce brain hormone (BH), which regulates the secretion of ecdysone. · Ecdysone also promotes the development of adult features and molting § Juvenile hormone (JH) promotes the retention of larval characteristics. AP Biology Copyright © 2002 Pearson Education, Inc. , publishing as Benjamin Cummings

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