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UNSW Cell Biology

2008 ANAT3231 Lecture 08 - Cell Junctions


This lecture introduces the concept of cell adhesion. Unicellular organisms use to adhere to the environment, nutrition or pathogenesis. Multicellular organisms require adhesion for cells to adhere to each other and the extracellular matrix. Cell adhesion occurs through specific cellular specializations and molecules and has both static and dynamic functions. This topic will be revisited in lectures on extracellular matrix, cell cytoskeleton and signalling.

Lecture Text: Lecture Word Document (182 Kb)

Lab 5: Immunochemistry 



Cell Adhesion

Page Links: Introduction | Objectives | Lecture Audio | Textbooks | Abnormalities | References | Online Textbooks | Web Links | Web Movies | 2007 Lecture Slides | Comments Acronyms


Lecture Audio

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Links: Lectopia Login Page | Cell Biology Podcast Page | Current Course Outline 2008

Why Adhesion?


Unicellular Eukaryotes

Multicelluiar Eukaryotes

Types of Adhesion

Adhesive Functions

Links: Image: Cell-Cell Adhesion in Leukocyte Transmigration | Movie: Cell-Cell Adhesion in Leukocyte Transmigration

Adhesion Characteristics

  • Transmembrane glycoproteins
  • Normally permanent
  • Except migrating cells and embryonic
  • Changes with development
  • Loose adhesion when mature or disease
  • Erythrocytes, cancer

Types of Adhesion Molecules

  • Cadherins
  • Immunoglobulin Superfamily
  • Selectins
  • Gap Junctions
  • Integrins



  • Contain 5 cadherin repeats
  • Each comprising sandwich of beta sheets
  • requires calcium ions to bind
  • Homophilic binding through end element
    • Like with like
  • Functional unit a dimer


Immunoglobulin Superfamily

  • Vertebrates have 100+
  • In addition to adhesion they also have role in immune system
  • Contain varying number of Ig-related domains
  • Comprising sandwich of beta sheets
  • Held together by hydrophobic interactions

Immunoglobulin Superfamily

  • G. Edelman
    • Nobel Prize in Physiology or Medicine in 1972
    • "for their discoveries concerning the chemical structure of antibodies"
  • studying the nervous system
  • Cell Adhesion Molecules (CAMs) family
    • Neuronal cell adhesion molecules (N-CAM)
    • N-CAM, Ng-CAM L-CAM, I-CAM



Neuronal cell adhesion molecules

(Image: Stress, cognitive impairment and cell adhesion molecules, Carmen Sandi, Nature Reviews Neuroscience 5, 917- (December 2004) doi:10.1038/nrn1555)


  • Vertebrates have only in circulatory system
  • Role in adhesion of leukocytes (blood cells) to endothelium (vessel wall)
  • Cooperate with integrins and Ig-SF receptors
  • Selectins 2 Heterophilic interactions
  • Bind counterreceptors
  • Glycosylated proteins
  • Bind through C terminal lectin domain of selectin


  • Mammals have genes for 18 alpha and eight beta integrins
  • Role in cell adhesion to extracellular matrix (ECM) basement membranes
  • Induction of cell polarization by adhesion
  • Cell migration through ECM will discuss in ECM lecture


Cell Junction Types

  • Desmosomes (macula adherens)
  • Adherens Junctions (zonula adherens)
  • Septate Junctions
  • Tight Junctions
  • Gap Junctions

Epithelial Junctions


EM Desmosomes

EM Desmosome

EM Desmosome


  • Discovered by K.R. Porter in 1954
  • intermediate filaments anchor the dense plaque that occurs under the membrane of each cell
  • desmos = bond
  • skin, lining of internal body cavity surfaces
  • disappear when cells are transformed
TEM Desmosome

Links: Desmosome Structure and EM | Expression pattern of desmosomal components in the epidermis | human desmosomal disorders |


Adherens Junctions

  • microfilaments anchor the plaque that occurs under the membrane of each cell
  • plaques not as dense also occur as hemiform
  • heart muscle, layers covering body organs, digestive tract
  • transmembrane proteins
  • Cadherin
Adherens Junctions

Adherens Junctions

Septate Junctions

TEM Septate JunctionSEM Septate Junction

Tight Junctions

  • Discovered by M.G. Farquhar and G.E. Palade in 1963
  • zonula occludens
  • Fusion of 2 plasma membranes acts as a “seal”
  • Epithelia lining
  • digestive system gut, ducts, cavities of glands, liver, pancreas capillary walls urinary bladder

Gap Junctions

  • Discovered by J.P. Revel & M.J. Karnovsky in 1967
  • allowing direct communication between cells (open & close)
  • close membranes 2 - 3 nm apart
  • connexins form hollow 1.5 nm diameter cylinders
  • heart muscle, smooth muscle electrical and chemical integration as a single functional unit
  • Also in embryonic development
Gap Junction
  • gap junction
  • two hemichannels (connexons)
  • each formed from 6 connexin molecules
  • rapidly turned over
Gap Junction

Junctions Overview - Typical Epithelia

Cell Adhesion    

Tight Junction

seals neighbouring cells

Adherens Junction

joins actin bundles between cells


joins intermediate filaments between cells

Gap Junction

cell-cell communication, passage of small molecules


anchors cell intermediate filaments to to basal lamina (extracellular matrix)


Extracellular Matrix


  • Mammals have genes for 18 alpha and eight beta integrins
  • Role in cell adhesion to extracellular matrix (ECM)
  • basement membranes
  • Induction of cell polarization by adhesion
  • Cell migration through ECM
  • Mainly receptors for ECM proteins
  • Fibronectin, laminin, collagen
  • Some heterotypic binding Ig superfamily
  • Interact with cell cytoskeleton signalling
Cell ECM Adhesion

Focal Adhesions

  • links the outside of the cell (ECM) through transmembrane proteins (integrins) with the cell cytoskeleton (actin microfilaments)
  • extracellular matrix
  • integrins
  • actin cytoskeleton

Focal Adhesions

Focal Adhesions (red) Actin microfilaments (green)


(Image: Christoph Moehl)



pemphigus and bullous impetigo- antibodies made against one of their own desmosomal cadherin proteins

antibodies bind to and disrupt the desmosomes that hold together skin epithelial cells

severe skin blistering, leakage of body fluids

palmoplantar keratoderma

Arrhythmogenic right-ventricular cardiomyopathy (ARVC)


not the cause but transformed cells loose adhesion, able to "break away" and spread (metastisis).

Links: Cadherin Knockouts | human desmosomal disorders | NCBI - Genes and Diseases | NCBI - OMIM |


There is a complete list of online textbook links at 2008 ANAT3231 Lecture 08 - Cell Junctions - References

Web Links

Web Movies

Molecular Cell Biology

First link is directly to Quicktime move, followed by associated textbook figure with legend. Look at the movie first, then look at the labelled image.



2007 Lecture Slides

(MH - note that content will not match exactly current lecture structure but has been selected as having similar content)

lecture04 1 slide/page (view only) (53 pages, 1 Mb)

lecture04 6 slides/page (print) (9 pages, 516 Kb)

lecture04 outline (print no images) (6 pages, 92 Kb)

See also Lecture Slides Text on this current page


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In 2008 a new way of presenting course content online is being trialled. Please let me know of any difficulties/suggestions or things that work well.

Notice also that in some slides I have added annotations in brackets with my initials (MH - )


Links: Current Course Outline 2008