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Cell-cell adhesion
• Cell adhesion molecules (CAMs)
– Lots of them
– Involved in many cellular processes
• Cadherins
– Adhesive glycoproteins
Cell juctions
• Adhesive junctions
– Strong links
• Tight junctions
– Prevent leaks between cells
• Gap junctions
– Forms direct link between cells
Adhesive junctions
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Desmosomes
Hemidesmosomes
Adherens junctions
Focal adhesions
All contain
- intracellular attachment proteins—link to
cytoskeleton
- transmembrane linker proteins—link the
cells
Desmosomes—rivets between cells
Adherens junctions
• Belt around cell
• Connects to actin, not
tonofilaments
• Look a lot like
desmosomes
• Found in
– Heart
– Epithelial layers
• Oftern form belt
• Called “focal adhesion”
if connects to ECM
Tight junctions
Gap junctions
• Direct electrical connection
• Formed by connexons
– Protein=connexin
• Prominent in muscle and nerve—e.g.
electrical tissues
• Form of cell-cell communication
Cell walls
Plant cell walls
• Cellulose (40%)
• Branched polysaccharides
– Hemicellulose (20%)
– Pectins (30%)
• Extensins--glycoproteins (10%)
• Lignins—woody tissues
– Insoluble aromatic alcohols
– Cross-link to form wood
Plasmodesmata
Signal Transduction
General Scheme of Cell Signalling
Types of Receptors
• G-protein linked receptors
– cAMP
– Ca2+
– Inositol triphosphate
– Diacylglycerol
• Protein-kinase receptors
– Serine/threonine kinases
– Tyrosine kinase
G Protein linked receptors
G proteins
• Large heteromeric G proteins
– Alpha—binds GTP/GDP
– Beta
– Gamma
• Together they control the alpha subunit
• Small monomeric G proteins
– Generally called by another name
– Example: ras
Adenylate cyclase
• Activated by G proteins
• Makes cAMP
• cAMP activates cAMP dependent
protein kinase
– aka protein kinase A (PKA)
Pg 261
Diseases
• Cholera
– Vibrio cholerae
– Toxin modifies a G protein
– Continually activates adenylate cyclase
• Whooping cough
– Bordetella pertussis
– Pertussis toxin
– Inactivates a G protein that inhibits
adenylate cyclase
Inositol triphosphate and
diacylglycerol second messengers
Protein Kinase-associated
Receptors
Tyrosine kinase receptors
• Activated by ligand binding
– Often growth factors
• Form dimers
• Autophosphorylation
– On tyrosines
• SH2 domain
– Src homology (domain) 2 region
– Bind to phosphorylated tyrosines
• Activate various second messengers
Serine/threonine
kinases
• Two different
subunits
• Direct
phosphorylation of
transcription
regulators