Signal 1

From CellBiology

Cell Signaling 1

This lecture is an introduction to a series of lectures on cell signaling. The first lecture is a general introduction to the different signaling mechanisms and the following two lectures look in detail at some specific examples of signaling pathways.

Note that you have already been introduced to signaling in many of your other lecture topics (searching PubMed for "cell signaling" gives 448,244 results).

Archive: 2010 lecture | 2009 lecture | 2008 lecture


Movie - Neutrophil chasing Bacterium

iLecture: Lecture 17 Audio


  • Understand main types of signaling mechanisms
  • Understand concept of receptor and ligand
  • Understand membrane, cytoplasmic and nuclear receptors
  • Brief understanding of steroid hormone pathway
  • Brief understanding protein growth factor pathway
  • Understand differences between select membrane receptors (G protein structure, tyrosine kinases)

Lecture Summary

  • Messengers and Receptors
  • chemical signals
  • cellular receptors
  • signal transduction
  • intracellular pathways
  • second messengers
  • Examples of signaling

Signaling Mechanisms

MCB Movie - Extracellular Signaling

  • Endocrine - Hormone (at a distance)
  • Paracrine - Locally
    • Neurotransmitter - Specific form of paracrine
  • Autocrine - Local (self)
    • Contact Dependent
Signal transduction pathways.png

Links: Cell - Modes of Cell-Cell Signaling | MCB - Cell-to-Cell Signaling: Hormones and Receptors | MCB - Overview of Extracellular Signaling | Cell - Cell Signaling | MCoB - Cell Communication | MCoB - General Principles of Cell Communication | Adherens Junction Dynamics | Commercial Database - Pathways

Cell Communication

  • Contact Mediated - display molecules on cell surface, recognized by receptor on another cell
  • Non-Contact Mediated - chemical signal, nearby or at a distance
  • Common Signals Signals and Receptors

Chemical Signal Types

  • water soluble
  • lipid soluble

Movie: Hormone Signaling

Extracellular Signal Steps

  • Signaling Molecule
  1. Synthesis
  2. Release by signaling cell
  3. Transport to target cell
  4. Detection by a specific receptor protein
  5. Change by receptor-signal complex (trigger)

There can also be a feedback mechanism following signaling.

Cell Surface Receptors

  • four main classes
    • G protein–coupled receptors
    • ion-channel receptors
    • receptors linked to cytosolic tyrosine kinases
    • receptors with intrinsic catalytic activity
  • ligand binding to cell-surface receptor
    • trigger intracellular pathways
    • modulate cellular metabolism, function, or development
  • Removal of the signal
    • often terminates cellular response

Second Messengers


Cyclic adenosine monophosphate (cAMP)

Cyclic guanosine monophosphate.png

Cyclic guanosine monophosphate (cGMP)

  • Cyclic nucleotides - cAMP, cGMP (will cover also in next lecture G protein signalling)
  • Calcium Ions
  • Inositol 1,4,5-trisphosphate (IP3)
  • Diacylglycerol (DAG) - modified lipid activates PKC
  • Protein Kinase A - PKA, B, C (phosphorylate other proteins)
  • regulate the activity of cellular proteins (enzymes and non-enzymatic)

Links: Cell - Common intracellular signaling proteins Elevation of cytosolic Ca2+ via the inositol-lipid signaling pathway | Movie: Second Messengers in Signaling Pathways

Steroid Responses

Steroid hormone receptor signaling
Hypothalamus endocrine system.jpg


Other Endocrine Axes

MCB - Characteristic Properties of Principal Types of Mammalian Hormones | MCoB - Some signaling molecules that bind to nuclear receptors | Cell - Action of steroid hormones

Steroid Hormone Receptors (SHRs)

Steroid hormone receptor signaling

Cytosol location

  • receptor bound to inhibitor
  • ligand binding activates receptor
  • translocates to nucleus on ligand binding

Nuclear location

  • binds ligand and DNA
  • becomes transcription factor
  • estrogen receptor, two forms ERα [NR3A1] and ERβ [NR3A2]
  • cortisol binding glucocorticoid receptor (GR) [NR3C1]
  • aldosterone binding mineralocorticoid receptor (MR) [NR3C2]
  • progesterone receptor (PR) [NR3C3]
  • dihydrotestosterone (DHT) binding androgen receptor (AR) [NR3C4]


Nuclear Receptor Signaling

Receptor Structure

Nuclear Receptor
  • steroid binding region - near C-terminus
  • DNA binding - central region
    • zinc finger motif
    • alpha helix and 2 beta sheets held in place by cysteine or histidine residues by a zinc atom
    • multiple fingers typical
  • DNA response element
  • Enhancer
Links: Box 1.12Steroid receptors, zinc fingers and DNA binding

Receptor Types

48 human nuclear receptor types

Steroid hormone receptor family
  • Type I Receptors
    • Sex hormone receptors (sex hormones) - Androgen receptor, Estrogen receptor, Progesterone receptor
    • Glucocorticoid receptor (glucocorticoids)
    • Mineralocorticoid receptor (mineralocorticoids)
  • Type II Receptors
    • Vitamin A receptor
    • Vitamin D receptor
    • Retinoid receptor
    • Thyroid hormone receptor
  • Orphan receptors
Links: nuclear-receptor superfamily three classes | Image - Models of sex steroid action in target tissue


  • (icosanoids) prostaglandins, prostacyclins, thromboxanes and leukotrienes
  • lipids acting as signaling molecules
    • made from essential fatty acids (EFAs) oxidation (arachidonic acid)
  • act by binding to cell surface receptors, rapidly broken down (anti-inflammatory drugs act by downregulating eicosanoid synthesis)
  • act locally in autocrine or paracrine signaling pathways
Links: Eicosanoid biosynthesis

Nitric Oxide

  • (nitrogen monoxide) another signaling method that crosses lipid membranes
  • simple gas, very quick short-lived signal
    • synthesised from arginine by nitric oxide synthase
  • does not bind intracellular receptor
    • regulates intracellular enzymes

Example - dilation of blood vessels. (nitroglycerine for heart converted to NO)



Essential Cell Biology

  • Essential Cell Biology Chapter 15

Molecular Biology of the Cell

Alberts, Bruce; Johnson, Alexander; Lewis, Julian; Raff, Martin; Roberts, Keith; Walter, Peter New York and London: Garland Science; c2002

Molecular Cell Biology

Lodish, Harvey; Berk, Arnold; Zipursky, S. Lawrence; Matsudaira, Paul; Baltimore, David; Darnell, James E. New York: W. H. Freeman & Co.; c1999

The Cell- A Molecular Approach

Cooper, Geoffrey M. Sunderland (MA): Sinauer Associates, Inc.; c2000

Search Online Textbooks



  • PubMed is a service of the U.S. National Library of Medicine that includes over 18 million citations from MEDLINE and other life science journals for biomedical articles back to 1948. PubMed includes links to full text articles and other related resources. PubMed
  • PubMed Central (PMC) is a free digital archive of biomedical and life sciences journal literature at the U.S. National Institutes of Health (NIH) in the National Library of Medicine (NLM) allowing all users free access to the material in PubMed Central. PMC
  • Online Mendelian Inheritance in Man (OMIM) is a comprehensive compendium of human genes and genetic phenotypes. The full-text, referenced overviews in OMIM contain information on all known mendelian disorders and over 12,000 genes. OMIM
  • Entrez is the integrated, text-based search and retrieval system used at NCBI for the major databases, including PubMed, Nucleotide and Protein Sequences, Protein Structures, Complete Genomes, Taxonomy, and others Entrez

Search Pubmed


<pubmed>21346732</pubmed> <pubmed>18396093</pubmed>| PMC <pubmed>18163464</pubmed>] <pubmed>17189856</pubmed> <pubmed>17630848</pubmed>


External Links

External Links Notice - The dynamic nature of the internet may mean that some of these listed links may no longer function. If the link no longer works search the web with the link text or name.

2012 Course Content

Lectures: Cell Biology Introduction | Cells Eukaryotes and Prokaryotes | Cell Membranes and Compartments | Cell Nucleus | Cell Export - Exocytosis | Cell Import - Endocytosis | Cell Mitochondria | Cell Junctions | Cytoskeleton Introduction | Cytoskeleton - Intermediate Filaments | Cytoskeleton - Microfilaments | Cytoskeleton - Microtubules | Extracellular Matrix 1 | Extracellular Matrix 2 | Cell Cycle | Cell Division | Cell Death 1 | Cell Death 2 | Signal 1 | Signal 2 | Stem Cells 1 | Stem Cells 2 | 2012 Revision | Development

Laboratories: Introduction to Lab | Microscopy Methods | Preparation/Fixation | Immunochemistry | Cell Knockout Methods | Cytoskeleton Exercise | Confocal Microscopy | Microarray Visit | Tissue Culture 1 | Tissue Culture 2 | Stem Cells Lab | Stem Cells Analysis

2012 Projects: Group 1 | Group 2 | Group 3 | Group 4 | Group 5 | Group 6 | Group 7 | Group 8 | Group 9

Dr Mark Hill 2015, UNSW Cell Biology - UNSW CRICOS Provider Code No. 00098G