Cell Communication Chapter 5 Multicellular Organisms Behave as

Cell Communication Chapter 5

Multicellular Organisms • Behave as a community – Cells talk – Neighbors carry on private conversations – Messages are sent over distances • Phone • Mail – Public announcements are made – Alarms are rung when there is danger

Signal Transduction Pathways • Conversions of signals from one form to another in a cell – Verbal instructions written text email voice mail action • Eventually a response will occur due to the original signal

Signals in Cells • Chemicals – Hydrophilic – can’t enter cell membrane • • Proteins Amino acids Peptides Nucleotides – Hydrophobic – can enter cell membrane • Steroids - hormones • Gasses

Communication • Signal cell Target cell – – Cell to cell recognition Cell Junctions Local Regulators Distance Regulators

Cell to cell recognition • Glycoprotiens, glycolipids, and other molecules on plasma membranes serve as recognition markers. • Important for immune response and embryonic development

Cell Junctions • Plasmodesta – plant cells • Gap Junctions – animal cells • Allow communication between the cytoplasm of neighboring cells. Plasma membranes Gap junctions between animal cells Plasmodesmata between plant cells Figure 11. 3 (a) Cell junctions. Both animals and plants have cell junctions that allow molecules to pass readily between adjacent cells without crossing plasma membranes.

Local Regulators Figure 11. 3(b) Cell-cell recognition. Two cells in an animal may communicate by interaction between molecules protruding from their surfaces. • Communicate and influence cells in close proximity • Growth factors – cause multiplication and growth of target cells • Paracrine Signaling – simultaneous response by more than one cell • Synaptic Signaling – Nervous system – Neurotransmitters diffuse from one nerve cell to stimulate the next

B 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. Target cell is stimulated (b) Synaptic signaling. A nerve cell releases neurotransmitter molecules into a synapse, stimulating the target cell.

Distance Regulators Long-distance signaling Endocrine cell • Hormones • Carried in the bloodstream of animals Blood vessel Hormone travels in bloodstream to target cells – Endocrine System Circulatory System Target cell • Carried in the sap of plants Figure 11. 4 C (c) Hormonal signaling. Specialized endocrine cells secrete hormones into body fluids, often the blood. Hormones may reach virtually all body cells.

Cell Signaling 11_06 Signaling. Overview_A. swf EXTRACELLULAR FLUID Plasma membrane Reception CYTOPLASM Transduction Response Receptor Activation of cellular response Relay molecules in a signal transduction pathway Signal molecule Figure 11. 5 • 1. Reception – detection of message by a receptor protein on a target cell • 2. Transduction – receptor changes and initiates a cascade of events • 3. Response – activation of target

Reception Hormone (testosterone) • Receptors – ligands – specific to signaling molecules • Intracellular Receptors – cytoplasm or nucleus EXTRACELLULAR FLUID Plasma membrane Receptor protein Hormonereceptor complex – Usually steroid or hormone receptors - hydrophobic • Plasma Membrane Receptors – proteins in the cell membrane – Hydrophilic receptors Figure 11. 6 DNA m. RNA NUCLEUS CYTOPLASM New protein

Plasma Membrane Receptors • G-protein-linked receptor • Receptor tyrosine kinase (kinase is an enzyme that phosphorylates other proteins to activate them) • Ligand-gated ion channel

G-Protein-Linked Receptor • Signal molecule attaches to receptor and activates • G-protein is activated by the replacement of GDP with GTP • G-protein activates an enzyme which triggers a cascade in the cell to the target. – Used for vision and smell – 60% of medicines activate Gproteins

re 11. 7 Signal-binding site Segment that interacts with G proteins G-protein-linked Receptor Plasma Membrane Activated Receptor Signal molecule GDP CYTOPLASM G-protein (inactive) Enzyme GDP GTP Activated enzyme GTP GDP Pi Cellular response Inctivate enzyme

Receptor Tyrosine Kinase • Signals bind to receptors activating 2 kinases at a time – dimer • ATP further activates the dimers • Once activated relay proteins trigger cascades within the cell until the targets are reached. – Used to trigger multiple reactions at once – Cell growth and reproduction – Abnormal tyrosine kinases are thought to cause some cancer

11. 7 Signal-binding sitea Signal molecule Helix in the Membrane Tyrosines Tyr Tyr Tyr Tyr Tyr Receptor tyrosine kinase proteins (inactive monomers) CYTOPLASM Dimer Activated relay proteins Tyr Tyr P Tyr Tyr P P Tyr P 6 Activated tyrosinekinase regions (unphosphorylated dimer) ATP 6 ADP Fully activated receptor tyrosine-kinase (phosphorylated dimer) Inactive relay proteins Cellular response 1 Cellular response 2

Ligand-Gated Ion Channels Signal molecule (ligand) • Signal molecule attached to ligand opening a gate for specific ions • Once Ions enter specific reactions take place Gate closed Ions Ligand-gated ion channel receptor Plasma Membrane Gate open Cellular response – Na+ – Ca+ Gate close Figure 11. 7

Transduction 11_13 Signal. Transduction_A. swf • Cascade • Step 1 step 2 step 3 step 4 reaction • Activated by phosphorylation – ATP ADP + P – Protein Kinases • Deactivated by dephosphorylation – P removed – Protein phosphatases

Second Messengers • Small, non protein, water soluble, ions • Cyclic AMP – Levels regulate gene expression in bacteria • Calcium Ions – Ca 2+ • Receptors on the outside of the membrane are the 1 st messengers

Cyclic AMP • Created from ATP from adenyl cyclase • Used with G proteins – 1 st or 2 nd messenger NH 2 N N O O O N N – O P O P O Ch 2 O O O Figure 11. 9 N N O Pyrophosphate P Pi N N Adenylyl cyclase O OH OH ATP NH 2 O CH 2 Phoshodiesterase O P O O OH Cyclic AMP N N O HO P O CH 2 O O H 2 O OH OH AMP

First messenger (signal molecule such as epinephrine) Adenylyl cyclase G protein G-protein-linked receptor GTP ATP c. AMP Protein kinase A Cellular responses

Ca 2+ • Most widely used 2 nd messenger • Increase in Ca 2+ muscle contraction and cell division • Causes greening in plants in response to sunlight • Used with all 3 membrane receptors – G-protein – Tyrosine Kinase – Gated Ion Channel EXTRACELLULAR FLUID ATP Plasma membrane Ca 2+ pump Mitochondrion Nucleus CYTOSOL Ca 2+ pump ATP Key Ca 2+ pump Endoplasmic reticulum (ER) High [Ca 2+] Low [Ca 2+]

14 Response Growth factor Reception Receptor Phosphorylation cascade Transduction CYTOPLASM Inactive transcription factor Active transcription factor P Response DNA Gene NUCLEUS m. RNA • Signals are amplified as they are sent from messenger to messenger. • Signals are specific to target cells and enzymes • Not all cells respond to a signal

Concept Map & Summary Hydrophobic Signal Cell Signals Transduction Hydrophillic Response