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Adenylate Cyclase: An enzyme of the lyase class that catalyzes the formation of Cyclic amp and pyrophosphate from Atp. EC 4.6.1.1.

What are Second Messengers?

JoVE 10720

Because many receptor binding ligands are hydrophilic, they do not cross the cell membrane and thus their message must be relayed to a second messenger on the inside. There are several second messenger pathways, each with their own way of relaying information. G-protein coupled receptors can activate both phosphoinositol and cyclic AMP (cAMP) second messenger pathways. The phosphoinositol path is active when the receptor induces phospholipase C to hydrolyze the phospholipid, phosphatidylinositol biphosphate (PIP2), into two second messengers: diacylglycerol (DAG) and inositol triphosphate (IP3). DAG remains near the cell membrane and activates protein kinase C (PKC). IP3 translocates to the endoplasmic reticulum (ER) and becomes the opening ligand for calcium ion channels on the ER membrane- releasing calcium into the cytoplasm. In the cAMP pathway, the activated receptor induces adenylate cyclase to produce multiple copies of cAMP from nearby adenosine triphosphate (ATP) molecules. cAMP can stimulate protein kinase A (PKA), open calcium ion channels, and initiate the enzyme- Exchange-protein activated by cAMP (Epac). Similar to cAMP, is cyclic guanosine monophosphate (cGMP). cGMP is synthesized from guanosine triphosphate (GTP) molecules when guanylyl cyclase is activated. As a second messenger, cGMP induces protein kinase G

 Core: Cell Signaling

Intracellular Signaling Cascades

JoVE 10721

Intracellular signaling cascades amplify a signal originating extracellularly and directs it to its intended intracellular target resulting in transcription, translation, protein modifications, enzyme activation, cellular metabolism, mitosis, and/or apoptosis.

The most basic of signaling cascades involves the activation of second messengers and the release of kinases. Kinases activate or deactivate proteins and enzymes by adding a phosphate group to them. Phosphatases remove phosphate groups resulting in the deactivation or reactivation of proteins. The cyclic AMP (cAMP) pathway is named for its second messenger, cAMP. This pathway is most often initiated when a ligand binds to a G-coupled protein receptor. The G-protein decouples from the receptor and triggers adenylate cyclase to synthesize cAMP from ATP. For each ligand-receptor interaction, multiple cAMP molecules are generated—amplifying the signal. cAMP activates protein kinase A (PKA). PKA is a tetramer molecule with two regulatory subunits and two active subunits. When four cAMP molecules interact with a PKA molecule, it releases the two active subunits. These PKA subunits phosphorylate target proteins and enzymes. In the case of gene expression, PKA activates CREB, a transcription factor in the nucleus. The steps that precede the intracellular signaling cascade that is the lig

 Core: Cell Signaling

Endocrine Signaling

JoVE 10719

Endocrine cells produce hormones to communicate with remote target cells found in other organs. The hormone reaches these distant areas using the circulatory system. This exposes the whole organism to the hormone but only those cells expressing hormone receptors or target cells are affected. Thus, endocrine signaling induces slow responses from its target cells but these effects also last longer. There are two types of endocrine receptors: cell surface receptors and intracellular receptors. Cell surface receptors work similarly to other membrane bound receptors. Hormones, the ligand, bind to a hormone specific G-protein coupled receptor. This initiates conformational changes in the receptor, releasing a subunit of the G-protein. The protein activates second messengers which internalize the message by triggering signaling cascades and transcription factors. Many hormones work through cell surface receptors, including epinephrine, norepinephrine, insulin, prostaglandins, prolactin, and growth hormones. Steroid hormones, like testosterone, estrogen, and progesterone, transmit signals using intracellular receptors. These hormones are small hydrophobic molecules so they move directly past the outer cell membrane. Once inside, and if that cell is a target cell, the hormone binds to its receptor. Binding creates a conformational change in the receptor

 Core: Cell Signaling

Rapid Detection of Neurodevelopmental Phenotypes in Human Neural Precursor Cells (NPCs)

1Department of Neuroscience and Cell Biology, Rutgers Robert Wood Johnson Medical School, 2Center for Advanced Biotechnology and Medicine, Department of Neuroscience and Cell Biology, Rutgers Robert Wood Johnson Medical School, 3The Child Health Institute of NJ, Department of Obstetrics, Gynecology, and Reproductive Services, Rutgers Robert Wood Johnson Medical School, 4The Child Health Institute of NJ, Department of Neuroscience and Cell Biology, Rutgers Robert Wood Johnson Medical School, 5Department of Genetics, Rutgers University

JoVE 56628

 Developmental Biology

High-throughput Parallel Sequencing to Measure Fitness of Leptospira interrogans Transposon Insertion Mutants During Golden Syrian Hamster Infection

1Veterans Affairs Greater Los Angeles Healthcare System, 2Departments of Medicine, David Geffen School of Medicine at University of California Los Angeles, 3Departments of Urology, David Geffen School of Medicine at University of California Los Angeles, 4Departments of Microbiology, Immunology, and Molecular Genetics, University of California Los Angeles

JoVE 56442

 Immunology and Infection

Drosophila Courtship Conditioning As a Measure of Learning and Memory

1Department of Human Genetics, Radboud University Medical Center, 2Radboud Institute of Molecular Life Sciences, Radboud University, 3Donders Institute for Brain, Cognition, and Behaviour, Centre for Neuroscience, Radboud University, 4Research Institute of Molecular Pathology, Vienna, Austria, 5Department for Health Evidence, Radboud University Medical Center, 6Janelia Research Campus, Howard Hughes Medical Institute, 7Department of Physiology and Pharmacology, Schulich School of Medicine and Dentistry, Western University, 8Department of Biology, Faculty of Science, Western University

JoVE 55808

 Neuroscience

Measuring G-protein-coupled Receptor Signaling via Radio-labeled GTP Binding

1The Solomon H. Snyder Department of Neuroscience, Johns Hopkins University School of Medicine, 2Department of Neurology and neurosurgery, Johns Hopkins University School of Medicine, 3Departments of Pharmacology and Molecular Sciences, Johns Hopkins University School of Medicine, 4Department of Psychiatry and Behavioral Sciences, Johns Hopkins University School of Medicine

JoVE 55561

 Biochemistry

Open Source High Content Analysis Utilizing Automated Fluorescence Lifetime Imaging Microscopy

1Photonics Group, Department of Physics, Imperial College London, 2Institute for Chemical Biology, Department of Chemistry, Imperial College London, 3MRC Clinical Sciences Centre, Hammersmith Hospital, 4Chemical Biology Section, Department of Chemistry, Imperial College London, 5Retroscreen Virology Ltd, 6Pfizer Global Research and Development, Pfizer Limited, Sandwich, Kent, UK, 7Centre for Histopathology, Imperial College London

JoVE 55119

 Biology

Right Ventricular Systolic Pressure Measurements in Combination with Harvest of Lung and Immune Tissue Samples in Mice

1Department of Environmental Medicine, New York University School of Medicine, Tuxedo, 2Division of Allergy, Pulmonary, & Critical Care Medicine, Department of Medicine, Vanderbilt University Medical Center, 3Division of Pulmonary Medicine, New York University School of Medicine

JoVE 50023

 Immunology and Infection
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