Cell Surfaces and Junctions

1
Cell Surfaces and Junctions

• Presentation to environment
• Defense mechanisms
• Maintain Structure
• Allow communication between cells

2
Plant Cell Walls

• Flexible primary wall is later reinforced by more
  rigid secondary walls
• Area between cells is filled with Middle lamella
• Contains pectin which is a sticky gelatinous
  molecules
• Plasmodesmata are channels between cells that
  allow cytoplasm exchange

3
Extracellular matrix

• Many types of glycoproteins
• Proteoglycans are more carbohydrate than protein
• Form branched complexes
• Fibronectins act as docking site
• Bound to Integrins
• Integrins span membrane and are bound to
  cytoskeleton

4
Role of ECM

• Gives tissue stability by linking areas of cells
  together
• Like cargo net
• Allows communication between cells
• Fibronectin and integrins are involved in signal
  sending and receiving
• ECM is essential in development
• Provide landmarks for extending structures
• Neurons and vascular tissue

5
Intercellular junctions

• Tight junctions connect cells together and block
  of seepage of extracellular fluids
• Desmosomes anchor adjacent cells together
  structurally
• Linked to Intermediate filaments
• Gap junctions allow molecules to pass from cell
  to cell
• Comparable to plasmodesmata in plants

6
Overview of cell revisited
7
Emergent properties

• Something extra that makes the whole greater than
  the sum of the parts
• In cells the coordinated interaction between
  organelles and the regulation of
  cellular/molecular events
• At the tissue level the cell surfaces and
  junctions allow communications and coordination
  of a larger scope