Cell Adhesion

Cells in their Environment: Adhesion and the Matrix 


Cells interact with and receive signals from their environment through physical connections  and chemical signals 


Cells care a lot about who they stick to, who they choose to be with 


CAMs - Cell Adhesion Molecules help cells connect to the right cells 

Two classes we focus on: 

Cadherins - cell to cell adhesion

  • Cell cell adhesion strengthened by adding up many weak interactions 

  • Can add in cis or trans ways 

Cell - cell adhesion sort out cells of different types into clusters 

  • Cells will only stick to cells that they like

    • Due to cadherins that confer the molecular specificity 

Tips of cadherins can also recognize each other 

  • Example: Cadherins which are calcium-dependent 

    • E-cadherins and N-Cadherins 

    • There are layers of adapter proteins that connect cadherins to cytoskeleton 


Integrins - cell to matrix binding 

They straighten when they are activated 

Integrin tails closed off, not stuck 

When straightened and opened, they are stuck to something because their domains are opened up

They cluster into focal adhesion complexes which help cells pull forward 

  • Focal adhesion structures  have 5 distinct layers 

Cells connect to the extracellular matrix, which is made up of a meshwork of polymers 

Extracellular matrix essentially crazy mess of proteins that connects cells and tissues together 

  • Laminin is one of the ECM proteins that is multi-adhesive 

    • Lots of globular domains which bind to different things 

    • Anchor shaped structure 

    • Cross link anchor shaped structure and you have a big cross linked meshwork of proteins to form the extracellular matrix 

  • Collagen networks are also a crosslink of heterogeneous polymers

    • Also contains laminin 

    • Has a triple helix structure 

      • Each triple helices joins with two others to form another triple helices (9 polypeptide chains) similar to rope 

    • 25% of protein mass of body is collagen 


How is collagen built?

  1. Collagen propeptides inside ER find each other and  form triple helix through addition of OH groups  

  2. Propeptide domain added to it and then they go to golgi 

  3. Propeptide gets cleaved in extracellular space; collagen now ready to link and assemble 

Case Sample: Scurvy 

Scurvy caused by lack of Vit C 

Vit C is a cofactor in enzyme that hydroxylates collagen propeptides so if you don’t have  enough, your body can’t do the hydroxylation process so body stops making collagen 

  • Important because secretion of collagen helps with wounds, especially after you eat 

    • If u cant produce collagen, can’t feel and heal these wounds